Did Deinonychus and other “raptors” use their foot claws to restrain prey? Art by Emily Willoughby, image from Wikipedia.

When paleontologist John Ostrom named Deinonychus in 1969, he provided the spark for our long-running fascination with the “raptors.” Similar dinosaurs had been named before–Velociraptor and Dromaeosaurus were named four decades earlier–but the skeleton of Ostrom’s animal preserved a frightening aspect of the dinosaur that had not yet been seen among the earlier finds. The assembled remains of Deinonychus included the dinosaur’s eponymous “terrible claw”–a wicked, recurved weapon held off the ground on the animal’s hyperextendable second toe. Combined with the rest of the dinosaur’s anatomy, Ostrom argued, the frightening claw indicated that Deinonychus must have been a active, athletic predator.

But how did Deinonychus and its similarly-equipped relatives use that awful toe claw? The appendage looks fearsome, but paleontologists have not been able to agree on whether the claw was using for slashing, gripping, pinning, or even climbing prey. Some researchers, such as Phil Manning and collaborators, have even argued that the claws of Velociraptor and related dinosaurs were best suited to scaling tree trunks–a conclusion consistent with the contentious hypothesis that the ancestors of birds were tree-climbing dinosaurs.

Left hind foot of Deinonychus antirrhopus. Image from Wikipedia.

All this assumes that the claws of deinonychosaurs correspond to a special behavior, but can foot claw shapes really give away the habits of dinosaurs? That’s the question posed by a new PLoS One study by zoologist Aleksandra Birn-Jeffery and colleagues.

Based on observations of living animals, researchers have often tied particular claw shapes to certain behaviors–relatively straight, stubby claws likely belong to an animal that runs on the ground, while tree-climbing species have thin claws with small, sharp points. But nature isn’t quite so neat as to have a single, tell-tale claw shape for perchers, ground-runners, climbers, and predators. Even then, researchers don’t always interpret claw shapes the same way–depending on who you ask, the foot claws of the early bird Archaeopteryx either indicate that it was a climber or could only run on the ground.

To parse this problem, Birn-Jeffery and co-authors studied the geometry of the third toe claw–on dinosaurs, the middle toe claw–in 832 specimens of 331 species, together representing different lifestyles of birds, lizards, and extinct dinosaurs. The claw shapes didn’t strictly conform to particular behaviors. In the climber category, for example, the frill-necked lizard has lower claw curvature than expected, and, among predatory birds, the common buzzard, secretary bird, and greater sooty owl has less sharply recurved claws that anticipated for their lifestyle.

When the dinosaur data was dropped into the mix, the deinonychosaurs didn’t seem to fit in any single category. The sickle-clawed carnivores fell into the range shared by climbers, perchers, predators, and ground dwellers–these dinosaurs could be said to be anything from wholly terrestrial runners to perchers. And even though the researchers identified a general claw shape that corresponded to walking on the ground–deeper claws with less curvature–the dinosaurs did not strictly fit into this category alone.

Some dinosaurs, such as Microraptor, had claws that might have been suited to climbing. However, dinosaurs that we might regard as behaviorally similar showed differences–Velociraptor seemed to best fit the ground-dweller category, while the larger Deinonychus seemed to have claws more akin to those of predatory birds. This doesn’t mean that Microraptor was definitely a climber, or that Velociraptor wasn’t a predator. As the authors show, the different behavioral categories are not so easily distinguishable as previously thought, and saying that an animal definitely engaged in a particular behavior because of claw shape alone tempts oversimplification.

No wonder there has been such a range of interpretation about dinosaur foot claws! While the new study focused on the third toe claw rather than the famous, second deinonychosaur toe claw, the point of the analysis still applies. Claw geometry alone is not a reliable indicator of behavior. That’s to be expected–as the authors point out, claws are multi-functional, are are unlikely to represent just one type of behavior or habitat. Birds that use their claws to perch may also use them to kill prey, or birds that primarily live in the trees may also forage on the ground. Claw shape is constrained by different aspects of natural history, and reflect flexibility rather than strict adherence to a particular lifestyle. Deinonychosaur claws definitely hold clues to the natural history of dinosaurs, but drawing out those clues is a difficult, convoluted process.

Reference:

Birn-Jeffery, A., Miller, C., Naish, D., Rayfield, E., Hone, D. 2012. Pedal Claw Curvature in Birds, Lizards and Mesozoic Dinosaurs – Complicated Categories and Compensating for Mass-Specific and Phylogenetic Control. PLoS ONE. 7,12: e50555. doi:10.1371/journal.pone.0050555

The arms of Therizinosaurus–as yet, the rest of the dinosaur is missing. Photo by FunkMonk, image from Wikipedia.

The most famous set of arms in the history of dinosaurs belong to Deinocheirus–eight foot long appendages from a huge ornithomimosaur that roamed Mongolia around 70 million years ago. But the immense ostrich-mimic wasn’t the only giant omnivore of its time, nor the only one made famous by its imposing arms. About 20 years before the discovery of Deinocheirus, a joint Soviet-Mongolian expedition found extremely long, tapering claws and a few other bones from a gigantic reptile. The identity of this animal took decades to untangle.

Paleontologist Evgeny Maleev described the paltry remains in a 1954 paper. Based on rib fragments, a bone from the hand, and three claws, Maleev believed that he was looking a gargantuan turtle. He named the creature Therizinosaurus cheloniformis–roughly, the “turtle-like scythe lizard.”

The animal’s claws played a key role in the identification. No terrestrial animal had such claws, he argued. Such armaments “may have been originally used by the animal for cutting aquatic vegetation or for another function, constrained by movement and acquiring food.” And even though Maleev only had pieces to work with, he proposed that Therizinosaurus was about 15 feet long with claws at least three feet long. This aquatic, apparently armor-less turtle lived in a time of hadrosaurs, tyrannosaurs, and sauropods.

Therizinosaurus wasn’t recognized as a dinosaur until 1970. In that year, paleontologist Anatoly Konstantinovich Rozhdestvensky published a re-evaluation of Maleev’s fossils that found the rib to be from a sauropod dinosaur, but the hand bone and the claws to be from some as-yet-unknown theropod. This recognition only spawned a new mystery–what sort of theropod dinosaur was Therizinosaurus, and what was the creature doing with such fearsome claws?

