A specimen of the non-avian dinosaur Sinosauropteryx, showing the ruff of simple protofeathers along the back and tail. Image from Wikipedia.

Poet Emily Dickinson once wrote, “Hope is the thing with feathers.” To fossil bird expert Alan Feduccia, however, anything with feathers is a bird and emphatically not a feathered dinosaur.

For decades Feduccia has been one of the most prominent members of a small and steadfast group of researchers who reject the growing body of evidence that birds are the descendants of one lineage of feather-covered coelurosaurian dinosaurs (the large and varied group which included tyrannosaurs, oviraptorosaurs, deinonychosaurs, therizinosaurs and others). Feduccia and like-minded peers have been provided no solid alternate hypotheses about where, when, why and how birds originated—they point to some yet-unknown lineage of creatures that might have lived more than 200 million years ago—but they insist that birds cannot be dinosaurs. Yet Feduccia’s argument in his new book Riddle of the Feathered Dragons is not quite that simple. Near the book’s conclusion, Feduccia writes “if [a creature] has avian feathers, it is a bird”—a view popular among dinobird denialists that some dinosaurs were, in fact, “hidden birds.”

Non-avian, feathered dinosaurs have been known to paleontologists since 1996. In the 16 years since the first such creature was found—a small theropod dinosaur preserved with fuzzy protofeathers and named Sinosauropteryx—scores of plumage-bearing dinosaur specimens have been discovered. These creatures exhibit a variety of different feather types, which has helped paleontologists, ornithologists and developmental biologists understand how feathers went from simple, wispy structures to complex, asymmetrical feathers that allow birds to fly.

Feduccia disagrees. He says that the protofeathers on Sinosauropteryx and other dinosaurs are, instead, collagen fibers from inside the animal’s body. This would keep dinosaurs comfortably scaly for those who don’t like the idea that birds are derived dinosaurs. But a number of coelurosaurian dinosaurs, such as Anchironis, Microraptor and others, have been preserved with more complex feathers that more closely approximate those seen on living birds. These structures cannot be simply cast off as collagen fibers or other quirks of preservation, and so Feduccia makes a strange argument. Microraptor and kin are not dinosaurs, Feduccia argues, but are instead birds that lost the ability to fly and were molded into the form of dinosaurs through a circuitous evolutionary pathway. By employing a very narrow definition of what a feather is, and by asserting that only birds can have feathers, Feduccia tries to rearrange evolutionary relationships through semantics.

When Sinosauropteryx was discovered, the dinosaur seemed to be an enigma. Paleontologists were not optimistic about the prospect of finding dinosaurs with feathers. Such intricate structures would only be recovered in instances of exceptional preservation. But additional discoveries since 1996 have confirmed that the find was not a fluke. And the fuzzy structures preserved along the backs of these dinosaurs contain an important clue that they are, in fact, protofeathers. In 2010 a pair of papers was published regarding the reconstructed feather colors of dinosaurs. These findings were based on melanosomes—microscopic organelles found in feathers that, depending on their shape and distribution, create different colors and sheens. Such structures would be expected in feathers, but not collagen, and so when paleontologists were able to identify melanosomes in the fuzz of Sinosauropteryx, they provided new evidence that the dinosaur carried protofeathers.

Perhaps more importantly, however, there is no indication that creatures such as Oviraptor and Velociraptor were birds. Analysis after analysis has found them to be unequivocal, non-avian dinosaurs within the coelurosaur subgroup. Although Feduccia hypothesizes that birds originated from some mysterious Triassic ancestor, and then bird-like dinosaurs evolved from early birds, there is not a shred of evidence that such an evolutionary repeat ever took place. The idea is an attempt to remove uncomfortable facts in the way of a preconceived view.

Many of the book’s arguments take on a “because I said so” tone. Feduccia states that dinosaurs could not have been covered in protofeathers at any point because their archaic plumage would have gotten wet and mucky in the rain. Likewise, Feduccia argues that dinosaurs could not have evolved the long arms necessary for flight, and he casts dinosaurs as relatively sluggish ectotherms that had more in common with lizards and crocodiles than birds. None of these points are discussed in detail or backed up with sufficient evidence. Readers are left to take Feduccia at his word.

Ultimately, though, many of Feduccia’s objections boil down to a rejection of a methodology known as cladistics. This method of determining relationships among organisms is based on the analysis of shared derived characteristics—specialized features found in two organisms or lineages and their most recent common ancestor. Researchers look for numerous traits, record whether the traits in question are present or absent, and then insert that mass of data into a computer program that produces a hypothesis about the relationships among the various organisms included in the study. The point is not to find direct ancestors and descendants, but to figure out who is most closely related to whom. The method is not perfect—which organisms are included, the choice of traits for comparison and the way those traits are scored all affect the outcome. Still, this process has the benefit of requiring researchers to show their work. Each evolutionary tree resulting from such methods is a hypothesis that will be tested according to new evidence and analyses. If someone disagrees with a particular result, they can sift through the collected data to see if an inappropriate trait was included, an essential organism was left out, or if there was some other problem. Cladistics is useful not because it results in a perfect reflection of nature each time, but because it allows researchers to effectively examine, test and improve ideas about relationships.

Cladistic analyses have repeatedly found that birds are nested within a subgroup of coelurosaurian dinosaurs called maniraptorans. The result has only become more robust as additional archaic birds and non-avian feathered dinosaurs have been found. Feduccia argues that such results are deeply flawed, but he does not provide a viable alternative for how we should identify the relationship of birds to other organisms (an essential task if we are to figure out how birds originated). Categorizing organisms on general appearances, or making feathers synonymous with birds alone, will only confuse our understanding of prehistoric life. And, contrary to his protests, Feduccia seems to welcome cladistic results that support his own views. In a section of the book on the weird oviraptorosaurs, Feduccia plays up the importance of a 2002 paper that used a cladistic analysis to support the conclusion that these creatures were archaic, secondarily-flightless birds, even though additional studies have not supported this interpretation.

Riddle of the Feathered Dragons is an intensely frustrating read. The tome is a 290-page position piece that ultimately leaves the reader stranded. Feduccia is so concerned with turning feathered dinosaurs into birds that he ultimately neglects to present any reasonable hypothesis for where birds came from. The poor production of the volume only makes things worse (the illustrations are so tightly packed in places that they make it difficult to find where the captions end and the regular flow of the chapter picks up again.)

Although I wholly disagree with Feduccia, I had hoped that Riddle of the Feathered Dragons would explicate what opponents of the dinosaurian origin of birds believe about where avians came from. Simply repeating “birds are not dinosaurs” is not enough—positive evidence must play a role in forming an alternative hypothesis. The riddle of the “feathered dragons” is not where birds came from. The puzzle is why some scientists continue to insist that birds cannot be dinosaurs.

Since Jack Horner and James Gorman’s book How to Build a Dinosaur debuted almost three years ago, periodic lectures, interviews and articles have piqued the public’s curiosity about reverse-engineering a non-avian dinosaur from an avian one. Perhaps a “chickenosaurus” isn’t as outlandish as it sounds.

The possibility of creating a long-tailed chicken with teeth and claws is based on the fact that birds are living dinosaurs. A relatively minimal amount of tinkering could turn a bird into something like its non-avian ancestors. But, during the dinomania of the late 1980s and early 1990s, the idea that birds were derived from dinosaurs was still something that made people tilt their heads and say “What?” Rather than focus on efforts to turn birds into something akin to a dromaeosaur, dinosaur documentaries envisioned the real evolutionary changes by which one lineage of non-avian dinosaurs were adapted into early birds. Even better, two shows animated this change.

Within the array of Mesozoic programming from the early 1990s, one of my favorite shows was The Dinosaurs! This four-part PBS miniseries featured scientists investigating the details of dinosaur lives, and different prehistoric vignettes were presented in colorful animated sequences. The one that stuck with me most powerfully was a short scene about the origin of birds. A small, green dinosaur akin to Compsognathus runs through a forest, but when the theropod pauses on a branch it rapidly grows feathers. In an instant the small coelurosaur changed into Archaeopteryx. The 19th century naturalist Thomas Henry Huxley was absolutely right when he imagined that, when clothed in feathers, a dinosaur like Compsognathus would look little different from archaic birds.

But a similar clip from an earlier, 1989 episode of the series The Infinite Voyage is even better. The episode, “The Great Dinosaur Hunt,” is an excellent snapshot of how perspectives on dinosaurs were changing in the wake of the “Dinosaur Renaissance,” and the program included a similar coelurosaur-to-bird transformation. This time, though, the change starts with a fuzzy, feather-covered dromaeosaurid similar to the sickle-clawed Deinonychus. Rather than focus on the outside of the dinosaur, though, the show gives viewers an animated X-ray view as the skull, arms, shoulders, legs and hips are gradually modified in a transition through Archaeopteryx and modern birds. The change didn’t happen exactly like this—Deinonychus was a larger dinosaur that lived millions of years after Archaeopteryx—but different anatomies represent the general pattern of the evolutionary change.

I still have a fondness for those animations. Part of that affinity is probably due to nostalgia, but I also think that they beautifully illustrate a point that is often taken for granted now. The fact that birds are modern dinosaurs is reiterated in books, museum displays, CGI-ridden documentaries and blogs, but rarely do we see the transitional changes actually laid out in front of us. Both animations could use some updates, but they still vibrantly encapsulate one of the most fantastic transitions in the history of life on earth.

An early 19th century representation of Megalosaurus at the Crystal Palace gardens. Thomas Henry Huxley's work gave dinosaurs a much more bird-like look. Image by Flickr user Loz Flowers.

Winter is the season for dinosaur dinners. Both Thanksgiving and Christmas traditionally feature avian dinosaurs as the main gustatory event, and according to paleontological legend, it was this custom that inspired one 19th century naturalist to realize the connection between roasted birds and Jurassic dinosaurs.

Mark Norell, Lowell Dingus and Eugene Gaffney recounted the story in their book Discovering Dinosaurs. “One Christmas Day,” they wrote, “[Thomas Henry] Huxley was carving a turkey for his annual feast. As he dissected the drumstick he was struck by an unmistakable similarity between his Christmas dinner and the fossils of the theropod Megalosaurus back in his office.” From that day on, the story goes, Huxley was convinced that there was a deep genetic connection between dinosaurs and birds. I heard to same story from my Paleontology 101 professor at Rutgers University. It is a charming bit of lore. And it’s also wrong.

