Smithsonian.com

East coast dinosaurs are few and far between. Unlike the exposed formations in the western badlands, much of the dinosaur-bearing strata in the eastern states are hidden beneath forests, lawns and parking lots. But you can still find signs of dinosaurs if you know where to look.

Amateur ichnologist Ray Stanford has a knack for finding dinosaur tracks and traces in the Baltimore, Maryland and Washington, D.C. area. Among his recent finds are an impression of a baby ankylosaur–on display at the Smithsonian National Museum of Natural History–and a track made by an adult of a similar dinosaur on the grounds of NASA’s Goddard Space Flight Center. As our paleontology curator Matthew Carrano says in the video above, Stanford’s talent for tracking dinosaurs has helped fill out our understanding of east coast dinosaurs in deposits where bones are scarce.

The dinosaur William Parks described as Dyoplosaurus, showing where the bones would have fit on the actual animal. From Arbour et al., 2009.

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.

References:

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.

I have a confession to make. Before this weekend, I’d never watched even a single episode of Doctor Who. (Shock. Horror.) I’m a bad nerd, I know. But when BBC One announced that the second episode of the show’s seventh season was titled “Dinosaurs on a Spaceship”, I knew I had to finally check out the goofy sci-fi staple.

I’m not going to say much about the plot of the show itself. When you have dinosaurs, Queen Nefertiti and a pair of insecure sentry robots voiced by David Mitchell and Robert Webb on the same ship–among other things–it’s better to simply let the program speak for itself. All you need to know is that an alien ark is harboring a number of dinosaurs rescued from earth before the non-avian varieties perished around 66 million years ago. I will say this, though: the dinosaurs in this episode of Doctor Who look infinitely better than the wonky puppets in the “Invasion of the Dinosaurs” episode of the original series. (Worst. Dinosaurs. Ever.)

Let’s start with the non-dinosaurian aspect of the alien ship’s prehistoric bestiary first. At one point, the Doctor and companions are attacked by a flock of Pteranodon. (Because where you find dinosaurs, flying monsters are never far behind.) The experts behind Pterosaur.net are better qualified to comment on these flying, non-dinosaurian archosaurs than I, but, my apologies to the Doctor, “pterodactyl” isn’t the proper term for these animals. The proper general term for these flapping archosaurs is “pterosaur.” “Pterodactyl” is an outdated term derived from the genus name of the first pterosaur recognized by science, but the term isn’t used by specialists anymore. It’s time to put “pterodactyl” to rest.

The rest of the Cretaceous cast is relatively thin. A pair of ornery ankylosaurs–modeled after Euoplocephalus–make a smashing entrance early on in the show, and our heroes soon cross a snoozing Tyrannosaurus youngster. Sadly, the juvenile tyrant is neither fuzzy nor sufficiently awkward-looking. Thanks to specimens such as “Jane“, we know that young Tyrannosaurus were leggy, slim and had relatively shallow skulls. They didn’t have the bone-crushing skull profile of their parents or the graceful bulk. And, as I’ve remarked many times before, young tyrannosaurs may very well have been fluffy flesh-rippers. The Doctor Who version, unfortunately, looks like a shrunken version of an adult.

Two different dinosaur species get most of the screen time, though. A friendly–or, at least, not overly aggressive–Triceratops helps the Doctor and friends out of a few tight spots. Like the ankylosaurs, though, the ceratopsid is a little bit too tubby and doesn’t run quite right. A Triceratops is not a horse. Likewise, the dinosaur’s tail was a bit too limp. The organ, essential to balance, flopped around like a big green sausage. All the same, the big herbivore was rather cute.

The dromaeosaurids, on the other claw, were not so friendly. They mostly keep to the shadows until the final act and are ferocious enough to temporarily endanger the crew. All the same, the unidentified “raptors” suffered the curse of the bunny hands and insufficient feathery coats. Filmmakers seem reluctant to drape feathers over dromaeosaurids, but, for any effects artists who may be reading, we know that these dinosaurs had exquisite plumage covering almost their entire body. If you’re going to have raptors, they should be intricately feathery. Nevertheless, I liked the idea that dinosaurs could ruffle their feathers to communicate with each other, and potential threats. You may want to laugh at a Deinonychus all puffed up, but that will be the last sound you ever make before it starts to eat you.

[For another take on the episode's dinosaurs, see Marc Vincent's post at Love in the Time of Chasmosaurs.]

Soft tissue traces of the ankylosaur Tarchia. Black asterisks denote large osteoderms, scale impressions are pointed out by an arrowhead and small ossicles are identified by the arrow. From Arbour et al., 2012.

