A restoration of Nyasasaurus in its Middle Triassic habitat, based on the known bones and comparisons to closely related forms. The description of Nyasasaurus was one of the year’s most important dinosaur stories. Art by Mark Witton.

There’s always something new to learn about dinosaurs. Whether it’s the description of a previously-unknown species or a twist in what we thought we knew about their lives, our understanding of the evolution, biology, and extinction is shifting on a near-daily basis. Even now, paleontologists are pushing new dinosaurs to publication and debating the natural history of these wonderful animals, but the end of the year is as good a time as any to take a brief look back at what we learned in 2012.

For one thing, there was an exceptional amount of dino-hype this year. A retracted paper that mused on the nature of hypothetical space dinosaurs, a credulous report on an amateur scientist who said he had evidence that all dinosaurs were aquatic, and overblown nonsense about dinosaurs farting themselves into extinction all hit the headlines. (And the less said about the Ancient Aliens dinosaur episode, the better.) Dinosaurs are amazing enough without such sensationalist dreck, or, for that matter, being transformed into abominable human-raptor hybrids by Hollywood.

Not all the dinosaurs to wander into the media spotlight were atrocious, though. The glossy book Dinosaur Art collected some of the best prehistoric illustrations ever created, and the recently-released All Yesterdays presented dinosaurs in unfamiliar scenes as a way to push artists to break from severely-constrained traditions. Dinosaurs were probably much more unusual than we have ever imagined.

Indeed, new discoveries this year extended the range of fluff and feathers among dinosaurs and raised the question of whether “enfluffledness” was an ancient, common dinosaur trait. Paleontologists confirmed that the ostrich-like Ornithomimus–long suspected to have plumage–sported different arrangements of feathers as it aged. New insight on the 30-foot-long carnivore Yutyrannus affirmed that even big tyrannosaurs were covered in dinofuzz. And while both Ornithomimus and Yutyrannus belonged to the feathery subset of the dinosaur family tree that includes birds, the discovery of fluff on a much more distantly related theropod–Sciurumimus–hints that feathers were a much older, more widespread dinosaur feature than previously expected. Paired with previous finds, Sciurumimus suggests that protofeathers either evolved multiple times in dinosaurian history, or that the simple structures are a common inheritance at the base of the dinosaur family tree that was later lost in some groups and modified in others.

While some traditionalists might prefer scaly dinosaurs over fuzzy ones, feathers and their antecedents are important clues that can help paleontologists explore other aspects of paleobiology. This year, for example, researchers reconstructed dark, iridescent plumage on Microraptor on the basis of fossil feathers, and, as display structures, feathery decorations will undoubtedly have a role to play in the ongoing debate about how sexual selection influenced dinosaur forms.  Feathers can also be frustrating–a new look at the plumage of Anchiornis and Archaeopteryx will undoubtedly alter our expectations of how aerially capable these bird-like dinosaurs were and how they might have escaped predatory dinosaurs that dined on the prehistoric fowl. Such lines of inquiry are where the past and present meet–after all, birds are modern dinosaurs.

Feathers aren’t the only dinosaur body coverings we know about. Skin impressions, such as those found with the ankylosaur Tarchia, have also helped paleontologists discern what dinosaurs actually looked like. Pebbly patterns in Saurolophus skin can even be used to differentiate species, although paleontologists are still puzzled as to why hadrosaurs seem to be found with fossil skin traces more often than other varieties of dinosaur.

And, speaking of ornamentation, a damaged Pachycephalosaurus skull dome might provide evidence that these dinosaurs really did butt heads. How the adornments of such dinosaurs changed as they aged, though, is still a point of controversy. One of this year’s papers threw support to the idea that Torosaurus really is a distinct dinosaur, rather than a mature Triceratops, but that debate is far from over.

Other studies provided new insights into how some dinosaurs slept, the evolutionary pattern of dinosaur succession, what dinosaur diversity was like at the end of the Cretaceous, and how dinosaurs grew up, but, of course, how dinosaurs fed is a favorite place that lies at the intersection of science and imagination. A poster at the annual Society of Vertebrate Paleontology meeting deconstructed how Tyrannosaurus rex–suggested to have the most powerful bite of any terrestrial animal ever–tore the heads off of deceased Triceratops. The herbivorous Diplodocus, by contrast, munched soft plants and stripped branches of vegetation rather than gnawing on tree bark, and the tiny, omnivorous Fruitadens probably mixed insects with its Jurassic salads. Studying dinosaur leftovers also explained why paleontologists didn’t find more of the mysterious Deinocheirus, which thus far has been identified by only one incomplete fossil–the long-armed ornithomimosaur was eaten by a Tarbosaurus.

