November 12, 2012
Triceratops is among the most cherished of dinosaurs. Even that might be a bit of an understatement. Fossil fans threw a conniption when they mistakenly believed that paleontologists were taking the classic “three-horned face” away, after all. But where did the charismatic chasmosaurine come from? Triceratops didn’t simply spring from the earth fully formed–the ceratopsid was the descendant of a long tail of evolutionary forerunners. And in 2007, paleontologist Xiao-chun Wu and collaborators described a 68-million-year-old dinosaur that might represent what one of the close ancestors of Triceratops was like–Eotriceratops.
In 2001, while on an expedition to search the Horseshoe Canyon Formation around the Dry Island Buffalo Jump Provincial Park in Alberta, Canada, Glen Guthrie discovered the partial skeleton of a huge ceratopsid dinosaur. This was the first identifiable dinosaur skeleton found in the top quarter of the formation, and, as Wu and coauthors later argued, the bones represented a new species. They called the animal Eotriceratops xerinsularis.
Paleontological devotees know that “eo” translates to “dawn.” The tiny mammal Eohippus was the “dawn horse” (which Victorian anatomist Thomas Henry Huxley famously characterized for the steed of a tiny “Eohomo“), and there are plenty of dawn dinosaurs such as Eoraptor, Eodromaeus, Eobrontosaurus and Eolambia. The prefix is a kind of honorific, used to indicate the hypothesized beginning of a major lineage or significant change. In the case of Eotriceratops, Wu and colleagues found that the dinosaur was the oldest known member of the evolutionary ceratopsid club containing Triceratops, Torosaurus and Nedoceratops (which, depending on who you ask, may or may not be the same dinosaur).
The individual Guthrie found had fallen apart between death and burial. Aside from some vertebrae, ribs and ossified tendons, the scattered specimen was primarily represented by a dis-articulated skull. When reconstructed, though, the head of Eotriceratops stretched almost ten feet long–about a foot longer than the largest-known Triceratops skull. And while different in some characteristics, Eotriceratops had the same three-horned look of its later relatives Triceratops and Torosaurus.
This isn’t to say that Eotriceratops was directly ancestral to Triceratops, Torosaurus, Nedoceratops or whatever combination of the three paleontologists ultimately settle on. Eotriceratops could be the closest relative of Triceratops to the exclusion of Torosaurus, which would support the idea that those later dinosaurs were separate genera. Then again, Wu and coauthors pointed out that Eotriceratops might be the most basal member of the subgroup, which would make sense given that it was older than the other three genera. In either case, Eotriceratops can give us a rough idea of the Triceratops and Torosaurus prototype, but we lack the resolution to know if Eotriceratops was ancestral to any later dinosaur. Eotriceratops undoubtedly had some significance in the evolution of the last three-horned dinosaurs, but we need many more fossils to know this little-known dinosaur’s role in the story. Every dinosaur paleontologists find comes with a handful of answers and a myriad of new mysteries.
This post is the latest in the Dinosaur Alphabet series.
Wu, X., Brinkman, D., Eberth, D., Braman. 2007. A new ceratopsid dinosaur (Ornithischia) from the uppermost Horseshoe Canyon Formation (upper Maastrichtian), Alberta, Canada. Canadian Journal of Earth Sciences 44: 1243-1265
November 9, 2012
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.
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
November 5, 2012
If I started this Dinosaur Alphabet series just a few years ago, I wouldn’t have included Dyoplosaurus. Up until 2009, the dinosaur was hiding within another genus of heavily-armored ankylosaur. But after decades of discovery and debate, Dyoplosaurus is back, and the Cretaceous club-tail has its own role to play in wider discussions about the tempo and mode of dinosaur evolution.
