November 15, 2012
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.
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.
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.
August 21, 2012
About a year ago, I briefly joined the Carthage College and Burpee Museum of Natural History field crews as they searched the Hell Creek Formation around Ekalaka, Montana. There were bits of Triceratops strewn across the landscape. Even though I only spent a few days among the rolling grasslands and islands of Late Cretaceous outcrop, there wasn’t a day that went by that I didn’t see at least a fragment of the great three-horned herbivore–from isolated teeth to skulls that had crumbled apart, Triceratops was a constant companion. Indeed, as Jack Horner and colleagues affirmed in a census of Hell Creek fossils last year, Triceratops is the most commonly-found dinosaur in this swath of Late Cretaceous North America.
Move a little to the north, though, and the trail of Triceratops fades. While I was virtually tripping over Triceratops everywhere I went in eastern Montana, the gigantic ceratopsian isn’t quite so abundant in Saskatchewan and is a rarity in the Late Cretaceous rock of Alberta. So while paleontologists have already discovered many Triceratops specimens from the United States, Canadian paleontologists made headlines last week when they found what appears to be an especially big representative of this famous dinosaur in Alberta.
The CBC, Calgary Herald, Edmonton Journal and other news outlets have covered the story. Earlier this summer, former Royal Tyrrell Museum employee Tim Schowalter stumbled across the Triceratops site on an old road cut near Drumheller (a place famous for its proximity to dinosaur-rich badlands). From there, Royal Tyrrell Museum paleontologist François Therrien led the excavation of the Triceratops “log jam.” Included in the lot are large vertebrae and ribs over six feet long, indicating that this was a Triceratops of considerable size. Unfortunately, though, the site contains only a partial skeleton, and the dinosaur’s skull seems to be missing. The official Royal Tyrrell Museum Twitter account said that “there are some odd looking bones that could be cranial”, but explained that the institution’s paleontologists will have to prepare the bones before they can be sure.
Without a skull, this new Triceratops won’t have much effect on the ongoing debate over whether Torosaurus is really just a grown-up Triceratops or a distinct genus or dinosaur. That discussion has relied almost entirely on the skulls of these dinosaurs–as far as we know, the only reliable way to tell the two forms apart. But, as Therrien commented in some news reports, the newly-uncovered dinosaur may help paleontologists determine whether there were significant variations between Triceratops that lived in Montana, Saskatchewan and Alberta. The dinosaur is a new point of reference as paleontologists examine the record of Triceratops. And, after all, every dinosaur skeleton contains various clues about how that individual lived. The trick is carefully extracting those threads in order to flesh out the ancient lives of the dinosaurs.
May 19, 2011
Tarbosaurus, the great tyrannosaur of Cretaceous Mongolia, hunted in packs. That is the exceptional claim made by University of Alberta paleontologist Philip Currie in a press release, and news outlets all over the world have picked up the story. Just imagine rapacious tyrannosaur families tearing over the prehistoric countryside; it is a terrifying notion that the press release heralds as a “groundbreaking” discovery that will forever change paleontology.
But does the actual evidence live up to all the hype? Unfortunately, the answer is no. The proposal of pack-hunting dinosaurs is old news in paleontological circles, and the hard evidence to support the claims about Tarbosaurus has not yet been released.
Packaged under the theme “Dino Gangs,” the media release, book, and cable-network documentary arranged by Atlantic Productions hinge on a Tarbosaurus bonebed found in Mongolia’s Gobi Desert. The site was one of 90 Tarbosaurus localities surveyed by Currie and the Korea-Mongolia International Dinosaur Project, but it is unique in that it preserves the remains of six individual animals of different life stages. How the animals died and became buried is unknown. Even so, the press claims that these dinosaurs were a single family group that hunted together.
There was no scientific paper attached to the release, and I received no reply from Atlantic Productions when I inquired whether a technical description of the site will soon be published. The media release–reporting conclusions without providing evidence–was presented on its own.