We also met a slew of new dinosaurs this year, including the many-horned Xenoceratops, the archaic coelurosaur Bicentenaria, the sail-backed Ichthyovenator, the stubby-armed Eoabelisaurus, and the early tyrannosaur Juratyrant. This is just a short list of species I wrote about–a few that add to the ever-increasing list.

To properly study dinosaurs and learn their secrets, though, we must protect them. One of the most important dinosaur stories this year wasn’t about science, but about theft. An illicit Tarbosaurus skeleton – pieced together from multiple specimens smuggled out of Mongolia–has brought wide attention to the fossil black market, as well as the poachers and commercial dealers who fuel it. The fate of this dinosaur remains to be resolved, but I’m hopeful that the dinosaur will be returned home and will set a precedent for more vigorously going after fossil thieves and their accomplices.

Out of all the 2012 dinosaur stories, though, I’m especially excited about Nyasasaurus. The creature’s skeleton is as yet too fragmentary to know whether it was true dinosaur or the closest relative to the Dinosauria as a whole, but, at approximately 243 million years old, this creature extends the range of dinosaurs back in time at least 10 million years. That’s another vast swath of time for paleontologists to examine as they search for where dinosaurs came from, and those discoveries will help us better understand the opening chapters in the dinosaurian saga. That’s the wonderful thing about paleontology–new discoveries open new questions, and those mysteries keep us going back into the rock record.

And with that, I must say goodbye to Dinosaur Tracking. On Tuesday I’m starting my new gig at National Geographic’s Phenomena. I’ve had a blast during my time here at Smithsonian, and I bid all my editors a fond farewell as I and my favorite dinosaurs head off to our new home.

Editor’s Note: Best wishes to Brian on his future travels and we all thank him for his hard work over the past 4 (!) years, writing every day about something new on dinosaurs. It’s not nearly as easy as he makes it look. – BW

Archaeopteryx had a wing that was different from that of modern birds, and, as seen here, might have been a glider more than a powered flyer. Art by Carl Buell, courtesy of Nicholas Longrich.

How did feathered dinosaurs take to the air? Paleontologists have been investigating and debating this essential aspect of avian evolution for over a century. Indeed, there have been almost as many ideas as they have been experts, envisioning scenarios of dinosaurs gliding through trees, theropods trapping insects with their feathery wings and even aquatic Iguanodon flapping primitive flippers as flight precursors (I didn’t say that all the ideas were good ones). The biomechanical abilities of bird ancestors and their natural history has always been at the center of the debate, and a new Current Biology paper adds more fuel to the long-running discussion.

At present, hypotheses for the origin of avian flight typically fall into one of two categories. Either bird ancestors accrued the adaptations necessary for flight on the ground and, through evolutionary happenstance, were eventually able to take off, or small tree-dwelling dinosaurs used their feathery coats to glide between trees and, eventually, flapped their way into a flying lifestyle. There are variations on both themes, but feathers and the characteristic avian flight stroke are at the core of any such scenario. In the case of the new paper, Yale University paleontologist Nicholas Longrich and colleagues draw from the plumage of early bird Archaeopteryx and the troodontid Anchiornis to examine how feathers changed as dinosaurs started to fly.

In modern flying birds, Longrich and coauthors point out, the wing arrangement typically consists of “long, asymmetrical flight feathers overlain by short covert feathers.” This pattern creates a stable airfoil but also lets the flight feathers separate a little during the upstroke of a wing beat, therefore reducing drag. When the paleontologists examined the fossilized wings of Archaeopteryx and Anchiornis, they found different feather arrangements that would have constrained the flight abilities of the Jurassic dinosaurs.

Both prehistoric creatures had long covert feathers layered on top of the flight feathers. Anchiornis, in particular, appeared to have an archaic wing form characterized by layers of short, symmetrical flight feathers and similarly shaped coverts. Archaeopteryx showed more specialization between the flight feathers and the coverts but still did not have a wing just like that of a modern bird. As a result, Longrich and collaborators hypothesize, both arrangements would have stabilized the wing at the cost of increased drag at low speeds, making it especially difficult for Anchiornis and Archaeopteryx to take off. As an alternative, the researchers suggest that these dinosaurs might have been parachuters who jumped into the air from trees, which might hint that “powered flight was preceded by arboreal parachuting and gliding.”