Canadian paleontologist William Parks named the ankylosaur in 1924. Just a few field seasons earlier, in 1920, a University of Toronto crew found the partial skeleton of an armored dinosaur in the Late Cretaceous rock along the Red Deer River in Alberta. “The anterior part of the skeleton had been long exposed and had suffered in consequence,” Parks later wrote, but the team was still able to collect part of the skull, some tooth fragments, ribs and, best of all, the articulated hip and tail. Some of the armor remained in place, and the preservation was delicate enough to include skin impressions and the long ossified tendons that helped support the ankylosaur’s tail. If only the front half had remained intact!
This partial skeleton wasn’t the first ankylosaur to be found in the Late Cretaceous of North America. But, Parks wrote in his report, the animal’s tail club was “distinctly different from any previously described and, as far as I am aware, from any that have been collected.” Based on this slender oval of bone and other features, Parks distinguished the skeleton as Dyoplosaurus acutosquameus. And while the front half of the animal was almost entirely missing, the detail of the back half gave paleontologists a detailed look at how the armor, bones and tendons of ankylosaurids were arranged.
Then researchers sunk Dyoplosaurus. In 1971, in a huge revision of the ankylosaurs, paleontologist Walter Coombs proposed that Dyoplosaurus was not so unique as Parks had proposed. A jaw fragment found with the original Dyoplosaurus specimen was virtually identical to part of a jaw referred to the more famous armored dinosaur Euoplocephalus, Coombs wrote, and therefore Parks’ dinosaur should be considered a Euoplocephalus.
Since this other ankylosaur was named on the basis of even more fragmentary material, the addition of the “Dyoplosaurus” specimen gave paleontologists a new reference for what the hips, tail, and armor of Euoplocephalus looked like. More than that, the find extended the range of Euoplocephalus through Alberta’s Late Cretaceous rock. The “Dyoplosaurus” material was found in a roughly 76-million-year-old park of the Dinosaur Park Formation, and bones referred to Euoplocephalus had also been found in the geologically younger Horseshoe Canyon Formation. Altogether, Euoplocephalus seemed to persist for almost ten million years–quite a feat given that many neighboring genera and species of dinosaur came and went during the same span of time.
As paleontologists found additional ankylosaurs and compared previously discovered material, though, it became apparent that Euoplocephalus had become an osteological umbrella that was hiding more than one dinosaur genus. Indeed, since the original Euoplocephalus material consisted of a partial skull and a half ring or neck armor, it was difficult for paleontologists to compare and accurately refer specimens when there was a lack of overlapping material. As researchers investigated more complete material that was undeniably Euoplocephalus, it became apparent that other specimens from a wide range of time and displaying a wide range of variation had been incorrectly assigned to this dinosaur. Among the incorrectly lumped dinosaurs was Dyoplosaurus.
Ankylosaur expert Victoria Arbour and her colleagues resurrected Parks’ ankylosaur in 2009. While the anatomy of the animal’s skull fragment wasn’t easily distinguishable from the original Euoplocephalus fossils, details of the hips and vertebrae, especially in the tail, distinguished Dyoplosaurus from all other ankylosaurs. From the hips back, Dyoplosaurus was a distinct dinosaur.
Despite what Parks had written, though, Arbour and her coauthors cautioned that the tail club of Dyoplosaurus was not an easy-to-spot difference. As far as paleontologists know now, ankylosaurid dinosaurs were not born with tail clubs. The osteoderms that formed the bludgeon grew later in life, and, since Parks’ Dyoplosaurus specimen was relatively small compared to Euoplocephalus specimens, it’s possible that the dinosaur’s tail club had not finished growing. When comparing dinosaurs, it’s always important to keep the animal’s stage of development in mind–features that may seem to characterize a new species may only indicate immaturity.
Other ankylosaurs are probably hiding within Euoplocephalus. Properly identifying and categorizing them will take years. Studies of hadrosaurs, ceratopsians, tyrannosaurs and other dinosaurs have shown that Late Cretaceous dinosaurs on the western subcontinent of Laramidia–isolated from their eastern cousins by the vanished Western Interior Seaway–that the genera and species differed along the latitudes. Rather than finding the same dinosaurs from Alberta to Utah, paleontologists have found distinct assemblages of dinosaurs that belie isolated evolutionary pockets. And analyses of Canada’s Late Cretaceous species have tracked turnover patterns among the dinosaurs, timing the pulse of evolution and extinction. Splitting out Dyoplosaurus is one more step towards understanding what North America’s dinosaurs can tell us about how evolution works.