More complete forelimb and shoulder material described by Rinchen Barsbold in 1976 showed that Therizinosaurus had extraordinarily robust arms–quite a departure from the trend seen in large carnivorous dinosaurs, in which the arms seemed to become smaller as skulls became more heavily-built. At a time when theropod was generally considered to be synonymous with “carnivorous dinosaur”, it’s not surprising that experts speculated that Therizinosaurus was a monstrous predator who used claws, rather than teeth, to slice up the hadrosaurs and sauropods of its time. That’s the way I encountered the dinosaur in the books I read as a kid–a little-known, Cretaceous hadrosaur-shredder.

What researchers didn’t recognize was that Therizinosaurus represented an entirely new variety of theropod dinosaur. More complete skeletons of related forms such as Segnosaurus, Erlikosaurus, Alxasaurus, and Beipiaosaurus revealed the presence of a previously-unknown group of dinosaurs with long necks, beaked mouths, fat bodies, and stout arms tipped with ludicrously-long claws. These were omnivorous or herbivorous dinosaurs, not carnivores, although paleontologists didn’t immediately agree on what lineage they belonged to. Some thought they might be aberrant ornithischians–on the opposite side of the dinosaur family tree from theropods–or strange variations on the sauropod theme. By the mid-90s, however, paleontologists recognized that these truly were theropods, and ones belonging to the maniraptoran group that also encompasses the strange alvarezsaurs, beaked and crested oviraptorosaurs, the sickle-clawed deinonychosaurs, and birds. This group of tubby, feathery dinosaurs became known as the therizinosaurs.

Although Maleev didn’t recognize it when he named Therizinosaurus, he had found one of the most spectacular dinosaurs of all time–a giant, fluffy, omnivorous dinosaur that challenged what we thought we knew about theropods. Still, our image of Theriziniosaurus relies on the skeletons of more complete, closely-related dinosaurs. So far, we only really know what the arms of this dinosaur looked like, and the hindlimb elements described in the 1980s may or may not belong to another creature. We’re still waiting for the true nature of this undoubtedly bizarre dinosaur to come into focus.

References:

Barsbold, R. 1976. New data on Therizinosaurus (Therizinosauridae, Theropoda) [translated]. In Devâtkin, E.V. and N.M. Ânovskaâ (eds.), Paleontologiâ i biostratigrafiâ Mongolii. Trudy, Sovmestnaâ Sovetsko−Mongol’skaâ paleontologičeskaâ kspediciâ, 3: 76–92.

Maleev, E.A. 1954. “New turtle−like reptile in Mongolia [translated].” Priroda, 1954, 3: 106–108.

Zanno, L. 2010. A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora). Journal of Systematic Palaeontology. 8, 4: 503–543.

The arms of the huge ornithomimosaur Deinocheirus. How did such herbivorous theropods get to be so big? Photo by Eduard Solà, image from Wikipedia.

When I was first becoming acquainted with dinosaurs in the mid 1980s, “theropod” was synonymous with “carnivorous dinosaur.” Large or small, from Tyrannosaurus to Compsognathus, every theropod I knew of sustained itself on the flesh of other organisms. But it was just about that time that new discoveries and analyses revealed that many theropod dinosaurs were omnivores, or even herbivores. The ostrich-like ornithomimosaurs, beaked oviraptorosaurs and utterly bizarre therizinosaurs, in particular, embodied a switch from an ancestral meat-filled diet to one more reliant of fruit and foliage. Not only that, but these herbivorous theropods grew almost as large as the biggest carnivores–the ornithomimosaur Deinocheirus, the ovriraptorosaur Gigantoraptor and Therizinosaurus were all enormous Cretaceous dinosaurs. But why did these plant-chomping dinosaurs become giants?

In the latest of a spate of papers considering herbivorous theropods, paleontologists Lindsay Zanno and Peter Makovicky paired evolutionary trees with mass estimates derived from femora lengths and a bit of number crunching to see if there was any distinct evolutionary pattern that might explain why Deinocheirus and similar herbivorous theropods grew to such large sizes. Were these Late Cretaceous dinosaurs just the culmination of an evolutionary trend towards ever-larger body size–called Cope’s Rule–or was something else at work?

Zanno and Makovicky didn’t find any sign of directional selection for larger body size. Even though the earliest representatives of the ornithomimosaurs, oviraptorosaurs and therizinosaurs in Asia were much smaller than their Late Cretaceous relatives, the paleontologists point out that this signal has probably been biased by preservation. The 125-million-year-old deposits that contain small members of these groups seem to be skewed towards “mid-sized vertebrates,” the authors point out, and don’t seem to preserve larger dinosaurs that might belong to the same lineages. Indeed, therizinosaurs of about the same age from North America, such as Falcarius, were larger than species in Asia, meaning that herbivorous dinosaurs might have occupied a range of body sizes and evolved larger body sizes at multiple intervals. There was no simple, straight-line trend of bigger and bigger bodies through time.

Nor did a herbivorous lifestyle alone seem to account for gigantism among these dinosaurs. Even though big herbivores gain particular benefits from their size in terms of breaking down tough, low-quality foods more efficiently, Zanno and Makovicky doubt that this relationship drove the evolution of increased body size in the dinosaurs. Instead, they favor “passive processes” that might be tied to ecology and whether these dinosaurs were omnivores more than herbivores. And, as the paleontologists stress, the pattern relies on how complete we think the dinosaur record is. Some ecosystems might be preferentially preserving larger or smaller dinosaurs, which has the potential to skew the big picture. While Zanno and Makovicky ruled out some possibilities, we still don’t really know what accounts for the multiple herbivorous theropod growth spurts.

Post-Script: After four years working with Smithsonian magazine’s wonderful crew, and over 1,000 posts about various aspects of dinosauriana, it’s time for me to move on. I’ll be leaving Dinosaur Tracking next month. Don’t fret, I’ll still be digging into dinosaur science, but I’ll be at a new blog elsewhere on the web (stay tuned for details). I am deeply indebted to my editors Brian Wolly, Sarah Zielinski and, of course, Laura Helmuth (now doing a great job at Slate), as well as the rest of the Smithsonian staff for inviting me to come here and geek out about dinosaurs every day. And many thanks to all of you–the readers and commenters who have helped make this blog a success. You have all made blogging for Dinosaur Tracking an absolute pleasure.

