Reconstructing a Coelophysis Flock
The catastrophic death assemblage preserved at the Ghost Ranch, New Mexico Coelophysis (Whitaker) Quarry provides a unique opportunity to illustrate a population of Late Triassic theropod dinosaurs. Measurements of 56 individuals at the Quarry suggest a population quite different from those shown in typical illustrations of the “Ghost Ranch Flock.”
Right about now the above text and image should be going up at the PaleoArt Poster Exhibit running alongside the Opening Reception for the SVP Annual Meeting.
Over the past year, I’ve worked with Larry Rinehart to develop skeletal reconstructions of Coelophysis at different growth stages, based on his statistical and allometric studies of the fossils preserved in blocks from the Ghost Ranch Quarry. The preliminary results of that study, and the skeletal reconstructions we’ve developed so far, will be presented during the poster session this Saturday. (For interested readers who aren’t at the conference, check back here when the embargo lifts on Saturday evening for more details.)
One interesting facet that came out of this study was the “demographics” of the Ghost Ranch population—over 40% of the preserved specimens came from small juveniles less than 2kg in weight (like those shown above). Large adults (like AMNH 7223 and 7224, the specimens that most depictions of Coelophysis are probably based on) make up less than 10% of the known specimens of C. bauri. This fits pretty well with the population dynamics of modern crocodiles, and it has some rather dynamic visual implications for artists restoring scenes showing large groups of Coelophysis. I wanted to come up with a quick study portraying this new interpretation of the “Ghost Ranch Flock”
If a population consists of many more children than adults, its a cinch that relatively few Coelophysis hatchlings made it to adulthood. While the case for cannibalism in Coelophysis is still contested, I figured that throwing in an adult grabbing a meal to go in the background would underscore the potential difficulties faced by C. bauri youth. This, along with many other details in the picture, is based on evidence from the NMMNH Coelophysis block—in this instance, some very coelophysoid-looking bones in the coprolites and cololites found aside/inside the skeletons of adults in the block.
—Matt Celeskey.
File under: Dinosaurs, Triassic.
Comments on record: (1)
The Archosauria
It’s a virtual, multi-blog version of a paleoart show! Zach of When Pigs Fly Returns, Scott from Coherent Lighthouse, and Raven from The Caw Box have teamed up to create a show called The Archosauria, which is on display this month at Side Street Espresso in Anchorage, AK.
Pieces from The Archosauria, a collection of drawings and paintings depicting all manner of antorbitally fenestrated reptiles, are showing up online at When Pigs Fly Returns and Coherent Lighthouse.
—Matt Celeskey.
File under: Mesozoic, Paleo-Pop, Reptiles.
Comments on record: (2)
Chinlechelys tenertesta
- New Turtle: Chinlechelys tenertesta
- Name Means: Delicately-shelled Chinle Turtle
- Relations: Basal Turtle
- Holotype: NMMNH P-16697, partial skeleton including pieces of carapace, plastron, neck spine, etc.
- Location: New Mexico, U.S.A.
- Age: Late Triassic, ~205,000,000 years ago
- Info: The fragments that make up the holotype of Chinlechelys include one and one-half dorsal vertebrae that are fused to a thin bit of shell in a distinctively turtle-like manner. Other pieces include a chunk of the plastron, or lower shell, and a piece from the rear of the carapace (upper shell) with bits of rib on the underside. Two spikes of armor were found that may have protected the animal’s neck—similar spikes adorned the necks of more completely known Triassic turtles like the European Proganochelys.
The more impressive bits of Chinlechelys on display at the NMMNHS.- Joyce et al. consider Chinlechelys to be something of a “turtle-in-progress.” Its shell is extremely thin (1 to 3mm thick) and, unlike all other turtles, its ribs do not appear to be tightly fused to its carapace. This fossil could help resolve a long-standing controversy in turtle evolution—did the turtle shell evolve as the ribs widened and fused together into a dome-like shell, or did rows of armor plating in the skin expand until they fused together and integrated with the ribs and vertebrae for support? According to its describers, the thin shell and loosely integrated ribs of Chinlechelys provide compelling evidence for the latter scenario.