I don’t know where the story about Huxley and the Christmas turkey came from. It is one of those stories that seems simply to exist in the academic ether. (Even the Discovering Dinosaurs authors voiced their uncertainty about the tale in their book.) Fortunately for us, though, Huxley’s many scientific papers trace the development of his thoughts about birds and dinosaurs.

Huxley began associating reptiles—including dinosaurs—with birds on the basis of their anatomy in the early 1860s. Both groups appeared to be different variations of a common skeletal blueprint. But Huxley wasn’t thinking about this in evolutionary terms yet. He was primarily interested in the commonalities of structure and did not immediately start drawing evolutionary implications from the anatomical correspondences he recorded. That changed in 1866, when Huxley read the German naturalist Ernst Haeckel’s book Generelle Morphologie, an influential volume that connected organisms in a tangled “tree of life.” In regard to birds and reptiles, at least, Huxley realized that he had already established the basic outline of an evolutionary transition from a dinosaur-like creature—something resembling Compsognathus—to flightless birds and culminating in flying birds.

Huxley did not suggest that birds were the direct descendants of dinosaurs. So much geologic time was unaccounted for, and so few dinosaurs were known, that Huxley could not point to any known fossil creature as the forerunner of birds. Instead he made his argument on anatomical grounds and removed the issue of time. Dinosaurs were proxies for what the actual bird ancestor would have been like, and flightless birds (such as the ostrich and emu) stood in for what Huxley thought was the most archaic bird type. (We now know that Huxley got this backwards—the earliest birds could fly, and flightless birds represent a secondary loss of that ability.) As Huxley went about collecting evidence for his case, though, he also gave dinosaurs an overhaul. They were not the bloated, plodding, rhinoceros-like creatures that Richard Owen had envisioned. Dinosaurs were more bird-like than anyone had imagined.

In October of 1867, Huxley met with John Philips, an English geologist and a curator of Oxford’s museum. As Huxley related in his 1870 paper “Further Evidence of the Affinity Between the Dinosaurian Reptiles and Birds,” Philips wanted to discuss details of marine reptiles called ichthyosaurs in his museum’s collection, but as he and Huxley made their way over toward the displays they stopped to look at the bones of the carnivorous dinosaur Megalosaurus. Then Huxley spotted something peculiar:

As Prof. Phillips directed my attention to one after the other of the precious relics, my eye was suddenly caught by what I had never before seen, namely, the complete pectoral arch of the great reptile, consisting of a scapula and a coracoid ankylosed together. Here was a tangle at once unravelled. The coracoid was totally different from the bone described by Cuvier, and by all subsequent anatomists, under that name. What then was the latter bone? Clearly, if it did not belong to the shoulder-girdle it must form a part of the pelvis; and, in the pelvis, the ilium at once suggested itself as the only possible homologue. Comparison with skeletons of reptiles and of birds, close at hand, showed it to be not only an ilium, but an ilium which, though peculiar in its form and proportions, was eminently ornithic in its chief peculiarities.

Earlier naturalists had made a mistake. They had misidentified the shoulder girdle, and one part of what was thought to be part of the shoulder was actually part of the hip. Another strange piece, previously thought to be a clavicle, also turned out to belong to the pelvis. This rearrangement immediately gave the dinosaur a more bird-like character. It wasn’t only the small, gracile forms such as Compsognathus that shared skeletal features with birds. Philips himself had been pondering the bird-like characteristics of Megalosaurus even before Huxley arrived, and Huxley’s visit confirmed what Philips had previously suspected. The resulting, updated conception of Megalosaurus was closer to the animal as we know it today—a theropod dinosaur with a short forelimbs, long legs, a long tail for balance and a deep head filled with sharp, recurved teeth.

Huxley’s Christmas revelation is apocryphal. Rather than being instantly struck by the idea that birds and dinosaurs were closely related, Huxley carefully built up an argument over many years that birds evolved from something dinosaur-like. As far as I know, his only sudden realization regarding Megalosaurus involved the rearrangement of bones in Philips’ care at Oxford. And I think this brings up a crucial point often missed or glossed over in accounts of Huxley’s work. Through his efforts to untangle bird origins, Huxley was pivotal in revising the image of dinosaurs into active, bird-like animals. New fossil finds, as well as a new anatomical framework, changed dinosaurs from ugly beasts into graceful, unique creatures during the 1870s, thanks at least in part to Huxley’s efforts. (Too bad that succeeding generations of paleontologists would unravel this vision by casting dinosaurs as dumb, cold-blooded reptiles.) Even if Huxley didn’t say birds are dinosaurs, he certainly made dinosaurs more bird-like.

For more information on Huxley’s thoughts on dinosaurs and birds, please see my paper “Thomas Henry Huxley and the Reptile to Bird Transition” and chapter 5 of my book Written in Stone.

References:

Huxley, T.H. 1870. Further Evidence of the Affinity Between the Dinosaurian Reptiles and Birds. The Quarterly Journal of the Geological Society of London, vol. xxvi. 12-31

Norell, M., Dingus, L., Gaffney, E. 2000. Discovering Dinosaurs: Expanded and Updated. Berkeley: University of California Press. p. 11

A large stone slab containing mudcracks and many footprints left by small theropod dinosaurs, as illustrated in Hitchcock's "Ichnology of New England."

Edward Hitchcock was one of America’s first dedicated dinosaur paleontologists. He just didn’t know it. In fact, during the latter part of his career, he explicitly denied the fact. To Hitchcock, the tracks skittering over red sandstone in the Connecticut Valley were the marks of prehistoric birds from when the Creation was new. Hitchcock could not be dissuaded. As new visions of dinosaurs and the notion of evolution threatened to topple his life’s work, the Amherst natural theologian remained as immutable as the fossil footprints he studied.

Hitchcock was not the first to wonder about the prehistoric imprints. Members of the Lenape, a Native American group in Canada and the northeastern United States, had seen the bizarre, three-toed tracks and ascribed them to monsters and other beings. These were the footsteps of creatures that ruled the world before humans came to dominance. European settlers and their descendants had to stretch their mythology a little more to accommodate the tracks. Some thought such tracks might have been left by Noah’s raven after the biblical deluge, although many simply called them “turkey tracks” and apparently were little concerned with where they had come from.

It wasn’t until 1835 that James Deane, a doctor with a curiosity for natural history, found out about a sample of the peculiar tracks near Greenfield, Massachusetts. He knew that they represented prehistoric organisms, but he wasn’t sure which ones. He wrote to Hitchcock, then a geology professor at Amherst, to inquire about what could have left such markings in stone. At first Hitchcock didn’t believe Deane. There might be some quirk of geological formation that could have created track-like marks. But Deane was persistent. Not only did he change Hitchcock’s mind, but the geologist became so enthusiastic that he quickly became the most prominent expert on the tracks—a fact that frustrated Deane and led to tussles in academic journals over who really was the rightful discoverer of the Connecticut Valley’s lost world.

Hitchcock began publishing about the peculiar trace fossils in 1836. He was confident from the very start that they must have been created by prehistoric birds. (He was so enthused by the idea he even wrote poetry about the “sandstone birds.”) No variety of creature matched them better. The word “dinosaur” had not even been invented yet; the British anatomist Richard Owen would establish the term in 1842. The few dinosaurs that had been found, such as Iguanodon, Megalosaurus and Hylaeosaurus, were known only from paltry remains and all were believed to have been enormous variations of lizards and crocodiles. Dinosaurs were a poor fit for the tracks, and became even worse candidates when Owen gave them an anatomical overhaul. Owen not only named dinosaurs, he re-branded them as reptiles with mammal-like postures and proportions. The huge sculptures of the Crystal Palace exhibition, created with the help of artist Benjamin Waterhouse Hawkins, are a testament to Owen’s view of dinosaurs as reptiles that had taken on the anatomical attitudes of rhinoceros and elephants.

But Owen and other paleontologists did not agree with Hitchcock’s interpretation. They argued that the tracks could have been made by some unknown variety of amphibian or reptile. This was not so much because of the anatomy of the tracks—anyone could see that they were made by creatures with bird-like feet—but because no one thought that birds could have lived at so ancient a time or grown large enough to make the biggest, 18-inch tracks Hitchcock described. Even though early 19th century paleontologists recognized that life changed through the ages, they believed there was a comprehensible progression in which so-called “higher” types of creatures appeared later than others. (Mammals, for example, were thought to have only evolved after the “Secondary Era” when reptiles ruled since mammals were thought to be superior to mosasaurs, ichthyosaurs, and other creatures of that middle time.)

Hitchcock remained steadfast, and his persistence was eventually rewarded with the discovery of the moa. These huge, flightless birds recently lived on New Zealand—they were wiped out more than 500 years ago by humans—and in 1839 Richard Owen rediscovered the birds through a moa thigh bone. He hypothesized that the bone must have belonged to a large, ostrich-like bird, and this idea was soon confirmed by additional skeletal bits and pieces. Some of these ratites stood over nine feet tall. When the news reached Hitchcock in 1843, he was thrilled. If recent birds could grow to such sizes, then prehistoric ones could have been just as large. (And, though Hitchcock died before their discovery, preserved moa tracks have a general resemblance to some of the largest footprints from the Connecticut Valley.) Opinion about the New England tracks quickly changed. There was no longer any reason to doubt Hitchcock’s hypothesis, and paleontologists hoped that moa-like bones might eventually be found to conclusively identify the trackmakers.

Lacking any better hypotheses, Hitchcock prominently featured his avian interpretation of the three-toed tracks in his 1858 book The Ichnology of New England. It was a gorgeous fossil catalog, but it also came at almost precisely the wrong time. Gideon Mantell, the British doctor and paleontologist who discovered Iguanodon, was beginning to wonder if some dinosaurs primarily walked on their hind limbs in a bird-like fashion, and the Philadelphia polymath Joseph Leidy described Hadrosaurus, a dinosaur certainly capable of bipedal locomotion on account of having shorter forelimbs than hindlimbs, the same year that Hitchcock’s monograph came out. Dinosaurs were undergoing another major overhaul, and the few that were known at the time were being recast as relatively bird-like creatures. Even worse for Hitchcock, the following year another student of the Connecticut Valley tracks, Roswell Field, reinterpreted many of the footprints and associated traces as being made by prehistoric reptiles. Especially damning was the fact that deep tracks, left when the creatures sunk into the mud, were sometimes associated with drag marks created by a tail. Hitchcock’s tableau of ancient Massachusetts moas was becoming increasingly unrealistic.

