Part of a multi-step sequence by which Tyrannosaurus could have beheaded Triceratops, based on research by Fowler et al. Art by Nate Carroll.

For a dinosaur so terrifyingly powerful as Tyrannosaurus, there was no greater rival than Triceratops. Each was the acme of their respective lineage–one a hypercarnivorous bone-crusher, the other an immense three-horned herbivore. No wonder that artists, paleontologists, filmmakers and children on playgrounds have been pitting these dinosaurs against each other for over a century. Yet, despite how much we love to revel in the Cretaceous gore of such scenarios, we don’t really know whether Tyrannosaurus and Triceratops ever fought each other.

Earlier this week, Nature News reported on a delightfully gruesome Cretaceous vignette presented at the 72nd Society of Vertebrate Paleontology conference. After examining tooth marks on Triceratops frills, paleontologist Denver Fowler of the Museum of the Rockies in Bozeman, Montana, reconstructed how Tyrannosaurus could have torn the head off the great three-horned dinosaur to gain access to the herbivore’s succulent neck meat. There wouldn’t have been much flesh on the frill of Triceratops, Fowler pointed out, so it’s more likely that hungry tyrannosaurs used the bony collars for leverage to wrench the skull of the ceratopsid away from its body. Fowler also notes that he’s still studying these trace fossils and that a paper spilling the full details is in progress.

But the preliminary research only shows how Tyrannosaurus dined on Triceratops. Despite sensational ledes about the study that play up the “immortal battle” between the dinosaurs, the work doesn’t tell us anything about whether the enormous tyrant was capable of killing old three-horned face. Bitten bones and even fossil feces can help us fill out what was on the Maastrichtian menu for Tyrannosaurus, but they can’t tell us how our favorite Cretaceous carnivore acquired that meat.

Consider a damaged Triceratops pelvis described by Gregory Erickson and Kenneth Olson in 1996. The fossil was dotted with at least 58 punctures that were mostly likely created by an adult Tyrannosaurus. These were not injuries caused during predation, but they record the feeding behavior of a tyrannosaur as it ripped the hips off the Triceratops and  defleshed that mass of meat and bone as best it could. That’s as far as the evidence goes. Tracing those punctures back to the Cretaceous scene, the Tyrannosaurus is already standing over the felled Triceratops. What killed the Triceratops in the first place is a mystery.

So far, no one has found direct evidence of a Tyrannosaurus versus Triceratops battle. A healed bite wound on a Triceratops skeleton or an injured Tyrannosaurus bone corresponding to damage that could have only been made by a horn would provide paleontologists with a sign that these dinosaurs actually fought. After all, paleontologist Andrew Farke and colleagues recently found that tussling Triceratops  wounded each other, so there’s at least a possibility that Triceratops horns might have left tell-tale signs in the bones of an attacking Tyrannosaurus. For now, though, we are left with more indirect clues that will undoubtedly disappoint some dinosaur fans.

Tyrannosaurus was undoubtedly both a hunter and a scavenger. There is no longer any reasonable debate on that point. But, despite the dinosaur’s fearsome reputation, there’s no reason to think that Tyrannosaurus ate whatever it wanted. Tackling an adult Triceratops would have been a dangerous proposition, because of both the ceratopsid’s horns and bulk, so Tyrannosaurus might have avoided such risky encounters. Instead, as David Hone and Oliver Rauhut have pointed out, Tyrannosaurus and other large, carnivorous theropods may have preferentially hunted younger, less-imposing individuals, as well as the old and infirm. And there’s no reason to think that Tyrannosaurus would have passed up Triceratops carrion when the opportunity arose.

The ornaments of Triceratops don’t do much to help the predator-prey scenario, either. Although this dinosaur’s horns and frill have been characterized as weapons, the only direct evidence known of combat is for fights between adult Triceratops. Likewise, even though ceratopsids lived alongside tyrannosaurs for tens of millions of years, predator defense doesn’t seem to have anything to do with horn evolution. If horned dinosaurs developed horns to ward off attacks by big theropods, we would expect there to be an optimal form for defense, or at least severe constraints on the shapes of horns and frills so that they would still be effective. Instead, paleontologists have recorded a confounding array of different horn arrangements among ceratopsids, and the adornments appear to have more to do with communication within their species than defense against others. This is just as true for Triceratops as other horned dinosaurs. While some horns are better than none when confronted by a tyrannosaur, there’s no indication that the ornaments evolved as a predator defense strategy.

We need to reimagine what a confrontation between Tyrannosaurus and Triceratops would have looked like. Instead of two equally matched dinosaurs squaring off against each other, adult Tyrannosaurus probably ambushed young, unwary Triceratops or picked off sick individuals too weak to put up much of a fight. Tyrannosaurus had no sense of honor to uphold–the tyrant was an apex predator that had to maximize its chances of acquiring flesh, and the only safe adult Triceratops was a dead one. Perhaps, someday, a lucky researcher will stumble across evidence of our favorite Hell Creek scene at a field site or in a museum drawer. For now, though, we need to consider the magnificent Tyrannosaurus and Triceratops as real animals and not slavering monsters made to gore each other for our delight.

References:

Erickson, G., Olson, K. 1996. Bite marks attributable to Tyrannosaurus rex: Preliminary description and implications, Journal of Vertebrate Paleontology, 16:1, 175-178 DOI: 10.1080/02724634.1996.10011297

Farke, A., Wolff, E., Tanke, D. 2009. Evidence of Combat in Triceratops. PLOS ONE 4(1): e4252. doi:10.1371/journal.pone.0004252

Fowler, D., Scannella, J., Goodwin, M., Horner, J. 2012. How to eat a Triceratops: Large sample of toothmarks provides new insight into the feeding behavior of Tyrannosaurus. Society of Vertebrate Paleontology 72 poster.