- Reference: Joyce, W. G., Lucas, S. G., Scheyer, T. M., Heckert, A. B., and Hunt, A. P., 2008. A thin-shelled reptile from the Late Triassic of North America and the origin of the turtle shell Proceedings of the Royal Society B Published online (FirstCite). DOI: 10.1098/rspb.2008.1196
- Elsewhere on the Web:
—Matt Celeskey.
File under: Reptiles, Triassic.
Comments on record: (1)
Pachyrhinosaurus lakustai
- New Dinosaur: Pachyrhinosaurus lakustai
- Name Means: Lakusta’s Thick-nosed reptile.
(Al Lakusta discovered the Pipestone Creek Bonebed where the fossils of this dinosaur were found.)
- Relations: Ceratopsian
- Location: Alberta, Canada
- Age: Late Cretaceous, ~73,000,000 years ago
- Length: 6 meters, ~20 feet
- Weight: 1800 kilograms, ~2 tons
- Info: Pachyrhinosaurus lakustai is known from fossils first discovered more than 30 years ago in a densely packed bonebed in Alberta, Canada. Like the previously known species of Pachyrhinosaurus, P. canadensis, this new species had a thickened mass of bone (or boss) atop its nose as an adult. Unlike P. canadensis, the bosses of P. lakustai are present only in adults—juveniles of the new species were found to have horns like those of other ceratopsians. P. lakustai also differs from P. canadensis in smaller overall size and details of the ornamental spikes and bumps on its frill, according to the summary page of the newly released monograph describing this species.
- Reference: Currie, P. J., Langston, Jr., W., Tanke, D. H., 2008. A New Horned Dinosaur from an Upper Cretaceous Bone Bed in Alberta. NRC Press. 152pp. ISBN-13 9780660198194.
- Web coverage:
- Update (10/3/08): Lawrence Witmer and Ryan Ridgely have made their work on the brain cavity and inner ear of Pachyrhinosaurus lakustai available online. From their “common language summary”:
Indeed, the most remarkable aspect of the brain structure of Pachyrhinosaurus is how small and primitive it must have been…Despite the cranial ornaments suggestive of perhaps elaborate behavioral displays and other evidence suggesting herding behavior or even migration, the behaviors of Pachyrhinosaurus were probably relatively simple, stereotyped, and instinctual.
—Matt Celeskey.
File under: Cretaceous, Dinosaurs.
Comments on record: (0)
Aerosteon riocoloradensis
- New Dinosaur: Aerosteon riocoloradensis
- Name Means: Air bones from the Rio Colorado
- Relations: Basal (allosauroid?) tetanuran theropod
- Size: 9 meters/30 feet long
- Location: Cañadon Amarillo, Argentina
- Age: Late Cretaceous, ~84,000,000 years ago
- Info:
Key to the pneumatic features reported in Aerosteon riocoloradensis
from Sereno et al. 2008. See here for detailed caption.
The fossilized bones of Aerosteon are extensively pneumatized— that is, riddled with hollow spaces. In life, some of these spaces would have housed air sacs that helped maintain a steady flow of air through the dinosaur’s rigid lungs. Modern birds have inherited this type of respiratory system from their dinosaurian ancestors, who may have developed this distinctive aerated anatomy in order to breathe more efficiently, or lighten their load and keep balance while running on two legs, or as a built-in air-cooling system to keep from overheating. The extreme degree of pneumatization preserved in a relatively primitive theropod like Aerosteon helps researchers pinpoint when specific features of the avian respiratory system first evolved.
- Reference: Sereno, P. C., Martinez, R. N., Wilson, J. A., Varricchio, D. J., Alcober, O. A., Larsson, H. C. E., 2008. Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina PLoS ONE 3(9): e3303. doi10.1371/journal.pone.0003303.
- Web coverage:
- Update 10/6: Matt Wedel reviews the current state of research on dinosaur pneumaticity and raises some criticisms of Sereno et al.’s paper describing Aerosteon in two posts over on SV-POW.
—Matt Celeskey.
File under: Cretaceous, Dinosaurs.
Comments on record: (1)