Reference:

Zanno, L., Makovicky, P. 2012. No evidence for directional evolution of body mass in herbivorous theropod dinosaurs. Proceedings of the Royal Society B. 280. doi: 10.1098/rspb.2012.2526

This famous Edmontosaurus skeleton was found with intricate traces of skin over much of its body. Image in Osborn, 1916, from Wikipedia.

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.

Reference:

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

The giant sauropod Futalognkosaurus (at left) with some of its Cretaceous neighbors. Art by Maurilio Oliveira.

Which was the biggest dinosaur ever? We don’t know. Even though the size-based superlative draws a great deal of attention, paleontologists have uncovered so many scrappy sauropod skeletons that it’s difficult to tell who was truly the most titanic dinosaur of all. But, among the current spread of candidates, Futalognkosaurus dukei is one of the most complete giant dinosaurs yet found.

Discovered in 2000, and named in 2007 by Universidad Nacional del Comahue paleontologist Jorge Calvo and colleagues, Futalognkosaurus was one of many dinosaurs found in an exceptionally rich, roughly 90-million-year0old deposit in northwest Argentina. From fossil plants to pterosaurs, fish and dinosaurs, the one site entombed vestiges of a vibrant Cretaceous ecosystem. And, on that landscape, no dinosaur was as grand the newly named titanosaur.

Contrary to what you might expect given their skeletal sturdiness, the biggest sauropods are often found as partial skeletons. Our knowledge of Argentinosaurus, Puertasaurus, Supersaurus, Diplodocus hallorum and other giants is frustratingly incomplete, and figuring out how large they truly were relies on estimation from more complete representatives of other species.

The lack of complete tails from these dinosaurs makes the matter even more problematic. Dinosaur tails varied in length from individual to individual, and different subgroups had proportionally longer or shorter tails. In the case of Diplodocus hallorum, for example, a great deal of the dinosaur’s estimated  100-foot-plus length comes from the fact that other Diplodocus species had very long, tapering tails.

We don’t really know how long Futalognkosaurus was because, with the exception of a single vertebra, the dinosaur’s tail is entirely missing. Nevertheless, the sauropod that Calvo and coauthors described is remarkable for encompassing the entire neck, back and associated ribs, and the majority of the hips. Together, these elements represent over half the skeleton and comprise the most complete giant sauropod individual yet known.

Even if skeletal incompleteness keeps us from knowing exactly how big Futalognkosaurus was, the collected bones can leave no doubt that this was a truly enormous dinosaur. Calvo and coauthors estimated that the whole animal stretched between 105 and 112 feet in length, which would put it in the same class as the more famous (and less complete) Argentinosaurus. As the paleontologists at SV-POW! said when they posted images of Futalognkosaurus bones next to Juan Porfiri, who helped describe the dinosaur, there’s no doubt that the sauropod was “darned big.” The challenge is finding and filling in the parts of the dinosaur’s body that have not yet been found. There will undoubtedly be other challengers for the title of biggest dinosaur, but, for now, Futalognkosaurus remains our most detailed representative of the biggest of the big.

References:

Calvo, J., Porfiri, J., González-Riga, B., Kellner, A. 2007. A new Cretaceous terrestrial ecosystem from Gondwana with the description of a new sauropod dinosaur. Anais da Academia Brasileira de Ciências. 79, 3: 529-541

Calvo, J., Porfiri, J., González-Riga, B., Kellner, A. 2007. Anatomy of Futalognkosaurus dukei Calvo, Porfiri, González Riga, & Kellner, 2007 (Dinosauria, Titanosauridae) from the Neuquen Group, Late Cretaceous, Patagonia, Argentina. Arquivos do Museu Nacional 65, 4: 511–526.

Novas, F. 2009. The Age of Dinosaurs in South America. Bloomington: Indiana University Press. pp. 201-202

Only hindlimb elements of Alnashetri are known so far, but, based on the dinosaur’s relationships, the tiny theropod probably looked something like this Alvarezsaurus. Photo by FunkMonk, image from Wikipedia.

Many dinosaurs have gained fame thanks to their gargantuan size. A creature in the form of a dipldodocid or tyrannosaur would be wonderful at any scale, but the fact that Apatosaurus was an 80-foot-long fern-sucker and Tyrannosaurus was a 40-foot carnivore make their skeletal frames all the more spectacular. Even as an adult, long after my first encounter with their bones at the American Museum of Natural History in New York City, I still feel tiny when I look up at what’s left of the great dinosaurs.

But not all non-avian dinosaurs were gigantic. There were 100-foot giants, like the sauropod Argentinosaurus, but there were also pigeon-sized theropods such as the strikingly-colored Anchiornis. Indeed, a significant part of how we know dinosaurs really ruled the earth is because they occupied such a wide range of body sizes–from the breathtakingly large to the diminutive. And, earlier this month, Field Museum of Natural History paleontologist Peter Makovicky and colleagues added a previously unknown tiny dinosaur to the ever-growing roster of Mesozoic species.

Named Alnashetri cerropoliciensis, the small dinosaur is mostly a mystery. All that we know of it, Makovicky and coauthors report, are a set of articulated hindlimbs from a single animal found in the roughly 95-million-year-old rock of La Buitrera, Argentina. (The dinosaur’s genus name, the paper says, means “slender thighs” in a dialect of the Tehuelchan language.) Yet those appendages contain enough clues about the dinosaur’s identity that the researchers were able to figure out that the specimen represented a new species of alvarezsaur–one of the small, possibly ant-eating dinosaurs recognizable by their short, stout arms and long skulls set with tiny teeth. While the paleontologists acknowledge that their Alnashetri specimen might be a juvenile, Makovicky and collaborators estimate that the dinosaur was comparable to its relative Shuvuuia in size–about two feet long.

