November 16, 2012
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.
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
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.
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 8, 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.
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