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A reconstruction of Patagonykus. The newly-described Bonapartenykus was a close relative of this dinosaur. Image from Wikipedia.

Alvarezsaurs are Cretaceous mysteries. These small dinosaurs, a feathered subgroup of coelurosaurs, had long jaws studded with tiny teeth, and their arms were short, stout appendages that some researchers hypothesize were used to tear into anthills or termite mounds. But no one knows for sure. We understand very little about the biology of these dinosaurs, but even as we puzzle over their natural history, more previously unknown genera are being found. The latest is Bonapartenykus ultimus from the Late Cretaceous of Patagonia, and what makes this dinosaur so special is what was found with its bones.

Paleontologists Federico Agnolin, Jaime Powell, Fernando Novas and Martin Kundrát describe the new dinosaur in an in-press Cretaceous Research paper. The alvarezsaur was not in good shape when the researchers found it. While some of the bones, particularly those of the leg, were close to their original articulation, Bonapartenykus is represented by an incomplete set of partially damaged bones, without a skull. In life, the dinosaur is estimated to have been about eight and a half feet long. (Subtle characteristics of the preserved vertebra, shoulder girdle, and hips are what led Agnolin and co-authors to identify this animal as an alvarezsaur despite the paucity of bones.) But there was also something else. Next to the bones were the battered remnants of at least two dinosaur eggs. Could these be fossil evidence of a Bonapartenykus that was protecting its nest?

Determining who laid those eggs is a difficult task. No evidence of embryos has been found inside the egg, so we can’t entirely be sure of what kind of dinosaur was growing inside. The close association between the fossils is the primary line of evidence that the eggs might be attributable to Bonapartenykus. This is the hypothesis favored by Agnolin and co-authors, but they doubt that the small site represents parental care. There is no evidence of a nest. Instead the scientists suggest that the two eggs may still have been inside the dinosaur when it died—a hypothesis based on the previous discovery of an oviraptorosaur from China with a pair of eggs preserved where the dinosaur’s birth canal would have been. When the alvarezsaur perished, the eggs may have fallen out of the body and been preserved with the bones.

Yet I wonder if there might be alternative explanations. Just because fossils are found together does not necessarily mean that the organisms those fossils represent interacted in life. Making connections between organisms found at the same site requires a detailed understanding of taphonomy—what happened to those organisms from the time of death to discovery. In this case, the bones of  Bonapartenykus are scattered and poorly preserved, and the eggs were also partially broken. Did the animal simply fall apart, as the authors seem to suggest, or were the bones and eggs brought together through rushing water? Perhaps the body of Bonapartenykus was carried by a water flow to the location of the eggs, fell apart after the water receded and then was buried again. This is a bit of armchair speculation on my part, and the hypothesis proposed by Agnolin and co-authors is a reasonable one, but we need a detailed understanding of how this little fossil pocket formed if we are to understand the relationship between the eggs and the bones. The geological and taphonomic details of the fossil site are important for framing hypothesis about what happened so many millions of years ago. We may have to wait for more intricately preserved fossils to be sure. A Bonapartenykus preserved on a nest, or a female dinosaur with eggs preserved within her hips, would do nicely.

References:

Agnolin, F., Powell, J., Novas, F., & Kundrát, M. (2011). New alvarezsaurid (Dinosauria, Theropoda) from uppermost Cretaceous of north-western Patagonia with associated eggs Cretaceous Research DOI: 10.1016/j.cretres.2011.11.014

An Allosaurus threatens a Stegosaurus at the Natural History Museum of Los Angeles County. Photo by the author.

Wherever you go in the United States, you’re probably no more than a few hours away from a dinosaur skeleton. The “ruling reptiles” are virtually everywhere. From field sites to museum displays, the country is dotted with dinosaurs, and to coincide with Smithsonian magazine’s new Evotourism feature I have compiled a short “Dinotourism” subset of destinations for the Mesozoic-minded.

The Dinosaur Diamond: Utah and Colorado form the heart of dinosaur country. A scenic byway system called the Dinosaur Diamond links some of the top spots along the border of the two states. Among the highlights are the Allosaurus-rich bonebed at the Cleveland-Lloyd dinosaur quarry in the west; Dinosaur National Monument and the dinosaur-infested towns of Vernal and Dinosaur, Colorado to the north; Fruita, Colorado’s Dinosaur Journey Museum to the southeast; and dinosaur track sites around Moab, Utah to the south. Some of the points along the byway are also within a few hours of other dinosaur attractions around Salt Lake City and Denver, making the Dinosaur Diamond an especially handy system for anyone in want of a Jurassic road trip.

