October 2, 2012
The Early Jurassic is a mysterious time in dinosaur evolution. In North America, at least, paleontologists have uncovered scores of dinosaur tracks from this critical time when dinosaurs had been handed ecological dominance in the wake of a mass extinction, but body fossils are rare. In the orange sandstone that makes up so much of Arches and Canyonlands national parks in Utah, for example, only a handful of skeletons have ever been found. This formation–called the Glen Canyon, Navajo, Nugget or “Nuggaho” depending on who you ask–preserves immense sand dunes that recorded prehistoric footsteps but rarely bone. The recently described sauropodomorph Seitaad, and a group of as-yet-unnamed coelophysoids, are exceptionally rare finds.
Yet, from Connecticut to Arizona, there is one dinosaur that is constantly presented as an icon of dinosaurs circa 190 million years ago. This is Dilophosaurus–the 20-foot-long, double-crested theropod that gained dubious fame thanks to Jurassic Park. (Contrary to the film, there’s no evidence that this carnivore was a “spitter” with a collapsible neck frill.) At sites where Early Jurassic theropod tracks are found in abundance, Dilophosaurus is invoked as a possible trackmaker. But is this really so?
The remains of what would eventually be named Dilophosaurus were discovered in 1942 by Jesse Williams near Tuba City, Arizona. It took another 12 years before paleontologist Samuel Welles mistakenly attributed the bones to a new species of Megalosaurus –“M.” wetherilli–and the name Dilophosaurus itself wasn’t actually coined until 1970. Despite all this shifting around, though, Dilophosaurus wetherilli became a symbol of top Early Jurassic carnivores. Paleontologists had found plenty of Early Jurassic tracks made by a Dilophosaurus-size dinosaur, and now they finally had a body.
Frustratingly, though, we usually don’t know what dinosaur left a particular trace fossil unless the animal literally died in its tracks. While Dilophosaurus is a good fit for many large-size, Early Jurassic tracks, and may very well have left tracks at places such as St. George, Utah’s megatracksite, there’s no way to know for sure. And it seems unlikely that the same species of dinosaur that left tracks in Early Jurassic Utah also made footprints in the mud of what would become the Connecticut Valley. Who knows how many mid-sized theropods might have stalked lakeshores during this time? We don’t know, and the situation is made all the more irksome since the sediments which preserve tracks often don’t contain body fossils. We know these dinosaurs from the bottom of their feet but little else. Until future discoveries fill out the fauna of North America’s Early Jurassic, Dilophosaurus will remain the most familiar and iconic predator of its epoch.
Naish, D. 2009. The Great Dinosaur Discoveries. University of California Press: Berkeley. pp. 94-95
January 20, 2012
I have a fondness for roadside dinosaurs. Not because they’re accurate. Quite the contrary. Concrete and plastic dinosaurs beside America’s highways are often sad, malformed creatures that are truly terrible. Nevertheless, they are a reminder of the popularity and cultural importance of Mesozoic life, especially along roads that connect fossil-rich exposures where many authentic dinosaurs were found.
My vote for the best worst dinosaurs goes to the monstrosities at Stewart’s Petrified Wood shop near Petrified Forest National Park in Arizona. One sad, roughshod theropod is poised to chomp down on a poor mannequin, and a model in a shock wig rides a dilapidated sauropod surrounded by icicle lights (seen above in a photo by David Williams).
But I know there must be others out there. I want to hear your suggestions for the worst roadside dinosaurs. And if you have a snapshot, share the photos of the poor beasts. You can send your submissions to firstname.lastname@example.org. I’ll share the best of the worst later next week.
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.
July 29, 2011
If you haven’t heard of Camposaurus, you’re not alone. This is one obscure dinosaur (and not to be confused with the better-known and very different Camptosaurus). First described in 1998, this animal may hold a critical place in the evolutionary tree of theropod dinosaurs, although, then again, it might not.
Very little is known about Camposaurus. The only parts that have been found and definitively referred to this dinosaur, recovered from the Late Triassic rock of Arizona, are a few parts of the dinosaur’s lower limb bones. (The original description mentioned bones from other individuals, but it is unclear whether these really belong to Camposaurus.) Still, the anatomy of these parts identified the dinosaur as a neotheropod dinosaur, and its geologic context made it potentially the oldest known representative of the huge, diverse group of dinosaurs which contained genera such as Ceratosaurus, Allosaurus, Tyrannosaurus, Spinosaurus and many, many more. The Camposaurus fossils, as a consequence, could be important for calibrating the early evolutionary history of theropod dinosaurs.
Naturally, the fact that so little is known about Camposaurus has made it a controversial dinosaur. Paleontologists have been trying to figure out where it fits in the theropod family tree—and whether the dinosaur even deserves a distinct name—for over a decade. The known bones are so hard to properly diagnose that they seem more likely to confuse than enlighten. Now paleontologists Martin Ezcurra and Stephen Brusatte have published a reexamination of the paltry Camposaurus bones, and they affirm that the dinosaur will remain important to questions about the early days of theropod dinosaurs.
