March 19, 2012
When I think of ceratopsian dinosaurs, giant and well-ornamented forms such as Triceratops and Styracosaurus immediately spring to mind. These spiky creatures represent the acme of horned dinosaur decoration. But not all ceratopsians were insanely adorned heavyweights. There were small, lightly built ceratopsians running around the Late Cretaceous of Asia and North America, too, and last week paleontologists officially announced a pair of such dinosaurs.
Paleontologists first heard about Unescopceratops koppelhusae and Gryphoceratops morrisoni late last year, when a pre-print version of the paper describing the dinosaurs first appeared online. The publication of the official description this month gave the obscure dinosaurs a publicity boost. As paleontologist Michael Ryan explains in the video above, both dinosaurs were already known to scientists. One was a mystery dinosaur that had been described previously, and the other had been hiding in museum collections for decades. Very little is known about these ceratopsians, so the beautiful artwork combines known aspects of the dinosaurs with pieces from more completely known relatives. The announcement of Unescoceratops and Gryphoceratops serve as a reminder that not all the horned dinosaurs were enormous bruisers.
March 2, 2012
One of my favorite dinosaurs at the American Museum of Natural History is the Styracosaurus. The insanely ornamented creature is presented as if swimming through a wave of plaster, a pose meant to depict the way the dinosaur was found in the field. It is a beautiful mount, but the restored and reconstructed skeleton obscures the fact that the actual specimen is not so complete.
Veteran fossil hunter Barnum Brown discovered the Styracosaurus in 1915. He found the fossil within what is now Canada’s Dinosaur Provincial Park. Most of the dinosaur’s post-cranial skeleton was intact, but as Brown later noted in a 1937 paper he wrote with colleague Erich Schlaikjer, only a few parts of the skull were recovered. That lovely skull on the AMNH mount was mostly reconstructed on the hypothesis that the animal was really a Styracosaurus. Brown believed that the few parts which were collected were enough to name a distinct species of this dinosaur: Styracosaurus parksi.
Brown’s new species was the third flavor of Styracosaurus to be named. Paleontologist Lawrence Lambe named the first species, Styracosaurus albertensis, in 1913, and Charles Gilmore followed with Styracosaurus ovatus in 1930. Both were very spiky dinosaurs distinguished by the prominent spikes jutting out of the parietal bones on their frills. But Brown considered his dinosaur to be a separate species on the basis of slight differences in the few skull elements he had collected. The squamosal bone—another frill element—seemed to be longer and different in shape than the animal Lambe had named Styracosaurus albertensis.
Early 20th century paleontologists had a tendency to over-split dinosaurs on the basis of very slight differences. Naming a new genus or species was easy to justify during the early bone rushes. There were so few specimens, and researchers understood so little about how dinosaurs grew up, that variations among individuals or differences attributable to age were often taken as the hallmarks of distinct species. And traits thought to distinguish between dinosaur genera turned out to be less diagnostic than originally thought. Styracosaurus once seemed to be unique in having spiky parietals, for example, but similar features have since been found in closely related centrosaurine dinosaurs such as Achelousaurus, Einiosaurus, Centrosaurus brinkmani, Pachyrhinosaurus and, the new kid on the block, Spinops. In order to sort out Styracosaurus, in 2007 paleontologists Michael Ryan, Robert Holmes and A.P. Russell reviewed the material attributed to this dinosaur.
Ryan, Holmes and Russell counted only two Styracosaurus species as valid: S. albertensis and S. ovatus. Brown’s specimen, while incomplete, fell within the variation documented for S. albertensis, and so S. parksi was sunk. And at the genus level, Ryan and co-authors distinguished Styracosaurus from similar dinosaurs by the anatomy of the ornaments at each slot on the parietal part of the frill. The first ornament is typically a tiny nub, the second either appears as a small tab or hook, the third is a large spike and the fourth is also a large spike. (The remaining ornaments at positions five through seven vary in size and shape between individuals.)