Dinosaur Park: Dinosaurs are not only found out West. Maryland recently set aside a small patch of exposed Cretaceous time in the form of Dinosaur Park in the town of Laurel. If you plan your trip right, you may even get to poke around the remaining fossil-bearing layers on open-house days. Don’t expect to find any complete dinosaurs, though—you need a sharp eye to detect the small, isolated bones and teeth that come out of this site.

American Museum of Natural History: No list of top dinosaur sites would be complete without the American Museum of Natural History. The Allosaurus vs. Barosaurus battle in the Theodore Roosevelt Rotunda and the fourth floor dinosaur halls are magnificent galleries of dinosaurian celebrities, made all the more rich by the imprint of history. Even though the dinosaur halls received an overhaul in the 1990s—including some chiropractic work of Tyrannosaurus and the correct head for Apatosaurus—many of the old specimens could not be moved or altered, and so they remain in the same positions as they were mounted in when famous paleontologists such as Barnum Brown and Henry Fairfield Osborn stomped around the place. The AMNH is also remarkable for placing their dinosaurs in an evolutionary context. If you follow the pathways through the exhibits carefully, you can see the big picture of dinosaur evolution.

Petrified Forest National Park: Although this park in eastern Arizona does not boast many dinosaurs, that is exactly what makes it significant. Petrified Forest National Park preserves a spectacular landscape of the Late Triassic time before dinosaurs became the dominant vertebrates on land. The slender, graceful theropod dinosaur Coelophysis has been found here, but most of the animals this creature lived alongside belonged to groups such as the crocodile-like phytosaurs, the “armadillodiles” called aetosaurs, and powerful, deep-skulled predators called “rauisuchians,” among others you can see at the park’s visitor centers. If you want to see the vestiges of the early days of the dinosaurs, this national park is one of the most beautiful places to go.

Museum of the Rockies: There are plenty of dinosaur exhibits in American museums large and small, but the Museum of the Rockies in Bozeman, Montana sets itself apart by putting research and significant specimens up front. The skull of a juvenile Daspletosaurus, the “Wankel rex,” parts of “Big Al” and a complete growth series of Triceratops skulls are just a few of the remarkable displays in the museum’s dinosaur hall. Even better for hardcore dinosaur fans, the museum updates the plaques attached to the exhibits to highlight recently published research and even provides citations for those who want to track down the relevant papers when they get back home.

Yale Peabody Museum of Natural History: Yale University’s Peabody Museum of Natural History may initially seem to be a strange addition to this list. Their dinosaur hall is painfully drab and out of date (although a renovation is scheduled in the years to come). But what makes this place an essential stop for any dinosaur aficionado is Rudolph Zallinger’s Age of Reptiles mural. This fresco secco is a masterpiece of modern art and represents dinosaurs as paleontologists understood them during the mid-2oth century. (The often-reproduced smaller version on books and posters came from a draft Zallinger created for himself as a guide—the actual mural is different than the scaled-down reproductions you have seen before.) Even better, the dinosaur hall juxtaposes this outdated imagery with that which replaced it. At the back of the hall is a leaping Deinonychus—the sickle-clawed theropod described by Yale paleontologist John Ostrom in 1969 that helped spark the “Dinosaur Renaissance.” If you kneel down just right, you can see the predator against a background of Zallinger’s plodding dinosaurs.

St. George Dinosaur Discovery Site at Johnson Farm: Dinosaur bones are great, but tracks hold their own charms. After all, footprints represent the actual behavior of once-living animals, and the St. George dinosaur Discovery Site at Johnson Farm in southern Utah has an abundance of fossil tracks. Modeled after the working-museum model of Dinosaur National Monument, this site is a museum built over an early Jurassic track site covered by dinosaur footprints. Particular track specimens line a pathway around the museum, but visitors can also see the intact surface on which many footprints are still preserved.