The trick is determining whether Anchiornis and Archaeopteryx actually represent the form of bird ancestors, or whether the dinosaurs, like Microraptor, were independent experiments in flight evolution. At the Society of Vertebrate Paleontology conference in Raleigh, North Carolina last month, flight expert Michael Habib quipped that all that was needed to make dromaeosaurs aerially competent was the addition of feathers. If Habib is right, and I think he is, then there could have been multiple evolutionary experiments in flying, gliding, wing-assisted-incline-running and other such activities. There’s no reason to think that flight evolved only once in a neat, clean march of ever-increasing aerodynamic perfection. Evolution is messy, and who knows how many ultimately failed variations there were among flight-capable dinosaurs?

The three-step Anchiornis-Archaeopteryx-modern bird scenario of wing evolution fits our expectations of what a stepwise evolutionary pattern would look like, but, as the authors of the new paper point out, shifting evolutionary trees currently confound our ability to know what represents the ancestral bird condition and what characterized a more distant branch of the feathered dinosaur family tree. We need more feathery fossils to further investigate and test this hypothesis, as well as additional biomechanical and paleoecological information to determine whether such dinosaurs really took off from trees. We must take great care in distinguishing between what an organism could do and what it actually did, and with so much up in the air, the debate on the origin of flight will undoubtedly continue for decades to come.

Reference:

Longrich, N., Vinther, J., Meng, Q., Li, Q., Russell, A. 2012. Primitive wing feather arrangement in Archaeopteryx lithographica and Anchiornis huxleyi. Current Biology DOI: 10.1016/j.cub.2012.09.052

Pennycuick’s hypothetical Archaeopteryx ancestor, with membranes between the fingers and no feathers. From Pennycuick, 1986.

How dinosaurs took to the air is one of the longest-running debates in paleontology. Ever since the first skeleton of Archaeopteryx was discovered in 1861, researchers have wondered what the archaic bird might tell us about how flight evolved and how the feathery creature connected its reptilian ancestors with modern birds. Even now, when we know that birds are a feathered dinosaur lineage, the origins of flight remain a contentious issue constrained by the available fossil evidence and our ability to reconstruct how prehistoric creatures moved.

Before paleontologists confirmed that birds are dinosaurs, though, various researchers came up with speculative schemes to explain how birds originated. Naturalist William Beebe, for one, proposed that bird ancestors started off as parachuting reptiles that benefited from expanded scales (his conception of protofeathers). Other scientists came up with their own ideas, imagining everything from seagoing protobirds to gliding reptiles.

When ornithologist Colin Pennycuick wrote his paper “Mechanical Constraints on the Evolution of Flight” in 1986, however, paleontologists were warming to the idea that Archaeopteryx spanned the evolutionary space between living birds and dinosaurs like Deinonychus. This narrowed down the list of early flight scenarios to hotly debated “ground up” or “trees down” hypotheses for the origin of flight, and raised the possibility that feathers evolved among non-avian dinosaurs first. Within these debates, Pennycuick put forward his own idiosyncratic proposal.

Pennycuick believed that birds took to the air by way of the trees. Bird ancestors progressively shrunk in size over time, he believed, and started gliding before they could actually fly. He couldn’t envision that birds evolved from a running, leaping ancestor, as other researchers suggested. For Pennycuick, flight was a gradual extension of gliding.

But what did the ancestor of Archaeopteryx look like? Pennycuick assumed that feathers and flight were closely tied together–something that is not true at all and had already been pointed out by paleontologist John Ostrom in his work on bird origins. Feathers are important for display and insulation and were only later co-opted for flight. All the same, Pennycuick needed a gliding–but featherless–ancestor for Archaeopteryx to make his idea work. So he conjured something really weird.

Pennycuick was puzzled by the clawed fingers of Archaeopteryx. Why would a bird have differentiated fingers? Rather than look at the fingers as just a holdover from dinosaurian ancestry, Pennycuick assumed that they had some kind of flight function. The fingers of Archaeopteryx, he proposed, “could have supported a small, batlike hand-wing.” Such a structure would have been inherited from the featherless ancestor of Archaeopteryx, he proposed, “constituting the main wing area in the stage before feathers were developed.”

