November 21, 2012
Last week, I wrote about attempts by paleontologist Phil Bell and colleagues to extract biological secrets from fossilized traces of dinosaur skin. Among the questions the study might help answer is why so many hadrosaurs are found with remnants of their soft tissue intact. Specimens from almost every dinosaur subgroup have been found with some kind of soft tissue preservation, yet, out of all these, the shovel-beaked hadrosaurs of the Late Cretaceous are found with skin impressions and casts most often. Why?
Yale University graduate student Matt Davis has taken a stab at the mystery in an in-press Acta Paleontologica Polonica paper. Previously researchers have proposed that the abundance of hadrosaur skin remnants is attributable to large hadrosaur populations (the more hadrosaurs there were, the more likely their skin might be preserved), the habits of the dinosaurs (perhaps they lived in environments where fine-resolution fossilization was more likely) or some internal factor that made their skin more resilient after burial. to examine these ideas, Davis compiled a database of dinosaur skin traces to see if there was any pattern consistent with these ideas.
According to Davis, the large collection of hadrosaur skin fossils isn’t attributable to their population sizes or to death in a particular kind of environment. The horned ceratopsid dinosaurs–namely Triceratops–were even more numerous on the latest Cretaceous landscape, yet we don’t have as many skin fossils from them. And hadrosaur skin impressions have been found in several different kinds of rock, meaning that the intricate fossilization occurred in multiple types of settings and not just sandy river channels. While Davis doesn’t speculate about what made hadrosaurs so different, he proposes that their skin might have been thicker or otherwise more resistant than that of other dinosaurs. A sturdy hide might have offered the dinosaurs protection from injury in life and survived into the fossil record after death.
Still, I have to wonder if there was something about the behavior or ecology of hadrosaurs that drew them to environments where there was a greater chance of rapid burial (regardless of whether the sediment was sandy, silty or muddy). And the trouble with ceratopsids is that they have historically been head-hunted. Is it possible that we’ve missed a number of ceratopsid skin traces because paleontologists have often collected skulls rather than whole skeletons? The few ceratopsid skin fossils found so far indicate that they, too, had thick hides ornamented with large, scale-like structures. Were such tough-looking dinosaur hides really weaker than they appear, or is something else at play? Hadrosaurs may very well have had extra-sturdy skin, but the trick is testing whether that characteristic really accounts for the many hadrosaur skin patches resting in museum collections.
Davis, M. 2012. Census of dinosaur skin reveals lithology may not be the most important factor in increased preservation of hadrosaurid skin. Acta Paleontologica Polonica http://dx.doi.org/10.4202/app.2012.0077
Osborn, H. 1916. Integument of the iguanodon dinosaur Trachodon. Memoirs of the American Museum of Natural History. 1, 2: 33-54
Sternberg, C.M. 1925. Integument of Chasmosaurus belli. The Canadian Field Naturalist. XXXIX, 5: 108-110
November 12, 2012
Triceratops is among the most cherished of dinosaurs. Even that might be a bit of an understatement. Fossil fans threw a conniption when they mistakenly believed that paleontologists were taking the classic “three-horned face” away, after all. But where did the charismatic chasmosaurine come from? Triceratops didn’t simply spring from the earth fully formed–the ceratopsid was the descendant of a long tail of evolutionary forerunners. And in 2007, paleontologist Xiao-chun Wu and collaborators described a 68-million-year-old dinosaur that might represent what one of the close ancestors of Triceratops was like–Eotriceratops.
In 2001, while on an expedition to search the Horseshoe Canyon Formation around the Dry Island Buffalo Jump Provincial Park in Alberta, Canada, Glen Guthrie discovered the partial skeleton of a huge ceratopsid dinosaur. This was the first identifiable dinosaur skeleton found in the top quarter of the formation, and, as Wu and coauthors later argued, the bones represented a new species. They called the animal Eotriceratops xerinsularis.
Paleontological devotees know that “eo” translates to “dawn.” The tiny mammal Eohippus was the “dawn horse” (which Victorian anatomist Thomas Henry Huxley famously characterized for the steed of a tiny “Eohomo“), and there are plenty of dawn dinosaurs such as Eoraptor, Eodromaeus, Eobrontosaurus and Eolambia. The prefix is a kind of honorific, used to indicate the hypothesized beginning of a major lineage or significant change. In the case of Eotriceratops, Wu and colleagues found that the dinosaur was the oldest known member of the evolutionary ceratopsid club containing Triceratops, Torosaurus and Nedoceratops (which, depending on who you ask, may or may not be the same dinosaur).
The individual Guthrie found had fallen apart between death and burial. Aside from some vertebrae, ribs and ossified tendons, the scattered specimen was primarily represented by a dis-articulated skull. When reconstructed, though, the head of Eotriceratops stretched almost ten feet long–about a foot longer than the largest-known Triceratops skull. And while different in some characteristics, Eotriceratops had the same three-horned look of its later relatives Triceratops and Torosaurus.