If Hitchcock ever doubted his interpretation, he never let on. He reaffirmed his conclusions and modified his arguments in an attempt to quell dissent. In his last book, A Supplement of the Ichnology of New England, published in 1865, a year after his death, Hitchcock used the recently discovered Jurassic bird Archaeopteryx as a way to save his interpretation. Tail drags were no obstacle to the bird hypothesis, Hitchcock argued, because Archaeopteryx was generally regarded as being the primordial bird despite having a long, reptile-like tail. Perhaps such a bird could have been responsible for the trace fossils Hitchcock called Anomoepus, but the tail drags left by the animals that dwelled in Jurassic New England were also associated with tracks indicating that their maker walked on all fours. In response, Hitchcock cast Archaeopteryx as a quadrupedal bird—a representative of a new category different from the classic, bipedal bird tracks he had promoted for so long.

Other paleontologists took a different view. If Archaeopteryx looked so primitive and lived after the time when the red Connecticut sandstone was formed, then it was unreasonable to think that more specialized, moa-like birds created Hitchcock’s tracks. Furthermore, a few bones found in a Massachusetts quarry of roughly the same age in 1855 turned out to belong to a dinosaur—a sauropodomorph that Othniel Charles Marsh would later name Anchisaurus. The bird bones never turned up, and all the while dinosaur fossils were becoming more and more avian in nature. By the 1870s the general paleontological opinion had changed. New England’s early Jurassic was not filled with archaic birds, but was instead home to dinosaurs which were the forerunners of the bird archetype.

Our recent realization that birds are the direct descendants of one group of coelurosaurian dinosaurs has led some of Hitchcock’s modern day fans to suggest that he was really right all along. In an essay for the Feathered Dragons volume, paleontologist Robert Bakker extolled Hitchcock’s scientific virtues and cast the geologist’s avian vision for the tracks as essentially correct. Writer Nancy Pick, in her 2006 biography of the paleontologist, wondered, “What if Hitchcock clung to his bird theory because he was right?” But I think such connections are tenuous—it is a mistake to judge Hitchcock’s work by what we have come to understand a century and a half later.

While Bakker is right that Hitchcock stuck to his bird hypothesis early on because dinosaurs were not known in the 1830s to 1850s to be suitably avian, this does not explain why Hitchcock refused to entertain a dinosaurian origin for some of the tracks when evidence for such a connection began to accumulate. By sticking to the same point, Hitchcock went from being right to being so wrong that he tried to fit creatures like Archaeopteryx into the footprints to preserve his point. More importantly, though, Hitchcock promoted a variety of creationism that we would probably label as intelligent design today—he detested the idea of evolution by means of natural selection that Charles Darwin articulated in 1859. Hitchcock would not have accepted the idea that birds are the evolutionary descendants of dinosaurs. He likely would have rejected the idea of avian dinosaurs that some writers wish to attribute to him.

Hitchcock himself acknowledged that he was a stubborn man. Perhaps his obstinacy prevented him from accepting new ideas during a critical period of change within geology, paleontology and natural history. We may never know. Unless a letter or journal entry articulating his thoughts on the subject appear, his anti-dinosaur interpretation will remain a mystery. All we know for sure is that, regardless of whether he agreed with the label or not, Hitchcock was one of the first interpreters and promoters of North American dinosaurs.

References:

Bakker, R. 2004. “Dinosaurs Acting Like Birds, and Vice Versa – An Homage to the Reverend Edward Hitchcock, First Director of the Massachusetts Geological Survey” in Feathered Dragons. Currie, P.; Koppelhus, E.; Shugar, M.; Wright J. eds. Bloomington: Indiana University Press. pp. 1-11

Pick, N. and Ward, F. 2006. Curious Footprints: Professor Hitchcock’s Dinosaur Tracks & Other Natural History Treasures at Amherst College. Amherst: Amherst College Press.

Switek, B. 2010. Written in Stone. New York: Bellevue Literary Press. pp. 91-104

A reconstructed model of a young Tyrannosaurus at the Natural History Museum of Los Angeles County. Were these little tyrants covered in feathers? Photo by the author.

From museum displays to comic books and feature films, Tyrannosaurus rex has been celebrated as one of the biggest, meanest and ugliest predatory dinosaurs of all time. The image of this long-extinct carnivore as the apex of the apex predators has a nearly unstoppable amount of cultural inertia. Maybe that’s why people get upset when paleontologists and artists suggest that the tyrant dinosaur was at least partly covered in a coat of feathers. (Cracked.com even listed an illustration of a feathered Tyrannosaurus as one of “17 Images That Will Ruin Your Childhood.”) Such images make it seem as if the old “prize-fighter of antiquity” has gone soft—how could such an imposing predator go in for such a silly look? Tyrannosaurus was no turkey, right?

To date, no one has found the fossilized remnants of feathers with a Tyrannosaurus skeleton. A few patches of scaly skin are known from some big tyrannosaur specimens, and those scraps represent about all we know for sure about the body covering of the largest tyrants. So why is Tyrannosaurus so often depicted with a coat of dino-fuzz these days? That has everything to do with the evolutionary relationships of the great tyrannosaur lineage.

Until the early 1990s, paleontologists often placed tyrannosaurus with Allosaurus, Spinosaurus, Torvosaurus and others inside a group called the Carnosauria. These were the biggest of the carnivorous dinosaurs. But the group didn’t make evolutionary sense. As new discoveries were made and old finds were analyzed, paleontologists found that the dinosaurs within the Carnosauria actually belonged to several different and distinct lineages that had branched off from one another relatively early in dinosaur history. The tyrannosaurs were placed within the Coelurosauria, a large and varied group of theropod dinosaurs which includes dromaeosaurs, therizinosaurs, ornithomimosaurs, oviraptorosaurs and others. Almost every single coelurosaur lineage has been found to have feather-covered representatives, including the tyrannosaurs.

In 2004, paleontologist Xing Xu and colleagues described Dilong paradoxus, a small, roughly 130-million-year-old theropod which may be one of the earliest tyrannosauroid dinosaurs known. (The Tyrannosauroidea contains all the big, famous tyrannosaurids, such as Tyrannosaurus and Albertosaurus, as well as their closest relatives.) Small patches of filamentous protofeathers were found along the dinosaur’s neck and tail, indicating that—at least during their early evolutionary history—tyrannosaurs may have been covered in feathers, too. But the relevance of Dilong to the question of feathered tyrannosaurs partially rests on what Dilong turns out to be. The initial description cast the dinosaur as a tyrannosauroid, but subsequent analyses have differed as to whether Dilong is an early tyrannosauroid (as in Carr and Williamson, 2010) or belongs to some other coelurosaur group (as in Turner et al., 2011).

For the sake of argument, though, let’s say that Dilong was not a tyrannosauroid and actually belonged to a different coelurosaurian lineage. Would this mean that tyrannosaurs didn’t have feathers? Certainly not. Feathers were a widespread trait within the coelurosaurs, and simple, fuzzy protofeathers may go back to the last common ancestor of the group. Otherwise feathers would have to have evolved near the base of every lineage, and there is no indication that feathers evolved so many times. The spread of feathers among almost all coelurosaur groups hints at a shared origin.

Since so many other coelurosaurs had feathers, it is fair to infer that tyrannosaurs also did. This hypothesis is no more unreasonable than saying that close relatives of the earliest mammals such as Morganucodon were covered in fur on the basis of their evolutionary relationships. And, to pick another dinosaurian example, no one has yet described an ornithomimid dinosaur with evidence of feathers, yet we are comfortable attributing feathers to them because they are coelurosaurs. (Maybe their vaguely ostrich-like appearance helps a bit in this regard.) If feathers can reasonably be inferred for ornithomimosaurs on the basis of their family tree, then we can do so for tyrannosaurs.

So, within this evolutionary bracket, what kind of feathers might have clothed Tyrannosaurus and kin? The simple dino-fuzz of Dilong is a fair bet. Perhaps such a body covering would have served for insulation, but then again, the patchy distribution of filaments on Dilong and other coelurosaurs has raised the suggestion that some dinosaurs were only partly coated in feathers. Whatever their distribution on tyrannosaur bodies, though, the feathers probably didn’t look like those which allowed other coelurosaurs to eventually take to the air. After all, feathers were probably used for display and the regulation of body temperature first, and since no tyrannosauroid even came close to flying we should expect for them to have relatively simple feathers related to these functions.

A fuzzy juvenile tyrannosaur puppet at the Natural History Museum of Los Angeles County. Photo by author.

Regarding Tyrannosaurus specifically, the tyrant king may have had feathers only during the early years of life. A fuzzy coat may have helped hatchling and juvenile Tyrannosaurus regulate their body temperature, but as the animals grew, the benefits provided by insulation may have disappeared. (Retaining heat is a problem often faced by small animals, while shedding excess heat is a problem faced by larger animals due to changes in surface-to-volume ratios as animals grow.) Maybe an adult Tyrannosaurus would have patches of protofeathers here and there, as in Peter Schouten’s illustration of the dinosaur, But given the evidence at hand, it is likely that baby Tyrannosaurus would have been fuzzier than their parents.

Frustratingly, though, we may never know for sure what sort of feathers Tyrannosaurus might have had, or during what part of life. Circumstances of fine preservation are required to detect feathers, and even then, sometimes only patches are preserved. The types of environments Tyrannosaurus lived in were not exactly amenable to the kind of rapid, fine-detail preservation required to detect feathers. Even in cases where skin patches are preserved, it is difficult to know whether there might have been protofeathers on other parts of the body, or whether some of those feathers fell off or otherwise eluded preservation. Delicate structures require delicate preservation to detect.