Where the feathers of Archaeopteryx came from, Pennycuick couldn’t say. He mused on the need for feathers in the transition from gliding to flight, but he didn’t offer an explanation for how feathers evolved. He only mentioned that “The development of down feathers as thermal insulation is a separate process that may or may not have preceded the development of flight feathers.”

The fuzzy dinosaur Sinosauropteryx proved Pennycuick wrong a decade later. Paleontologists like Ostrom and artists such as Gregory S. Paul had long suspected that feathers were a widespread trait among bird-like theropod dinosaurs, and a flood of exceptional fossils has shown that feathers and their precursors have a deep, deep history. Dinofuzz, or structurally similar body coverings, might even go back to the root of the Dinosauria. How evolutionary forces molded those adornments, however, and what drove the evolution of flight feathers, remain as aggravatingly contentious as ever.

[Hat-tip to paleontologist Victoria Arbour for bringing this paper to my attention]

Reference:

Pennycuick, C. 1986. Mechanical Constraints on the Evolution of Flight. Memoirs of the California Academy of Sciences. 8, 83-98

Another year, another fantastic spate of dinosaur discoveries. Even as 2011 draws to a close, the findings keep rolling in—from the way Deinonychus used its killer cutlery to the first record of sauropod dinosaurs from Antarctica and sexual selection among dinosaurs. There has been such a glut of interesting papers that it would be impossible to mention every bit of dinosauriana from this year, but here is a partial listing of some of the stories that caught my eye.

Dinosaur Growth

Everyone knows that there are lots of unknown dinosaur species left to be discovered. What has become increasingly contentious is the question of how many species can be counted among what has already been collected. This year saw a continuation of the 2010 “Toroceratops” debate with a paper on the enigmatic Nedoceratops by Andrew Farke early in the year, followed by a response to his paper by John Scannella and Jack Horner this month. Likewise, paleontologists suggested that the hadrosaur Anatotitan and the tyrannosaur Raptorex were really just growth stages of other known dinosaurs (the latter being similar to Tarbosaurus, a juvenile of which was also described this year).

Dinosaur senses

How did dinosaurs perceive their world? Two significant papers approached this question—one focused on smell (see the video above), and the other vision. As with studies of dinosaur growth, though, investigations of dinosaur senses can be controversial. Last week’s issue of Science included a comment and reply about the idea that the bony rings preserved in the eyes of some dinosaurs might be used to reconstruct the time of day when the animals were most active.

Archaeopteryx

This year marked the 150th anniversary of the discovery of Archaeopteryx. But 2011 has been full of ups and downs for the Urvogel. Even though an 11th specimen of the feathered dinosaur was announced, a controversial paper proposed that the creature was not an early bird but rather a non-avian dinosaur more distantly related to the first birds. Exactly what Archaeopteryx is and what that interpretation means for our understanding of bird evolution will continue to be debated.

New species

New dinosaurs are named just about every week, but two in particular caught my eye: Brontomerus, a sauropod whose name translates to “thunder thighs,” and Teratophoneus, a short-snouted tyrannosaur. (I just realized that both were found in Utah, though, so perhaps I have a bias for my adoptive state!)

That is just a smattering of findings from 2011. Shout out your favorite 2011 dinosaur discoveries in the comments. And, if you want to see how 2011 compares to previous years, see my lists from 2010 and 2009.

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.

Other fossilized beasts might be more intimidating than Archaeopteryx, but few others have played such an important role in our understanding of evolution. Courtesy of Brian Wolly.

A dispatch from Smithsonian.com’s associate web editor Brian Wolly:

Earlier this month, I took an extended vacation overseas ostensibly for a friend’s wedding but also to explore continental Europe. The wedding date conveniently allowed me to be in Munich for the start of Oktoberfest, an overwhelming experience in and of itself that’s better left for another Smithsonian blog. But when I read in my guidebook that Munich had a paleontology museum, and a free one at that, I couldn’t pass up the chance to contribute to Dinosaur Tracking. Since Bavaria’s very own Archaeopteryx was named 150 years ago today, on September 30, 1861, here’s my account of the small but charming Paläontologisches Museum München.