How Alnashetri resembled other alvarezsaurs, and where it departed in form, will have to wait for more complete specimens. Further research is also needed to narrow down when this dinosaur lived, but for the moment, Alnashetri appears to be the oldest alvarezsaur found in South America. If only we knew more of this dinosaur! As Makovicky and coauthors conclude, “continued fieldwork and future discoveries hopefully will provide more information on the anatomy of Alnashetri and allow a more definitive evaluation of its affinities and its significance for understanding biogeography and evolutionary trends such as body size evolution within alvarezsaurids.” At least the enigma has a name.

Reference:

Makovicky, P., Apesteguía, S., Gianechini, F. 2012. A new coelurosaurian theropod from the La Buitrera fossil locality of Rio Negro, Argentina. Fieldiana Life and Earth Sciences, 5: 90-98

A reconstruction of an Einiosaurus skull in a ceratopsid gallery at the Natural History Museum of Los Angeles. Photo by Maarten Heerlien, image from Wikipedia.

Xenoceratops was a gnarly-looking ceratopsid. There’s no doubt about that. Much like its horned kin, the dinosaur sported a distinctive array of head ornaments from the tip of its nose to the back of its frill. But that’s hardly the entire story behind this newly named dinosaur.

Contrary to many news reports that focused almost entirely on the dinosaur’s appearance, the real importance of Xenoceratops is in its geological and evolutionary context. The dinosaur is the first identifiable ceratopsid from the relatively unexplored Foremost Formation in Canada, and the creature appears to be at the base of a major horned dinosaur subdivision called centrosaurines. While the dinosaur’s name is certainly aesthetically pleasing, Knight Science Journalism Tracker watchdog Charlie Petit rightly pointed out that the ceratopsid isn’t really any more or less fantastic-looking than close cousins such as Styracosaurus, Spinops and Pachyrhinosaurus. The real importance of the dinosaur–a new data point in an ongoing investigation of a little-known part of the Cretaceous–was obscured by a narrowed focus on the dinosaur’s spiky headgear.

Dinosaurs are perpetually struggling to find context in news reports. Indeed, Xenoceratops is just the latest example and not an anomaly. Theropod dinosaurs are often introduced as Tyrannosaurus rex relatives, even when they’re not particularly closely related to the tyrant king, and journalists had such a fun time giggling over calling Kosmoceratops the “horniest dinosaur ever” that the clues the ceratopsid offered about dinosaur evolution in western North America were almost entirely overlooked. Reports on newly discovered dinosaurs usually contain the vital statistics of when the animal lived, where it was found, how large it was and whatever feature strikes our immediate attention, but the tales dinosaurs have to tell about life, death, evolution and extinction are rarely pulled out by journalistic storytellers.

Fossils don’t divulge their stories all at once, though. Paleontologists spend years drawing paleobiological secrets from dinosaur bones–who was related to whom, grand evolutionary patterns and rates of faunal turnover, and how the animals actually lived. These slowly emerging lines of evidence don’t often receive the same degree of attention. The discovery of a new bizarre species immediately garners journalistic attention, but once the dinosaur has been added to the roster, details about the animal’s life are often forgotten unless the creature earns a new superlative or has been found to have some tenuous connection to T. rex.

Rather than just gripe, though, I want to highlight how discovering and naming a dinosaur is only the initial step in paleontology’s effort to reconstruct prehistoric life. Consider Einiosaurus procurvicornis, a dinosaur I’m selecting here for no other reason than I promised a friend that I’d write about the dinosaur soon.

In 1995, paleontologist Scott Sampson named Einiosaurus from remains of multiple individuals strewn through two bonebeds discovered in Montana’s Late Cretaceous Two Medicine Formation. A geologically younger relative of Xenoceratops by about 4 million years, adults of this ceratopsid species are immediately recognizable by a forward-curved nasal horn, a pair of long, straight spikes jutting from the back of the frill and a suite of more subtle cranial ornaments.

Even before Einiosaurus had a name, though, researchers knew that the collected bones of this dinosaur presented a rich fossil database. Five years before Sampson’s paper, paleontologist Raymond Rogers drew on the two ceratopsid bonebeds to argue that multiple individuals of the species had died in prehistoric droughts. Rather than being places where the bodies of solitary animals accumulated over time, Rogers proposed, the rich assemblages recorded mass mortality events which claimed young and old ceratopsids alike.

The bone assemblages and their geological context outline many tragic dinosaur deaths. But clues about dinosaur lives are preserved inside those bones. For her master’s work at Montana State University, paleontologist Julie Reizner examined the bone microstructure of 16 Einiosaurus tibiae from a single bonebed to reconstruct how these dinosaurs grew and outline their population structure.

The research is still awaiting publication in a journal, but according to Reizner’s 2010 thesis and a poster she presented at the annual Society of Vertebrate Paleontology meeting last month, the histological evidence indicates that these horned dinosaurs grew rapidly until about three to five years of age, when their growth significantly slowed. The dinosaurs did not cease growing entirely, but, Reizner hypothesizes, the slowdown might represent the onset of sexual maturity. Additionally, all the dinosaurs in her sample were either juveniles or subadults–there were no infants or adults (or dinosaurs that had reached skeletal maturity and ceased growing). Even among the two groups, there doesn’t seem to be a continuum of sizes but instead a sharper delineation between juveniles and subadults. If this Einiosaurus bonebed really does represent a herd or part of a herd that died at about the same time, the age gap might mean that Einiosaurus had breeding seasons that occurred only during a restricted part of the year, thus creating annual gaps between broods.

Restored soft tissue profile of Einiosaurus, modified from Hieronymus et al., 2009.

Other researchers have drawn from different bony indicators to restore what the faces of Einiosaurus and similar dinosaurs would have looked like. While the underlying ornamental structures are still prominent in ceratopsid skulls, the horns, bosses and spikes would have been covered in tough sheaths. Thus, in 2009, Tobin Hieronymus and colleagues used the relationship between facial integument and bone in living animals to reconstruct the extent of skin and horn on ceratopsids. While the preservation of the Einiosaurus material frustrated their efforts to detect all the skin and horn structures on the skull, Hieronymus and colleagues confirmed that the nasal horn was covered in a tough sheath and that Einiosaurus had large, rounded scales over the eyes. Artists can’t simply stretch skin over the dinosaur’s skull in restorations–the bone itself shows the presence of soft tissue ornamentation that rotted away long ago.