Natural History Museum of Los Angeles County: What’s better than one Tyrannosaurus? A Tyrannosaurus trio. That’s the view taken by the Natural History Museum of Los Angeles County‘s new dinosaur exhibit, which presents a growth series of three Tyrannosaurus rex as its centerpiece. But that’s not all. The new exhibit mixes updated skeletal mounts of Carnotaurus, Triceratops and other dinosaurs with beautiful artwork and interactive displays. The top floor of the exhibit, in particular, features multiple displays on paleobiology and how paleontologists extract information about dinosaur lives from fossil bone. An additional perk—the museum has detailed dinosaur puppets that regularly put on shows and sometimes wander the museum halls. The adorable, fuzzy Tyrannosaurus juvenile alone is worth a visit.

Fernbank Museum of Natural History: During the past two decades, South America has yielded some of the most impressive dinosaur giants. The casts of two such creature form the centerpiece of Georgia’s Fernbank Museum of Natural History. Although reconstructions of the enormous theropod Giganotosaurus can be seen at other museums, the Fernbank is special in presenting the carnivore alongside a cast of the absolutely immense sauropod Argentinosaurus—perhaps the largest dinosaur of all time. If you want to have that feeling of being dwarfed by Mesozoic giants, this display is what you might be looking for.

Field Museum of Natural History: If Chicago’s Field Museum of Natural History has one claim to dinosaurian fame, it is “Sue,” a nearly complete Tyrannosaurus rex. There’s no better place to get a feel for what the great Cretaceous tyrant was actually like. But don’t let Sue’s star power outshine the museum’s other dinosaurs. In addition to the big Brachiosaurus out front, the Field also places dinosaurs in the context of evolution in their Evolving Planet exhibition. Paleo-art fans will also find much to enjoy—the Field is home to some classic renderings of prehistoric life by the highly-skilled paleo-artist Charles R. Knight.

Dinosaur Provincial Park: This isn’t an American dinosaur site, but is important enough and close enough to squeeze its way into the list. Located in Alberta, Canada, the strata of Dinosaur Provincial Park has supplied many of the world’s major museums, including the AMNH, with spectacular dinosaur fossils and continues to yield more information about dinosaur biology, ecology and evolution near the end of their reign. This park is also within a few hours’ drive of the Royal Tyrrell Museum and the dinosaur-populated town of Drumheller, Alberta.

This is just a short list of a few highlights—there are plenty of other field sites and museums out there, including Smithsonian’s National Museum of Natural History (a.k.a. The Evolution Museum). Do you have additional recommendations? Let us know in the comments.

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 Suarophaganax (left) harries an enormous Diplodocus at the New Mexico Museum of Natural History and Science. Photo by Flickr user gwarcita.

Tyrannosaurus rex has been the standard for dinosaur ferocity for more than a century. This dinosaur was the “prize fighter of antiquity,” as the New York Times proclaimed in 1906, but there have been a number of heavyweight challengers for the title of prehistory’s deadliest dinosaur. Among the most recent have been Spinosaurus, Giganotosaurus and Carcharodontosaurus—different sorts of predators that may have out-stretched and out-weighed the tyrant king. In 1941, Natural History ran a feature article on an excavation in the Late Jurassic rock of Oklahoma that turned up the “greatest predator of his time”—a dinosaur “equal in ferocity to Tyrannosaurus rex though he preceded this famous monster by 65 million years.” This was Saurophaganax, a huge predator with a twisted history.

The roughly 150-million-year-old predator was a New Deal dinosaur. According to the article, written by Grace Ernestine Ray, in 1931 cattlemen Pard Collins and Truman Tucker stumbled across some very large bones in the vicinity of Kenton, Oklahoma. They told University of Oklahoma paleontologist J. Willis Stovall about their discovery, and after seeing the bonebed littered with remains of Apatosaurus, Stegosaurus and other classic Morrison Formation dinosaurs, the professor applied to the Works Progress Administration, an agency that put unskilled laborers to work during the Great Depression, for support to excavate the site.

Excavations began in May of 1935 and ran through 1938. The effort did not go smoothly. As paleontologist Dan Chure noted in a review of the project in his dissertation on allosaurids, one of the WPA. policies was that laborers should live in the same county where the work was being done. Since Cimarron County, Oklahoma wasn’t rich in experienced paleontologists and preparators, this meant that the dig was primarily operated by local ranchers and farmhands who may have never even seen a fossil before. Stovall gave the crews a few tips on what to do, but many bones were accidentally destroyed as the workers tried to exhume and prepare them. Worse, no one kept adequate field data, and the uncertainty of the laborers about what was a bone and what was just a concretion led to an extremely high number of “specimens” to come out of the site. The WPA succeeded in that destitute farmers were given plenty of work, but the inexperience of the field hands and the lack of supervision at the site created a terrible mess for anyone hoping to figure out what had happened at that place 150 million years ago.