But the Styracosaurus genus was recently winnowed down even further. Most Styracosaurus specimens belonged to the northern species S. albertensis, but the species S. ovatus was represented by a single specimen found in Montana. This significantly extended the range of Styracosaurus, at least until paleontologists Andrew McDonald and Jack Horner suggested in 2010 that the Montana dinosaur really represented a different genus. On the basis of the partial frill and other skull fragments, they named the dinosaur Rubeosaurus. It was another weird horned dinosaur with a huge nasal horn, and the third parietal horns were directed inward, towards each other, rather than outward like in Styracosaurus. Within just a few years, three species of Styracosaurus were cut down to just one.
Brown, B., Schlaikjer, E. 1937. The skeleton of Styracosaurus with the description of a new species. American Museum Novitates. 955, 1-12
Andrew T. McDonald & John R. Horner, (2010). “New Material of “Styracosaurus” ovatus from the Two Medicine Formation of Montana”. Pages 156–168 in: Michael J. Ryan, Brenda J. Chinnery-Allgeier, and David A. Eberth (eds), New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium, Indiana University Press, Bloomington and Indianapolis, IN.
Ryan, M., Holmes, R., Russell, A. (2007). A revision of the late campanian centrosaurine ceratopsid genus Styracosaurus from the Western Interior of North America
Journal of Vertebrate Paleontology, 27 (4), 944-962 DOI: 10.1671/0272-4634(2007)27[944:AROTLC]2.0.CO;2
October 18, 2011
On Sunday, I drove two and a half hours to meet a dinosaur. My journey was part of a trend this year. As I have traveled around the west, from Montana to New Mexico, I have sought out dinosaurs that I have never seen before, and while at this year’s National Association of Science Writers conference in Flagstaff, I found out that the Arizona Museum of Natural History in Mesa has a mount of a unique horned dinosaur called Zuniceratops. That was all I needed to know before getting on the southbound highway.
Though unfamiliar, Zuniceratops is not a brand new dinosaur. The creature was initially described by paleontologists Douglas Wolfe and Jim Kirkland in 1998, and even got a few minutes of relative fame in 2001′s When Dinosaurs Roamed America. Not too shabby for a relative newcomer, but what horned dinosaur can compete with the celebrity of Triceratops and ridiculously well-ornamented genera such as Styracosaurus? Zuniceratops was relatively small, had only two brow horns, and doesn’t look quite as imposing as its later Cretaceous relatives, but those characteristics are part of why this dinosaur is significant to paleontologists looking at the big picture of horned dinosaur evolution.
The bones of Zuniceratops were found in the roughly 89-million to 93-million-year-old rock of western New Mexico’s Zuni Basin. This makes the dinosaur one of the oldest known ceratopsians found in North America, and, as described by Wolfe and Kirkland, the remains of Zuniceratops exhibit a mosaic of features shared with both earlier ceratopsians (such as Protoceratops) and the later, more familiar ceratopsids (such as Triceratops). While the body of Zuniceratops appeared to retain a more archaic, lightly built form, the prominent brow horns, the arrangement of the teeth (set up like a pair of scissors to shear vertically through food), a curved part of the hip called the ischium, and other characteristics underlined a close relationship to the ceratopsid dinosaurs that would eventually become so common on the continent.
But Zuniceratops was not a “missing link” or an ancestor to any of the ceratopsid dinosaurs. Instead, it is a peculiar dinosaur with a suite of features that may help us understand the transition between the more archaic ceratopsians and the early ceratopsids. The arrangement of anatomical characters in Zuniceratops gives us a general picture of what was happening among the horned dinosaurs at the time. After all, the grand pattern of evolution is a wildly branching tree of life, and in technical terms, Zuniceratops falls on a branch just outside the ceratopsid group—a relatively close cousin—but it did not share some of the telltale characteristics of the famous dinosaur group. Hopefully, as more dinosaurs like Zuniceratops are found, paleontologists will gain a clearer picture of how the greatest of the horned dinosaurs evolved.