As with most dinosaur species, we still know relatively little about the biology of Einiosaurus. We are limited to what is preserved in the rock, the technologies at our disposal and the state of paleontological theory. All the same, Einiosaurus is much more than a pretty face. The dinosaur was part of a rich, complex Cretaceous ecosystem, and one in a cast of billions in earth’s evolutionary drama. To me, at least, that is the most entrancing aspect of paleontology. We have only barely begun to plumb the depths of dinosaur diversity, and researchers will continue to introduce us to new species at a breakneck pace, but the true wonder and joy of paleontology lies in pursuing questions about the lives of animals we’ll sadly never observe in the flesh.

References:

Hieronymus, T., Witmer, L., Tanke, D., Currie, P. 2009. The facial integument of centrosaurine ceratopsids: Morphological and histological correlates of novel skin structures. The Anatomical Record 292: 1370-1396

Reizner, J. 2010. An ontogenetic series and population histology of the ceratopsid dinosaur Einiosaurus procurvicornis. Montana State University master’s thesis: 1-97

Rogers, R. 1990. Taphonomy of three dinosaur bone beds in the Upper Cretaceous Two Medicine Formation of northwestern Montana: evidence for drought-related mortality. PALAIOS 5 (5): 394–413.

Sampson, S. 1995. Two new horned dinosaurs from the Upper Cretaceous Two Medicine Formation of Montana; with a phylogenetic analysis of the Centrosaurinae (Ornithischia: Ceratopsidae). Journal of Vertebrate Paleontology 15 (4): 743–760.

The reconstructed skull of Eotriceratops. The actual specimen is not complete, but, based on the recovered elements and the dinosaur’s relationships, we know the dinosaur would have looked similar to Triceratops. Photo by Roland Tanglao, image from Wikipedia.

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.

Reference:

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

A restoration of Xenoceratops by Danielle Dufault, courtesy David Evans.

It’s a good time to be a ceratopsid fan. Since 2010, paleontologists have introduced us to a slew of previously unknown horned dinosaurs, and new discoveries are continuing to trickle out of field sites and museums. Long-forgotten specimens and unopened plaster jackets, especially, have yielded evidence of ceratopsids that researchers overlooked for decades, and this week Royal Ontario Museum paleontologist David Evans and colleagues have debuted yet another horned dinosaur that was hiding in storage.

The Late Cretaceous exposures of Alberta, Canada’s Belly River Group are rich with ceratopsid fossils. For over a century, paleontologists have been pulling bones of the fantastically ornamented dinosaurs from these badlands. Yet most of the ceratopsids from this area have been found in the Dinosaur Park Formation, and researchers have paid less attention to the older strata of the Oldman and Foremost Formations nearby.

The Foremost Formation, in particular, has received little attention because diagnostic dinosaur remains seem to be rare within its depths, but a few notable specimens have been found in this slice of time. In 1958, paleontologist Wann Langston, Jr. and a crew from what is now the Canadian Museum of Nature pulled fragments of several ceratopsid specimens from 78-million-year-old deposits in the Foremost Formation. Those bones and skeletal scraps sat in collections for years until they caught the eye of Evans and Michael Ryan (the lead author of the new study) as they made the research rounds for their Southern Alberta Dinosaur Project. Although fragmentary, Langston’s fossils were from a new genus of ceratopsid.

Evans, Ryan and Kieran Shepherd have named the dinosaur Xenoceratops foremostensis in their Canadian Journal of Earth Sciences study. The dinosaur’s name–roughly “alien horned face”–isn’t a testament to the ceratopsid’s distinctive array of horns but to the rarity of horned dinosaur fossils within the Foremost Formation. Indeed, despite Danielle Dufault’s gorgeous restoration of the dinosaur, Xenoceratops is presently represented by skull fragments from several individuals. The researchers behind the new paper pieced them together to create a composite image of what this dinosaur must have looked like, and, in turn, discern its relationships.

Based upon the anatomy of one of the dinosaur’s frill bones–the squamosal–Evans and coauthors are confident that Xenoceratops was a centrosaurine dinosaur. This is the ceratopsid subgroup containing other highly decorated genera such as Styracosaurus, Spinops, Centrosaurus and another dinosaur given a new name in the same paper, Coronosaurus (formerly “Centrosaurus” brinkmani). The other ceratopsid subgroup, the chasmosaurines, encompass Triceratops, Torosaurus and other genera more closely related to them than Centrosaurus.

At approximately 78 million years old, Xenoceratops is currently the oldest ceratopsid known from Canada, beating out its cousin Albertaceratops by half a million years. Given the age of Xenoceratops, and the fact that it had long brow horns and a short nasal horn, instead of the long nasal horn-short brow horns combo seen in its later relatives, it isn’t surprising that the dinosaur seems to be at the base of the centrosaurine family tree. This means that Xenoceratops can help paleontologists examine what the early members of this significant ceratopsid group were like and how drastically centrosaurine ornamentation changed. “Xenoceratops has very well developed frill ornamentation comprised of a series of large spikes and hooks, occurring at multiple parietal loci, that foreshadows the great diversity of these structures in other species that occur later in the Campanian,” Evans says, and this indicates that “complex frill ornamentation is older than we may have thought.”

Still, Evans cautions that Xenoceratops is presently a very scrappy dinosaur. We need more fossils to fully reconstruct this dinosaur and confirm its place in the ceratopsid family tree. The dinosaur’s “true significance in terms of ceratopsid origins will only be revealed with further discoveries,” Evans says, particularly between the time of the slightly older Diabloceratops found in southern Utah, and the even more archaic, roughly 90-million-year-old ceratopsian Zuniceratops. “Our record of ceratopsians in this critical part of their family tree is still frustratingly poor,” Evans laments. In fact, paleontologists know relatively little about dinosaur diversity and evolution during the middle part of the Cretaceous–a critical evolutionary time period for ceratopsians, tyrannosaurs and other lineages that came to dominate the Late Cretaceous landscape. If we are ever going to solve the mystery of how ceratopsids evolved, and why they were such garishly adorned dinosaurs, we must search the lost world of the mid-Cretaceous.

References:

Ryan, M., Evans, D., Shepherd, K. 2012. A new ceratopsid from the Foremost Formation (middle Campanian) of Alberta. Canadian Journal of Earth Sciences 49: 1251-1262

The reconstructed skull of Eolambia–based on a partial adult skull and scaled juvenile elements–and a restoration by artist Lukas Panzarin. From McDonald et al., 2012.

