What I've Read: New Perspectives on Horned Dinos

What I've Read: New Perspectives on Horned Dinosaurs: The Royal Tyrell Museum Ceratopsian Symposium
Indiana University Press (2010), Michael J. Ryan, ed.

I was turned on to this book by Darrien Naish's blog Tetrapod Zoology on scientificamerican.com. I was able to get it through my library through interlibrary loan.

New Perspectives isn't so much a book as a compendium of scientific papers presented at the Ceratopsian Symposium held September 22-24, 2007 at the Royal Tyrell Museum of Paleontology in Drumheller, Alberta, Canada. (Interestingly, though the Symposium was held in Canada, the book was published by Indiana University Press. Go figure. )

A word of warning: while I found the book fascinating, I remind you again these are scientific papers, meaning most people will find them rather dry, obtuse, if not outright dull, reading. So rather than summarize each paper, I hope to hit some of the "highlights" and share a few of the fascinating things I learned about ceratopsians in this book.

I learned ceratopsians had a long history: the earliest ceratopsian known is Yinlong from the Oxfordian Upper Jurassic of China (~159 MYA), and they evolved and diversified right up to the end of the Cretaceous. By the Aptian age of the Early Cretaceous (~120 MYA), they had spread throughout the world's Northern Hemisphere, and possibly further, based on fragmentary ceratopsian material found in Europe, eastern North America, and a possible find (Serendipaceratops) in Australia. Ceratopsians seem to have liked environments near water; their fossils are typically found in what were once wetlands, lake and river environments, river deltas, and areas prone to seasonal flooding.

For most of their history, though, and across most of their near-worldwide range, the vast majority of ceratopsians were small, bipedal forms like Chaoyangsaurus, Psittacosaurus, Magnirostris, and Cerasinops. Only in one place—what is today western North America*—and only in the last 35 million years of their existence, did they evolve the huge, spectacularly horned and frilled forms we love—the ceratopsids.

One of my favorite parts of this book is a beautiful 2-page spread (reproduced here) with front and side views of reconstructed skulls of most of the known ceratopsids (at the time of writing). The skulls are in reverse chronological order, so the first to evolve are at the bottom, and the last to come are at the top. For your convenience, I've relabeled them for you. All of these varied forms lived only in the area of the North American Rocky Mountains westward, the area geologists call Laramidia.

Once upon a time, about 100 million years ago, North America was divided in two by a vast inland sea full of monsters called the Western Interior Seaway. The eastern half of North America—roughly from the Mississippi River east—was an island continent called Appalachia. We know dinosaurs lived in Appalachia, but know little about them as dinosaur fossils in Appalachia are few and fragmentary. We know more about what lived on the Western continent Laramidia. This was the old stomping grounds of the über-predator Tyrannosaurus rex, and its old nemesis Triceratops—along with every other ceratopsid that ever lived.*

Even more interesting is that the apparent abundance of ceratopsians on Laramidia is partly an illusion; each ceratopsian taxon (genus and/or species)—even Triceratops—is known from only one limited geographic area, in only one rock stratum (layer). This tells paleontologists that rather than roaming the length and width of Laramidia like the Recent bison of the Great Plains, ceratopsids lived in geographically limited ranges, with usually no more than two or three species sharing the same local ecosystem at any one time (see this example from Canada's Dinosaur Park Formation). Usually this was one species of chasmosaurine (Triceratops line) and one or two species of centrosaurine (Centrosaurus line). The only exception to this being at the very end of the Cretaceous, after the Centrosaurines seemed to have gone extinct (about 4 million years prior to the end Cretaceous, see here).

Furthermore, ceratopsids evolved quickly for such large animals: with rare exceptions, most ceratopsid taxa lasted less than a million years!

Finally, I have a new favorite ceratopsid: Tatankaceratops.  Why no one thought to call this guy "Tank" is beyond me.  At about the size of a modern bison, Tank was little for a ceratopsid. (its generic name comes from tatanka, the Sioux word for bison.) Found in the Hell Creek formation, it was also one of the last, living literally alongside Triceratops, Torosaurus, and T. rex.  I've copied Tank's reconstructed skull here, if anyone wants to try a reconstruction (hint! hint!!)

A few more highlights from the Symposium:

A hypothesis that the basal ceratopsian Protoceratops was nocturnal, based primarily on its eyes—as measured by the sclerotic rings (eye bones) left behind—being much larger than they should be in an animal its size (Longrich, p. 308);

A new reconstruction of forelimb posture in Chasmosaurus and other ceratopsids based on fits to trackways and peculiar bone pathology of their hands, indicating most weight was borne on the first three digits (the "thumb," "index finger" and "middle finger.") Reconstruction here (Rega, Holmes, and Tirabassio, p. 340);

Two contradictory papers: one from Krauss et al (p. 282)  that used 2-D animation (i.e. Photoshop) to show how ceratopsids, especially those with large holes—"parietal fenestrae"—in their frills were able to "lock horns" without "puncturing" each other, and one by Tank and Rothschild (p 355) that concludes ceratopsids never "locked horns" because no evidence of horn injuries was found on any of the ceratopsid frills they studied;

Triceratops and other horned dinosaurs may have kept their cool with their horns, based on extensive blood vessel traces found in Triceratops horn cores. These would have run just under the horny outer sheath of the horns and allowed them to dump excess heat from their blood before it entered the braincase (Happ, p.271);

A hypothesis Psittacosaurus may have been aquatic, like modern beavers based on multiple lines of evidence, mostly from re-examination of Psittacosaurus remains. According to Ford and Martin (p. 328), Psittacosaurus had several adaptations consistent with aquatic life, like:

1. eyes and nostrils placed high on the head (like hippos);
2. arms and legs with much wider ranges of motion than other dinosaurs (They have been found in an alligatorlike "sprawling" stance as well as the usual bipedal one) and this would have made them strong swimmers;
3. A flexible tail, which may have carried a fin (the "bristles" found on one specimen);
4. Stones in their stomachs to help them dive (which would be otherwise unnecessary as they could chew their food).

In addition, Psittacosaurus remains are usually found in what were once lake environments, which Ford and Martin says supports their hypothesis.

In any case Psittacosaurus has the most named species of any ceratopsian—more than any dinosaur genus I know of—and they had a lovely illustration of Psittacosaurus species I reproduced here.

Finally, in keeping with the idea of wet ceratopsians, Mallon and Holmes (p. 189) examine the headless—but otherwise nearly intact—remains of a ceratopsid from Horseshoe Canyon, Alberta once referred to Anchiceratops. They believe based on details of its anatomy and the paleoenvironment where it was found it may have spent much of its life in the water, like today's hippos.

*except maybe for Turanoceratops, found in Asia.