Want to know more about other unsung dinosaurs? Check out previous entries in the Dinosaur Alphabet.
Arbour, V. Burns, M. Sissons, R. 2009. A redescription of the ankylosaurid dinosaur Dyoplosaurus acutosquameus Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus. Journal of Vertebrate Paleontology 29, 4: 1117–1135. doi:10.1671/039.029.0405
Parks, W. 1924. Dyoplosaurus acutosquameus, a new genus and species of armored dinosaur; and notes on a skeleton of Prosaurolophus maximus. University of Toronto Studies Geological Series 18: 1–35.
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.
March 22, 2012
Out of all the parts of a dinosaur’s skeleton, nothing is as prized as the skull. While an entire Tyrannosaurus is a frightening visage, the jaws are what we fear the most. Triceratops is a stout herbivore, but the highly decorated skull is what makes the dinosaur a fan favorite. And the entire character of Apatosaurus, née “Brontosaurus,” changed when paleontologists recognized that they had mounted the wrong head on the dinosaur’s body. No surprise, then, that many paleontologists have been dinosaur head-hunters.
Royal Tyrrell Museum paleontologists Darren Tanke and Rhian Russell recently solved one case of a decapitated dinosaur, they explained at the 16th annual symposium of the Alberta Palaeontological Society. In 1992, paleontologists prospecting in Alberta’s Dinosaur Provincial Park came across an abandoned dinosaur quarry. The site was one of many unrecorded quarries scattered throughout the park—remnants of early 20th century expeditions that did not necessary excavate or record data to modern scientific standards. But the early fossil hunters hadn’t collected everything in the rock. The 75-million-year-old site still contained the parts of the hips legs, and tail of a large hadrosaur, while the front half of the skeleton seemed to have eroded away. For whatever reason, the fossil collectors decided to abandon the quarry without collecting the whole dinosaur.
Paleontologist Phil Currie found a hadrosaur lower jaw at the site in 1992, but this did not seem remarkable since the site was part of a bonebed with many fossils. The site was recorded and sometimes visited, but who dug the quarry and when remained a mystery. Then, last year, someone found a hadrosaur toe bone and a scrap of newspaper at the quarry. The newspaper carried a 1920 date, and there was only one person working in the area at that time: George F. Sternberg.
With a little historical detective work, Tanke and Russell found that Sternberg, accompanied by his wife and young son, collected a single hadrosaur specimen in 1920. The fossil was a skull of Corythosaurus, although the specimen was missing the lower jaws. The skull is on display at the University of Alberta in Edmonton, while the jaw and toe bone are at the Royal Tyrrell Museum and the remainder of the skeleton is in the field.
But why did Sternberg leave so much of the fossil in the ground? Maybe, Tanke and Russell propose, he thought that the skull was the only part worth collecting. The dinosaur’s body between the skull and the hips—including the neck, chest and arms—was disarticulated, and lacking a trained field crew to excavate what remained, maybe Sternberg decided to pick up the skull and leave the body. We may never know for sure.
Still, the fact remains that a single dinosaur is now split among several places—two museums and a field site. This is not an isolated case. Other headless dinosaur bodies undoubtedly exist in the field, and these fossils might be collected and stored in different museums. And even sites that have been carefully excavated may yield additional bones as erosion scrapes away at the rock, and different paleontologists may eventually find parts of skeletons that have already been mostly collected. This is why detailed records are so important in paleontology. Even if a skeleton is scattered hither and yon, there is at least the hope that the parts can be reunited someday.
Tanke, D., Russell, R. 2012. Headless wonder: Possible evidence of a head-hunted dinosaur skeleton in Dinosaur Provincial Park, Alberta. Alberta Palaeontological Society Sixteenth Annual Symposium Abstracts. 14-17