Hadrosaurs were not the most charismatic dinosaurs. Some, such as Parasaurolophus and Lambeosaurus, had ornate, hollow crests jutting through their skulls, but, otherwise, these herbivorous dinosaurs seem rather drab next to their contemporaries. They lacked the garish displays of horns and armor seen among lineages such as the ceratopsians and ankylosaurs, and they cannot compete with the celebrity of the feathery carnivores that preyed upon them. Yet in the habitats where they lived, hadrosaurs were among the most common dinosaurs and essential parts of their ecosystems. What would tyrannosaurs do without ample hadrosaurian prey?

While many hadrosaurs might seem visually unremarkable next to their neighbors, the wealth of these dinosaurs that paleontologists have uncovered represent a huge database of paleobiological information waiting to be tapped for new insights into dino biology and evolution.

In order to draw out dinosaur secrets, though, paleontologists need to properly identify, describe and categorize the fossils they find. We need to know who’s who before their stories can come into focus. On that score, paleontologist Andrew McDonald and colleagues have just published a detailed catalog of Eolambia caroljonesa, an archaic hadrosaur that was once abundant in Cretaceous Utah.

Eolambia is not a new dinosaur. Discovered in the roughly 96-million-year-old rock of the Cedar Mountain Formation, this dinosaur was named by paleontologist James Kirkland–a coauthor on the new paper–in 1998. Now there are multiple skeletons from two different localities representing both sub-adult and adult animals, and those specimens form the basis of the full description.

While the new paper is primarily concerned with the details of the dinosaur’s skeleton, including a provisional skull reconstruction accompanied by an excellent restoration by artist Lukas Panzarin, McDonald and coauthors found a new place for Eolambia in the hadrosaur family tree. When Kirkland announced the dinosaur, he named it Eolambia because it seemed to be at the dawn (“eo”) of the crested lambeosaurine lineage of hadrosaurs. But in the new paper McDonald, Kirkland and collaborators found that Eolambia was actually a more archaic animal–a hadrosauroid that falls outside the hadrosaurid lineage containing the crested forms.

Much like its later relatives, Eolambia would have been a common sight on the mid-Cretaceous landscape. The descriptive paper lists eight isolated animals and two bonebeds containing a total of 16 additional individuals. They lived in an assemblage that was right at the transition between the early and late Cretaceous faunas–tyrannosaurs, deinonychosaurs and ceratopsians have been found in the same part of the formation, as well as Jurassic holdouts like sauropods. How this community fit into the grander scheme of dinosaur evolution in North America is still coming together, though. The Early and Middle parts of the Cretaceous are still poorly known, and paleontologists are just getting acquainted with Eolambia, its kin and contemporaries.

References:

McDonald, A., Bird, J., Kirkland, J., Dodson, P. 2012. Osteology of the basal hadrosauroid Eolambia caroljonesa (Dinosauria: Ornithopoda) from the Cedar Mountain Formation of Utah. PLOS One 7, 10: e45712

In this restoration by Emiliano Troco, a Sauroniops feeds on a juvenile Spinosaurus. (And yes, all the dinosaurs in this image are fluffy.) Image courtesy Andrea Cau.

Earlier this year, paleontologists Andrea Cau, Fabio Dalla Vecchia and Matteo Fabbri described a strange, 95-million-year-old skull scrap from an unknown dinosaur. Acquired by a commercial collector from Morocco’s Kem Kem beds and later donated to Italy’s Museo Paleontologico di Montevarchi, the bone showed signs that it belonged to a carcharodontosaurid–massive cousins of the familiar Allosaurus. There was something odd about the fossil. The bone was a frontal–situated at the top of the skull just above and in front of the dinosaur’s eye opening–but, unlike the same bone in related species like Carcharodontosaurus, a small dome protruded from the middle of the specimen. No caracharodontosaurid has been found with a dome before.

The skull fragment of Sauroniops, showing where it would have fit on a carcharodontosaur skull (human skull for scale). Image courtesy Andrea Cau.

While a single piece of skull isn’t much to go on, Cau and colleagues nevertheless were able draw on the dome and other subtle features to determine that the frontal didn’t belong to any previously known dinosaur. Still, at the conclusion of their brief Acta Palaeontologica Polonica report, the scientists cautioned against naming a new species from an isolated skull bone. “Although the combination of features present in [the frontal] is unique and should support the institution of a new species,” Cau and coauthors concluded, “pending more complete specimens we feel it would be inappropriate to erect a new taxon.”

Cau, Dalla Vecchia and Fabbri quickly changed their minds. While the rest of the dinosaur remains unknown, after reanalyzing the frontal the paleontologists decided that it was truly unique enough to merit establishing a new name. The subtly-domed dinosaur is now known as Sauroniops pachytholus–the genus name a tribute to the demonic Sauron of the Lord of the Rings series, and the species name for the thick dome on the dinosaur’s head.

I emailed Cau to ask why he changed his mind about the dinosaur so quickly. During the year between the time the two papers were submitted, Cau replied, several papers were published showing that carcharodontosaurids–such as the high-spined Acrocanthosaurus from North America–had frontal bones that were so distinct that they could be use to tell one theropod genus from another. That inspired Cau to take another look at the domed specimen from Morocco.

Ultimately, Cau wrote, “the collected data showed that the unique morphology of our specimen was as diagnostic as those available from the type specimens of other African carcharodontosaurids (e.g., the holotypes of Eocarcharia [a single postorbital bone], Carcharodontosaurus iguidensis [a single maxilla], Veterupristisaurus [a single caudal vertebra]).” If all these dinosaurs were based on isolated bones, Cau explained, “then there are no real objections for erecting Sauroniops even from a single frontal.”

Frustratingly, though, the limited material means that we only have the barest outline of what Sauroniops was like in life. The size of the frontal, compared to the bone in other carcharodontosaurs, indicates that the dinosaur probably exceeded thirty feet in length. The carnivore was probably just as big as the better-known Carcharodontosaurus, which it lived alongside, but such estimates always await the test of more fossils.