Located on the campus of Ludwig Maximillian University, the museum has a quaint, meditative quality that outstrips its otherwise aged appearance. When I visited, high school art students were sketching the fossils of their choosing; had they not been there, I’d have been mostly on my own. All the captions were in German, understandably, so I was left with just my imagination to decipher the stories behind these dinosaurs and other fossils. Considering that most of what I know about dinosaurs I learned from Brian, I had a great time comparing notes from three years of producing the blog to the objects in front me. For instance, on the second floor was the museum’s shrine to Archaeopteryx, including a couple of model reconstructions and the Munich specimen, a subject that we’ve covered heavily in this space. The 150-million-year-old Archaeopteryx historically has been considered the direct ancestor of birds, a designation that is recently under dispute.

On a rainy Sunday afternoon, the museum was the perfect antidote for my Oktoberfest-addled brain. For more photos, check out the gallery and let us know in the comments what other great paleontology museums you’ve discovered on your vacations.

View our gallery of photos from the Munich Paleontology Museum.

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

A 44-million-year-old fossil of a feather louse. From Wappler et al., 2004.

Hunting dinosaurs is a dangerous business. Scores of fictional, time-traveling hunters have learned this lesson the hard way, but arguably the most unfortunate was the protagonist of Brian Aldiss’ short story “Poor Little Warrior.” All Claude Ford wanted to do was get away from his disappointing life and unhappy marriage by gunning down prehistoric monsters. Slaughtering a swamp-dwelling Brontosaurus briefly satisfied his escapist desires, but, unfortunately for Ford, the dinosaur had been home to scores of lobster-sized parasites that scurried off their dead host and onto the closest, warmest living thing.

Paleontologists have not yet found such monstrous Mesozoic parasites, but familiar pests did afflict dinosaurs. Tiny trematode and nematode worms lived in the guts of predatory dinosaurs, and Tyrannosaurus itself was plagued by a harmful microorganism commonly found among modern pigeons. But not all dinosaur parasites were internal. Although not as terrible as Aldiss’ creatures, prehistoric lice may have made the lives of many dinosaurs very itchy.

The prehistory of lice is poorly understood. Out of five supposed fossil lice scrutinized by entomologist Robert Dalgleish and colleagues in 2006, only one, a 44-million-year-old specimen described by Dalgleish, Torsten Wappler and Vincent Smith two years earlier, turned out to be the genuine article. Curiously, though, the single fossil specimen appeared to be a close relative to feather lice found on modern birds, and the researchers who described it suggest that birds may have “inherited [lice] from early-feathered theropod dinosaurs.”

(A 100-million-year-old relative of lice was announced in 2006, but it was a “booklouse” that was not an animal parasite.)

As yet, no feathered dinosaur specimen has been found with preserved lice, but a Biology Letters study just published by Smith and a different team of collaborators suggests that the pests might have taken up residence on some Cretaceous species. This hypothesis is based on comparisons of modern louse lineages. Since the prehistoric feather louse and the older “booklouse” remain the only finds close to the early history of lice, the scientists behind the new research used the genetics of living louse species to estimate when their respective lineages would have diverged from one another.

What the scientists came up with was a hypothetical tree of louse evolution. The genetic divergence estimates suggest that parasitic lice were diversifying just after 100 million years ago in a Late Cretaceous world teeming with hosts. Exactly which hosts these insects parasitized is unknown.

Even though news reports about the new study have focused on the likelihood that at least some dinosaurs were bothered by lice, the aim of the research was to use a fresh line of evidence to ascertain the timing of when lineages of modern birds and mammals began to appear. This is a subject of some dispute among scientists. Many paleontologists place the major radiation of modern bird and mammal groups after the end-Cretaceous mass extinction about 65 million years ago, but scientists using genetic and molecular techniques have suggested that these lineages originated deeper in the Cretaceous. Since lice are relatively host-specific and are associated with particular groups of birds and mammals, Smith and co-authors used the evolutionary pattern of lice to draw bird and mammal lineages back into the heyday of the dinosaurs. The lice appeared to track what was believed to be the early origins of modern groups.

But the tight connection between extant louse families and lineages of modern mammals and birds is an assumption. If the new study is correct, parasitic lice proliferated during the Late Cretaceous, when there were already plenty small mammals and feathered dinosaurs running around.