Holtz, T. 2008. A Critical Reappraisal of the Obligate Scavenging Hypothesis for Tyrannosaurus rex and Other Tyrant Dinosaurs, pp. 370-396 in Larson, P. and Carpenter, K. (eds) Tyrannosaurus rex: The Tyrant King. Bloomington: Indiana University Press.

Hone, D., Rauhut, O. 2009. Feeding behaviour and bone utilization by theropod dinosaurs. Lethaia 43.2 (2009): 232-244.

A reconstruction of Acrocanthosaurus at the North Carolina Museum of Natural Sciences in Raleigh, North Carolina, where this year’s SVP reception was held. Photo by Famille Wielosz-Caron, image from Wikipedia.

The annual Society of Vertebrate Paleontology meeting is a test of endurance. The science comes fast and furious in presentations, posters, hallway conversations and shouted exchanges over the din of the bar, with no consideration for how dehydrated, weary or hungover you might be. (Paleontologists study hard and party harder.) By the last day, my brain ached with details of flying Microraptor, bounding crocodiles, marsupial bone microstructure and dozens of other topics. When my friends at the conference asked “What did you like best?” after the technical sessions finally concluded, I was only capable of grunts and indelicate gestures.

I’ve had a day to settle down and process what I saw. And I know this–at SVP, dinosaurs rule. This isn’t to say that the conference is all about the Mesozoic celebrities. I saw many excellent talks on prehistoric fish, mammals, amphibians and other forms of ancient life. But, for a dinosaur fan, SVP offers a glut of dinosaur science from new discoveries about the beloved Tyrannosaurus rex to brand-new species that have only just come out of the ground.  Since this blog is called Dinosaur Tracking, I’m going to focus on some of the stand-out dinosaur science I saw during the meeting.

Montana State University graduate student Jade Simon’s presentation focused on giant Cretaceous dinosaur eggs found in Idaho, but the implications of the discovery were what really grabbed by attention. According to Simon and her collaborators, the pair of elongated, oblong eggs most closely match those found in the nests of oviraptorosaurs–beaked, feathered theropods like Citipati and eponymous Oviraptor. Yet the two eggs were so large that they suggested a dinosaur of prodigious size, on the scale of the 25-foot-long Gigantoraptor recently found in China. If Simon and coauthors are correct, then an enormous, as-yet-undiscovered oviraptorosaur strutted around Idaho around 100 million years ago. The next step–finding this fantastic creature’s bones.

Simon wasn’t the only researcher showing off dinosaur eggs. Just prior to her presentation, meeting attendees were treated to a pair of talks about dinosaur embryos found in the Late Jurassic rock of Portugal. These deposits are similar in age to those of the famous Morrison Formation of the American west and share many of the same types of dinosaurs. An embryo studied by Ricardo Araújo and coauthors appears to be a nascent Torvosaurus–a giant Jurassic carnivore that topped Allosaurus in bulk–and paleontologist Octávio Mateus followed with a skeletal embryo of Lourinhanosaurus, a mid-size theropod dinosaur found in the same formation. The embryo described by Mateus stood out because it was found by his parents–amateur paleontologists–in a nest of 100 eggs, including crocodile eggs mixed in with those of dinosaurs. Was this nest a communal site used by many mothers? The embryo and the nest it was found in will definitely help us better understand how some baby dinosaurs entered the world.

The SVP crowd also got treated to previews of various dinosaurs that are slowly making their way to press. Researcher Corwin Sullivan presented some scrappy evidence that a second giant tyrannosaur might have lived alongside the recently named Zhuchengtyrannus, and Nathan Smith showed off some new material from what may be two new species of sauropodomorph dinosaurs collected from Antarctica. Oliver Rauhut added to the list with a new theropod from Argentina that looks like a more archaic version of Allosaurus, and visitors to the poster session got to check out what might be a new species of Diabloceratops that Eric Lund and his colleagues have been working on. Most of the new dinosaur presentations followed the same format–where the fossils were found, how much of the skeleton was found, what sort of dinosaur the species is–but, in time, we should get fuller details of these dinosaurs in progress.

But not all the presentations at the conference were on new field discoveries. Increasingly, paleontologists are scanning, slicing and otherwise studying fossils in new ways, drawing ever more data about dinosaur biology from old bones. The first talk I walked into, by Eric Snively, reconstructed the neck musculature of Allosaurus for insights into the feeding behavior of this Jurassic hypercarnivore. As it turned out, Allosaurus probably had quite a strong neck and used this power to stabilized its flexed head while ripping flesh from prey–think of a giant, toothy falcon. In another session, Jason Bourke created virtual models to examine whether sauropod dinosaurs such as Camarasaurus and Diplodocus had their nasal openings on the tops of their heads–as was shown when I was a kid–or had nostrils further down the snout. The airflow models better fit the nose-at-end-of-snout model, although, as Bourke pointed out, there’s still quite a bit we don’t know about sauropod soft tissues.

Unsurprisingly, Tyrannosaurus got some love, too. Sara Burch reexamined the shoulders and forelimbs of old T. rex in an attempt to reconstruct the dinosaur’s musculature. Among other things, Burch found that the dinosaur’s arms underwent significant functional changes over time. The arms of the tyrant weren’t fading away, but modified for different uses than that of earlier relatives. What exactly the dinosaur was doing with its infamously small arms, though, we still don’t know.