According to Ezcurra and Brusatte, there are two subtle features which set Camposaurus apart from other early theropods, such as the well-known Coelophysis. The first is a distinctive ridge on one of the lower leg bones—the tibia—where it articulates with the fibula, and the second is the absence of a knob of bone on part of the ankle. Such subtle differences can make all the difference between whether a dinosaur genus or species is kept as distinct, ends up being lumped into another taxon, or remains a problematic mystery.
Ezcurra and Brusatte also attempted to figure out where Camposaurus fit among other theropod dinosaurs. As had been previously suspected, the dinosaur turned out to be most closely related to Coelophysis—so close, in fact, that Camposaurus might turn out to be a species of Coelophysis itself. Additional fossils will be needed to be sure, and, at Chinleana, paleontologist Bill Parker brings up an important point about the significance of the specimen in terms of its age.
Camposaurus has been thought to be the oldest known neotheropod dinosaur based upon the geologic details of the place it was found, known as the Placerias quarry. This site was thought to correspond to a certain part of Triassic rock called the Mesa Redondo Member of the Chinle Formation, but Parker reports that he has found this to be in error. The quarry is actually in slightly younger rock than has been proposed, meaning that Camposaurus is not as old as had been assumed. It’s still a very old theropod, but how old it really is and its relationship to other theropods remains tentative.
The takeaway from all these paleontological jots and tittles is that our knowledge of early dinosaurs is still in a state of flux. Determining the identities, relationships and ages of Triassic dinosaurs is an ongoing task, and our understanding will continue to change as new fossils are found. At the moment, the Camposaurus fossils play an important role in providing some of the only context we have for the early evolution of the neotheropod dinosaurs, and hopefully paleontologists will soon find the fossil clues that will allow us to understand how this great lineage got its start.
EZCURRA, M., & BRUSATTE, S. (2011). Taxonomic and phylogenetic reassessment of the early neotheropod dinosaur Camposaurus arizonensis from the Late Triassic of North America Palaeontology, 54 (4), 763-772 DOI: 10.1111/j.1475-4983.2011.01069.x
October 8, 2010
Compared to some of its later, gargantuan cousins, the 190-million-year-old sauropodomorph dinosaur Sarahsaurus aurifontanalis was a rather tiny herbivore. Only 14 feet long, this dinosaur lived in the early days of the Jurassic, and, according to a team of paleontologists led by Jackson School of Geosciences paleontologist Timothy Rowe, this newly-described dinosaur from Arizona does not fit with the popular image of dinosaurs as creatures that quickly evolved to be large and overran the planet.
The dinosaur story starts around 251 million years ago, in the wake of the catastrophic Permian mass extinction. More than 90 percent of all known marine species vanished and more than 70 percent of all species on land also fell into extinction, but the surviving lineages underwent a major evolutionary radiation. Among these groups were the dinosauromorphs, small creatures that we can recognize as being more closely related to dinosaurs than any other group of prehistoric reptiles, and around 230 million years ago one lineage of these dinosaurs gave rise to the first true dinosaurs. Like their ancestors, dinosaurs remained relatively small and were marginal parts of ecosystems in the southern hemisphere. Then, at the transition between the end of the Triassic and the beginning of the Jurassic, there was another major extinction event. Dinosaurs were lucky enough to survive, and Sarahsaurus was one of the forms that originated in the few million years after this second extinction pulse.
Until recently, Early Jurassic dinosaurs akin to Sarahsaurus were thought to have been part of a dinosaurian invasion of the Northern Hemisphere in which they quickly became the dominant land animals on the global stage. (Though it should be noted that the meat-eating theropod dinosaurs had made the jump north by the end of the Triassic and survived the extinction event.) Compared alongside other sauropodomorph dinosaurs from around this time period in North America, however, the new find suggests that there was instead a drawn-out pattern of dispersal in which dinosaurs moved north multiple times before finally gaining a foothold. This is evident the way Sarahsaurus relates to two of its Early Jurassic cousins: Anchisaurus from Connecticut and the recently-described Seitaad from Utah. Had sauropodomorphs moved to North America only once it would be expected that these dinosaurs would be one another’s closest relatives, but instead they fell within different parts of the sauropodomorph family tree. Each is representative of a different dispersal event from the south to the north.
Given its degree of completeness—the majority of its skeleton was recovered—Sarahsaurus is also relevant for understanding the timing of evolutionary changes going on among sauropodomorph dinosaurs just prior to the evolution of truly large sauropod dinosaurs. As interpreted by Rowe and co-authors, Sarahsaurus had column-like hind legs and other skeletal peculiarities often seen among larger dinosaurs. This may mean that many of the classic sauropod traits evolved in small animals first and then were co-opted as lineages of sauropods grew larger (a trend similar to what Raptorex hinted at for tyrannosaurs). The dispersal and evolution of the Early Jurassic sauropods requires further study to test this hypothesis, but it may be that changes among small dinosaurs made the evolution of giants possible.
Timothy B. Rowe, Hans-Dieter Sues, and Robert R. Reisz (2010). Dispersal and diversity in the earliest North American sauropodomorph dinosaurs, with a description of a new taxon Proceedings of the Royal Society B : 10.1098/rspb.2010.1867