Smith and co-authors state that Archaeopteryx was the oldest-known feathered dinosaur at approximately 150 million years old, but Anchiornis may have pre-dated its more famous cousin by 10 million years or so. Either way, feathers and feather-like body coverings had already been present for over 50 million years before parasitic lice evolved. Smith and colleagues also cite the oldest known fossil hair as dating to about 55 million years ago, but paleontologists have found the exquisitely preserved bodies of much older mammals with intact fur, the approximately 125-million-year-old Eomaia being just one example. As with feathered dinosaurs, furry mammals were around for a long time before the first lice, and studies of fossil mammal evolution have also confirmed that there were many now-extinct groups of mammals present during the Late Cretaceous. Perhaps parasitic lice got their start on feathered dinosaurs and archaic mammals and were only inherited by lineages with living descendants later on.

Smith may have summed up the significance of the new findings best in a quote he gave to the New York Times: “The louse phylogeny adds one more piece of data to this puzzle. It says lice are old, predate the Cretaceous-Paleogene boundary, and must have been living on something.” What those “somethings” were remains unclear. Evolutionary estimates based on genetics make predictions about what may yet be found, and it will be up to paleontologists to test these hypotheses with the remains of long-dead creatures.

References:

DALGLEISH, R., PALMA, R., PRICE, R., & SMITH, V. (2006). Fossil lice (Insecta: Phthiraptera) reconsidered Systematic Entomology, 31 (4), 648-651 DOI: 10.1111/j.1365-3113.2006.00342.x

Smith, V., Ford, T., Johnson, K., Johnson, P., Yoshizawa, K., & Light, J. (2011). Multiple lineages of lice pass through the K-Pg boundary Biology Letters DOI: 10.1098/rsbl.2011.0105

Wappler, T., Smith, V., & Dalgleish, R. (2004). Scratching an ancient itch: an Eocene bird louse fossil Proceedings of the Royal Society B: Biological Sciences, 271 (Suppl_5) DOI: 10.1098/rsbl.2003.0158

The official 150th Anniversary Archaeopteryx Commemorative 10 Euro Silver Coin issued by the Federal Republic of Germany.

Over the past fifteen years, paleontologists have described more than twenty species of feathered dinosaurs. Even dinosaurs once thought to have dry, scaly skin, such as Velociraptor, have turned out to have feathers. But paleontologists have actually known of at least one feathered dinosaur since the mid-19th century. They just did not know to call it a dinosaur.

In 1861, the German paleontologist Hermann von Meyer described two remarkable fossils preserved in slabs of 150-million-year-old limestone. The first was a single feather—a sure sign that birds have been around for quite a long time—but the second was not as easy to interpret. A partial skeleton surrounded by feathers, the creature seemed to be almost equal parts reptile and bird. Since the skeleton had come from the same type of limestone quarry as the feather, though, von Meyer concluded that both fossils represented the same animal, and he applied the name he had given the feather to the skeleton. Together, these were the first recognized remains of Archaeopteryx lithographica.*

Archaeopteryx immediately became one of the most famous fossil creatures ever discovered. The trouble was that no one could agree on what it was or its relevance to the evolution of other animals. Richard Owen, who purchased the skeleton for what is now London’s Natural History Museum, thought that Archaeopteryx was the earliest known bird, whereas his rival Thomas Henry Huxley thought that it was an evolutionary dead end that did not tell naturalists much about how birds actually evolved. Even though many naturalists recognized that Archaeopteryx was important to questions about how birds evolved from reptiles, there was very little agreement about how that change occurred.

It has only been in the past few decades, with the confirmation that birds are just modified dinosaurs, that Archaeopteryx has been placed in its proper evolutionary context. Although now pre-dated by the feathered dinosaur Anchiornis, Archaeopteryx remains one of the oldest feathered dinosaurs known and is still central to questions about bird origins. (Whether it is actually the earliest bird, though, depends on how we define what a bird is, something that has become increasingly difficult as paleontologists have found more dinosaurs with bird-like characteristics.) The several specimens of Archaeopteryx now known are some of the most exquisite and most important fossils ever found, and so it is fitting that this feathered dinosaur gets a little extra attention for its big 150.

Over at Pick & Scalpel, paleontologist Larry Witmer reports that Germany will be issuing a special 10-Euro commemorative coin imprinted with the famous Berlin specimen of Archaeopteryx (which was discovered in 1877). These will be available on August 11th of this year, just a few days before the 150th anniversary of the first written mention of the fossil. Germany’s Humbolt Museum will also be opening a new exhibit called “Feathered flight—150 years of Archaeopteryx.” For now, that is all that is formally planned to celebrate Archaeopteryx, but Witmer promises that he’ll be adding photos to a Facebook Archaeopteryx gallery throughout the year, and I plan on writing a few posts about this famous fossil as we approach the big August anniversary.