Within the various new areas of research, though, dinosaur histology has been providing paleontologists with some of the most tantalizing details of prehistoric biology. My friend Carolyn Levitt presented her new research on the microstructure of Kosmoceratops and Utahceratops bones. These horned dinosaurs didn’t show any lines of arrested growth (LAGs) in their bones–rings thought to mark annual slowdowns in bone growth and often used to roughly age dinosaurs–while previously studied dinosaurs from more northern sites in North America do show these markers. This might mean that, like mammals, dinosaurs maintained high-running metabolisms but their growth was still influenced by environmental pressures, such as cold or dry seasons, in their surrounding environment. In a time of scarce resources, dinosaurs in highly seasonal habitats probably slowed their growth while those in lusher environments did not face the same pressures. Indeed, the dinosaurs with the most LAGs were the northernmost, while Utahceratops and Kosmoceratops were the southernmost sampled.

In a similar vein, a poster by Julie Reizner looked at the histology of the horned dinosaur Einiosaurus and what the microstructure details might say about the ceratopsid’s biology. The sampled dinosaurs, found in a rich bonebed, suggest that growth in Einiosaurus slowed at about three to five years of age, which might mean that these dinosaurs made a dash for reproductive maturity before their growth slowed. The fact that Reizner’s animals were predominately young and perished long before full skeletal maturity–or, in other words, still had some growing to do–is consistent with the idea that dinosaurs generally lived fast and died young.

And I would be remiss if I didn’t mention that there was an entire session devoted to Appalachia–a Late Cretaceous subcontinent formed when a shallow sea split North America in two, of which my former New Jersey home was a part. Paleontologists have made fascinating discoveries on the sister continent, Laramidia, but Appalachia has often been ignored given that we as yet knew little of the dinosaurs that lived there. Still, there is much to be learned by going back to the fragmentary and rare dinosaurs of that early eastern landmass. In addition to featuring Dryptosaurus, New Jersey’s fearsome tyrannosauroid, Stephen Brusatte reexamined the few remains of “Ornithomimus” antiquus. This ostrich-like dinosaur probably belonged to a different genus and was not as primitive as previously thought. Shortly after Brusatte’s talk, Matthew Vavrek spoke about dinosaurs found in the high Arctic of Appalachia. Hadrosaurs, deinonychosaurs, tyrannosaurs and others lived along the northwestern coast of the continent and may help use better understand the differences between Appalachia and Laramidia. The most frustrating aspect of all of this is that the eastern dinosaurs are so poorly known–we need more dinosaurs.

The findings I mention here are just a scattered sampling of SVP, based upon the talks and posters I personally encountered. With three sessions going at the same time, it was utterly impossible to see everything. (Please chime in about your own favorite presentations in the comments.) Nevertheless, it was amazing to see paleontologists showing off new finds and going back to fossil collections for new information. We’re learning more, at a faster rate, than ever before. As multiple experts said to me during this conference, it’s a great time to be a paleontologist. The SVP dinosaur sessions left no doubt of that, and I can hardly wait for next year.

Thankfully, many other paleontologists have been sharing their thoughts about the conference through the #2012SVP Twitter hashtag and on their blogs. For an outsider’s perspective on the conference, see Bora Zivkovic’s rundown of the meeting, as well as Victoria Arbour’s summary of SVP silliness. Out of everything, though, I think this year’s attendees will all remember the conference center’s whoopee cushion chairs–caught on video by Casey Holliday’s lab. I hope that next year’s conference in Los Angeles is just as exhausting, and just as fun.

The tyrannosaur Gorgosaurus in a classic death pose (although note that the tail is almost entirely missing and speculatively reconstructed). Image from Diller and Brown, 1923.

After a week packed with presentations, posters and lots of paleo-goodness, the 71st annual Society of Vertebrate Paleontology meeting is over. There’s not much to be sad about, though. If the conference is any indication, we’re going to be seeing lots of fascinating dinosaur stories in the coming weeks, months and years.

There were far too many dinosaur presentations to attend them all, but the big-picture trend is that paleontologists are able to pull ever-more information about dinosaurs out of their bones and geological context. Last week I wrote about the meeting’s Laramidia session, in which paleontologists pondered the distribution and evolution of horned dinosaurs, hadrosaurs, tyrannosaurs and other Late Cretaceous celebrities up and down the western subcontinent. These discussions consequently fed into the ongoing debate about how diverse dinosaurs were and whether we have named too many species. In a poster presented on the last day of the conference, Museum of the Rockies paleontologist Denver Fowler proposed that some horned dinosaurs such as Mojoceratops, Titanoceratops and Kosmoceratops are really different stages of previously named dinosaurs such as Chasmosaurus and Pentaceratops. There was quite a bit of discussion and arguments about this proposal—just as with the idea that Torosaurus is really a grown-up Triceratops—but that’s not a bad thing. By combining anatomy, histology, biogeography and other lines of argument, paleontologists may be able to get some better resolution about how dinosaurs actually lived and the big patterns of their evolution. Yes, there are going to be controversies and debates, but that is a positive thing that speaks to the current vibrancy in the field of study.

The strange oviraptorid dinosaur, on display at the Carnegie Museum of Natural History, mentioned by Matt Lamanna at this year's SVP meeting. Photo by the author.

Attendees also got an early look at previously unknown and little-studied dinosaurs. On Saturday morning Max Langer from the Universidade de São Paulo presented a report on an early sauropodomorph dinosaur found in the Late Triassic Santa Maria Formation of Brazil. The skull was vaguely reminiscent of Eoraptor—a dinosaur hypothesized to be a sauropodomorph and not a theropod in a paper published early this year—and this new dinosaur was apparently close to the origins of the varied and successful group of dinosaurs which would eventually contain giants such as Apatosaurus and Giraffatitan. But not all the undescribed dinosaurs mentioned at the session were new. At the SVP reception held at the Carnegie Museum of Natural History last year, I saw the reconstructed skeleton of a strange oviraptorid dinosaur from North America. This toothless, crested creature is known from several partial skeletons but has been little studied until now. That’s why I was glad to see a presentation by Carnegie Museum of Natural History paleontogist Matt Lamanna, which presented the animal as the best-known oviraptorid dinosaur from our continent. Even though ovirpatorids remains have been found in North America before, they were so scrappy that their counterparts in Asia filled in most of what we know about these dinosaurs. The yet-unnamed oviraptorid Lammana described will help fix this problem, and will provide another way for paleontologists to investigate the trade of different dinosaur lineages between North America and Asia during the Late Cretaceous.