What we can say is that the idea of a feather-covered Tyrannosaurus is a reasonable hypothesis. We still know so little about the body covering of this dinosaur that artists can reasonably restore the dinosaur with scaly skin, a coat of feathers, or a patchwork of both (I would especially like to see more renditions of that third possibility). Perhaps future fossil discoveries will provide us with a clearer picture of what Tyrannosaurus looked like, but the current unknowns are fascinating. Asking what Tyrannosaurus looked like is not just a matter of speculation—obtaining an answer requires that we consider the patterns and processes of evolution, as well as the methods we use to restore creatures that have been dead for millions upon millions of years. Feather-covered or not, though, I wouldn’t want to call Tyrannosaurus a turkey to its face. If I did, I don’t think I could run away fast enough to avoid becoming the dinosaur’s Thanksgiving dinner.

From everyone here at Dinosaur Tracking, we hope that you enjoy your holiday dinosaur and have a warm Thanksgiving.

References:

Carr, T., & Williamson, T. (2010). Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea
Journal of Vertebrate Paleontology, 30 (1), 1-16 DOI: 10.1080/02724630903413032

Turner, A., Pol, D., & Norell, M. (2011). Anatomy of Mahakala omnogovae(Theropoda: Dromaeosauridae), Tögrögiin Shiree, Mongolia American Museum Novitates, 3722 (3722), 1-66 DOI: 10.1206/3722.2

Xu, X., Norell, M., Kuang, X., Wang, X., Zhao, Q., & Jia, C. (2004). Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids Nature, 431 (7009), 680-684 DOI: 10.1038/nature02855

A cast of the sauropod Diplodocus at the Utah Field House of Natural History in Vernal, Utah. Our current understanding of sauropods like this differs greatly from hypothetical restorations of "living dinosaurs" in Africa. Photo by the author.

In the annals of science fiction, humans and non-avian dinosaurs have been brought together in a variety of ways. Genetic engineering experiments and time travel are probably the most common these days, but I have always had a soft spot for tales of “lost worlds.” What could be more fantastic than dinosaurs that somehow escaped extinction and persisted in some isolated spot for 65 million years? My childhood self really wanted someone to find a living Tyrannosaurus, Apatosaurus, or Triceratops in some remote locale, and that wish was fed by reports that one elusive dinosaur was hiding in Africa.

First thing first—living dinosaurs certainly do exist. We know them as birds, and a combination of fossil discoveries and laboratory research has confirmed the evolutionary connection between birds and feather-covered maniraptoran dinosaurs. But from time to time, people have proposed that non-avian dinosaurs may also still be hanging around.

The most famous of the supposed living dinosaurs I heard about was Mokele-mbembe. This unknown creature—often restored as a swamp-dwelling, tail-dragging sauropod akin to old restorations of “Brontosaurus“—is said to inhabit the dense jungle in what is now Cameroon and the Democratic Republic of the Congo. At least, that’s the way I was introduced to the legendary animal in the late 1980s. A blurry photograph of a lump in a lake and an ambiguous sound recording made by Herman Regusters during a 1981 expedition to find the animal were cited as possible evidence that a semi-aquatic sauropod was swimming around Lake Tele, and the feature film Baby: Secret of the Lost Legend fleshed out the hypothetical dinosaurs. Tall tales and legends of Mokele-mbembe had been circulating for decades before, and sensationalist basic cable television programs still fund expeditions to try and find the animal from time to time.

Is there any good evidence that a sauropod still wades through the muck of African swamps? Sadly, no. I would be thrilled if a living, non-avian dinosaur really did turn up somewhere, but such a fantastic find would have to be backed up by equally fantastic evidence. Despite the fact that multiple expeditions have been sent to the Democratic Republic of the Congo over many years, there is no solid evidence that Mokele-mbembe is a dinosaur or even a real, unknown species of animal. I seriously doubt anyone will ever find any evidence of such a creature at all, and part of the reason why related to a paper published by University of Queensland zoologists Diana Fisher and Simon Blomberg last year.

The major message of Fisher and Blomberg’s study was positive: Some modern mammal species thought to be extinct may still survive in small, hard-to-find pockets of their former ranges. But the researchers also noted that the effort put into finding supposedly extinct species makes a difference as to whether we should expect to find those animals. The researchers found that species that still survived were often found after three to six searches, but if more than eleven searches were made with no results—as is the case for the Tasmanian tiger and Yangtze river dolphin—then the species is probably actually extinct. Since so many searches have been made for Mokele-mbembe with no solid results, I don’t think that there’s actually any large, hidden species there to find.

There is a flipside to that argument, although it also doesn’t bode well for the rumored dinosaur. Many of the searches for Mokele-mbembe have been made by self-described explorers who have little to no relevant field experience in tracking and studying wildlife. Some of these folks are even religious fundamentalists who are striving to somehow undermine evolutionary theory. Their credibility is highly suspect, but you would think that at least one group would have blundered into the animal by now. After all, there has to be a population of animals which would be leaving tracks, scat and occasionally bodies. The evidence for huge creatures living in the swamp should be readily apparent, and the best the many dinosaur hunters can come up with are tall tales and misshapen globs of plaster that look nothing like the tracks the casts are claimed to be.

But the most obvious problem is that there’s no trace of sauropods in the fossil record—at all—in the 65 million years since the end-Cretaceous extinction. Nothing. The last of these dinosaurs died out long ago, and there is not even a scintilla of evidence that sauropods survived past the close of the Mesozoic. If sauropods survived at all we would expect to find some indication of their existence in the fossil record. These were not small animals or creatures that were hidden away in the deep sea. Given the number of terrestrial fossil deposits and they way they have been sampled, Cenozoic sauropods would have turned up by now if they had survived.

There are plenty of other problems with the idea that there’s a sauropod trundling around in the swamps of the Congo Basin. One of the most ridiculous aspects of Mokele-mbembe stories is that the supposed dinosaurs resemble what the searchers expected sauropod dinosaurs to look and act like based on inaccurate restorations. The hypothetical dinosaurs act just like their counterparts in old Charles R. Knight and Zdeněk Burian paintings. Actual, living sauropods would have looked markedly different from those old restorations, and according to recent research, sauropods would have been really lousy swimmers due to the considerable volume of air-filled spaces in their bodies. A sauropod would not be able to act like a crocodile and hide underwater as Mokele-mbembe supposedly does. The weakness of the “Mokele-mbembe as sauropod” hypothesis is underscored by the fact that the supposed anatomy and behavior of the animal is clearly based on outdated images of dinosaurs. As Darren Naish pointed out in his brilliant April Fool’s Day post on Mokele-mbembe from this year, the idea that the animal was an old-school, tail dragging sauropod grates against everything we have learned about sauropods during the past three decades.

Paleontologist Don Prothero also took a few good whacks of Mokele-mbembe in a recent Monster Talk episode. Not surprisingly, Prothero points out that many of the reports about the animal are extremely inconsistent. A number of supposed sightings don’t refer to anything dinosaur-like at all, and even those that do are inconsistent and ambiguous. On top of that, Prothero and the show’s hosts bring up the fact that fanatics in search of Mokele-mbembe can easily misconstrue what local people might be saying about the animal because of a lack of shared cultural background and other translation problems. While visiting explorers often use the term “Mokele-mbembe” to refer to a supposed dinosaur or similar animal, the word can also refer to something that is not real or has no physical manifestation. If film crews and self-described explorers keep passing through and spending money in the region, it’s not surprising that people will tell the monster hunters what they want to hear.

The take-home lesson is this: If you want to find sauropods, sign up to volunteer on a professional fossil excavation with well-trained scientists.

The Thermopolis specimen of Archaeopteryx at the Wyoming Dinosaur Center. Photo by the author.

Since the time the English anatomist Richard Owen described Archaeopteryx as the “by-fossil-remains-oldest-known feathered Vertebrate” in 1863, the curious creature has been widely regarded as the earliest known bird. Lately, though, the status of the iconic animal has been up for debate. Earlier this summer, one team of paleontologists proposed that Archaeopteryx was not a bird but actually a feather-covered, non-avian dinosaur more closely related to genera like Microraptor and Troodon. Now a different team of paleontologists has published a paper in Biology Letters that says Archaeopteryx was an early bird after all.

The ongoing back and forth over Archaeopteryx reminds me of the old Looney Tunes bit where Bugs Bunny and Daffy Duck keep going back and forth over which hunting season it is. “Duck season.” “Wabbit season!” “Duck season” “WABBIT SEASON!” In the same way, the argument over Archaeopteryx could seemingly go on indefinitely. The reasons why have everything to do with how both science and evolution work.

The study of prehistoric life, like any other science, is not restricted to the slow and steady accumulation of facts. Facts are most certainly acquired through studies in the field and lab alike, but to tell us anything significant about dinosaurs, these facts must be understood according to theories and hypotheses. An exasperated Charles Darwin conveyed this truth eloquently in an 1861 letter he wrote to colleague Henry Fawcett:

About thirty years ago there was much talk that geologists ought only to observe and not theorise; and I well remember some one saying that at this rate a man might as well go into a gravel-pit and count the pebbles and describe the colours. How odd it is that anyone should not see that all observation must be for or against some view of it is to be of any service!

Facts, theories and hypotheses are all necessary and interacting parts of the scientific process. As new discoveries are made and ideas are tested, the context by which we understand what dinosaurs were and how they lived changes. This is to be expected—there are always more questions and mysteries about dinosaurs than readily available answers. In the case of Archaeopteryx, we know this feather-covered dinosaur lived on a group of roughly 150-million-year-old islands that would eventually become southeastern Germany. Whether or not Archaeopteryx belonged to that successful lineage of feathered dinosaurs called birds, though, is something that depends on other feathered dinosaur discoveries and the techniques used to test ideas about relationships among animals.

Teasing out relationships among prehistoric animals is a comparative science. The key is finding traits that are shared in some organisms due to common ancestry but are absent in others. This can be a tricky process. Due to a shared way of life, for example, unrelated organisms may have developed superficially similar traits through a phenomenon called convergent evolution. Paleontologists must carefully choose the traits being compared, and the discovery of additional dinosaurs adds more grist to the comparative mill.