And then there’s the dome. Why did such a large theropod have a prominent bump on its head? In other theropod lineages, such as the abelisaurids, bumps, knobs and horns are common forms of ornamentation. Perhaps the same was true for Sauroniops–thanks to Acrocanthosaurus and the sail-backed Concavenator, we know that carcharodontosaurs showed off with visual signals. Then again, Cau and coauthors speculate that the dome might have been a sexual signal or might have even been used in head-butting behavior. I think the last hypothesis is unlikely, especially since we don’t know what the microstructure of the dome looks like and there’s no evidence of pathology, but it’s still a distant possibility.

So Sauroniops has a name and a family. Like its cousins Kelmayisaurus and Shaochilong, though, we don’t know very much about this dinosaur’s appearance or biology. The lone frontal is a tantalizing glimpse at a dinosaur that paleontologists will have to hunt down in the deserts of Morocco. With some luck, and a lot of persistence, we may eventually become better acquainted with the dome-skulled dinosaur.

For more on this discovery, see Cau’s blog post at Theropoda.

References:

Cau, A., Dalla Vecchia, F., Fabbri, M. 2012. Evidence of a new carcharodontosaurid from the Upper Cretaceous of Morocco. Acta Palaeontologica Polonica 57, 3. 661-665

Cau, A., Dalla Vecchia, F., Fabbri, M. 2012. A thick-skulled theropod (Dinosauria, Saurischia) from the Upper Cretaceous of Morocco with implications for carcharodontosaurid cranial evolution. Cretaceous Research, in press. DOI: 10.1016/j.cretres.2012.09.002

A reconstruction of Deinosuchus at the Natural History Museum of Utah. Photo by the author.

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.

Part of a multi-step sequence by which Tyrannosaurus could have beheaded Triceratops, based on research by Fowler et al. Art by Nate Carroll.

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.

References:

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.

Not only was Ornithomimus feathered, but the dinosaur’s fluffy coat changed as it aged. Lovely art by Julius Csotonyi.

Another week, another feathery dinosaur. Since the discovery of the fluffy Sinosauropteryx in 1996, paleontologists have discovered direct evidence of fuzz, feather-like bristles and complex plumage on over two dozen dinosaur genera. I love it, and I’m especially excited about a discovery announced today. In the latest issue of Science, University of Calgary paleontologist Darla Zelenitsky adds another enfluffled species to the dinosaurian ranks. Even better, the specimens raise hopes that many more dinosaurs might be preserved with their feathery coats intact.

Zelenitsky’s downy dinosaurs are not newly discovered species. Ornithomimus edmontonicus was initially described by famed bone hunter C.H. Sternberg in 1933, and it is one of the characteristic Late Cretaceous species found in Alberta, Canada’s fossil-rich Horseshoe Canyon Formation. In Sternberg’s time, these dinosaurs were thought to be scaly, but recent finds of so many feathery dinosaurs has raised the likeliehood that the “ostrich mimic” dinosaur was at least coated in some sort of dinofuzz.

A family tree of Saurischian dinosaurs, showing lineages within this group with direct evidence for feathers. From Zelenitsky et al., 2012.

The prediction of fluffy Ornithomimus came from the spread of feathers on the coelurosaur family tree. The Coelurosauria is a major dinosaur group that encompasses tyrannosaurs, compsognathids, ornithomimosaurs, alvarezsaurs, oviraptorosaurs, deinonychosaurs and birds. To date, evidence of feathers has been found in every coelurosaur lineage except one–the ornithomimosaurs. The spread of feathers hinted that some sort of plumage was present in the common ancestor of all coelurosaurs and therefore should have been inherited by the ornithomimosaurs, but, until now, no one had found direct evidence.

A trio of Ornithomimus skeletons have finally confirmed what paleontologists expected. Zelenitsky enthusiastically explained the details to me by phone earlier this week. In 1995, when Zelenitsky was a graduate student, paleontologists uncovered an articulated Ornithomimus with weird marks on its forearms. No one knew what they were. But in 2008 and 2009 a juvenile and an adult Ornithomimus turned up with preserved tufts of filamentous feathers. “When we found these specimens,” Zelenitsky said, “we made the link to the 1995 dinosaur.” All those strange marks on the arms of the previously discovered Ornithomimus, Zelenitsky and colleagues argue, are traces of longer, shafted feathers.

Even though paleontologists expected feathery Ornithomimus, the discovery was still a surprise. “I was in disbelief,” Zelenitsky said. “They’re the first feathered dinosaurs from the Americas, and the first ornithomimosaurs with feathers, as well. It was shocking to say the least.”

But there’s more to the find than simply adding another species of fluffy dinosaurs to the list. The fact that the adult and juvenile animals had different kinds of plumage adds new evidence that coelurosaurs changed their fluffy coats as they aged. “The one juvenile was completely covered in filamentous type feathers,” Zelenitsky said. What the adults looked like comes from the two other specimens. One adult skeleton, lacking forearms, preserves fuzzy feathers, and “the second adult had markings on the forearm.” Together, the specimens indicate that adult Ornithomimus were mostly covered in fuzz but developed more complex arm feathers by adulthood.

Sex is probably behind the plumage change. “We infer that because these wing feathers are not showing up until later in life, they were used for reproductive purposes,” Zelenitsky said. Perhaps adult Ornithomimus used flashy arm feathers to strut their stuff in front of potential mates. Then again, based upon the resting and brooding postures of other theropod dinosaurs, adult Ornithomimus could have used their proto-wings to cover their nests. We don’t know for sure, but the developmental change appears to be another example of dinosaurs undergoing significant changes as they approach sexual maturity. This discovery, and others like it, will undoubtedly play into the ongoing discussion about the role of sexual selection in dinosaur biology and evolution.

Best of all, the new study indicates that paleontologists may soon find more feathered dinosaurs in unexpected places. The Ornithomimus skeletons were found in prehistoric river deposits composed of sandstone. Since almost all feathered non-avian dinosaurs have been found in fine-grained sediment–such as those around Liaoning, China–paleontologists thought that coarser-grained sandstone deposits were too rough to record such fine details. Now we know better. “That’s the really exciting part of it,” Zelenitsky says. If traces of dinosaur feathers can be preserved in sandstone, the twist opens up the possibility that paleontologists might find fluff and feathers with a greater array of dinosaurs–including the tyrannosaurs, deinonychosaurs, therizinosaurs and other coelurosaurs of North America. The trick is recognizing the traces before they’re destroyed during excavation and preparation. Rock saws and airscribes can all too easily obliterate the delicate fossils. A word to researchers–keep your excavation tools sharp, and your eyes sharper.