New technologies and sophisticated methods are also being used to fill out our understanding of dinosaur biology. Paleontologists are agreed that dinosaurs were active, dynamic and fast-growing animals, but how they achieved this lifestyle is still a matter of investigation. In a talk in the theropod dinosaur session, paleontologist Mark Goodwin from the University of California Museum of Paleontology in Berkeley presented results that tested the conclusions of an earlier study about the physiology of Tyrannosaurus rex. The earlier study had used oxygen isotopes—chemical signals locked in bones and teeth that can be compared to determine things like temperature—to determine that Tyrannosaurus was probably a homeothermic endotherm, that is, it generated heat internally and maintained a constant body temperature. But when Goodwin took a greater sample of chemical isotopes from Tyrannosaurus bones, he found that the body temperature of the animal probably fluctuated. This would mean that Tyrannosaurus, like some birds, was an endothermic heterotherm—the dinosaur generated heat internally but had a body temperature that varied on a regular basis. Thinking of dinosaurs as “hot-blooded” or “cold-blooded” doesn’t do justice to the variety of physiological characteristics biologists know about.

The terminal end of dinosaur lives also got some attention in a presentation by Alicia Cutler of Brigham Young University on why the classic head-back, tail-up death pose is so common in dinosaurs. Cutler used fresh and frozen chickens to see how immersion in water affected the posture of the dead birds. Although not all her videos of the experiments worked, those that did showed that the necks of the chickens arched back almost immediately upon becoming immersed in water. The pose was not the result of drawn-out periods of dessication as some paleontologists had thought. In addition to previously proposed hypotheses, such as the idea that the pose could be created during the death throes of the animals, the experiments may help fill in our understanding of how particular dinosaurs died and became preserved.

Obviously, I have left out many studies. I can’t possibly do justice to the entire meeting, and I undoubtedly missed some intriguing presentations and posters. (Although, on the other hand, if I absorbed everything my brain probably would have exploded from paleo-overload.) There were many previews of soon-to-be-published work and ongoing research, and the smattering I was able to see underscored the point that our understanding of dinosaurs is constantly in flux and growing ever deeper. I can hardly wait for next year’s meeting in North Carolina, where I may even be able to present something about a research project I am just now embarking on. Stay tuned.

The skull of Utahceratops, one of the unusual dinosaurs from southern Utah. From Sampson et al., 2010.

Southern Utah sure has changed from how it was during the Late Cretaceous. Today the area known as Grand Staircase-Escalante National Monument is a dry, rocky place where plants are few and far between. But during a swath of time between 90 and 70 million years ago, the area was a lush, swampy habitat near the great interior seaway that cleaved North America in two. Giant crocs and weird dinosaurs lived in this coastal environment, itself just one part of a vast island continent which was once isolated from other parts of the world. This isolation undoubtedly influenced dinosaur evolution. And it’s possible that distinct pockets within the continent itself caused dinosaur evolution in the north and south to play out very differently. During a specialized technical session yesterday at the annual Society of Vertebrate Paleontology meeting, paleontologists gathered to present the fauna of North America’s lost western continent, called Laramidia.

I did not attend the entire session, but I did catch all the talks in the latter half. Together they created a rough picture of just how different the world once was. For one thing, southern Utah was home to some strange and imposing crocs. Paleontologist Randall Irmis from the University of Utah and the Natural History Museum of Utah reviewed the array of prehistoric crocodyliforms found in Grand Staircase-Esclanate National Monument, including the huge, dinosaur-eating “terror croc” Deinosuchus. There are still some mysteries waiting to be resolved, and discoveries are still being prepped out in the lab, but many of the ambush predators found in the area were alligatoroids—creatures more closely related to modern day alligators than to living gharials or crocodiles.

Damaged bones indicate that one of those long-lost crocs once sunk its teeth into a small dinosaur. In fact, the attacking croc even left part of its tooth behind. In the following talk, University of Iowa paleontologist Stephanie Drumheller highlighted bite marks found on the skeleton of a small, bipedal, unnamed herbivorous dinosaur found in the Kaiparowits Formation of southern Utah. Using high-resolution visualization techniques and comparisons with damage to bones created by modern crocodylians when they feed, Dumheller was able to narrow down the list of possible suspects to a roughly three-foot-long crocodyliform. There is more than one potential candidate among animals of this size, but Drumheller’s work showed that some dinosaurs had as much to fear from relatively small crocs as from huge predators such as Deinosuchus.

Of course, there were large, predatory dinosaurs running around in the same area during this time. Natural History Museum of Utah paleontologist Mark Loewen delivered an overview of theropod dinosaurs found in the Late Cretaceous rock of Grand Staircase-Escalante National Monument with a focus on the weird tyrannosaurs found there. These predators, such as the recently named Teratophoneus, had relatively short, deep skulls set with impressive teeth that set them apart for their cousins living during the same time in the northern part of Laramidia. Exactly why these dinosaurs evolved this way is unknown, but the distinct nature of the tyrants and other dinosaurs from the same deposits have led paleontologists to wonder if there was some sort of physical barrier which isolated them and caused them to undergo distinctive changes. As strange as they might look, though, at least one might provide some resolution as to where the ever-popular Tyrannosaurus rex came from. Drawing on a talk on the animal he gave last year, Loewen suggested that a yet-undescribed tyrannosaur from southern Utah’s Wahweap Formation may represent the form of the long-sought Tyrannosaurus ancestor.