Farke, A., Sampson, S., Forster, C., & Loewen, M. (2009). Turanoceratops tardabilis—sister taxon, but not a ceratopsid Naturwissenschaften, 96 (7), 869-870 DOI: 10.1007/s00114-009-0543-8
Wolfe, D.G. & Kirkland, J.I. (1998). “Zuniceratops christopheri n. gen. & n. sp., a ceratopsian dinosaur from the Moreno Hill Formation (Cretaceous, Turonian) of west-central New Mexico”. Lower and Middle Cretaceous Terrestrial Ecosystems, New Mexico Museum of Natural History and Science Bulletin 24: 307–317.
Wolfe, D. G. (2000). New information on the skull of Zuniceratops christopheri, a neoceratopsian dinosaur from the Cretaceous Moreno Hill Formation, New Mexico. pp. 93–94, in S. G. Lucas and A. B. Heckert, eds. Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin No. 17.
September 26, 2011
Variation is one of the basic elements that makes evolution possible. The tiny differences between individuals in a population provide the raw material for natural selection to act upon and cause evolutionary changes. This can readily be seen among living animals, but identifying and understanding variation among dinosaurs is much more difficult. Paleontologists typically have only a handful of specimens, represented by incomplete materials, from a range of sites which may span hundreds of thousands, if not millions, of years. Nevertheless, studying how individual dinosaurs of well-sampled species vary from one another can help researchers investigate details of dinosaur diversity and dinosaur lifestyles. Among the latest dinosaurs to be studied this way is Anchiceratops ornatus, a relatively obscure horned dinosaur from the Late Cretaceous of Canada.
As reviewed by paleontologist Jordan Mallon and colleagues in the recent Journal of Vertebrate Paleontology study, Anchiceratops has had a tangled history. Fossil hunter Barnum Brown named the first species, Anchiceratops ornatus, in 1914, and in 1929 experienced dinosaur excavator Charles M. Sternberg described a second species he called Anchiceratops longirostris on the basis of what he thought was a more gracile, slender skull. The two species were later lumped together into just one, A. ornatus, and despite a lack of rigorous testing, the disparity between the two skulls has been attributed to sexual differences between males and females. (Though sexual dimorphism has often been proposed for dinosaurs, no clear-cut, entirely convincing case has been found.)
But there are more than two Anchiceratops skulls. The trouble with dinosaur discoveries is that additional fossils of already named genera or species often don’t get described unless they are exceptional in some way or are used in a project that requires comparisons between multiple individuals. In the case of Anchiceratops, a total of ten more or less complete skulls have been found that can be attributed to the genus, and these fossils form the basis of the new study. Each of the skulls varied significantly from others in the sample—something that was expected based on big samples of other horned dinosaurs such as Triceratops and Centrosaurus. But did any of the differences hint that some of the dinosaurs belonged to a separate species, or that certain characteristics could be used to distinguish the dinosaur sexes?
Mallon and co-authors used measurements of particular parts of the skull to compare the ten specimens in the sample in what’s called a morphometric analysis. The results of each test plotted the skulls out on a graph that represented the variation in the sample. If there were two different species or sexes, then the scientists would expect to see two distinct clusters of skulls on the graphs. No such pattern was found. Even though the sample size was small, the results indicated that there was no detectable male-female split. Additionally, the anatomy of the skulls and the lack of clustering offered no support to the idea that there was more than one species of Anchiceratops. There appears to have only been one species, Anchiceratops ornatus, preserved in the rocks of the Horseshoe Canyon Formation dating between about 71 million to 69 million years ago. Two million years is a pretty good run compared to the amount of time other horned dinosaur species persisted: In the older Dinosaur Park Formation in the same area, horned dinosaur species appear to have hung on for only about 700,000 years or so.