*I say “first recognized” because an Archaeopteryx specimen was discovered in 1855 and misidentified as a small pterosaur by von Meyer in 1875. Its true identity was not discovered until John Ostrom reexamined it in 1970.

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

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.

A restoration of the early bird Jeholornis by artist Matt Martyniuk. From Wikipedia.

Since the description of the fuzzy-feathered dinosaur Sinosauropteryx in 1996, paleontologists have been inundated with a still-flowing flood of fossil evidence confirming that birds are living dinosaurs. More than that, many of the characteristics we once thought were unique to birds—from air-sacs to infestations of peculiar microorganisms—were common among dinosaurs, too, and every year it seems that dinosaurs become just a little more bird-like. This does not mean that we now understand everything we need to know about the origin of birds, however. With so many unique fossils changing our understanding at such a rapid rate, the exact details of when the first birds evolved and which lineage of feathered dinosaurs they originated from are still unclear.

Our changing understanding of bird origins is addressed in the Chinese Science Bulletin by paleontologists Xu Xing, Ma Qing Yu and Hu Dong Yu. The key to this evolutionary pattern is Archaeopteryx, a 150-million-year-old feathered dinosaur traditionally regarded as the earliest known bird. This sets the origin of birds in the Late Jurassic, but many of the feathered coelurosaurs—the larger group of theropod dinosaurs which birds are nested in—known so far lived after Archaeopteryx. The earlier, Jurassic dinosaurs that would have been ancestral to both birds and the other feathered dinosaurs have been notoriously difficult to find, but better sampling of Jurassic-age strata have provided more context for the origin of birds and feathered dinosaurs.

In their review, the authors list the recent discovery of many Jurassic and Early Cretaceous coelurosaurs, from the early tyrannosaur Proceratosaurus to the strange, tiny dinosaur Epidexipteryx. Together these specimens help flesh out the pattern of early coelurosaur evolution by allowing scientists to determine which traits are archaic and which are later specializations, and this may shake up the traditional picture of bird origins.

Two scenarios for the relationships of early birds and their closest relatives among dinosaurs. On the left, dinosaurs such as Epidexipteryx are the closest relatives of early birds, including Archaeopteryx. On the right is an alternate scenario in which Archaeopteryx is closely related to dinosaurs such as Troodon and Velociraptor, while all other early birds were more closely related to oviraptorosaurs and Epidexipteryx. In this arrangement, the authors propose that all these dinosaurs could be rightly called "birds." From Xu, et al. 2010.

Parsing the evolutionary relationships of birds requires a fair amount of esoteric scientific terms. Even though the deinonychosaurs—a group made up of troodontids such as Saurornithoides and dromaeosaurids such as Velociraptor—have typically been taken as the closest relatives of the first birds, the new paper proposes that they are a bit further removed from bird origins. The breakdown would look something like this. Archaeopteryx, placed in the context of all the feathered dinosaurs we now know of, would group with the deinonychosaurs, whereas all definitive early birds would be more closely related to Epidexipteryx and oviraptorosaurs such as Citipati and Incisivosaurus. (See the evolutionary tree on the right above.)

This new arrangement has yet to be fully tested and analyzed—it is a provisional hypothesis which will rest on further discoveries—but if correct it raises the sticky question of what we call a bird. If we keep Archaeopteryx as a bird in this arrangement, then all the deinonychosaurs, the oviraptorosaurs, and Epidexipteryx would be birds, too. Then again, we could strip Archaeopteryx of its long-held title of “earliest known bird” and give that title to Jeholornis, thus keeping the more traditional image of what a bird is. Admittedly, the latter option makes more sense to me than extending the “bird” designation to such a wide group of feathered dinosaurs, but no doubt what is or is not an early bird will be something that paleontologists will be grappling with for some time to come. Frustrating, perhaps, but it is also wonderful that we have so many well-preserved fossils that the distinction between bird and non-avian dinosaur has become so difficult to figure out!

References:

Xu, X., Ma, Q., & Hu, D. (2010). Pre-Archaeopteryx coelurosaurian dinosaurs and their implications for understanding avian origins Chinese Science Bulletin DOI: 10.1007/s11434-010-4150-z

An SRS-XRF scan of the Thermopolis Archaeopteryx, showing the skull, one of the hands, part of the backbone, and other parts of the skeleton. The green color indicates the presence of zinc. From the PNAS paper.