But some of the most spectacular dinosaurs of all were the horned dinosaurs of Laramidia. Andrew Farke from the Raymond M. Alf Museum of Paleontology highlighted the rapid rate of discovery in the southwestern United States that is altering our understanding of ceratopsid evolution. While dinosaurs such as Zuniceratops appear to indicate that the earliest ceratopsid dinosaurs—the lineage including horned dinosaurs such as Styracosaurus and Utahceratops—evolved in North America, the exact time and place of their origin is unknown. Furthermore, the relationships among the various ceratopsid dinosaurs discovered in Laramidia to date is mysterious—better resolution is needed to understand how the dinosaurs evolved in space and time. Though we’re quickly adding new ceratopsid genera thanks to some great new fossil finds, we are going to have to wait for future fossil finds and revised analyses to really understand the big evolutionary picture for this group.

The several talks that followed, by paleontologists Caleb Brown of the University of Toronto, David Evans from the same institution, and Terry Gates of the Field Museum, respectively, highlighted other evolutionary and geographical patterns within other dinosaurs and smaller animals in Laramidia. During his talk on hadrosaurs found in the northern part of Laramidia, for example, Evans pointed out that there was at least some interchange between the northern and southern parts of the continent. The recently named hadrosaur Acristavus has been found in both the northern and southern parts, so perhaps barriers between the two areas were not so impenetrable to dinosaurs after all. Likewise, Gates pointed out that we require a much finer picture of what the ancient environments of Laramidia were like and a clearer understanding of which slices of rock correspond in the northern and southern parts of the continent. Better constraints on these issues will allow paleontologists to make the more exact comparisons needed to draw out evolutionary patterns.

The final talk was delivered by Natural History Museum of Utah paleontologist Scott Sampson. He  noted that paleontologists had previously thought that many major dinosaur groups of the Late Cretaceous—the hadrosaurids, the ceratopsids and the tyrannosaurids, among others—had evolved in Asia and later invaded North America. Sampson argued the opposite. New evidence may indicate that these groups emerged within Laramidia and then dispersed to Asia after about 70 million years ago (though some groups of dinosaurs that evolved in Asia likely came into North America, too). There may have been a great dinosaur interchange between what is now Alaska and Russia. Though a number of the talks in the session emphasized the need for additional information before we can draw out the patterns, Sampson did make the case that Laramidia was an important center of dinosaur evolution. As discoveries accumulate, and as paleontologists find new ways to analyze the fossil data, the major evolutionary story will come into focus.

Top image from:

Sampson SD, Loewen MA, Farke AA, Roberts EM, Forster CA, et al. (2010) New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism. PLoS ONE 5(9): e12292. doi:10.1371/journal.pone.0012292.g003

A Protoceratops nest containing up to 15 baby dinosaurs. From Fastovsky et al., 2011.

“The fossil record is incredible when it preserves things,” paleontologist Jack Horner said during his talk about dinosaurs and evolution the other night, “but it’s not a complete record.” Many of the sessions and posters I have seen at the annual Society of Vertebrate Paleontology meeting so far are a testament to that truth, either in a positive or negative sense.

In one of the most talked-about presentations delivered so far, McMaster University masters student Ben Novak brought up some substantial obstacles that he and his co-authors have discovered to the hypothesis that remnants of dinosaur soft tissues and proteins have been found in the fossil record. The evidence for long-lived Tyrannosaurus goo may not be as good as previously thought, Novak explained, and the record of proposed dinosaur soft tissue remnants accumulated so far should be reexamined. The fossil record may not be as kind to us with dinosaur remnants as we would like.

Then again, there were notices of some exquisite finds which will provide researchers with a way to better understand dinosaur lives. A poster created by paleontologists Jingmai O’Connor, Zhou Zhonghe and Xu Xing from Beijing’s Institute of Vertebrate Paleontology and Paleoanthropology presented fossil evidence for a Cretaceous turducken. Inside the gut contents of the non-avian, feathered dinosaur Microraptor were the partial remains of a prehistoric bird, and the fact that the bird probably lived in the trees may provide some supporting evidence for the notion that Microraptor may have also been an arboreal animal. Like anything presented at the conference, these findings will be further researched, scrutinized and hopefully published, but such preliminary announcements illustrate the difficulties and the wonders of the fossil record.

But not all the cool announcements are exclusive to SVP. Significant new discoveries pop up regularly in journals, and one that caught my eye is the first description of a Protoceratops nest by University of Rhode Island paleontologist David Fastovsky and colleagues in the Journal of Paleontology. This discovery has been a long time coming.

During the 1920s, American Museum of Natural History expeditions to Mongolia brought back, among other things, dinosaur eggs that they attributed to the horned dinosaur Protoceratops. The researchers were so confident in this assignment that the remains of a small theropod dinosaur found in the same deposits as the supposed Protoceratops eggs was named Oviraptor: “egg thief.” Restorations of Protoceratops parents guarding their nests from Oviraptor hungry from an omelet proliferated through dinosaur books. But reexamination of those eggs during the 1990s showed that paleontologists had the story wrong. Developing dinosaurs preserved inside some eggs were actually oviraptorid dinosaurs—the “egg thief” was more likely a parent! Good thing for us Oviraptor can’t sure for defamation of character.

How Protoceratops nested once again became a mystery, as paleontologists continued to amass more evidence of oviraptorid nests. The closest thing to a Protoceratops nest was an aggregation of small, juvenile dinosaurs found in China and attributable to an evolutionary cousin known as Psittacosaurus. But the new paper by Fastovsky and colleagues documents a rare discovery than can give us some insight into how Protoceratops reproduced and grew up.