This is not the first time tyrannosaurs have been reconstructed as living in packs. In 1997 Currie relocated a rich dinosaur bonebed in Alberta, Canada that had been discovered by the fossil hunter Barnum Brown in 1905. The site was dominated by remains of the tyrannosaur Albertosaurus—at least a dozen individuals of this species were found in this one place. Why one site should contain so many tyrannosaurs was difficult to explain, but in a 1998 paper published in Gaia, Currie proposed that the Albertosaurus were living in a social group and that the site was evidence of gregarious behavior among the dinosaurs. More than that, Currie proposed that there was a “division of labor” within the Albertosaurus packs. Compared with the adults, juvenile Albertosaurus would have been much faster runners thanks to their different leg proportions, and so Currie suggested: “The faster, more agile juveniles may have been responsible for driving potential prey towards the larger, more powerful adult tyrannosaurids.” Currie has suggested the same thing for Tarbosaurus in the “Dino Gangs” press release.
But the idea that young and old tyrannosaurs worked together to tackle prey rests upon the inference that the bonebeds contain social groups. This is not necessarily so. There are many ways to make a bonebed, and the fine geological details of such fossil-rich sites contain essential information about how the bodies of the different individuals became preserved together. Proximity does not always indicate sociality, as Currie himself noted in a paper published with David Eberth last year about the Albertosaurus quarry.
Although the idea that the Albertosaurus quarry indicates complex social interactions among pack-hunting dinosaurs is a sexy hypothesis, Currie and Eberth noted that the animals could have been brought into close association by some kind of environmental catastrophe. “[T]he evidence for a significant storm and associated flooding event at the [Albertosaurus] site and in the surrounding area is well documented,” the scientists wrote, and they suggested that solitary Albertosaurus might have been driven together into a small area by the floodwaters. Pack behavior among the animals could not be taken as a given. The Albertosaurus were together when they died, but exactly how they died and why they were so close to each other remains unclear.
In the 2005 book Carnivorous Dinosaurs, Currie and several co-authors reported on a bonebed found in Montana that contained several hadrosaurs and remains of three tyrannosaurs identified as Daspletosaurus. Though the scientists suggested that the tyrannosaurs might have been interacting socially before they died, how the animals died and became buried was unknown. The same was true of a site in Argentina described by Currie and colleague Rodolfo Coria. The bonebed contained seven individuals of a large predatory dinosaur unrelated to tyrannosaurs named Mapusaurus. Although the site could have represented a social group, Currie and Coria concluded that “It is conceivable that this bonebed represents a long term or coincidental accumulation of carcasses.”
There is no slam-dunk evidence that tyrannosaurs or other large predatory dinosaurs hunted in packs. Even in the case of Deinonychus—a small, sickle-clawed “raptor” traditionally thought to be a cooperative hunter—evidence of multiple individuals in association with prey species has recently been questioned. In the end, trackways that record the footsteps of multiple raptors moving together has provided better evidence that these dinosaurs were sometimes social. No such evidence exists for tyrannosaurs yet. (Only one footprint attributed to a tyrannosaur has been found so far.)
Various processes can bring bones together into a single fossil deposit. A bonebed might represent a social group killed and buried by a flood, scattered bodies or bones that were washed together by water currents, or a natural trap where multiple individual animals died over a long period of time, among other possibilities. How the animals died, how long it took for the fossil deposit to accumulate, and other questions must be answered before hypotheses about behavior can be drawn out. As for the Tarbosaurus bonebed, no technical details of the site have yet been released. There is no science to talk about at this point. The site might record the death of a dinosaur pack, but that is just one of many possibilities that have yet to be ruled out.
The hubbub over the “Dino Gangs” press release is intensely frustrating. No scientific information is available, and the supposedly jaw-dropping findings are almost exactly the same as those proposed on the basis of a different site in 1998. The press release is full of bombastic language about how it is now time to rewrite the dinosaur books and how this discovery will forever change our understanding of dinosaur behavior. None of the information provided so far will do any such thing. The new find is one more discovery that will add to our understanding of dinosaurs, but is not wildly different from what has been discovered or proposed before. If there is something truly exceptional about the Tarbosaurus bonebed, it has yet to be revealed.