Ankylosaurs can be frustrating dinosaurs. In life, armor covered the bodies of these dinosaurs from snout to tail, but those bony adornments often fell out of place between the death and ultimate burial of the ankylosaurs. Reconstructing an ankylosaur, therefore, requires that paleontologists not only figure out the articulations of the bones but also the arrangement of the armor. Every now and then, though, researchers discover one of these dinosaurs with some armor still in place. According to an in-press Acta Palaeontologica Polonica paper, ankylosaur expert Victoria Arbour and colleagues have just identified one such specimen from the Late Cretaceous of Mongolia.

The dinosaur in question is most likely a specimen of Tarchia–an ankylosaur that could grow to about 26 feet long and, like many of its close relatives, carried a tail club. Rather than being a brand new find, though, this Tarchia was originally discovered in 1971 during the Polish-Mongolian Palaeontological Expedition and was sent to the Geological Museum in Oslo, Norway in 1998. Now, after over three decades, the dinosaur gets its time in the scientific spotlight.

What makes this Tarchia so significant isn’t the completeness of the skeleton. Only the left side of the back half of the body, including most of the tail, is preserved. What’s special is that parts of the dinosaur’s armor are still in place, including triangle-shaped bits of armor along the dinosaur’s slender tail and impressions of the tough sheaths that covered some of the armor in life. Indeed, the bony armor of dinosaurs was not exposed to the outside but was covered in a hard keratinous coating–horns, claws, plates and spikes were all covered in this, often making weapons sharper and ornaments more expansive.

While such soft tissue fossils are relatively rare, Arbour and her co-authors follow what paleontologist Phil Bell recently suggested on the basis of hadrosaur skin impressions–that preserved soft tissue impressions such as these might eventually be useful in distinguishing between different genera or species of dinosaur. In fact, this may be particularly important in cases like this exceptional ankylosaur. While the specimen is most similar to other specimens of Tarchia, it also differs in some minute tail characteristics. Are the differences the result of growth or individual variation, or could they be signs of a previously-unrecognized species? Detailed comparisons of skin impressions, in addition to skeletal differences, may help paleontologists winnow down the possibilities. We just need a better collection of ankylosaur soft tissue traces first.

Reference:

Arbour, V.M., Lech-Hernes, N.L., Guldberg, T.E., Hurum, J.H., and Currie P.J. (2012). An ankylosaurid dinosaur from Mongolia with in situ armour and keratinous scale impressions Acta Palaeontologica Polonica DOI: 10.4202/app.2011.0081

The AMNH skeleton of Styracosaurus, one of the dinosaurs from the upper zone of the Dinosaur Park Formation. Image from Brown and Schlaikjer, 1937 via Wikipedia.

Dinosaurs didn’t all live at the same time. Not counting the avian species that have thrived during the last 65 million years, dinosaurs proliferated throughout the world during a span of over 160 million years. As I’ve pointed out before, it’s amazing to think that less time separates us from Tyrannosaurus than separated Tyrannosaurus from Stegosaurus.

Even within specific geologic formations, not all the dinosaurs found in those layers lived side by side. Dinosaur-bearing strata accumulated over millions and millions of years and record both ecological and evolutionary changes. Look closely enough, and you can even see particular communities of dinosaurs give way to different assemblages. In an in-press Palaeogeography, Palaeoclimatology, Palaeoecology paper, Jordan Mallon and colleagues have done just that.

Canada’s Dinosaur Park Formation is one of the most spectacular slices of Late Cretaceous time found anywhere in the world. Spanning approximately 76.5 to 74.8 million years ago, the formation has yielded lovely specimens of dinosaurs such as the crested hadrosaur Corythosaurus, the spiky ceratopsid Styracosaurus, the lithe tyrannosaur Gorgosaurus, the heavy-armored ankylosaur Euplocephalus and many others. Not all of these dinosaurs were neighbors, though. Since 1950, at least, paleontologists have recognized that some kinds of dinosaurs are restricted to certain slices of the formation, and the dinosaur community changed over time. Mallon and co-authors decided to have another look at the dinosaur turnover, focusing on the large herbivores and investigating what might have shook up the dinosaur populations during the time the Dinosaur Park Formation was being laid down.

The paleontologists identified two broad divisions in the Dinosaur Park Formation, which they call “megaherbivore assemblage zones.” Each zone lasted roughly 600,000 years each. There are a lot of names here, so bear with me. In the lower zone, the horned dinosaur Centrosaurus and the crested hadrosaur Corythosaurus are found throughout; other dinosaurs restricted to this half of the formation include the ceratopsid Chasmosaurus russelli, the hadrosaurs Gryposaurus and Parasaurolophus, and the ankylosaur Dyoplosaurus.

Yet there are some dinosaurs that first appear in the lower zone and persist into next one. The ceratopsid Chasmosaurus belli, the ankylosaur Euoplocephalus and the hadrosaurs Lambeosaurus clavinitialis and Lambeosaurus lambei show up in the lower zone but pass through into the second zone as well. And, as with the lower swath, there were dinosaurs that were only found in the second zone. The hadrosaurs Prosaurolophus and Lambeosaurus magnicristatus, as well as the horned dinosaurs Styracosaurus, Vagaceratops and a pachyrhinosaur, are only found in the upper zone.