Archaeopteryx is actually a perfect example of how new discoveries can change our perception of relationships. When the first skeleton was discovered in 1861, nothing quite like it had been found. Archaeopteryx seemed to stand by itself as the first bird. Over a century later, though, the discovery of dinosaurs such as Deinonychus, an updated understanding of dinosaurs and the eventual discovery of many, many feathered dinosaurs illustrated that Archaeopteryx exhibited a number of transitional features that illustrated how the first birds evolved directly from feathered dinosaurs.

The trouble is that Archaeopteryx appears to be so close to the emergence of the very first birds. At the moment, Archaeopteryx is most often regarded as being an archaic member of the group called the Avialae, which contains all birds (Aves) and forms more closely related to them than to other dinosaurs. What this means is that, as our understanding of what a bird actually is changes, the position of Archaeopteryx might shift. The animal might have been one of the earliest birds within the avialian group, or Archaeopteryx might have been just outside the bird group among non-avian dinosaurs.  This is simply how science works and is a wonderful—if frustrating—demonstration of the fact of evolution.

Birds did not simply pop out of nowhere. The earliest avians went through a long period of transformation, and the continuum between feathered, non-avian dinosaurs and the first birds, which paleontologists are now filling in, demonstrates the beauty of major evolutionary change. The debate over the position of Archaeopteryx is happening now precisely because of all the evidence for this evolutionary change that has been accumulated in the past two decades. No matter what Archaeopteryx turns out to be, the creature will remain important to both the historical development of our ideas about evolution and the actual, prehistoric transition from non-avian to avian dinosaurs.

For more on changing perspectives on long-known dinosaurs, see this week’s post on the fate of the horned dinosaur Torosaurus.

References:

Lee, M., & Worthy, T. (2011). Likelihood reinstates Archaeopteryx as a primitive bird Biology Letters DOI: 10.1098/rsbl.2011.0884

Xu, X.; You, H.; Du, K.; Han, F. (2011). An Archaeopteryx-like theropod from China and the origin of Avialae Nature, 475, 465-470 DOI: 10.1038/nature10288

The 11th skeleton of Archaeopteryx. Photo by Helmut Tischlinger.

For Archaeopteryx, 2011 has been a year of ups and downs. Paleontologists celebrated the 150th anniversary of when the iconic feathered dinosaur was named. But shortly afterwards, a controversial paper in Nature in July proposed that the creature—widely hailed as the first bird—was further removed from avian ancestry than previously thought. Now Archaeopteryx is back on the upswing. According to a press release circulated by the New Munich Trade Fair Centre in Germany, paleontologists now have an 11th specimen of the famous fossil creature to study.

Until this week, ten Archaeopteryx skeletons were known to paleontologists, not including the fossil feather the German paleontologist Hermann von Meyer used to give the animal its name. Peter Wellnhofer, the world’s foremost expert on the “urvogel,” detailed the backstory of each fossil in his comprehensive book Archaeopteryx: The Icon of Evolution. The London specimen and the Berlin specimen are the best known—particularly the latter, arguably one of the most visually stunning fossils ever found—but there’s also the busted-up Maxberg specimen, another that was initially confused for a pterosaur (the Haarlem specimen) and a slab known as the Solnhofen specimen that was originally thought to contain the skeleton of the small coelurosaurian dinosaur Compsognathus.

As far as I am aware, the new specimen does not have a name and has yet to be described in the literature, but this Archaeopteryx appears to be one of the more complete and well preserved of the lot. In fact, the preservation and position of the bones are reminiscent of the Thermopolis specimen I saw in Wyoming this past year, although this new Archaeopteryx is missing one forelimb and the skull. Don’t be fooled by the fact that, at first glance, the fossil looks a little jumbled up. If you start by following the tip of the tail (on the right), the articulated vertebral column leads to the hips and splayed legs before curving up and back in the classic dinosaur death pose. The arm is displaced below the hips but remains articulated.

We will have to wait for the descriptive paper to learn the important characteristics of this new find, as well as where the slab came from. But if you happen to be in the vicinity of the New Munich Trade Fair Centre in Germany, you can see the 11th Archaeopteryx for a limited engagement at “The Munich Show” from October 28-30.

The skeleton of Xiaotingia (head is to the left). From Xu et al., 2011.

Sometimes my timing is just plain awful. I had waited for years to see an authentic specimen of Archaeopteryx—the feather-covered fossil celebrated for 150 years as the first bird—but by time I finally got my chance, on the afternoon of July 27, news sources were trying to out-pun each other over the unceremonious demotion of the evolutionary icon. I scanned through the reports while sitting in the parking lot of the Wyoming Dinosaur Center, where the only Archaeopteryx in North American is on display. “Archaeopteryx Knocked From Roost as Original Bird” claimed WIRED Science, and the BBC played up the drama with “Feathers Fly in First Bird Debate.”

All this hubbub was stirred up by an article published a few hours before I rolled up to the museum in Thermopolis, Wyoming. In the issue of Nature published that day, paleontologist Xu Xing and colleagues described a previously unknown species of feathered dinosaur from the exceptionally fossil-rich beds of Liaoning, China. An interesting find, but given the number of feathered dinosaurs discovered during the past 15 years, not exactly something that newspapers would flip over. (As a freelance science writer, believe me that convincing some editors that dinosaurs are worth talking about is an uphill struggle.) What made all the difference was the way the new fossil was used to challenge the traditional position Archaeopteryx has held.

The backstory for the news goes back to 2009. In that year Xu and other paleontologists described a feather-covered creature they called Anchiornis. At first they thought it was an early bird, but a follow-up paper identified it as a feathered troodontid dinosaur. The newly described creature was very similar to Archaeopteryx—so much so that the discovery made me wonder if the beloved “urvogel” might eventually be stripped of that title, especially since Anchiornis might be even more ancient than the 150-million-year-old Archaeopteryx.

Now there’s Xiaotingia zhengi—another small theropod dinosaur draped in well-developed plumage. The holotype specimen which formed the basis of the new Nature paper exhibits the mostly complete skeleton on its side, and altogether the specimen looks like a tan and brown smudge of bones and feather impressions. It is said to date back to about 155 million years ago, but like many such fossils from China, the exact date is frustratingly uncertain because the fossil was purchased from a dealer and not scientifically excavated. In terms of the anatomical nitty-gritty, though, Xiaotingia looks quite similar to both Archaeopteryx and Anchiornis. Even though the skull was crushed, for example, Xiaotingia appears to have had a short skull fitted with small, peg-like teeth.

But the part of the study that garnered the most attention was the evolutionary analysis which removed Archaeopteryx and its closest kin from the base of the bird family tree. According to the paper, the dinosaurs Archaeopteryx, Anchiornis and Xiaotingia were united by several subtle characteristics, such as the lengths of the hand bones and the shape of the wishbone. The study places these dinosaurs closer to the sickle-clawed deinonychosaurs—the group which contains genera like Troodon and Deinonychus—than to the earliest birds.

Now here’s the part that was grossly underreported. “It should be noted,” the authors of the new paper wrote, “that our phylogenetic hypothesis is only weakly supported by the available data.” Headlines proclaimed the downfall of Archaeopteryx even though the actual evidence for such a change, as the authors of the study admitted, is not particularly strong. The uncertainty stems from the fact that some of the features seen in early birds may have appeared independently in more distantly related dinosaurs, so determining which traits are true signs of family ties and which evolved independently in different lineages is a difficult task. For example, the authors of the new study point out the similarity between the skulls of early birds such as Jeholornis and Sapeornis with oviraptorsaurs—all seem to have relatively deep and short skull profiles. But is this a real sign of close relationships, or a case of convergent evolution? There is no definite answer yet. When trying to tease out relationships, paleontologists must choose wisely or else features that evolved independently might be mistaken for common inheritance from a shared ancestor.

Likewise, previous studies by the same authors have frequently shifted the positions of feathered dinosaurs thought to be close to bird ancestry. The instability of the evolutionary trees being produced should make us proceed with caution. Take Anchiornis for example. It was originally described as a bird, then said to be a troodontid dinosaur, and is now cast as one of the closest relatives to Archaeopteryx in a lineage further removed from birds than previously thought. The patterns of relationships change from one publication to the next. It isn’t uncommon for relationships between dinosaurs to be unstable or uncertain, though. The relationships between dinosaur species are hypotheses that are subject to change with the addition of new information and context. Some hypotheses are stronger or better supported than others, but just because an evolutionary tree is published does not mean that it’s necessarily accurate or will remain the same as new discoveries are made.

This isn’t the first time that the avian relationships of Archaeopteryx have been challenged. General doubts have percolated through the paleontological community about Archaeopteryx for decades. Back when the first recognized Archaeopteryx specimens were found—a feather in 1860 and the first body fossil in 1861—nothing like it had been found before. Sites of exceptional preservation—where feather and body impressions could be found along with preserved bone—were rare, and Western naturalists had no idea that China held a rich store of feather-covered dinosaurs waiting to be discovered. Under these conditions Archaeopteryx seemed to be a dead ringer for the earliest known bird: After all, only birds had feathers. Not everyone was entirely agreed that Archaeopteryx was important to the origin of the first birds. Thomas Henry Huxley proposed that birds were derived from a dinosaur-like ancestor—something akin to Compsognathus—and had gone through a flightless, ostrich-like stage before taking to the air. This would make Archaeopteryx an aberrant side branch, Huxley proposed, not part of the direct line of descent.

The general consensus, despite Huxley’s work, became that Archaeopteryx really was the first bird. The trouble was that there was not much connecting it to its ancestral stock or later fossil birds. It sat right in the middle of everything—a key part of the transition without the appropriate bookends. Eventually, in the late 20th century, the discovery of dinosaurs like Deinonychus provided an appropriate rootstock for birds. In fact, the work of John Ostrom, the chief describer of Deinonychus, on Archaeopteryx solidified a connection that students of paleontology now take for granted. The deinonychosaurs (or the “raptors”) were the closest to birds given the close resemblance between them an Archaeopteryx.

Additional fossil finds have complicated the picture. Dinosaurs such as the four-winged Microraptor looked generally similar to Archaeopteryx, yet remained classified in the non-avian dinosaur group. More than that, the discovery of so many feathered dinosaurs brought previous lines of reasoning into question. Feathers, bird-like nesting behavior, bones infiltrated by air-filled sacs, and other features kept moving “avian” traits further back down the family tree. Many traits only seen among birds today appeared at a much earlier date among dinosaurs—Archaeopteryx was not nearly as unique as had originally been thought.