The nest in question was found in the roughly 84- to 75-million-year-old strata of the Upper Cretaceous Djadokhta Formation in central Asia. Rather than being a nest full of eggs, though, this Protoceratops nest is packed with baby dinosaurs. Fastovsky and co-authors count as many as 15 juvenile animals inside the nest, but these were not newborns. The degree of skeletal development among the little dinosaurs and a lack of eggshells within the nest indicates that they had already been in the nest for some time. Sadly, these little dinosaurs were buried alive, probably by a sandstorm.

What this discovery indicates about parental care in Protoceratops is uncertain. No adult dinosaur was found in association with the babies. Perhaps the adult continued to care for the little dinosaurs while they remained in the nest, or perhaps they left the nest and the baby dinosaurs remained together in the nest area. With any luck, future discoveries will provide more insight into these points. Nevertheless, the new find adds to the growing body of evidence that many dinosaurs stuck together as juveniles. Their tragedy is a boon for paleontologists hoping to understand dinosaur lives.

References:

Fastovsky, D., Weishampel, D., Watabe, M., Barsbold, R., Tsogtbaatar, K., & Narmandakh, P. (2011). A Nest of Protoceratops andrewsi (Dinosauria, Ornithischia) Journal of Paleontology, 85 (6), 1035-1041 DOI: 10.1666/11-008.1

A Daspletosaurus skull at the Museum of the Rockies, where Jack Horner is the curator of paleontology. Photo by the author.

What can dinosaurs teach us about evolution? Charles Darwin mostly ignored them during his career, and evolutionary patterns are often easier to study in creatures that left more numerous fossils, such as trilobites and the tiny, armored plankton called foraminiferans. Yet, as paleontologist Jack Horner explained during a lecture at the 71st annual meeting of the Society of Vertebrate Paleontology last night, what we have come to know about dinosaurs can illustrate big-picture evolutionary facts.

Despite the fact that Horner was addressing an audience of scientifically minded peers, his talk was very simple. I wouldn’t be surprised if it became a regular lecture on Horner’s speaking circuit to schools and public venues. There were no technical graphs of data points or tables of measured variables. Instead, Horner began with the nuts and bolts of how to find  a dinosaur in the Montana badlands. Many people have the impression that paleontologists just walk out into the badlands and dig holes, but as Horner pointed out, simply digging random holes won’t help you find anything. Dinosaurs are gifts of erosion—we find dinosaurs when they are already coming out of the ground. From there, Horner explained, he typically tasks a cadre of graduate students with the back-breaking parts of the excavation and soon whatever there is of the dinosaur skeleton becomes exposed.

Once those bones are out of the ground and cleaned up, all the fun technical nitpicking can start. Horner used dinosaur color as an example. Although I was disappointed that he didn’t mention our recently gained ability to detect the colors of some dinosaurs from fossil feathers, Horner pointed out that we don’t really know anything for sure about the color patterns of most dinosaurs. Horner also mentioned his own work on some evolutionary patterns among Cretaceous dinosaurs in the Two Medicine Formation, specifically whether the horned dinosaur Rubeosaurus was gradually modified into Pachyrhinosaurus in a straight line of descent through several other transitional types within the geologic formation or whether the different dinosaurs in question represent a branching evolutionary pattern. “We paleontologists love to argue about this,” he said, and pointed out that the assembled group had come to the conference to argue, after all. But, Horner quickly added, we don’t argue about the fact of evolution. We can go back and forth indefinitely about the minutiae of paleobiology and the patterns of evolutionary change, but vertebrate paleontologists agree that evolution is a fact.

So what do dinosaurs have to do with the fact of evolution? Horner outlined five different proofs of evolution: three proofs that Darwin cited, a “test” proof, and what Horner called the ultimate proof. The first on the list was simply descent with modification. Horner cited the many strange breeds of dogs and chickens as an analog for how organisms can become drastically modified over the course of history. Humans specifically selected for those changes in the domesticated animals, but as Darwin illustrated in On the Origin of Species and other works, the changes that dogs, chickens and other animals have undergone underscores the fact that the same thing is happening due to entirely natural causes every second and every day. To greater or lesser extents, lineages of organisms change over time, and the fossil record demonstrates this beautifully.

Next on the list were rudimentary features: structures that once served a particular function but became vestigial organs that don’t carry out that same function anymore. (Keep in mind, though, that “vestigial” does not mean “useless.”) Horner cited the modified wings of flightless birds and the remnants of hind limbs in whales as modern day examples, and identified the small forelimbs of Tyrannosaurus as another. Since the time the tyrant dinosaur was discovered, paleontologists have been asking, “What did it use those arms for?” Horner concluded that Tyrannosaurus probably didn’t do more than scratch its belly after a big meal with them. That point is debatable, but we do know that tyrannosaur forelimbs did become greatly reduced in size during the evolutionary history of their lineage. Horner’s hypothetical “chickenosaurus” even made a cameo here. Tweaks in the genetics and development of chickens can cause the reappearance of long-lost traits, such as teeth, and by carrying out these experiments Horner hopes to understand which genes and developmental quirks were key in the evolution of birds from non-avian dinosaurs.

In a phrasing that sounded appropriately Victorian, Horner then moved on to evolutionary proof from the “geological succession of organic beings.” Simply put, we find fossils in layers, in successions of strata that together span hundreds of millions of years. Fossils are not all together in one big clump (as would be expected if the entire fossil record were attributable to the biblical flood as many young earth creationists claim). You’re not going to find a prehistoric horse in the 150-million-year-old Jurassic limestone quarries of Germany, and you’re certainly not going to find a dinosaur in the 505-million-year-old rock of the Burgess Shale. But Horner said that he encourages creationists who want to believe in alternate histories to go looking for the out-of-place fossils they think they’re going to find. “I encourage people who don’t believe in evolution to look for horses in Jurassic Solenhofen limestone,” Horner said, especially since those searches may be much more useful in turning up new specimens of the feathered dinosaur and archaic bird Archaeopteryx.

