November 1, 2012
If an Allosaurus fell in the Jurassic, would it leave a trace fossil? We know that resting dinosaurs can leave body impressions behind, as shown by a theropod trace found in St. George, Utah, but what if a dinosaur lost its footing and fell over onto a mudflat or sand dune? Such events surely must have happened. The question is whether the embarrassing moments ever became set in stone.
A trace fossil would be the obvious mode of preservation for a dinosaur fall. A messy footprint, recording the slip, paired with a body impression would be a gorgeous snapshot of a dinosaur’s tumble. Sadly, no one has yet found such a fossil, but paleontologists have identified a more subtle clue of a dinosaur fall. In 2007, paleontologist Oliver Wings and colleagues described a Middle Jurassic dinosaur tracksite described in China. Among the dozens of tracks was what appeared to be a slip footprint–parallel grooves made when the dinosaur’s foot slipped backward or foreword over the wet mud of the ancient environment.
But tracks and other impressions may not be the only way dinosaur falls might be recorded. When I brought up the idea of a fossilized dinosaur tumble on Twitter yesterday, Sam Barnett brought up Allosaurus gastralia, or rib-like belly bones, that showed signs of fracture due to a fall. I hadn’t heard of these specimens before, so I checked a review of theropod pathologies published by Ralph Molnar in 2001. The broken bones got a nod, with a reference to a more thicker biography of dinosaur injuries called Dinosores published two years before by Darren Tanke and Bruce Rothschild. I kept pulling at the thread, hoping to find something more.
A 1998 New Scientist story by Jeff Hecht called “The deadly dinos that took a dive” outlined the idea. In a preview of research he was getting ready to show off at that year’s DinoFest symposium in Philadelphia, Rothschild mentioned that an Allosaurus specimen showed “exactly the pattern of fractures that would be caused by a belly flop onto hard ground while running.” But I wanted to know more. What, exactly, was it about the breaks that indicated a clumsy fall?
Unfortunately, I wasn’t able to find any more detailed information. I don’t have any doubt that Allosaurus and other dinosaurs suffered fractures from falls. That’s an inevitable interaction between biology, geology and physics when you have animals walking and running around the Mesozoic. The trick is connecting the pathology with the cause. Still, I have to wonder if virtual models that estimate bone stress–such as the finite element analysis models used in bite mechanics studies–might help paleontologists investigate what happened to dinosaurs when they fell. If paleontologists can trip up a virtual Allosaurus and investigate how those computerized bones respond to the stress of a fall, maybe researchers can predict where breaks might occur and compare the models to the fossil record. For now, though, we can do little more than imagine an Allosaurus falling face-first on a mudflat, shaking itself off, and ignoring the pain in its ribs as it tromped off.
[Hat-tip to Heinrich Mallison for pointing me to the trackway study, on which he was one of the coauthors.]
Claessens, L. 2004. Dinosaur gastralia; origin, morphology, and function. Journal of Vertebrate Paleontology 24, 1. 89-106
Molnar, R. 2001. Theropod paleopathology: A literature survey. pp 337-363 in Tanke, D. and Carpenter, K. eds. Mesozoic Vertebrate Life. Bloomington: Indiana University Press.
Rothschild, B., Tanke, D. 2005. Theropod paleopathology: state of the art review. pp 351-365 in Carpenter, K. ed. The Carnivorous Dinosaurs. Bloomington: Indiana University Press.
Tanke, D., Rothschild, B. 2002. DINOSORES: An annotated bibliography of dinosaur paleopathology and related topics—1838–2001. New Mexico Museum of Natural History and Science. Bulletin, 20.
Wings, O., Schellhorn, R., Mallison, H., Thuy, B., Wu, W., Sun, G. 2007. The first dinosaur tracksite from Xinjiang, NW China (Middle Jurassic Sanjianfang Formation, Turpan Basin) – a preliminary report. Global Geology 10, 2. 113-129
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.
August 14, 2012
Australia isn’t well-known for exceptional dinosaur fossils. Even though the continent contains some spectacular tracksites, such as the “Dinosaur Stampede,” many of the dinosaurs discovered in Australia over the past few years are only known from scraps. Among the exceptions are a trio of dinosaurs first described in 2009 from remains found in Queensland–a pair of sauropods and a theropod nicknamed “Banjo.” These roughly 110-million-year-old dinosaurs were all represented by partial skeletons, and there is even more material from these animals than was originally detailed. Paleontologists are continuing to prepare and study dinosaur bones from the site. The latest tidbit from the site concerns Banjo’s arm.