Unfamiliar dinosaurs also have their role to play in this shake-up. Paleontologists are still discovering and delineating dinosaur groups, and one of the most latest is a collection of small, strange creatures called scansoriopteryids. Little is known about these dinosaurs. Known from a handful of little-studied specimens, these unusual dinosaurs appear to be closely related to some of the first unequivocal birds. If this is true then the deinonychosaurs were not nearly as close to bird ancestry as was previously thought, although the scansoriopteryids have been so poorly studied that they are among the most enigmatic of all known dinosaurs.

At this point, how closely Archaeopteryx is related to the first birds is an open question which requires more detailed study. Xu and colleagues conclude that it may not have belonged to the official bird group and was just a very bird-like, non-avian dinosaur. This is not a major categorical difference—remember, the bird lineage is just a subgroup of the coelurosaurian dinosaurs—but represents the distinction among a few minor, tell-tale features near the base of a transition. Teasing out the details of such relationships keep paleontologists quite busy. As you approach the base of a group it becomes increasingly difficult to differentiate between the first members of a novel lineage and their ancestral stock. If you were to compare a modern bird to the dinosaurs which gave rise to birds the differences would be relatively obvious and distinct, but at the point of transition, the evolutionary picture is difficult to resolve. Rather than being an embarrassment, this wonderful frustration emphasizes the truth of evolutionary change.

There’s a lot of tradition and academic inertia behind calling Archaeopteryx the earliest known bird, but that’s something we can no longer take for granted. I think that’s a good thing. The question of what Archaeopteryx is provides a gauge of how much we have learned about bird origins and opens up the field for new debates. Creationists and other members of the anti-science crowd may try to turn the news to their advantage, but in fact, the uncertainty about Archaeopteryx highlights the fact that scientists are beginning to resolve a transition that we have only had the outlines of previously. And Archaeopteryx remains a beautiful example of how transitional features can be detected in the fossil record. Paleontologists only rarely detect direct lines of descent, but creatures that possess intermediate or transitional features help flesh out the way in which great transformations happened. Even if Archaeopteryx falls on the non-avian rather than avian side of the dinosaur family tree, it is still a feathered dinosaur with many traits once thought to be unique to birds. That, alone, is a powerful illustration of evolution, and I have no doubt that Archaeopteryx will remain a classic symbol of how life has drastically transformed.

What Archaeopteryx was and its significance in bird evolution is obviously a very complicated matter, but nuance is not exactly something that news reports do well. I think a number of reports boiled down a complex debate into oversimplified statements. In a video supplement to their story, the Guardian reported, “’Oldest Bird’ Archaeopteryx was a dinosaur, say scientists.” “Of course it was!” I thought—all birds are the descendants of dinosaurs and therefore can be called dinosaurs themselves. Whether Archaeopteryx is a bird or not, it’s still a feathered dinosaur—the headline is equivalent to saying, “Early human Australopithecus afarensis was a mammal, say scientists.” Equally frustrating was the Christian Science Monitor’s “Archaeopteryx may not have been a bird, but just a feathery dinosaur.” JUST a feathery dinosaur? As if feather-covered dinosaurs have suddenly become mundane. More than that, the significance of Archaeopteryx and the many other fuzzy and feathery dinosaurs that have been discovered is that they blur the boundary between what were thought to be two distinct groups and help inform one of the most magnificent evolutionary transformations in the history of life.

But the worst headlines came from news services that just went straight for the most sensationalist spin possible. “Newly discovered dinosaur could disprove ‘earliest bird’ theory” said the Telegraph, though the article itself included only the ambiguous conclusion that the new research “would force experts to reassess current assumptions about how modern birds evolved.” What assumptions? What is being questioned and what are the alternative ideas? The article does not give readers any context, and the headline has just enough of a creationist gloss to make me cringe. Likewise, in what may have been the worst coverage of the story, the Herald Sun asserted “Charles Darwin may have just lost Evolution Exhibit A, otherwise known as Archaeopteryx.” Not only does the story wrongly assert that Charles Darwin used Archaeopteryx as his favorite example of evolution—something I debunked in my book Written in Stone—but the entire piece presents paleontologists as stubborn cranks who are making things up as they go along, or that the change in perspective on Archaeopteryx somehow undercuts what Darwin proposed about evolution. Nonsense. New discoveries are changing our understanding of the natural world every day, and a slight change in perspective acts as a referendum on Darwin’s evolutionary theory only to those with only a superficial understanding of how science actually works.

We will probably continue to see similar headlines and articles as the discussion about Archaeopteryx continues. Paleontologists should question the place and relevance of Archaeopteryx in bird evolution—we should be wary of the pull 150 years of tradition might have as we sift through new finds—but the new study only offers a weakly supported hypothesis that requires a great deal of additional study to test. Archaeopteryx, despite the title given to a summary of the new Nature paper by paleontologist Lawrence Witmer in the same issue, is not yet “An icon knocked from its perch.” As Witmer says in his News & Views piece, the discovery of dinosaurs that are now competing with Archaeopteryx for the title of Earliest Bird means that “we’ve got some fresh work to do,” especially since “Just as Xiaotingia moved Archaeopteryx out of the birds, the next find could move it back in—or to somewhere else within this fuzzy tangled knot that makes up the origins of birds and bird-like dinosaurs.”

So what if Archaeopteryx turns out to be a feathered dinosaur more closely related to Deinonychus than the earliest true birds? Even if this turns out to be the case, the creature will still have played a major part in the history of evolutionary through and helped confirm the connection between dinosaurs and birds. The exact transitional series could turn out to be different, but Archaeopteryx will remain significant in terms of how feathers, and perhaps even flight, evolved. We have a tendency to cherish creatures that slot in neatly within patterns of major evolutionary change—the famous transitional forms of life’s major transformations—but in order to understand those changes we need many other fossils to provide background and context. As far as the evolution of birds is concerned, I have no doubt that Archaeopteryx will remain an important part of that context.

But I wasn’t thinking about all that as I stood in front of the glass case containing the Thermopolis Archaeopteryx in the Wyoming Dinosaur Center. I had not seen the paper at that point, after all, and I pushed the blare of the headlines out of my mind so that I might just stand there and appreciate something beautiful. Call it a bird, a feathered dinosaur, or whatever you like, Archaeopteryx was a gorgeous animal which combined the sleek and deadly anatomy of a predatory dinosaur with the exquisite plumage we so admire in its modern-day cousins. Archaeopteryx was a mosaic of the archaic and what we have thought of as modern—a 150-million-year-old portent of fantastic transformations that, through our understanding of them, have altered the way we see our place in this constantly evolving world.

References:

Witmer LM (2011). Palaeontology: An icon knocked from its perch. Nature, 475 (7357), 458-9 PMID: 21796198

Xu, X.; You, H.; Du, K.; Han, F. (2011). An Archaeopteryx-like theropod from China and the origin of Avialae Nature, 475, 465-470 DOI: 10.1038/nature10288

In the novel Jurassic Park, the fictional scientists of the InGen corporation tried to cook up a batch of dinosaurs using fragments of DNA preserved in Mesozoic mosquito blood. An inventive idea, certainly, but not one that would actually work. In the wake of the book’s blockbuster film adaptation, though, paleontologist Robert Bakker commented that there might be another way to make a dinosaur, or at least something dinosaur-like. Birds, after all, are the living descendants of dinosaurs, and by fiddling with the genetic toggles of living birds, scientists might be able to reverse-engineer a dinosaurian creature.

Now, 18 years later, the “chickenosaurus” project is actually underway, but under the guidance of another well-known paleontologist. Two years ago Jack Horner published his outline of the project with writer James Gorman in the book How to Build a Dinosaur, and he recently provided an overview of the project at a TED talk in Long Beach, California. (Horner also delivered a TED lecture in Vancouver, but on the growth stages of dinosaurs.) The goal isn’t to perfectly re-engineer a Deinonychus or other dinosaur—that is impossible. Instead, Horner wants to use this project to investigate the role of genes and development in evolution, with the resulting creature acting as a “poster chick” for scientific investigation. Maybe a long-tailed chicken with teeth won’t satisfy those who dream of owning a pet dinosaur, but at the very least, the science might tell us something about how living dinosaurs—that is, birds—originated.

Feathers, air sacs, nesting behavior—the earliest birds owed a lot to their dinosaurian ancestors. The first birds also inherited a strong sense of smell.

Modern birds have not been thought of as excellent scent-detectors, save for some super-smellers such as turkey vultures, which detect the scent of rotting carcasses. We typically think of avians as more visual creatures, and in some birds, the part of the brain that processes information from smells is relatively small.

But birds actually have a diverse array of scent-detecting capabilities, and a poor sense of smell may be a more recent characteristic of some lineages. After all, birds have been around for over 120 million years. We wouldn’t expect that birds have always been the same from the time they originated.

We obviously can’t directly test the ability of fossil organisms to detect scents, but, as shown in a study published this week by Darla Zelenitsky and colleagues, the shape of prehistoric brains may hold some crucial clues about the senses of extinct animals. The key was the olfactory bulb. This is a part of the brain—highlighted by the yellow flash in the video above—that is specialized for perceiving scents.

To estimate how important an animal’s sense of smell was, the scientists looked at the size of the olfactory bulb. This follows from a well-established principle in brain anatomy called proper mass—the more important the function of a brain part is to an animal, the larger that brain region will be. In other words, if an animal had a relatively large olfactory bulb it likely relied heavily on scent, whereas a tiny olfactory bulb would indicate the unimportance of scent to that animal. By comparing modern bird brains with virtual brain casts of extinct birds and non-avian dinosaurs, Zelenitsky and co-authors tracked how the sense of smell developed in dinosaurs and the earliest birds.

The brain anatomy of 157 living and fossil species was examined in the study. What the scientists found did not match the conception that birds lost their smelling skills early. Quite the opposite.

Multiple lines of evidence have confirmed that birds evolved from maniraptoran dinosaurs—a subgroup of coelurosaurs containing dinosaurs such as Deinonychus, Struthiomimus, Oviraptor and others—and the brain studies showed that sense of smell improved during the evolution of this group. The dinosaur Bambiraptor, for example, had a sense of smell comparable to that of turkey vultures and other birds that rely on scents to track down food.