Not everything was lost. Stovall recognized that some of the bones found at the site, called Pit I, belonged to a carnivorous dinosaur that seemed much bigger than the usual Allosaurus found in strata of the same age. He had a mind to call the creature Saurophagus maximus, for surely it was an enormous “eater of saurians.” That’s about the time that Grace Ray visited the site for her Natural History story. A pair of mistakes further complicated the history of the dinosaur.

On the first page of Ray’s article, “Big For His Day,” there is a photograph of Stovall, his student Wann Langston, Jr. and Langston’s friend William Price poking away at what appears to be an articulated leg of a huge, Allosaurus-like dinosaur still encased in rock. But the photo was staged. Though embarrassed my his part in the faked photo, Langston later explained what happened. The magazine desired a dramatic photo of dinosaur bones coming out of the ground, but there were no bones at the quarry suitable for the story’s opener. Instead, Stovall threw some big theropod bones in his truck with Langston and Price along for the ride. The group picked a place just outside of Norman, Oklahoma, dug a hole in reddish Permian rock (many millions of years older than the Jurassic strata in which the dinosaur was actually found), arranged the bones and posed for the staged snapshot.

Ray’s story was also the first place the dinosaur’s proposed name appeared in print—Stovall’s “Saurophagus” had not yet been given a scientific description when the June 1941 issue of Natural History came out. Some paleontologists thought this publication would be sufficient to officially name the name, thus the journalist Ray, rather than the paleontologist Stovall, would get credit for publishing the moniker. But others disagreed and additionally pointed out that the name Saurophagus had already been given to a type of bird (appropriately, a tyrant flycatcher). The huge dinosaur didn’t have a real name until 1995, when Dan Chure revised the known material and proposed the modified title of Saurophaganax.

(I couldn’t help but be amused by Ray’s reporting, which made the entire pursuit sound better organized than it actually was. In particular, I had to laugh at her closing comments about why Stovall’s monster grew to such a gigantic size: “Despite his strength and power and his technique in terrorizing the enemy, Saurophagus would never have been able to pass the medical test of a military draft board, neither would Mrs. Saurophagus have qualified as a “perfect 36.” They were hopelessly overweight, and it is improbable that any amount of dieting would have remedied the situation. Overactive glands may account for their stupendous size, as in the case of other dinosaurs.” [emphasis mine])

But there may be a few more tragic twists to the story before the bones of Saurophaganax can rest. This large dinosaur—estimated to have measured about 43 feet long, comparable to Tyrannosaurus—looked like a pumped-up version of Allosaurus. Maybe that is what Saurophaganax actually was. Allosaurus and Saurophaganax were closely related, lived during the same time, and co-existed with the same dinosaurian fauna. Even though Chure kept Saurophaganax as distinct on the basis of minute characteristics of the vertebrae, other studies have proposed that the dinosaur fell within the expected growth trajectory of Allosaurus. Perhaps the differences between Allosaurus and Saurophaganax are due to size and age. The discovery of a juvenile Saurophaganax would help distinguish the dinosaur as distinct from Allosaurus, but if only giant, Allosaurus-like forms are found then it’s possible that the giant Jurassic predators are Allosaurus that just happened to live long enough to reach greater body sizes. (It’s also worth nothing that Epanterias, a huge Late Jurassic theropod once thought to be unique, is often attributed to Allosaurus.) Recent histological research has indicated that Allosaurus lived fast and died young—possibly before they reached full skeletal maturity—and we would therefore expect exceptionally large specimens to be rare.