Why Anchiceratops ornatus was a longer-lived species than geologically older dinosaurs in the same neighborhood is unknown, but Mallon and colleagues offer several hypotheses. Perhaps, due to the lower dinosaur diversity in the Horseshoe Canyon Formation, Anchiceratops had less competition for food from other herbivores and therefore was able to persist for longer. Then again, the shrinking of the Western Interior Seaway during that time may have affected the history of the species. During the days of the Dinosaur Park Formation, the sea may have created fragmented habitats that resulted in the isolation of dinosaur populations which evolved into new species. Since the seaway was receding during the time of Anchiceratops, habitats were less fragmented and those environmental pressures were released, and so fewer species may have taken up the roomier and more continuous habitats. Alternatively, Anchiceratops may have been a relatively hardy species that could better cope with the environmental changes created by the regression of the sea and, as a result, persisted for longer than species that relied on specialized foods or habitats. At the very least, though, Anchiceratops appears to be a small dinosaur success story.
Mallon, J., Holmes, R., Eberth, D., Ryan, M., & Anderson, J. (2011). Variation in the skull of (Dinosauria, Ceratopsidae) from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta Journal of Vertebrate Paleontology, 31 (5), 1047-1071 DOI: 10.1080/02724634.2011.601484
March 11, 2011
What is Nedoceratops? That depends on who you ask. The single known skull could represent a transitional growth stage between Triceratops and Torosaurus head shapes in a single species of dinosaur, or it might be a unique species of horned dinosaur that lived alongside its better-known relatives.
The suggestion that Nedoceratops was truly a Triceratops caught in the act of rearranging its skull has sparked a renewed interest in this dinosaur. Though known to paleontologists for over a century, the dinosaur was often viewed as an oddball and did not even receive a full redescription until about a month and a half ago. Nedoceratops has never been as popular or well-known as its relatives Triceratops and Torosaurus, and so I was surprised to learn that a life restoration had once been made of this peculiar creature.
A paper on the restoration accompanied a 1905 scientific description published by Richard Swann Lull but mostly written by John Bell Hatcher. This was not a bit of scientific claim-jumping. Hatcher had been working towards completing a massive monograph on horned dinosaurs. It had been started by his former boss, O.C. Marsh, who died of typhus before he could finish the book. The task of wrapping it all up went to Lull, who decided to publish Hatcher’s description of the Nedoceratops skull separately in 1905. (At the time, Lull proposed that the dinosaur should be called Diceratops, though the name has been changed multiple times.)
Lull’s restoration was of a battered animal. Unlike other horned dinosaurs, Nedoceratops had two unequally-shaped holes in the squamosal bones on the sides of its frill. Hatcher thought these might be natural holes in the skull, but Lull argued that, since Triceratops, Torosaurus and Nedoceratops undoubtedly used their horns and frills like spears and shields, “It seems vastly more probable that [the squamosal holes] are ‘old dints of deep wounds’ received in combat.” The animal survived the presumed injury, and Lull thought some kind of “horny or leathery integument” would cover the gaps in the frill.
We now know that Lull was probably wrong. When I asked paleontologist Andy Farke—who redescribed the skull—what he thought about the strange skull holes of Nedoceratops, he replied:
The old thought was that these holes were the result of accidental “gorings” during horn-to-horn combat between rival dinosaurs. But, Darren Tanke and I recently noted that most aspects of the fenestrae argue against them being the result of injury. Instead, we think they were probably just the result of bone resorption in an area of the frill that was already thin to begin with. No horn thrusts required.
Even so, Lull’s restoration is remarkable. I cannot recall seeing any other model or sculpture of Nedoceratops, and it is a rare vision this contentious dinosaur in the flesh.
Farke, A. (2011). Anatomy and Taxonomic Status of the Chasmosaurine Ceratopsid Nedoceratops hatcheri from the Upper Cretaceous Lance Formation of Wyoming, U.S.A PLoS ONE, 6 (1) DOI: 10.1371/journal.pone.0016196
Lull, R.S. (1905). Restoration of the horned dinosaur Diceratops. American Journal of Science, 4 (4), 420-422