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 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.
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
June 10, 2011
Sometimes people who discovered dinosaurs had no idea what they had found. As recounted by paleontologist and historian Eric Buffetaut, for example, in 1824 the French naturalist Georges Cuvier illustrated what appeared to be a fossil crocodile tooth sent to him by the English paleontologist Gideon Mantell. Further searches of England’s Mesozoic rocks turned up similar teeth—attributed to a prehistoric crocodile Richard Owen named Suchosaurus in 1824—but what the 19th century scientists didn’t know what that the teeth actually represented a dinosaur. The Suchosaurus teeth belonged to one of the spinosaurs, a crocodile-snouted and sometimes sail-backed group of dinosaurs that began to be well understood by paleontologists after the 1986 description of Baryonyx. The European naturalists misidentified the dinosaur teeth because the complete skeletons necessary for them to make the correct, dinosaurian assignment for the teeth had not yet been found.
The changing identity of Suchosaurus is not the only example of mysterious bones later being recognized as belonging to dinosaurs. Othniel Charles Marsh initially mistook the horns of Triceratops for the armaments of a gigantic bison, and the recognition that the weapons belonged to a dinosaur helped establish the archetype of horned dinosaurs in the late 1880s. But even Marsh’s “bison,” found in 1887, was not the first specimen of a horned dinosaur to be discovered. Small pieces of the strikingly ornamented dinosaurs had been found at least three decades earlier.
John Bell Hatcher, one of Marsh’s cadre of paleontologists entrusted to describe the great horned dinosaurs, paid tribute to the earlier discovery of horned dinosaurs in his classic monograph The Ceratopsia. In 1855, Hatcher explained, the geologist and explorer Ferdinand Hayden picked up a variety of fossils from the strata around the mouth of the Judith River in central Montana. Today we know this area as a major center of Late Cretaceous dinosaur sites, but at the time, no one really knew the dinosaurian bounty that lay in the West, and the bits of pieces of the creatures were sent back to Philadelphia to be examined by the polymath Joseph Leidy.
Leidy thought that he could distinguish four different types of dinosaurs among the rather paltry remains, including that of a dinosaur he called Trachodon mirabilis—a name for one of the “duck-billed” dinosaurs that has since fallen out of use because the teeth are not distinctive enough to assign to a particular species. Given the unfamiliar nature of the fossils, though, it is no surprise that Leidy made a mistake in grouping the fossils. Among the lot Leidy attributed to Trachodon were single-rooted and double-rooted teeth. The single-rooted teeth were indicative of hadrosaurs—the type of animal Trachodon was traditionally reconstructed as—but the double-rooted teeth were later confirmed as belonging to horned dinosaurs. They could not have known it from such incomplete material, but Hayden had discovered and Leidy had described some of the first horned dinosaur fossils ever reported. As paleontologists discover more about dinosaurs, they create a richer context by which to compare old discoveries, and old puzzles finally gain solutions.
Buffetaut, E. 2010. Spinosaurs before Stromer: early finds of spinosaurid dinosaurs and their interpretations. In Moody, R.; Buffetaut, E.; Naish, D.; and Martill, D. Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society, London, Special Publications, v. 343, p. 175-188
Hatcher, J.; Marsh, O.; Lull, R. 1907. The Ceratopsia. Washington: Government Printing Office. pp. 3-4