Banjo’s official name is Australovenator wintonensis. This roughly 20-foot-long carnivore belonged to a group of Allosaurus-like theropods called Neovenatorids. Judging by the anatomy of their skulls and forelimbs, these dinosaurs used both jaws and claws to bring down prey, and a recent paper by Matt White and colleagues provides a detailed look at the formidable arms of Australovenator.
As mentioned by White and co-authors, the new bones include elements from the dinosaur’s upper arm, lower arm and hand. Together, these bones give paleontologists a near-complete view of Banjo’s arms. Like its close relatives, Australovenator had a stout thumb tipped with a large claw, while the other two fingers were more slender and bore smaller curved weapons. From a more detailed perspective, the paleontologists also suggest that the arms of Australovenator and its close relatives might be useful in parsing the evolutionary relationships among these predatory dinosaurs.
Exactly how Australovenator used its arms is unknown. White and collaborators mention that a biomechanical analysis of the dinosaur’s arm is underway, and that study will hopefully outline how Banjo and other Neovenatorids combined teeth and claws in their hunting strategy. The new paper is primarily a detailed inventory of Banjo’s hand, and even though behavioral interpretations are sexy–it’s hard to look at theropod claws and not wonder about the damage they could inflict–we need papers that fully reconstruct a dinosaur’s anatomy first. Once we know what’s we’re looking at, then we can investigate the amazing things dinosaurs were capable of.
White MA, Cook AG, Hocknull SA, Sloan T, Sinapius GH & Elliott DA (2012). New Forearm Elements Discovered of Holotype Specimen Australovenator wintonensis from Winton, Queensland, Australia. PloS One, 7 (6) PMID: 22761772
April 12, 2012
You can’t understand dinosaurs without a sense of time. We need to know when a dinosaur lived to comprehend how it fits into what paleontologist William Diller Matthew called “life’s splendid drama.” But we throw around Deep Time estimates, framed in millions of years, so often that it’s easy to become inured to the wider context of life’s history.
The Mesozoic Era, which lasted from about 250 million to 66 million years ago, is often called the Age of Dinosaurs. As a kid, this brought to mind one endless summer when dinosaurs flourished. And many of the books I read picked one environment from three different periods within the era to represent dinosaur life. Little Coelophysis was the canonical Triassic dinosaur; the huge sauropods and theropods of the Morrison Formation represented the Jurassic, and a Cretaceous Tyrannosaurus versus Triceratops face-off ultimately capped off the succession. With the periods juxtaposed this way, millions of years didn’t seem so very long.
But let’s unpack some of that scenery. Diplodocus, Apatosaurus, Allosaurus, Stegosaurus and their neighbors roamed western North America about 150 million years ago. This slice of time falls in the latter portion of the Jurassic. The traditional representatives of the latest Cretaceous scene—Tyrannosaurus and Triceratops—did not evolve until about 67 million years ago. By themselves, these dates are just labels, but think of them falling along evolution’s timeline. About 83 million years separated Apatosaurus from Tyrannosaurus and Allosaurus from Triceratops. The so-called Age of Mammals—which began when the non-avian dinosaurs were wiped out—has been going on for about 66 million years. Less time separates us from Tyrannosaurus rex than separated T. rex from Stegosaurus.
Consider how much life has changed in the past 66 million years. Archaic mammals flourished and ultimately went extinct long before anything like the world’s modern fauna appeared. Saber-fanged, knobbly-headed herbivores such as Uintatherium, lemur-like primates called adapiforms, razor-jawed carnivores known as creodonts and many other strange forms proliferated and disappeared. Even lineages familiar to us today, such as horses, rhinos and elephants, evolved and diversified and are now represented by just remnants of what once existed.