This isn’t to say that Eotriceratops was directly ancestral to Triceratops, Torosaurus, Nedoceratops or whatever combination of the three paleontologists ultimately settle on. Eotriceratops could be the closest relative of Triceratops to the exclusion of Torosaurus, which would support the idea that those later dinosaurs were separate genera. Then again, Wu and coauthors pointed out that Eotriceratops might be the most basal member of the subgroup, which would make sense given that it was older than the other three genera. In either case, Eotriceratops can give us a rough idea of the Triceratops and Torosaurus prototype, but we lack the resolution to know if Eotriceratops was ancestral to any later dinosaur. Eotriceratops undoubtedly had some significance in the evolution of the last three-horned dinosaurs, but we need many more fossils to know this little-known dinosaur’s role in the story. Every dinosaur paleontologists find comes with a handful of answers and a myriad of new mysteries.
This post is the latest in the Dinosaur Alphabet series.
Wu, X., Brinkman, D., Eberth, D., Braman. 2007. A new ceratopsid dinosaur (Ornithischia) from the uppermost Horseshoe Canyon Formation (upper Maastrichtian), Alberta, Canada. Canadian Journal of Earth Sciences 44: 1243-1265
October 26, 2012
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.
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.
October 5, 2012
The end of the Cretaceous ended in one of the most catastrophic mass extinctions of all time. Among the various forms of life that were toppled were the non-avian dinosaurs. Triceratops and company didn’t exactly fall like dominoes, but, in this short video created by Flippycat.com, domino dinosaurs replay the epic destruction. And stay tuned for the behind-the-scenes video at the end. Just as the last non-avian dinosaurs had an evolutionary backstory stretching back millions and millions of years, it took a long time to set up the toy dinosaurs for their downfall.
September 28, 2012
Triceratops was an A+ dinosaur. But, awesome as the hulking ceratopsid was, it didn’t have mutant superpowers. Indeed, despite a website’s claim to the contrary, there’s no evidence that this three-horned behemoth defended itself with poisonous quills.
Even though it was posted over a year ago, I’ve received a few emails this week asking about a Listverse post by user “TyB” titled “Top 10 Dinosaurs That Aren’t What They Were.” For the most part, the list is a simple summary of how new discoveries and ideas have revitalized images of dinosaurs. When the article gets to Triceratops, though, the scientific accuracy careens off the rails.
Rather than being covered in smooth, wrinkly skin, the article states, Triceratops had “alligator-like, flat scales, called scutes, on its belly, and the rest of its body was covered in large scales and knobs.” I don’t know of any published study on Triceratops’ body covering, but it wouldn’t be surprising if, like other dinosaurs, Triceratops had bumpy skin with larger knobs or ornaments here and there. But here’s where things get strange:
Its back and tail also had a series of weird, fist-sized bumps, each one holding a nipple-like structure which has yet to be explained by scientists. These structures may very well be anchoring points for porcupine-like quills, like those found on Triceratops’ older cousin, Psittacosaurus. Or perhaps, some scientists suggest, they were poison glands, oozing toxins to protect the Triceratops’ hindquarters from T-Rex attacks.
I have no idea what this blogger is talking about. I had never heard the idea of a poisonous Triceratops before reading the list, and I don’t know of any paleontologist who has advocated such a notion. I think I know where the post’s author got the basis for their idea, though. For years, there have been rumors of a Triceratops–now on display at the Houston Museum of Natural Science–that was preserved with skin impressions and possible evidence of bristles along the tail. The scuttlebutt, along with evidence of feather-like bristles in the archaic ceratopsian Psittacosaurus, spurred artists to start putting tufts of quills on Triceratops tails.
No one has formally published a description of these structures, though. Whether they’re truly bristles, some other true body covering or a preservational artifact is unknown. It’s not unreasonable to think that Triceratops had patches of bristles, but the truth is that there’s no positive evidence that such ornamentation actually adorned the dinosaur, either.
But I’m confounded by the suggestion that the base of the quills provided space for “poison glands.” Bristles on Triceratops are iffy to start with, and no one has ever demonstrated that dinosaurs used venom or other toxins for defense. In 2009, one group of researchers proposed that the feathered, sickle-clawed Sinornithosaurus had a venomous bite, but their suggestion was quickly refuted. There’s so evidence that dinosaurs were venomous, poisonous, toxic or otherwise relied on biological warfare. As far as I can tell, the toxic Triceratops is entirely the invention of the list’s author.
That’s not all. In the same post, the author states that “After examining the beak and jaws, paleontologists reached the conclusion that Triceratops may have been partially carnivorous, probably scavenging after T-Rex, or even scaring smaller predators away from their kills.” Again, no one has actually studied this in detail, but, unlike the poison hypothesis, this idea is actually plausible.
Paleontologist and artist Mark Witton raised this point in a description of a gorgeous Styracosaurus illustration he drew a few years ago. As Witton pointed out, the scissor-like jaws of big ceratopsids were probably capable of slicing through flesh as well as plants, and it’s not unreasonable to think that these dinosaurs occasionally picked over meaty carcasses to supplement their diets with some protein. After all, as paleontologist Darren Naish has illustrated, cows and deer do the same thing today. Herbivores can indulge in a meaty meal, just as carnivores sometimes chomp fruit and greens. What we need now is someone to model how a Triceratops skull would handle munching on flesh and bone to put some more science behind the speculation.