If Saurophaganax turns out to be synonymous with Allosaurus, then we will have to revise our understanding of how these widespread Jurassic predators lived and grew up. Such a change might also have some unexpected consequences. For one thing, bones attributed to Saurophaganax have been found in New Mexico and established the reason for the New Mexico Museum of Natural History and Science to put one on display attacking a large sauropod. That sauropod is a particularly large species of Diplodocus, formerly Seismosaurus, and it would be fitting for the predator to also be reassigned to a common, well-known Jurassic genus (though that by itself is not reason for doing so). But there may also be a sticky state symbol problem. Utah selected Allosaurus as its state fossil in 1988, and Oklahoma picked Saurophaganax as its state fossil in 2000. Should Saurophaganax turn out to be Allosaurus in disguise, Oklahoma will have to pick a new dinosaur or stick with the choice and say, “Well, our Allosaurus is bigger than yours, anyway.”

References:

Chure, D., 2000, A new species of Allosaurus from the Morrison Formation of Dinosaur National Monument (Utah-Colorado) and a revision of the theropod family Allosauridae. Ph.D. dissertation, Columbia University, pp. 1-964

Lee, A., & Werning, S. (2008). From the Cover: Sexual maturity in growing dinosaurs does not fit reptilian growth models Proceedings of the National Academy of Sciences, 105 (2), 582-587 DOI: 10.1073/pnas.0708903105

Ray, G. 1961. Big For His Day. Natural History 48, 36-39

A comparison of Triceratops (left) and Nedoceratops (right). From Scannella and Horner, 2011.

When the “Toroceratops” controversy broke in the summer of last year, I felt sorry for Nedoceratops. Hardly anyone said a word about this unusual horned dinosaur. Fans of Triceratops wept, wailed, and gnashed their teeth at their misapprehension that Museum of the Rockies paleontologists John Scannella and Jack Horner had exterminated the beloved horned dinosaur while paleontologists wondered if this dinosaurian mainstay of the Late Cretaceous could have grown into what had previously been called Torosaurus. But no one shed a tear at the proposition that Nedoceratops, too, might have been just a growth stage of Triceratops.

Known from a solitary skull on display at Smithsonian’s National Museum of Natural History, Nedoceratops has perplexed paleontologists since it was first described more than 100 years ago. The skull was found from the same end-Cretaceous strata that yielded Triceratops and Torosaurus, yet the dinosaur eventually labeled Nedoceratops was different from both. The skull had the general Triceratops-Torosaurus shape, but was distinguished by the lack of a nasal horn, a small opening in the preserved parietal portion of the frill, and two asymmetrical holes in the wing-shaped squamosal bones which made up the border of the frill. (These holes were thought to be old battle scars from some Cretaceous clash, but later studies showed these unusual perforations to be natural parts of the animal’s bone growth.) Scannella and Horner disagreed. Some of the unusual features, such as the apparent absence of a nasal horn, fell within the expected variation of Triceratops, and they interpreted the small hole in the parietal to be an early stage of the larger, rounded openings seen in the elongated frills of Torosaurus. Therefore, Scannella and Horner proposed, the Nedoceratops skull was a dinosaur virtually caught in the act of transitioning between the traditional Triceratops and Torosaurus forms, linking all three animals together into a single, late-life growth series.

Andrew Farke, a ceratopsian expert at the Raymond M. Alf Museum of Paleontology, came to a different conclusion when he published a reanalysis of the Nedoceratops skull earlier this year. The mix of features exhibited by Nedoceratops distinguished the dinosaur from both Triceratops and Torosaurus, Farke argued, which would remove the form with transitional features from the growth series. More than that, Farke offered up additional criticisms of the growth series Scannella and Horner proposed—Torosaurus might not be sunk, after all.

Now Scannella and Horner have published a response to Farke’s response. To an outsider, this might look like an echo of the 19th century “Bone Wars,” when the cantankerous naturalists Edward Drinker Cope and Othniel Charles Marsh battled each other in print over the proper identification and interpretation of dinosaurian remains. The headline for LiveScience’s report on the new paper states that the “debate rages,” though the argument is probably better cast of a difference of opinion that has generated some friendly competition. Farke and Scannella are close colleagues, and as Farke mentioned in a behind-the-scenes post on his Nedoceratops work, the paleontologists have helped critique and strengthen each other’s arguments prior to publication. The paleontologists are not about to assault each other at the next Society of Vertebrate Paleontology meeting, either.