The time between the last Triceratops and now has seen radical evolutionary changes. Now think of the 83 million years between the Jurassic and Cretaceous titans. During that time, the first flowering plants bloomed; the fish-like ichthyosaurs disappeared as plesiosaurs and mosasaurs became the predominant predators of the seas; vast herds of hadrosaurs and ceratopsids occupied places once dominated by sauropods; tiny tyrant dinosaurs transformed into apex predators, and early birds established themselves in ever-greater variety alongside their dinosaurian kin. These are just a few highlights, and that is part of the wonder and frustration of tracking the history of life on earth. We are offered only glimpses of an ever-changing picture, and when viewed separately, it’s easy to forget how those snippets relate to each other. But when we can step back, and consider how all those snippets run together, the long and ever-changing history of life on our planet seems all the more fantastic.
March 30, 2012
I have an Allosaurus on my arm. Heart of Gold Tattoo artist Jon McAffee put it there a few weeks ago. I think the tattoo—designed for me by friend and artist Glendon Mellow—came out beautifully. Contorted into the classic dinosaur death pose, the Jurassic apex predator is an expression of my passions and aspirations.
Paleontologists have uncovered scores of fascinating dinosaurs. I would have been proud to carry almost any dinosaur on my sleeve. But I knew my first science ink had to be Allosaurus. The dinosaur is not only the state fossil of Utah—I moved to the beehive state last year to get closer to dinosaurs—but the familiar predator is also an enigma.
Around 150 million years ago, when Allosaurus stalked across Jurassic Utah, the fern-covered landscape boasted an astounding diversity of huge dinosaurs. This was the time of giants such as Apatosaurus, Camarasaurus, Diplodocus, Brachiosaurus, Barosaurus and Stegosaurus, and these dinosaurs were prey for nightmarish carnivores such as Torvosaurus, Ceratosaurus and, of course, Allosaurus. There was scarcely a more fantastic time in the Age of Dinosaurs. But not all these dinosaurs were equally abundant. Among the big predators, Allosaurus is uncovered much more often than any of its knife-toothed competitors. At the Cleveland-Lloyd quarry outside Price, Utah, remains of more than 46 Allosaurus have been discovered so far, while only rare tidbits of other predators turned up. What was it about Allosaurus that made it the dominant carnivore of Jurassic Utah? I love mysteries like this. Allosaurus has been known to paleontologists for more than 130 years, but there are still some things about this creature that we just don’t know.
I asked Glendon to create the dinosaur in a death pose for a similar reason. (You can see Glendon’s step-by-step process at his blog.) If you ever find a near-complete, articulated dinosaur skeleton, chances are that the dinosaur is going to have its head thrown over its back and tail arched up. My Allosaurus got a little extra contortion for artistic purposes to bring the tail up to my shoulder, but you get the general picture. No one is entirely sure why this happens. Everything from a dinosaur’s final spasms before perishing to dessication after death have been implicated as possible causes, but the reason for the prevalence of the phenomenon is still hotly debated. Something so simple—the contortions of skeleton—is a thread leading back to unresolved questions about what happened to dinosaurs between death and discovery.
I can’t help but wonder about the life and death of an animal as beautiful and deadly as Allosaurus. And my tattoo is a reminder to keep chasing those mysteries. I do not talk about this very often—the memory is intensely embarrassing—but I never received my bachelor’s degree. After spending the better part of a decade working towards a degree in conservation ecology, I left Rutgers University just a handful of courses short of completing my program. Discouraged, disheartened and defeated do not even come close to describing how I felt. But paleontology gave me an outlet for my love of science, and writing about what I learned somehow came together into a career expressing my enthusiasm for creatures that flourished and vanished while our own ancestors were still scurrying through the undergrowth. Someday, I hope, I will go back to school and eventually commit myself to a graduate program in paleontology, but no matter what I do, I want to keep following the tales fossils have to tell. Though they might seem to simply be petrified bits of dead tissue, dinosaur bones are alive with stories about evolution and extinction. Even the most mundane bone fragment underscores powerful truths about the way life on earth has changed in an ever-evolving story of life. That’s what keeps me going back to the journal articles, museum collections and field sites where dinosaurs and ideas about dinosaurs thrive—puzzling over the long-lost life of Allosaurus enriches my own existence.
[My heartfelt thanks to Glendon for the wonderful design, and to Jon at Heart of Gold for his delicate hand realizing the tattoo. Stay tuned for a Science Ink sequel featuring another predator from Jurassic Utah.]