November 5, 2012
If I started this Dinosaur Alphabet series just a few years ago, I wouldn’t have included Dyoplosaurus. Up until 2009, the dinosaur was hiding within another genus of heavily-armored ankylosaur. But after decades of discovery and debate, Dyoplosaurus is back, and the Cretaceous club-tail has its own role to play in wider discussions about the tempo and mode of dinosaur evolution.
Canadian paleontologist William Parks named the ankylosaur in 1924. Just a few field seasons earlier, in 1920, a University of Toronto crew found the partial skeleton of an armored dinosaur in the Late Cretaceous rock along the Red Deer River in Alberta. “The anterior part of the skeleton had been long exposed and had suffered in consequence,” Parks later wrote, but the team was still able to collect part of the skull, some tooth fragments, ribs and, best of all, the articulated hip and tail. Some of the armor remained in place, and the preservation was delicate enough to include skin impressions and the long ossified tendons that helped support the ankylosaur’s tail. If only the front half had remained intact!
This partial skeleton wasn’t the first ankylosaur to be found in the Late Cretaceous of North America. But, Parks wrote in his report, the animal’s tail club was “distinctly different from any previously described and, as far as I am aware, from any that have been collected.” Based on this slender oval of bone and other features, Parks distinguished the skeleton as Dyoplosaurus acutosquameus. And while the front half of the animal was almost entirely missing, the detail of the back half gave paleontologists a detailed look at how the armor, bones and tendons of ankylosaurids were arranged.
Then researchers sunk Dyoplosaurus. In 1971, in a huge revision of the ankylosaurs, paleontologist Walter Coombs proposed that Dyoplosaurus was not so unique as Parks had proposed. A jaw fragment found with the original Dyoplosaurus specimen was virtually identical to part of a jaw referred to the more famous armored dinosaur Euoplocephalus, Coombs wrote, and therefore Parks’ dinosaur should be considered a Euoplocephalus.
Since this other ankylosaur was named on the basis of even more fragmentary material, the addition of the “Dyoplosaurus” specimen gave paleontologists a new reference for what the hips, tail, and armor of Euoplocephalus looked like. More than that, the find extended the range of Euoplocephalus through Alberta’s Late Cretaceous rock. The “Dyoplosaurus” material was found in a roughly 76-million-year-old park of the Dinosaur Park Formation, and bones referred to Euoplocephalus had also been found in the geologically younger Horseshoe Canyon Formation. Altogether, Euoplocephalus seemed to persist for almost ten million years–quite a feat given that many neighboring genera and species of dinosaur came and went during the same span of time.
As paleontologists found additional ankylosaurs and compared previously discovered material, though, it became apparent that Euoplocephalus had become an osteological umbrella that was hiding more than one dinosaur genus. Indeed, since the original Euoplocephalus material consisted of a partial skull and a half ring or neck armor, it was difficult for paleontologists to compare and accurately refer specimens when there was a lack of overlapping material. As researchers investigated more complete material that was undeniably Euoplocephalus, it became apparent that other specimens from a wide range of time and displaying a wide range of variation had been incorrectly assigned to this dinosaur. Among the incorrectly lumped dinosaurs was Dyoplosaurus.
Ankylosaur expert Victoria Arbour and her colleagues resurrected Parks’ ankylosaur in 2009. While the anatomy of the animal’s skull fragment wasn’t easily distinguishable from the original Euoplocephalus fossils, details of the hips and vertebrae, especially in the tail, distinguished Dyoplosaurus from all other ankylosaurs. From the hips back, Dyoplosaurus was a distinct dinosaur.
Despite what Parks had written, though, Arbour and her coauthors cautioned that the tail club of Dyoplosaurus was not an easy-to-spot difference. As far as paleontologists know now, ankylosaurid dinosaurs were not born with tail clubs. The osteoderms that formed the bludgeon grew later in life, and, since Parks’ Dyoplosaurus specimen was relatively small compared to Euoplocephalus specimens, it’s possible that the dinosaur’s tail club had not finished growing. When comparing dinosaurs, it’s always important to keep the animal’s stage of development in mind–features that may seem to characterize a new species may only indicate immaturity.
Other ankylosaurs are probably hiding within Euoplocephalus. Properly identifying and categorizing them will take years. Studies of hadrosaurs, ceratopsians, tyrannosaurs and other dinosaurs have shown that Late Cretaceous dinosaurs on the western subcontinent of Laramidia–isolated from their eastern cousins by the vanished Western Interior Seaway–that the genera and species differed along the latitudes. Rather than finding the same dinosaurs from Alberta to Utah, paleontologists have found distinct assemblages of dinosaurs that belie isolated evolutionary pockets. And analyses of Canada’s Late Cretaceous species have tracked turnover patterns among the dinosaurs, timing the pulse of evolution and extinction. Splitting out Dyoplosaurus is one more step towards understanding what North America’s dinosaurs can tell us about how evolution works.