Scientists have known about the feathered dinosaur Archaeopteryx for over a century and a half, but scientists are using new techniques to get a better look at this creature and its close relatives. Within the past few months alone, paleontologists have described how they have used laboratory techniques to determine what color some feathered dinosaurs might have been, how Archaeopteryx grew, how feathers were arrayed around the body of Microraptor and, in a new study published in PNAS, how some Archaeopteryx fossils may contain more fine detail than was previously appreciated.

Specimens of Archaeopteryx are rare and vary greatly in terms of their preservation, and one way in which paleontologists keep track of these fossils is by giving them informal names. The first skeleton to be discovered, the one which was purchased for the British Museum of Natural History (now the Natural History Museum) and described by Richard Owen, is known as the “London specimen,” and one of the more recent specimens to come to the attention of scientists has been called the “Thermopolis specimen” after its home at the Wyoming Dinosaur Center in Thermopolis, Wyoming. This latter specimen formed the basis of the new study in which an interdisciplinary team of scientists used X-ray technology to try and detect the chemical composition of the fossil.

By using a kind of scanning technology called SRS-XRF, the scientists expected to detect the distribution of chemicals in the skeleton and the surrounding rock. This would allow them to get a better idea of how the skeleton became fossilized and what it may have looked like in life. When the scientists ran a scan looking for phosphorous, for example, the shafts of the dinosaur’s arm feathers became highlighted, showing the chemical traces of the structures that were otherwise missed. A different scan also showed that the skeleton preserved a high amount of zinc, meaning that at least some of the original bone chemistry of the dinosaur had been preserved. Despite being over 145 million years old, some of the original chemical material of the fossil remained intact.

This study, like the report of the use of UV light to detect otherwise hidden patterns on fossils, is significant because it provides a new way for scientists to look at fossils. By using SRS-XRF technology, paleontologists can achieve a better understanding of how much original material might remain in a fossil and how that skeleton came to be preserved. Likewise, this method can help illuminate structures on slabs which are invisible to the naked eye, something that will no doubt have important applications for the exceptionally preserved specimens of feathered dinosaurs in China. Through such interdisciplinary work, paleontologists are better able to understand the life of the past and how it came to be preserved, and hopefully this study will help spur further research on other fossils.

Bergmann, U., Morton, R., Manning, P., Sellers, W., Farrar, S., Huntley, K., Wogelius, R., & Larson, P. (2010). Archaeopteryx feathers and bone chemistry fully revealed via synchrotron imaging Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1001569107

The Munich specimen of Archaeopteryx which was sampled in this study. From the PLoS One paper.

Modern birds grow amazingly fast. After hatching, many species grow to adult size in a matter of days to weeks. But a new study published in the journal PLoS One suggests that birds did not always exhibit the same rapid rate of growth. By looking at chips of bone taken from the legs of some of the earliest birds and their close dinosaur relatives, paleontologist Gregory Erickson and colleagues found that when it came to growing up, early birds like Archaeopteryx were a lot more like dinosaurs than their living relatives.

In order to study how Archaeopteryx and other early birds (such as Jeholornis and Sapeornis) grew, paleontologists had to move beyond gross anatomy and look at the microscopic structure of the fossilized bone sampled from the legs of the selected specimens. Different growth rates are represented by the presence of patterning of different kinds of bone, and what the scientists expected to find was rings of bone filled with holes for blood vessels that represent rapid growth. Instead they found bone tissue that was not well-supplied by blood vessels and was more similar to that of slow-growing animals, like living reptiles.

This presented something of a paradox. Larger dinosaurs that were closely related to birds, but not actually birds, had bone tissue indicative of rapid growth—yet the earliest birds did not. Why should this be? The scientists proposed that it may be a matter of size.

The larger the animal that was studied, the more their bones seemed to indicate fast growth. The small dinosaur Mahakala, by contrast, exhibited bone types more similar to that seen in the early birds. This suggested that growth patterns were tied to size and that the earliest birds had inherited their relatively slow growth rate from their small dinosaur ancestors. Indeed, while presently recognized as the earliest bird, Archaeopteryx had far more in common with its dinosaur forebears than modern birds, leading the authors of the paper to conclude, “Archaeopteryx was simply a feathered and presumably volant [flying] dinosaur.”