Despite the collegiality between the parties, however, Scannella and Horner object to Farke’s critique. For one thing, the Montana-based researchers argue, each of the seemingly unique features of Nedoceratops can be found within the variation of Triceratops (which they count as including Torosaurus-type animals). Though Triceratops is classically portrayed as being a “three-horned face,” when I asked about the apparently absent horn of Nedoceratops, Scannella pointed out that “there are many Triceratops specimens which show similar low, subtle nasal ornamentation—not quite to the degree seen in ‘Nedoceratops’ but certainly approaching that state.” Alternatively, the nasal horn of Nedoceratops might have been broken off or lost after death since the horn does not actually fuse to the nasal bones until late in life. At the moment no one knows for sure whether the horn was lost or was simply never there, but Scannella emphasizes that none of these scenarios hinders the idea that Nedoceratops might be better categorized as a Triceratops.

And that’s not all. Some of the features thought to mark the Nedoceratops skull as an old individual that had finished growing are ambiguous, Scannella and Horner say. The rough bone texture and fusion between certain skull bones—thought to be indicators of maturity, and even old age—are variable in Triceratops and don’t necessarily represent the age range of the animal accurately. They uphold their original interpretation of the dinosaur as a Triceratops, and I have to admit that I was amused that Scannella and Horner pointed out that Nedoceratops translates to “insufficient horned face” in their paper. Though this refers to the apparent lack of a nasal horn, there is a certain poetic justice to it in a paper which seeks to sink the name. “I think ‘insufficient horned face’ is a very appropriate name given that the genus likely represents variation within Triceratops,” Scannella said.

Scannella and Horner offer an explanation for the slit-like opening on one side of the specimen’s frill. (The completed Nedoceratops skull on display was partially reconstructed, so we don’t know for sure if there was a matching hole on the other half.) The projected sequence of transformation from Triceratops to a Torosaurus-type form predicts that there would be a stage in which the solid frill of Triceratops would develop depressions or holes that would eventually open to create large, circular fenestrae. Scannella explains the transformation happening like this:

As Triceratops matured, the parietal developed increasingly thin areas which eventually formed the holes previously thought to be characteristic of “Torosaurus.” If you take a typical Triceratops with a thick, solid frill and have it undergo this transformation to “Torosaurus,” there’s going to come a point where the parietal is going to begin to develop openings. These openings will likely start off rather small and continue to grow as resorption continues and the parietal expands. This is what we see in “Nedoceratops“—it’s a fairly mature specimen, the squamosals are slightly elongate (approaching the morphology observed in “Torosaurus“), and the parietal has a small opening in the same place where in Triceratops we see thinning occurring and in “Torosaurus” we see holes. So—one possibility is that this is a distinct genus of dinosaur that has tiny holes in its parietal. Another is that this is simply a Triceratops caught in the act of becoming “Torosaurus.” Jack and I favor the hypothesis that “Nedoceratops” is actually a transitional morphology, between Triceratops and “Torosaurus.”

One of the areas of debate has been the number of triangular, bony ornaments called epiossifications around the border of the Triceratops frill, which is composed of the parietal and squamosal bones. Previous studies have established that these bones start off being prominent, pointed ornaments, but as Triceratops aged these bones flattened out until they were barely visible. The question is whether the number of some of these epiossifications could change during growth, thus bridging the gap between the different number of these ornaments on the parietals of Triceratops and Torosaurus.

While Triceratops typically has five or six of these bones, called epiparietals, Torosaurus have been found with spots for 10 to 12, requiring the number to double if Scannella and Horner are right. This kind of addition has not been seen in well-sampled populations of horned dinosaurs before, but Scannella and Horner propose that such changes were indeed possible. As evidence, they cite a single epiossification marked by two peaks, which they hypothesize is an ornament in the process of splitting into two. Additional specimens will be needed to determine whether this double-peaked adornment truly was splitting during a transformative growth stage or is an unusual and unique variant. While Farke cautions that he hasn’t seen the specimen in question himself, he does offer an alternative interpretation. The double-peak shape “could also just be resorption of the tip without splitting a single element into two,” he says. “This is relatively common in ceratopsids—many of them tend to resorb the tips of the ‘high points’ on the skull, and that may be what is happening here.” If this is the case, then the epiossification would be part of the typical transformation into flatter adornments and not indicative of splitting.