Want to know more about other unsung dinosaurs? Check out previous entries in the Dinosaur Alphabet.
Arbour, V. Burns, M. Sissons, R. 2009. A redescription of the ankylosaurid dinosaur Dyoplosaurus acutosquameus Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus. Journal of Vertebrate Paleontology 29, 4: 1117–1135. doi:10.1671/039.029.0405
Parks, W. 1924. Dyoplosaurus acutosquameus, a new genus and species of armored dinosaur; and notes on a skeleton of Prosaurolophus maximus. University of Toronto Studies Geological Series 18: 1–35.
October 31, 2012
From the time of their origin around 230 million years ago, to the extinction of the non-avian forms 66 million years ago, dinosaurs ruled the Earth. That’s how we like to characterize the Mesozoic menagerie, anyway. We take the long success of the dinosaurs as a sign of their long-lived and terrifying domination, but, despite our belief that they were the most vicious creatures of all time, there were creatures that even the dinosaurs had reason to fear. Chief among them was Deinosuchus – North America’s “terrible crocodile.”
Between 80 and 73 million years ago, when North America was divided in two by the shallow Western Interior Seaway, the marshes and swamps along the coasts were ruled by Deinosuchus. Fossils of this Cretaceous cousin of modern alligators have been found from Mexico to Montana and in east coast states such as North Carolina and Georgia, tracing the margins of the western subcontinent Laramidia and its eastern counterpart, Appalachia. For the most part, paleontologists have found the bony armor, vertebrae, and teeth of Deinosuchus, but pieces of jaw and partial skeletons found in places such as Texas and Utah indicate that this alligatoroid was a giant, growing over thirty feet in length and approaching forty feet among the biggest individuals.
During the heyday of Deinosuchus, adults of the aquatic ambush predator were among the largest carnivores in their ecosystems. The enormous Tyrannosaurus rex was over five million years off, and the tyrannosaurs of the time were not quite so long or bulky. (Teratophoneus, found in southern Utah among strata that also yield Deinosuchus, was about twenty feet long, and Daspletosaurus from Montana grew to be about thirty feet long.) A fully mature Deinosuchus would have outstretched and outweighed the dinosaur competition, and would have undoubtedly been a deadly apex predator in the water habitats it haunted.
The skull of Deinosuchus testifies to its destructive potential. The alligatoroid’s skull was large, broad, and equipped with an array of teeth deployed to pierce and crush. Indeed, even though there were other giant crocodylomorphs of near-equal size during the Mesozoic (such as the narrow-snouted Sarcosuchus), Deinosuchus appears to be unique in having the anatomical necessities to take down hadrosaurs and other unwary dinosaurs at the water’s edge. And, thanks to tooth-damaged fossils, we know that Deinosuchus truly did dine on dinosaurs. Two years ago, Héctor Rivera-Sylva and colleagues described hadrosaur bones bearing tell-tale Deinosuchus toothmarks from Mexico, and similar finds have been reported from Texas. There may be other candidates in museum drawers elsewhere.
Of course, we don’t know whether the bitten bones record hunting or scavenging. Unless the injuries show signs of healing, toothmarks on bones record feeding rather than hunting behavior. The evidence only takes us so far. Adult Deinosuchus were apparently capable of taking down dinosaurs, but, as yet, there’s no direct evidence of such an incident. Indeed, while images of Deinosuchus chomping on dinosaurs fires our imagination, we actually know relatively little about how this alligatoroid fed and what it ate. Probably, like modern alligators, large Deinosuchus were generalists that snagged fish, turtles, and whatever carrion it happened upon. We don’t know for sure. Nevertheless, dinosaurs in the habitat of this monstrous croc would have been wise to carefully approach the water’s edge, looking for teeth and scutes hiding just beneath the surface.
October 23, 2012
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.
October 15, 2012
Out of the scores of non-avian dinosaurs discovered, some get all the love. Almost everyone can rattle off a few of the most famous–Triceratops, Stegosaurus and, of course, Tyrannosaurus rex (the only one we ever feel compelled to call by its whole name). But the Age of Dinosaurs was a 160-million-year reign filled with a startling variety of species that we’re only just beginning to become acquainted with. It’s truly a shame that we continually focus on the same handful when there were so many wonderful forms. Among the unsung dinosaurs is Agujaceratops, a horned herbivore that was only recently recognized for what it truly was.
The story of Agujaceratops goes back the better part of a century. During excavations in 1938 and 1939, a Works Progress Administration crew picked away at a dense dinosaur bonebed in what is now southwestern Texas’ Big Bend National Park. The team pulled more than 340 bones out of the roughly 75-million-year-old Late Cretaceous rock. Although they didn’t know it at the time, most of these bones belonged to a single species of dinosaur that no one had seen before.