Reference:

Zelenitsky, D., Therrien, F., Erickson, G., DeBuhr, C., Kobayashi, Y., Eberth, D., Hadfield, F. 2012. Feathered non-avian dinosaurs from North American provide insight into wing origins. Science. 338, 510-514

The peculiar, high-spined specimen that represents Becklespinax (left), and two possible restorations of the dinosaur by Darren Naish (right). From Naish and Martill, 2007.

Poor, neglected Becklespinax. Although this gaudy, sail-backed theropod was an impressive predator at the time it strode across England around 140 million years ago, the fragmentary remains of this dinosaur have a tangled history only recently highlighted by the discovery of a more completely-known relative. In the history of paleontology, Becklespinax the tale is a tragedy.

The bones of Becklespinax were among the earliest spate of dinosaur discoveries in England, before anyone really understand just how many dinosaurs there were and how widely they varied in form. No surprise, then, that when the British anatomist Richard Owen illustrated a strange set of three high-spined vertebrae in 1855, he assigned them to the carnivorous dinosaur Megalosaurus. After all, Megalosaurus was already a hodgepodge of theropod remains from different eras, so it’s no altogether surprising that Owen considered the strange vertebrae as part of the same animal. He was confident enough in his assessment that when Owen schooled the artist Benjamin Waterhouse Hawkins in dinosaur anatomy for the famous Crystal Palace reconstructions, the anatomist instructed the sculptor to give Megalosaurus a hump between the shoulders on account of the elongated neural spines in the one specimen.

Along with teeth and other bits, the strange sting of vertebrae were thrown together into the species Megalosaurus dunkeri by researchers such as Richard Lydekker. No one found any complete skeleton–just scattered pieces. Then, in 1926, paleontologist Friedrich von Huene proposed that the spines and teeth of this “Megalosaurus” were so different from others of its type that it deserved its own genus–”Altispinax.” So scientists kicked the name Altispinax around for awhile, but this was another hodgepodge dinosaur consisting of various specimens from different places and time periods. In 1991, dinosaur fan George Olshevsky suggested that the set of three vertebrae carry the name Becklespinax altispinax, and, so far, that name has stuck.

But just what sort of dinosaur was Becklespinax? Paleontologist and prolific blogger Darren Naish addressed this question a few years back. The dinosaur was clearly a relatively large theropod, probably over 20 feet long. But, during the late 19th and early 20th centuries, there was no other dinosaur quite like it. Without a more complete skeleton, it was impossible to tell. And even after other big theropods with elongated spines on their backs were discovered–such as the croc-snouted Spinosaurus from the Late Cretaceous of Africa and the deep-skulled Acrocanthosaurus from the Early Cretaceous of North America–the anatomy of Becklespinax didn’t match those forms.

Even worse, the extremely limited material confounded paleontologists who attempted to figure out what the back of Becklespinax looked like. Were those elongated spines a sign of a high sail that ran most of the length of the dinosaur’s back, as in Spinosaurus? Or did it indicate a short, high ornament near the hips? Naish illustrated both possibilities in a 2007 paper he wrote with colleague David Martill. The first vertebral spine contained yet another puzzle. This bone was shorter than the following two. This might have been a pathology, or even because the bones came from the front part of the sail as it was building to its full height. No one knew for sure.

Then along came Concavenator. In 2010, paleontologist Francisco Ortega and colleagues named this carnivorous dinosaur on the basis of a gorgeous, 130-million-year-old skeleton found in Spain. A cousin of the high-spined Acrocanthosaurus from North America, Concavenator also had a weird backbone–the carcharodontosaur had a high, shark-fin-shaped sail just in front of the hips.

In over a century and a half, no one has ever found a better or more complete specimen of the English dinosaur, yet Concavenator offered a glimmer of what Becklespinax might have looked like. Both were sail-backed theropods that lived in the Early Cretaceous of Europe. And while our knowledge of Becklespinax is frustratingly incomplete, the resemblance of the dinosaur’s known remains to the corresponding parts in Concavenator suggest that Becklespinax, too, was a sail-backed carcharodontosaur. Their relationship may even go deeper. While the two dinosaurs lived about 10 million years apart, Naish pointed out, it’s possible that both dinosaur species belong to the same genus. Concavenator corcovatus might, in fact, be rightly called Becklespinax corcovatus. Without a fuller view of what the skeleton of Becklespinax looked like, though, it’s impossible to tell.

Whatever Becklespinax is, paleontologists have almost certainly found other scraps from this dinosaur. The trick is correctly identifying and assembling the scattered pieces. It takes years to untangle the history and form of dinosaurs found during the 19th century, as paleontologist Roger Benson did with Megalosaurus. A skeleton–even a partial one–would be even better. Such a discovery would go a long way towards outlining the nature of the frustratingly-incomplete Becklespinax, although other questions would certainly remain.

Between Acrocanthosaurus, Becklespinax and Concavenator, the massive carcharodontosaurs of the Early Cretaceous were apparently well-decorated predators that bore distinctive ridges and sails on their backs. Why? What good would such ornaments be to large predators? Were they signals of dominance, advertisements of sexual desirability or even just easily-seen markers that an individual belonged to this species and not that one? No one knows. As debates about sexual selection and dinosaur ornamentation heat up, even rapacious carnivores will have a role to play.

Previous posts in this series:

A is for Agujaceratops

Reference:

Naish, D., and Martill, D. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, 164 (3), 493-510 DOI: 10.1144/0016-76492006-032

Ortega, F., Escaso, F., and Sanz, J. 2010. A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain Nature, 467 (7312), 203-206 DOI: 10.1038/nature09181

Stovall, J., & Langston, W. 1950. Acrocanthosaurus atokensis, a new genus and species of Lower Cretaceous Theropoda from Oklahoma. American Midland Naturalist, 43 (3): 696–728. doi:10.2307/2421859