This strong sense of smell was passed on to the earliest birds. Rather than decreasing, the relative olfactory bulb size remained stable during the evolutionary transition between non-avian dinosaurs and the first birds. Unexpectedly, olfactory bulb size then increased as archaic bird lineages proliferated, and the earliest members of the modern bird group—the neornithes—were even better-skilled at picking up scents than their predecessors. In fact, Zelenitsky and colleagues suggest, the improved sense of smell in the neornithes might have made them better foragers than earlier types of bird, and this may have some bearing on why they survived the end-Cretaceous mass extinction 65 million years ago while more archaic bird lineages perished.

The results of the new study reverses one of the long-standing misconceptions about birds and their evolution. Some modern bird lineages lost their powerful scent detecting abilities over time, but, early on, birds were as adept at picking up smells as their dinosaur ancestors. Paired with future studies focused on the parts of the brain associated with vision, studies like this will help us better understand how birds and dinosaurs navigated through their prehistoric worlds.

References:

Zelenitsky, D., Therrien, F., Ridgely, R., McGee, A., & Witmer, L. (2011). Evolution of olfaction in non-avian theropod dinosaurs and birds Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.0238

In 1991, the cable channel A&E ran a four-part prehistoric extravaganza hosted by Walter Cronkite and simply called Dinosaur! I was only eight when it aired, and I remember begging my parents to stay up to watch the episodes. Irrepressible little dinosaur fan that I was, I even convinced my third grade teacher to play a tape of the first episode in class one day.

The shows made quite an impression on me. I didn’t know who they were at the time, but for years afterward I could recall seeing paleontologists like Stephen Jay Gould, James Farlow, Dan Chure, David Weishampel, Bob Bakker, John Ostrom, and others explain the latest fossil discoveries. From time to time, puppet dinosaurs popped up in the show. Until Jurassic Park opened two years later, Dinosaur! seared the mid-1990s image of dinosaurs onto my brain, and I was delighted when I was able to dig up the series on YouTube.

What we have learned about dinosaurs in the 20 years since I last saw the show is astounding. Viewed from our current perspective, the show is something of a cultural fossil—a preserved trace of dinosaur science just as dinomania was sweeping the cultural landscape. There is perhaps no better way to ascertain how far we have come than by watching the final episode of the series, “The Tale of a Feather.”

The final episode focused on two interconnected themes: the dinosaurian origin of birds and the extinction of the non-avian dinosaurs. If only the paleontontologists in the show knew about the discoveries that were just around the corner. Dinosaur! debuted five years before feathered dinosaurs began pouring out of China, and today we know that many traits once thought to be unique to birds—from air sacs to nesting behaviors—were actually widespread among dinosaurs. The difference can most readily be seen in the dinosaur puppets used throughout the show. The puppets were generally drab colored and awkward. They weren’t giant lizards, but they were not especially dynamic or bird-like either, existing in a space between the lumbering hulks of earlier restorations and today’s extremely active dinosaurs. The evidence connecting birds and dinosaurs has far surpassed anything anyone thought possible and forever changed how we reconstruct dinosaur lives.

The show’s treatment of dinosaur extinction is also telling of the time it was made. In 1991, the idea that the end-Cretaceous mass extinction was caused by an asteroid strike was still highly controversial. Scientists could not even agree whether the extinction was sudden or gradual. Today the exact details of dinosaur extinction are still being debated, but the “death from above” hypothesis has become widely supported and defended. In a more subtle shift, two of the paleontologists on the show suggested that the sex of dinosaurs was determined by the temperature of their eggs, and that temperature shifts caused overwhelmingly male populations to be born. This idea—extinction due to a lack of females—has since been tossed out, and a forthcoming paper suggesting this same idea has rightly been panned by paleontologists.

It would be a mistake to deride the A&E program for what we now perceive as mistakes. At the time, it presented some of the latest discoveries about dinosaur lives, and in twenty years I am sure that I am going to look back at some of the things I have written and say, “oh geez, if I had only known then…” Old programs like Dinosaur! allow us to see how far we have come and gauge the evolution of dinosaur restorations over time. Who knows how Walking With Dinosaurs 3D or Reign of the Dinosaurs will look two decades from now?

The skeleton of Juravenator under UV light. If you look closely around the middle of the tail, you can see the traces of soft tissue. From Chiappe and Göhlich, 2010.

In 1861, as debates about evolution were brewing among naturalists, two important skeletons were discovered from the Late Jurassic limestone quarries of Germany. Both would be relevant to ideas about how birds evolved. Although not recognized as such until the late 20th century, Archaeopteryx was the first feathered dinosaur ever discovered and was a confirmation that birds had evolved from reptiles. The other creature, Compsognathus, represented a small, exceptionally bird-like dinosaur, and the anatomist T.H. Huxley took it as a proxy for the kind of animal from which birds originated. “There is no evidence that Compsognathus possessed feathers,” Huxley said during his 1877 American lecture tour, “but, if it did, it would be hard indeed to say whether it should be called a reptilian bird or an avian reptile.”

Now another feathered dinosaur has been discovered from the famous German limestone quarries. Named Juravenator starki in 2006, this dinosaur was a close relative of Compsognathus which lived just a little bit earlier on the same prehistoric archipelago. It is one of the most complete dinosaurs from these limestone deposits. From the tip of the snout to very nearly the end of the tail, the whole skeleton was preserved, but there was something special about this animal that could only be seen in the right light.

Earlier this year David Hone and colleagues published a paper showing how examining fossils under ultraviolet light can illuminate soft-tissue structures—like feathers—that would otherwise be hidden. Paleontologists Luis Chiappe and Ursula Göhlich applied the same technique to the Juravenator skeleton, and near the middle of the dinosaur’s tail they found an area of preserved soft tissue. The most easily seen parts of the soft tissue were patches of tiny bumps consistent with the skin impressions of other dinosaurs. Yet there were wispy protofeathers, too. Thanks to high-resolution photography, the remains of downy feathers were also detected, and these were similar to the structures that covered the body of a relative of Juravenator from China called Sinosauropteryx.

The presence of both scaly skin and filamentous feathers makes Juravenator unique among feathered dinosaurs. This combination has not been seen before, but it is consistent with laboratory models of how feathers evolved from scaly skin. Furthermore, it appears that Juravenator was not wholly covered by a coat of fluffy feathers like baby chicks, perhaps indicating that feathery structures appeared on some parts of the bodies of dinosaurs before others. Frustratingly, the extent of soft-tissue preservation on the first Juravenator specimen is extremely limited, but further discoveries of this animal may help us better understand the origins of feathered dinosaurs.

References:

Chiappe, L., & Göhlich, U. (2010). Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen, 258 (3), 257-296 DOI: 10.1127/0077-7749/2010/0125

Thomas Henry Huxley, circa 1870. Image from Wikipedia.

Evolution never got much time in my elementary school science classes. When the topic came up, inevitably near the end of the term, the standard, pre-packaged historical overview came along with it. Charles Darwin was the first person to come up with the idea of evolution, and, despite the ravings of religious leaders offended at our relationship to monkeys, the idea that natural selection adapted life into “endless forms most beautiful” quickly became established among the scientists of the day.

Like many textbook stories, the story of evolutionary discovery my classmates and I were presented with was clean, neat and hopelessly flawed. Darwin was not the first naturalist to propose that evolution was a reality; many of his colleagues thought that natural selection was too weak of a force to affect evolution, and for several decades following the 1859 publication of On the Origin of Species, many naturalists preferred alternative evolutionary mechanisms such as large-scale mutations and internal forces driving organisms onward and upward. Darwin was not even the first naturalist to come up with the idea of natural selection. Many naturalists had previously considered it and thought that it could at best preserve life as is and at worst destroy species. (As for Alfred Russel Wallace and the role he played in the development of evolutionary ideas, my classmates and I didn’t have a clue that he existed.)

The significance of Darwin’s work was in his demonstration of how natural selection could modify life and create a branching pattern of diversity over vast expanses of time. He had worked long and hard to collect all the necessary data to support his case. There was no “Newton’s Apple” type moment—another favorite science myth—in which a Galapagos finch perched on Darwin’s shoulder and whispered the secrets of evolution to the previously clueless naturalist. In Darwin’s time evolution was a frequently discussed issue, and the debate over what natural laws drove the change in species continued long after 1859.

Almost every major figure of the emerging field of evolutionary science has been miscast at one time or another. Richard Owen, one of the first evolutionists, has been traditionally portrayed as a brooding creationist for his opposition to natural selection. St. George Jackson Mivart met a similar fate despite the seriousness with which Darwin took his objections. Charles Lyell, on the other hand, became the white knight of geology who did away with the religiously fundamentalist views of catastrophic change popularized by Georges Cuvier (yet another myth). In order to preserve any semblance of the intellectual March of Progress each character must take up their proper place in the historical drama; they must fall along a simple chain of succession from ignorance to understanding. But among the most pernicious myths are those which seek to honor past scholars for the wrong reasons.

In 1996 a single photograph caused quite a stir at the annual Society of Vertebrate Paleontology meeting in New York City. The picture depicted a small dinosaur in the classic death pose—head thrown back and stiff tail levered straight up—but it was covered in a fuzzy coat of rudimentary feathers. Eventually named Sinosauropteryx, this creature was the first feathered dinosaur to be found since the first specimens of Archaeopteryx were chiseled out of German limestone quarries in the late 19^th century. It was a stunning confirmation of what many paleontologists had come to suspect on the basis of anatomy alone—that birds had evolved from dinosaurs, and many characteristic avian traits appeared among dinosaurs first. John Ostrom, Bob Bakker and other paleontologists were not the first to support this idea. The hypothesis had once been among the most prominent explanations for the origin and birds, and many authorities credited the Victorian naturalist Thomas Henry Huxley as being the first to propose it.

Huxley is often included among Darwin’s supporting cast. He was a prominent public voice for evolutionary science while Darwin mostly kept track of the discussions and debates about evolution through correspondence. In fact, Huxley was among the first scientists to propose graded lines of descent for birds, whales and horses, but his determination of these evolutionary transitions required a circuitous process of discovery and realization. Huxley’s ideas about bird origins, especially, were not a perfect anticipation of our current knowledge, but a set of nuanced hypotheses which relied on Huxley’s idiosyncratic conception of evolution.