Horner covered his last two points very quickly. The “test proof” for evolution, he proposed, comes through testing genetic relationships. We don’t yet have genetic material from Mesozoic dinosaurs, and we may never have it, so paleontologists will have to continue to rely on anatomy as they strive to sort out the dinosaur family tree. But the ultimate proof has nothing to do with the animals themselves. The ultimate proof of evolution, Horner quipped, is “ego.” Scientists are constantly arguing with each out about the patterns and processes of evolution, and scientists love to disprove ideas. Anyone who managed to show, beyond a shadow of a doubt, that evolution doesn’t happen would be the most famous scientist of all time, yet no one has been able to do this. Despite the best efforts of scientists to disprove ideas and their penchant for arguing over the nature of nature, the evidence for the fact of evolution keeps getting stronger and stronger.

The skull of the Carnegie's Allosaurus skeleton. In the background you can see a small part of the beautiful Jurassic mural by Bob Walters and Tess Kissinger.

A cast of the skull of Diabloceratops, which was formally described just this year.

A baby Apatosaurus among the ferns in the Jurassic dinosaurs exhibit.

A juvenile Camarasaurus.

A Tyrannosaurus rex protects its kill from a rival (off camera) in the museum's Cretaceous exhibit.

A Ceratosaurus runs down a fleeing Dryosaurus in an alcove along the Jurassic exhibit.

For more on SVP, see these posts:

Society of Vertebrate Paleontology Dispatch, Part 1

SVP Dispatch, Part 2: Did Sea Level Influence Dinosaur Diversity?

SVP Dispatch, Part 3: Raptorex – To Be or Not to Be?

On Laelaps: Hungry Carnivores Helped Create Keyna’s Primate Fossil Record

Plugging Into SVP

A restoration of the skeleton of Raptorex. From the Sereno et al., 2009.

One of the biggest dinosaur stories of 2009 was the discovery of a pint-sized tyrant called Raptorex. Described by a team of paleontologists led by Paul Sereno and dated to about 126 million years ago, the dinosaur showed that many definitive tyrannosaur characteristics—such a puny forearms—evolved when the predators were still small. But a story published in Nature‘s news section this week highlights some of the uncertainty about the specimen.

Despite becoming something of an instant dinosaurian celebrity, there have been two aspects of Raptorex that have caused paleontologists some degree of unease. The first is that it looks like a juvenile form of later, bigger tyrannosaurs, particularly the 70-million-or-so-year-old Tarbosaurus. In fact, this was how the fossil was unofficially diagnosed when it was purchased—more on that in a moment—although Sereno and co-authors cite the fusion of the sutures on the skull of the animal as an indication that it was a young adult animal. (Comparison with complete, juvenile Tarbosaurus skeletons could also help resolve this issue.) Likewise, it would be expected that juveniles of later tyrannosaurs would be similar in form to earlier species—such as Raptorex—with definitive, advanced tyrannosaurs traits only appearing much later during the growth of later species. If juvenile Tarbosaurus roughly looked like the adult stage of their ancestors, in other words, then it would be easy to confuse the two when viewed outside of their geologic context.

As with the debate over the suggestion that Torosaurus was the adult form of Triceratops, however, not all paleontologists agree that Raptorex is really the juvenile form of another dinosaur. Both cases are part of a larger effort to find out how dinosaurs changed as they grew and what this might mean for the identification of new species. As for Raptorex, though, anatomy alone can’t solve the problem, especially since the most important issue yet to be resolved involves the dinosaur’s geological age.

Rather than being found an excavated by scientists, the dinosaur is said to have been collected in the vicinity of Liaoning Province, China, by amateurs. After being dug up, it was later sold to a private collector who then contacted Sereno after having other scientists appraise the specimen. Frustratingly, whoever uncovered the fossil did not collect data about the place where the dinosaur was found, and most of what we know about geological context of the dinosaur comes from the rock which still clung to parts of its skeleton.

In addition to the type of rock it was found in, fossil shells and fish bones would appear to place Raptorex at about 126 million years ago in the Yixian Formation. Given that fish bones and shells of the kind found alongside Raptorex are seen in many fossil localities, however, more rigorous geological testing will be needed to determine where it came from and how old it was. Nailing down a date and locality for Raptorex is important. If Raptorex really is 126 million years old, then it could not be a juvenile of a known, giant tyrannosaur such as Tarbosaurus since it would have preceded it by about 50 million years. If Raptorex turns out to be the same geologic age as Tarbosaurus, however, then paleontologists will have to reexamine the skeleton in detail to determine whether it could be a juvenile form of a larger dinosaur.

These problems with Raptorex have been known to paleontologists since the time of its description, but the Nature News story brought it to the forefront. According to the report, Peter Larson and Jørn Hurum will be publishing a critical assessment of Raptorex which will identify the dinosaur as a juvenile Tarbosaurus. When and where that paper will be published is unknown, and there was no presentation of poster about the topic at the 70th annual SVP meeting.

Since this story broke during SVP, however, a few scientists did acknowledge the debate over Raptorex. In some of the tyrannosaur presentations given on Wednesday paleontologists pointed out that Raptorex was found to be distinct from Tarbosaurus in their independent analyses of tyrannosaur relationships, and a presentation about testing tyrannosaur growth by paleontologist Thomas Carr will likely provide a template for other scientists to test whether certain tyrannosaurs are juveniles of other forms.