This aspect of debate brings up the question of how useful epiossification counts might be for identifying distinct ceratopsids in the Hell Creek Formation. Individual variation, changes in growth and possibly even variation from one slice of time to the next might complicate matters. “As we are finding more and more Triceratops in the Hell Creek Formation of Montana,” Scannella says, “we are seeing specimens with quite a bit of variation in both the number and position of frill epiossifications–a finding which urges caution before considering epiossification number and position a set in stone indicator of taxonomic identity, at least in taxa closely related to Triceratops.” Farke takes a different view. “[Scannella and Horner are] almost certainly correct that there is stratigraphic variation in epiossification count (presumably related to evolutionary change in a lineage),” he says, but points out that “This would strengthen the argument that epiossification count has phylogenetic significance … [I]f early Torosaurus have one count and late Torosaurus have another count, this would suggest that this trait changes through time and we can use epiossification count to distinguish different species.” Though all this argument over ceratopsid ornaments might seem esoteric, it is a key part of the discussion over what Nedoceratops and Torosaurus truly were. Did some ceratopsid dinosaurs add—and even double— frill ornaments as they matured? The answer to that question will have a major influence on the future of this debate.

What was Nedoceratops? That still depends on who you ask, and there is more than one possible answer. Farke, while noting that “Scannella and Horner raise some valid critiques of my diagnosis of Nedoceratops” in the new paper, still doesn’t see the dinosaur as an intermediate growth stage. “[W]e do still disagree on the taxonomic relevance of things like the parietal fenestrae,” Farke says. “[T]hey cite [the fenestrae] as transitional morphology between the Triceratops-morph and the Torosaurus morph of a single animal’s growth trajectory, whereas I would posit it as the end-member morphology for whatever Nedoceratops is.” And these aren’t the only options. “Of course, Nedoceratops might be an unusual or pathological individual of Triceratops. I’m not particularly married to any hypothesis at this point,” Farke says.

If Nedoceratops is an intermediate growth stage between the classic Triceratops and Torosaurus body types, further sampling of the Hell Creek and Lance Formations should eventually turn up still-growing Triceratops with similar features. Then again, if Nedoceratops is a distinct genus we would expect to eventually find juvenile individuals which share specific features with the single known skull to the exclusion of Triceratops and Torosaurus. Or maybe Nedoceratops is just a weirdo Triceratops.

This isn’t just a bit of paleontological arcana. The scientific conversation about Triceratops growth emphasizes the difficulties of recognizing prehistoric species and understanding their biology. What were once considered to be different species may just be growth stages or variants of one dinosaur, and these revisions affect our understanding of dinosaur evolution, biology, and ecology. I asked Scannella for his thoughts on the implications for his hypotheses, particularly given the fact that many dinosaurs are known from single, and often partial, specimens:

Increasingly, we are learning that many skeletal features in a wide variety of dinosaurs change throughout development.  There is also individual variation to consider. If all the differences between specimens are considered taxonomically informative, then it is easy to see how 16 species of Triceratops were named based on small differences in cranial morphology. Dinosaurs changed as they grew—and so, we need to evaluate which features are the most taxonomically informative. This can be hard to do if there is only one specimen of a particular dinosaur. We can start by examining developmental trends in dinosaurs thought to be closely related to that one specimen – as we’ve done with “Nedoceratops.” Examination of the bone microstructure is also important, in order to get an idea of relative maturity.

Paleontologists have recognized the problems of identifying slightly different specimens as new species before, but the debate over Triceratops—as well as Tyrannosaurus, Pachycephalosaurus, and other Hell Creek dinosaurs—has helped reinvigorate interest in how little dinosaurs grew up. Paleontologists are still in the relatively early phases of this investigation, and there are far more questions than there are definitive answers. The clues that will resolve the question of whether Triceratops was the lone ceratopsid of the Hell Creek still wait in museum collections and the expansive fossil graveyard that is the badlands.

References:

Farke, A. (2011). Anatomy and Taxonomic Status of the Chasmosaurine Ceratopsid Nedoceratops hatcheri from the Upper Cretaceous Lance Formation of Wyoming, U.S.A PLoS ONE, 6 (1) DOI: 10.1371/journal.pone.0016196

Scannella, J., & Horner, J. (2010). Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny Journal of Vertebrate Paleontology, 30 (4), 1157-1168 DOI: 10.1080/02724634.2010.483632

Scannella, J., & Horner, J. (2011). ‘Nedoceratops’: An Example of a Transitional Morphology PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028705