A discovery isn’t important simply because a press release says it is. Scientific findings should not be judged by how glitzy a documentary is or how well a book sells. By the sound of it, Currie and his colleagues have found a spectacular fossil site that is brimming with information about prehistoric life. None of the details have been published yet, and, consequently, they have not been submitted to the process of scientific debate, so no one can definitively say how the Tarbosaurus bonebed will affect our understanding of these dinosaurs. The discovery of the fossil site is just one part of the story. The rest, including how the Tarbosaurus lived and died, will take time to draw out.
Coria, R., and Currie, P. (2006). A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina Geodiversitas, 28 (1), 71-118
Currie, P. (1998). POSSIBLE EVIDENCE OF GREGARIOUS BEHAVIOR IN TYRANNOSAURIDS Gaia, 271-277
Currie, P., & Eberth, D. (2010). On gregarious behavior in Albertosaurus Canadian Journal of Earth Sciences, 47 (9), 1277-1289 DOI: 10.1139/E10-072
Currie, P.; Trexler, D.; Koppelhus, E.; Wicks, K.; Murphy, N. (2005) An unusual multi-individual, tyrannosaurid bonebed in the Two Medicine Formation (Late Cretaceous, Campanian) of Montana (USA), in Carpenter, K. (ed.), The Carnivorous Dinosaurs. Indiana University Press, Bloomington; Indianapolis: 313-324.
April 28, 2011
TMP 2003.45.64 is not exactly a headline-making fossil. The left lower jaw of an Albertosaurus, most of the teeth have fallen out and the bone is only one part of a well-known species represented by many other skeletons. But, for those who know what they are looking for, this specimen bears the traces of ancient interactions between dinosaurs.
The Albertosaurus jaw portion is just one of many bones recovered during the past decade from a Late Cretaceous bonebed in Alberta, Canada’s Dry Island Buffalo Jump Provincial Park. This is a very unusual site. Remains from at least 26 Albertosaurus, ranging from about 2 to 24 years old, have been found from this deposit. Such a rich collection of skeletons from a single species has allowed paleontologists to better understand what the local population of Albertosaurus was like around 70 million years ago, including the prevalence of injury and disease.
What makes the lower jaw significant is that it bears a series of gouges. As determined by Phil Bell in his recent assessment of the pathologies in the Dry Island Albertosaurus, these furrows were driven into the bone by another tyrannosaur. This sort of damage has been seen before. Other fossils with pathology have indicated that tyrannosaurs often bit each other on the face while fighting, and this leaves a pattern of damage distinct from that created by microorganisms which open up smooth-walled lesions in the jaws.
Curiously, though, the Albertosaurus jaw Bell described was bitten at two different times. One long groove near the front of the jaw was smooth and relatively fresh, while three parallel toothmarks and a puncture wound further back on the jaw had healed. The repaired wounds showed that the Albertosaurus had survived a fight with another tyrannosaur, but the other bite was made near the time of death or soon afterward. As with a tyrannosaur jaw fragment with the tooth of another tyrannosaur embedded in it, described in 2009, the exact timing of the injury is practically impossible to determine.
The tooth-scored lower jaw was not the only injured bone found in the quarry. Bell listed five other pathological bones, including damaged ribs and toe bones from other individuals. The ribs had been fractured and healed, while the toe bones were marked by bony spurs called enthesophytes. These form at the attachments of ligaments or tendons. What this may mean for the Albertosaurus toe bones represent is unclear—enthesophytes can form for a variety of reasons, from repetitive stress to a simple genetic predisposition for them.
Future studies may identify other pathologies, but Bell points out that the occurrence of pathology among the 26 Albertosaurus individuals was low—only six injuries in as few as two individuals. Bonebeds of the large predatory dinosaurs Allosaurus and Majungasaurus both had higher incidences of pathology. It would seem that the Dry Island Albertosaurus population was not as injury-prone as some of these other dinosaur populations, but why this should be so remains a mystery.
Bell, P. (2010). Palaeopathological changes in a population of Albertosaurus sarcophagus from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada Canadian Journal of Earth Sciences, 47 (9), 1263-1268 DOI: 10.1139/E10-030