In general, though, conference attendees I spoke to were frustrated by the Nature news coverage of the event—since no formal critique of Raptorex was published or presented, there was nothing new to talk about outside issues already known to exist. The ongoing discussion over Torosaurus and Triceratops seemed to be a more prominent topic at this year’s conference, and the scientific debate over Raptorex awaits the publication of more data. Even when Hurum and Larson publish their paper, however, it will be unlikely to definitively close the case on Raptorex. Determining the true identity of this dinosaur will require multiple lines of evidence—from geology to bone histology—and this  discussion will likely drag out through the literature for some time to come.

David of Love in the Time of Chasmosaurs also covers this story here and here, as did Josh of The Finch and the Pea.

For more SVP coverage, see these posts:

Society of Vertebrate Paleontology Dispatch, Part 1

SVP Dispatch, Part 2: Did Sea Level Influence Dinosaur Diversity?

On Laelaps: Hungry Carnivores Helped Create Keyna’s Primate Fossil Record

References:

Sereno, P., Tan, L., Brusatte, S., Kriegstein, H., Zhao, X., & Cloward, K. (2009). Tyrannosaurid Skeletal Design First Evolved at Small Body Size Science, 326 (5951), 418-422 DOI: 10.1126/science.1177428

A snapshot of the world during the Cretaceous, about 90 million years ago. From Wikipedia.

Paleontologists are constantly reminding themselves of the incompleteness of the fossil record. What has been preserved is only a small fraction of all the organisms and environments that have ever existed. This makes detecting evolutionary patterns a bit of a challenge. In a presentation given at this year’s Society of Vertebrate Paleontology conference, Smithsonian paleontologist Matt Carrano dug into the long-standing question of whether changes in sea level triggered changes in dinosaur diversity.

Over the past few decades, paleontologists have produced a number of graphs depicting dinosaur diversity through time. They show a general trend toward increasing diversity from the Late Triassic through the end of the Cretaceous, but with a few fluctuations in between. The rise and the fall of the seas has been proposed as one of the drivers of these changes. Perhaps, it has been hypothesized, high sea levels might have favored dinosaur diversity by fragmenting some terrestrial habitats or isolating one area from another while simultaneously creating more environments where dinosaurs might be preserved. Then again, it has also been suggested that dinosaur diversity might go up when sea levels are low since there would be a larger land area. In order to detect whether any such trends existed, the scientists looked at the occurrence of about 749 dinosaur species through time and space, noting where paleontologists have gone looking for their bones, as well.

What the Carrano and his colleagues found was that the fluctuations in sea level did not influence dinosaur diversity as we know it today. Our perspective of dinosaur diversity is significantly shaped by where paleontologists have gone looking for fossils, the amount of effort expended there, and also by places that have yet to be extensively studied. Dinosaurs might be more plentiful and easier to find in Cretaceous rocks than Triassic ones, for example, which would account for why dinosaur diversity differs between the two time periods. Any scientific work proposing to look at dinosaur diversity has to take these sampling biases into account.

This is not to say that sea level change did not or could not have influence dinosaur diversity, though. Rising sea levels could have created island chains and other geographical pockets that could have driven dinosaur speciation, or low sea levels might have allowed dinosaur species to range more widely. (We know, for example, that the Western Interior Seaway caused Cretaceous dinosaurs to evolve in different ways in the eastern and western parts of North America.) Detecting these signals from the fossil record, however, will require in-depth sampling and a recognition of the way in which our search for dinosaurs skews the picture of their diversity. As stated by the authors of the paper that was the basis for the SVP presentation: “Considerable future work is required to establish how sampling biases may affect proposed long-term diversity trends and mass extinction events in the terrestrial realm.” If paleontologists want to get at the big picture of dinosaur diversity, they need to look at these biases and get digging at places which are still poorly known.

References:

Butler, R., Benson, R., Carrano, M., Mannion, P., & Upchurch, P. (2010). Sea level, dinosaur diversity and sampling biases: investigating the ‘common cause’ hypothesis in the terrestrial realm Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2010.1754

A restoration of the ankylosaur Euoplocephalus by Nobu Tamura. From Wikipedia.

The first day of the 70th annual Society of Vertebrate Paleontology meeting was chock-full of dinosaur talks. Fans of ornithischian dinosaurs—the hadrosaurs, ankylosaurs, stegosaurs, pachycehpalosaurs, horned dinosaurs and their kin—had a lot to cheer about. There is a flood of new species, and new evolutionary comparisons are refining the relationships of some familiar species and, in some cases, are suggesting that there is much left to be discovered. Two researchers agreed to let me give you a sneak peek at research that is changing our understanding of dinosaur diversity and evolution.

From documentaries to technical papers, the armored dinosaur Euoplocephalus has often been taken as the quintessential ankylosaur. It seemed to occupy a long range of time and be represented by a wide array of skeletal material. Things are not as clean and neat as they seem. Just last year University of Alberta grad student Victoria Arbour and two others showed that some of the bones scientists had been calling Euoplocephalus really belonged to the distinct genus Dyoplosaurus, which had been named in 1924. This was not the only ankylosaur that was hiding within Euoplocephalus. At least one, and possibly two, other ankylosaurs have probably been mistakenly lumped into the genus. Arbour is continuing her efforts to tease apart the taxonomic mess in the hope that we will be able to get a clearer picture of ankylosaur diversity at the end of the Cretaceous in North America.

The year 2010 might as well be known as the “Year of the Ceratopsians.” From the Torosaurus = Triceratops debate to peculiar ceratopsian forms found in unexpected places, our understanding of these dinosaurs is rapidly changing. Paleontologist Andy Farke and colleagues will soon be adding another taxa to the mix. As he introduced it to colleagues Sunday morning, the new species looks like “the love child of Centrosaurus and Styracosaurus.“  The only thing more bizarre than its looks was the fact that the specimen sat virtually unnoticed on a museum shelf for about a century. Nor was it the only new ceratopsian introduced during the first two days of the conference, and by present indications there are still many new species waiting to be found.