Five decades later, Texas Tech University paleontologist Thomas Lehman returned to the skeletal collection. The various pieces came from at least ten individual dinosaurs–from juveniles to adults–that were entombed in the same place. There was no single articulated skeleton, or even a complete skull, but by sifting through the remains Lehman reconstructed several skulls from the new horned dinosaur species. Drawing a comparison with Chasmosaurus, a previously known horned dinosaur found in Canada with similar anatomical motifs among the horns and frill, Lehman called his animal Chasmosaurus mariscalensis.
Not long after Lehman’s paper, other researchers happened upon a lovely specimen that confirmed the southern ceratopsid as a distinct dinosaur. In 1993, ceratopsian expert Catherine Forster and coauthors described a complete Chasmosaurus mariscalensis skull, showing that this dinosaur had much longer brow horns and a more saddle-shaped frill than other Chasmosaurus species to the north.
Yet, even though this study found that Chasmosaurus mariscalensis was more closely related to other Chasmosaurus species than to Pentaceratops–another southern ceratopsid that was a possible candidate for a Chasmosaurus descendant–the southern species didn’t look quite like the northern ones. The northern Chasmosaurus species had shorter brow horns and expanded, V-shaped frills that didn’t curve upwards in the same way. Why was the southern species so different? Perhaps, Forster and colleagues hypothesized, the southern species retained some archaic characteristics while the northern Chasmosaurus underwent greater modifications.
As paleontologists continued to scrutinize ceratopsids, however, the less the southern species looked like a Chasmosaurus. In a 2006 reevaluation of Chasmosaurus and Pentaceratops, New Mexico Museum of Natural History and Science paleontologist Spencer Lucas and collaborators placed “Chasmosaurus” mariscalensis in a new genus–Agujaceratops, named in honor of the Aguja Formation in which the dinosaur is found.
Along with other new discoveries–such as Kosmoceratops and Utahceratops from southern Utah–Agujaceratops changed the big picture of ceratopsid biogeography. As Lehman’s paper hints, some paleontologists used to think there was a kind of faunal continuum between northern and southern swaths of North America. In formations laid down at the same time (about 75 million years ago in this case), you’d expect there to be continuity between the dinosaur genera found down the latitudes. Bits and pieces of dinosaurs found in Utah, New Mexico, Texas and elsewhere were attributed to dinosaur genera discovered about 2,000 miles away in Canada. This didn’t only affect horned dinosaurs. Remains of southern tyrannosaurs, previously attributed to the northern predators Albertosaurus and Daspletosaurus, were recently found to be a previously unknown tyrant called Bistahieversor.
By way of new finds and reexaminations of old material, paleontologists have only just started to become acquainted with Agujaceratops, Bistahieversor and other dinosaurs of the southwest’s Late Cretaceous. At the species and genus levels, the southern dinosaurs are different. The big question is, why? Paleontologists know that a shallow, vanished seaway separated dinosaurs on eastern and western subcontinents for millions of years, but on that western subcontinent called Laramidia, there was apparently some other kind of barrier that isolated northern and southern dinosaur populations.
The hypothesis relies on basic evolutionary theory. Isolate populations of an ancestor species in different regions, and through factors such as natural selection and genetic drift, those populations will evolve in different ways. The fact that Agujaceratops, Kosmoceratops and Utahceratops are so different from Chasmosaurus and other northern cousins are a sign that such a barrier was in place. No one has found it yet, though, and a great deal of work remains to be done on whether all these dinosaurs were really contemporaries or reveal a much more complex evolutionary pattern. As these investigations continue, though, Agujaceratops will continue to play an important role as a symbol of isolation and evolution.
Author’s note: This is the first entry in a new series of posts, highlighting fantastic dinosaurs that are little known by the public. You won’t find Archaeopteryx, Brachiosaurus, Tyrannosaurus or other classics on this list. Those dinosaurs are famous enough already. Now it’s time to highlight some of their lesser-known cousins and contemporaries, from Agujaceratops to Zalmoxes.
Forster, C., Sereno, P., Evans, T., Rowe, T. 1993. A complete skull of Chasmosaurus mariscalensis (Dinosauria: Ceratopsidae) from the Aguja Formation (late Campanian) of West Texas, Journal of Vertebrate Paleontology, 13:2, 161-170. doi: 10.1080/02724634.1993.10011498
Lehman, T.1989. Chasmosaurus mariscalensis, sp. nov., a new ceratopsian dinosaur from Texas, Journal of Vertebrate Paleontology, 9:2, 137-162 doi: 10.1080/02724634.1989.10011749
Lucas, S., Sullivan, R., Hunt, A. 2006. Re-evaluation of Pentaceratops and Chasmosaurus (Ornithischia: Ceratopsidae) in the Upper Cretaceous of the Western Interior, in Lucas, S. G. and Sullivan, R.M., eds., 2006, Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35.
Sampson, S., Loewen, M., Farke, A., Roberts,E., Forster, C., 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
November 7, 2011
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.
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.