Huxley’s views about evolution were influenced by his friendship with Darwin. According to traditional lore, after reading Darwin’s theory in On the Origin of Species Huxley exclaimed, “How extremely stupid [of me] not to have thought of that!” But, a staunch defender of his friend though he was, Huxley’s reading of Darwin did not inspire him to start thinking about transitions in the history of life. Huxley thought that large-scale mutations—evolutionary jumps termed “saltations”—were more important than variations acted upon by natural selection, and so he did not expect the graded chains of transitional forms Darwin’s theory predicted.

A brilliant anatomist, Huxley was primarily concerned with identifying the common denominators of form among organisms. One association of special interest to Huxley was the correspondence between birds and reptiles. While teaching anatomy at the Royal College of Surgeons in 1863, Huxley taught his students that birds were “so essentially similar to Reptiles in all the most essential features of their organization, that these animals may be said to be merely an extremely modified and aberrant Reptilian type.” Rather than explicitly delineate how such a transition could have taken place, however, Huxley was at this point content to highlight the anatomical similarities alone. Life had most certainly evolved—there could no longer be any reasonable doubt—but Huxley’s preoccupation with form and his ambivalence about natural selection prevented him from digging into the subject to any great depth.

The publication of a different book caused Huxley to change course. In 1866 the German evolutionist Ernst Haeckel published Generelle Morphologie. When Huxley read it he started scribbling hypothetical lines of evolutionary descent in his notebooks. The correspondences Huxley had already recognized as a dedicated anatomist could be used to predict lines of descent, and in 1868 Huxley wrote to Haeckel:

In scientific work the main thing just now about which I am engaged is a revision of the Dinosauria—with an eye to the Descendenz Theorie! The road from Reptiles to Birds is by way of Dinosauria to the Ratitaez—the Bird ‘Phylum’ was Struthious, and wings grew out of rudimentary fore limbs. You see that among other things I have been reading Ernst Haeckel’s Morphologie.

To put it another way, Huxley saw a potential evolutionary pathway from small dinosaurs—such as the recently-discovered Compsognathus—through flightless birds and on to flying forms. But this was only an outline of a more nuanced view of evolutionary change Huxley was just beginning to bring together. In 1859 Huxley had presented his view that most major evolutionary transitions must have occurred during “non-geologic time,” or at a date so remote that there were no longer any rocks to record it. The transitional fossils that recorded the evolution of birds would forever be out of the reach of paleontologists, and so the known forms from the fossil record represented only long-lived lineages—“persistent types”—which were records of those earlier changes. Furthermore, even the bird-like dinosaur Compsognathus was found in the same strata as the earliest bird, Archaeopteryx, meaning that the actual transition must have occurred at some earlier time. Dinosaurs, Huxley proposed, could not have been ancestral to birds, but they did represent the form of those ancestors.

Huxley formally presented his ideas to his colleagues the same year that he wrote Haeckel, but his work on the subject was only just beginning. With an eye towards confirming a dinosaur-like ancestor of birds, Huxley pointed out avian traits in the skull of the large predator Megalosaurus and in the hips of the small herbivore Hypsilophodon. He also approached the question from the other side, citing the resemblance between the leg of an embryonic chick and the legs of dinosaurs.

Though only a handful of dinosaur taxa were known, from relative scraps of material, by the late 1860s—certainly far less than the over 1,000 genera known today—Huxley was able to point out bird-like traits in many of them. (Some of those resemblances turned out to be red herrings, e.g. the hip of Hypsilophodon only superficially looked like that of a bird. This dinosaur was not a bird ancestor, but at the time of its discovery it was the only dinosaur with complete hips and Huxley took it to be representative of the group.) Huxley stressed that the creatures included in his transitional sequence from dinosaurs to birds represented the forms of the true ancestors of modern birds. They were, in his words, “intercalary types” which were more like evolutionary “uncles and nephews,” and given the spotty nature of the fossil record the odds were against finding a well-documented series of true ancestors.

By 1870, however, Huxley’s work on the subject slowed. Unlike Darwin, he did not have enough money to retire to the life of a gentleman naturalist and had to write, teach and lecture to make a living. Between all his responsibilities and appointments, Huxley was nearly working himself to death, and in 1872 his wife Nettie sent him on a vacation to Egypt to recuperate. When Huxley returned he threw himself back into science, but in a different way. He largely eschewed paleontology in favor of laboratory anatomy, though he did not abandon the subject of bird origins all together.

In 1876 Huxley began a grand lecture tour of the United States, and among the subjects he had selected for the series was the evolution of birds. The Yale paleontologist O.C. Marsh had just discovered toothed birds from the Cretaceous sediments of Kansas the previous year—a finding that added a little more nuance to the transition Huxley was proposing—and the fossil evidence then known still indicated that birds originated from something akin to small, predatory dinosaurs. Huxley even went as far to say: “There is no evidence that Compsognathus possessed feathers; but, if it did, it would be hard indeed to say whether it should be called a reptilian bird or an avian reptile.”

Huxley did not perfectly anticipate our modern understanding that birds evolved from feathered maniraptoran dinosaurs. Using the rather paltry evidence that was available to him, he proposed a plausible scenario for bird ancestry which was meant to break down any potential anatomical barriers to such a change. Especially during the end of his career, Huxley pointed to his work on bird origins as an indication that evolution was a reality and could be supported with hard evidence from the fossil record even if the actual phases of the transition had not yet been found. Other naturalists such as E.D. Cope, Carl Gegenbaur and Andreas Wagner had also recognized the resemblance between dinosaurs and birds, but it was Huxley who turned these similarities into compelling evidence for evolution by means of natural selection. During a time when the fossil record appeared to be at odds with Darwin’s theory, Huxley endeavored to find examples of transitional forms and he found just that in the evolution of birds from reptiles.

I have no doubt that some readers may be disappointed by the dissolution of a favorite story. Huxley came tantalizingly close to predicting our present understanding but came up short. Yet, though reading Huxley’s original works, I think I am even more impressed by his work. He marshaled a wide array of evidence to create a framework for one of the major transitions in the fossil record but always kept in mind what remained unknown. Huxley’s insistence that we distinguish between direct ancestors and creatures which represent the expected form of those ancestors was especially ahead of its time—to this day paleontologists remind themselves to be careful when drawing out ancestors. Nevertheless, I can’t help but wonder what Huxley would think of all we have learned since his time. There are now scores of feathered dinosaur specimens that unquestionably show that many traits we once thought were unique to birds appeared in dinosaurs first. Rather than dinosaurs being bird-like, we should say birds are dinosaur-like. Call me presumptuous if you like, but I think Huxley would be delighted.

For more details, please see Chapter 5 of Written in Stone and my recently-published paper “Thomas Henry Huxley and the reptile to bird transition.”

References:

Switek, B. (2010). Thomas Henry Huxley and the reptile to bird transition Geological Society, London, Special Publications, 343 (1), 251-263 DOI: 10.1144/SP343.15

A figure of the "London specimen" of Archaeopteryx discovered in 1861. From the Catalouge of Fossil Birds in the British Museum (Natural History), 1891.

Among the many recurring themes on this blog, the evolution of birds from feathered maniraptoran dinosaurs is probably the most prevalent. Hardly a month goes by without a new study relevant to this major evolutionary transition, and as paleontologists discover more they continue to find that many traits once thought to be exclusive to birds were widespread among dinosaurs. Yet this understanding has only coalesced within the last 15 years. For over a century, the early evolution of birds remained a mystery, and numerous suggestions were made about avian origins.

For much of the past 150 years, how the first birds evolved and what sort of animals they originated from depended upon whom you asked. The English anatomist Thomas Henry Huxley proposed that there was a step-by-step transition from small dinosaur-like creatures through flightless birds (like ostriches) to flying birds, whereas his colleague Harry Govier Seeley vehemently disagreed and believed that birds had evolved from pterosaurs. The idea that birds had an aquatic origin—either evolving from swimming dinosaurs or becoming adapted to life in the sea before taking to the air—was also espoused by several naturalists. But one of the most amusing ideas I have yet encountered was an article by W.T. Freeman printed in an 1897 issue of Gentleman’s Magazine.

Freeman had developed his own peculiar way of looking at the history of life. A creationist, but of a different sort than today’s religious fundamentalists, he thought that there was a clear succession of organisms over time in which there were distinct species incapable of evolving into something else. As evidence for this, Freeman cited the fact organisms created near-perfect copies of themselves through reproduction. No organism gave birth to a different species, and even when two species interbred—an inappropriate interaction Freeman deemed “perverted”—the hybrid never became established as a new species.

Within this creationist system, Freeman believed he had found an explanation for Archaeopteryx. Recognized by many naturalists as an early bird with reptilian characteristics such as teeth and a long, bony tail, Archaeopteryx was regularly used as evidence that birds had indeed evolved from reptiles. (“Everything has, or has had, a definite purpose in life,” Freeman wrote, “and the archaeopteryx lived its life in order to bring bliss to the soul of the evolutionist.”) But Freeman took a different view. The mish-mash of bird and reptilian characters indicated that Archaeopteryx was nothing more than a sign of ancient indiscretions:

I suggest that in the earlier days there were ill-developed, low-typed, wallowing birds, also some highly developed reptiles. Perverted sexual instinct exists now, why not then, and as a result of this, why has not the archaeopteryx been an anomalous false hybrid that has been incapable, like other mongrels, of reproducing its kind?

When I first read this, I had to wonder if the essay was meant as some kind of joke or satirical jab at the science of evolution. How could anyone seriously believe that Archaeopteryx was the product of a union between birds and reptiles? Yet Freeman’s essay is serious from start to finish, and I was able to find at least one other essay by him about his off-kilter creationist beliefs.

Frustratingly for Freeman—but fortunately for our understanding of the natural world—the idea that Archaeopteryx was the monstrous offspring of reptile and bird never took off. The animal truly was the first feathered dinosaur ever found, and, even though it took over a century to arrive at this view, the multiple Archaeopteryx specimens discovered so far remain important to ongoing research about the evolution of birds.