So the big picture is that the lower zone is characterized by Centrosaurus and Corythosaurus, the upper zone is distinguished by Styracosaurus and Prosaurolophus, and there are some dinosaurs–such as Lambeosaurus and Chasmosaurus–that are smeared across the two. As the researchers note, it’s even possible to break down the two halves into even smaller subsets, although the picture gets a little muddier at these levels.

What does all this evolutionary dinosaur shuffling mean? Other researchers have proposed that the Dinosaur Park Formation represents a series of turnover pulses–after a period of stability, rapid ecological change wiped out some dinosaurs while creating opportunities for a new community. The now-vanished Western Interior Seaway has been invoked as a possible mechanism for this. As this shallow sea, which once split North America in two, expanded and encroached further inland, the area of the Dinosaur Park Formation became a mostly coastal, muddy, swampy habitat. This may have put pressure on some forms of dinosaur while providing opportunities for others. As the seaway fluctuated, the attendant changes would have altered the environment and therefore affected dinosaur populations.

According to Mallon and collaborators, though, there’s no strong evidence for the turnover pulse hypothesis. We simply don’t have the resolution to tell how closely certain dinosaurs were tied to particular habitats or niches, and shifts in ecology would have influenced dinosaur evolution. Other possible influences–such as dinosaurs migrating to the area from elsewhere, or the evolution of one species into another within the formation–are also frustratingly unclear. As the researchers state, “Whether the appearance and disappearance of the megaherbivorous taxa of the [Dinosaur Park Formation] was due to evolution, migration, or to a combination of these factors, is difficult to determine.” We don’t yet know what drove the alterations in the formation’s dinosaur communities.

Aside from the ongoing mystery about what caused the changes between the two zones, the revised look at the Dinosaur Park Formation also raises a few questions about dinosaur ecology. Despite the shifts in dinosaur communities, the paleontologists note, there were about six to eight different megaherbivorous dinosaur species living alongside each other. That’s a lot of big herbivores on the landscape, especially since the hadrosaurs and ceratopsids may have formed huge herds. Such vast, hefty dinosaur communities would have required a large amount of vegetation, and the disparate megaherbivores were in competition with each other for food. In order to live alongside one another, then, we can assume that there was some kind of niche partitioning–the dinosaurs were adapted to have restricted diets or live in particular habitats as a result of their competition for resources. How exactly this happened, though, requires further study into the ecology and evolution of these dinosaurs.

And there was something else that caught my eye. The new study focused on the megaherbivores, but what about the large carnivores? The large tyrannosaur Gorgosaurus was also present in the Dinosaur Park Formation and was rejected by the researchers as a zone marker because this theropod ranges throughout the formation. Think about that for a moment. We can see a significant amount of change and turnover among the big herbivores, but one of the large carnivores stays the same throughout the entirety of the formation. Why should this be so? Perhaps it has something to do with the fact that the ornamentation and headgear of hadrosaurs and ceratopsids changed quite a bit, but their general body plans were conservative–a Gorgosaurus could take down a Corythosaurus just as well as a Lambeosaurus.

Likewise, I wonder if the same pattern might hold true elsewhere. The Kaiparowits formation of southern Utah, laid down around the time of the Dinosaur Park Formation further north, also hosts an array of hadrosaurs, ceratopsids and ankylosaurs, but there seems to be just one large dinosaurian predator, the tyrannosaur Teratophoneus. (The giant alligator cousin Deinosuchus was another megacarnivore in the Kaiparowits.) We need more fossils to be sure, but perhaps, like Gorgosaurus, the short-snouted Teratophoneus remained the same as different large herbivores came and went. If this turns out to be the case, the lack of an arms race between predator and prey would be further evidence that the ornamentation of ceratopsids and other dinosaurs had more to do with decoration and combat among each other than defense.

Indeed, the new study of the Dinosaur Park Formation lays some important groundwork for future studies. Paleontologists are currently investigating and debating why the roughly 75-million-year-old dinosaurs from Alberta are different from the roughly 75-million-year-old dinosaurs from southern Utah. What factors drove the diversity and disparity of these dinosaurs across the latitudes, and who really lived alongside whom? So far, the Dinosaur Park Formation is the best-sampled slice we have, and there is much work to be done. With any luck, and a few more decades of careful sampling, we’ll be able to put together an intricate picture of how dinosaurs lived and evolved during this brief span of Late Cretaceous time.

Reference:

Mallon, Jordan C., Evans, David C., Ryan, Michael J., Anderson,, & Jason S. (2012). Megaherbivorous dinosaur turnover in the Dinosaur Park Formation
(upper Campanian) of Alberta, Canada Palaeogeography, Palaeoclimatology, Palaeoecology DOI: 10.1016/j.palaeo.2012.06.024