Part Five: Sketches from a Triassic BBQ
It’s been about two months now since my trip to the Snyder Quarry, a Late Triassic fossil site near Ghost Ranch in northern New Mexico. Most of my time there was spent with picks and hammers, but I did bring along a sketchbook and managed to come up with a few sketches during my time at the site.
The critter at the upper left is an aetosaur of marginal accuracy, doodled from memory one evening around the campfire. It is a rough attempt to restore Typothorax coccinarum, a good-sized reptile that has been likened to a cross between a crocodile and an armadillo, although I’ve always thought a coffee table made a more apt comparison. At least one individual from this stalwart species was preserved, in part, at the Snyder Quarry: a jumble of its characteristic armor plates was excavated there several years ago.
The preservation of the Snyder Quarry fossils tells an interesting story, the details of which were painstakingly worked out over several field seasons by Kate Ziegler. The Snyder Quarry is a very rich bonebed (some have even referred to it as a Lagerstätte) that preserves the bones of a variety of Late Triassic animals in spectacular detail. Very few of the bones are articulated but several are associated with other bones that are likely from the same animal, implying that there was some post-mortem disturbance of the remains but not enough to scatter them completely. Many of the long bones are oriented along a north-south axis, which suggests that they had been washed into their final resting place, but they show no signs of wear or abrasion associated with long or violent transport.
Many pieces of charcoal are preserved with the bones, and these provide an important clue as to what happened at the Snyder Quarry. Analysis of the charcoal showed that the wood burned to at least 400°C, at least as hot as a moderate ground fire, and possibly much hotter.
Place yourself in the aftermath of a Late Triassic forest fire. Giant conifers, perhaps relatives or descendants of the stately trees whose trunks will be preserved some 300 miles to the west in what is now Petrified Forest National Park, have been reduced to ash and charcoal, towering splinters of their former tropical glory. The remains of reptiles unable to escape the heat and smoke litter the ground, charred scale and sinew loosening the connections that held their skeletons together in life. Perhaps only a few hours have passed since the flames roared through, or a few days, or weeks, yet no living animals can be seen among the corpses. The devastation here is near-total: of the hundreds of bones collected from this site in years to come, only one will bear the scrape of a scavenging tooth.
A few dull pats in the thick layer of ash mark the onset of a rain that comes too late to this forest. The dry earth drinks these first drops greedily, but as the rain intensifies, the deforested landscape quickly receives more water than it can hold. Under the onslaught of a torrential tropical rain, the ground begins to slide. Charred tree limbs and scattered bones are swept up in a slurry of mud and ash, washed into the topographic lows of this Triassic landscape, and quickly buried. When they are next exposed to air and sunlight, more than 200,000,000 years will have passed.
Despite millions of years of burial, the charcoal that lies throughout the Snyder Quarry seems barely fossilized. Many pieces look nearly as fresh as coals from a campfire, and crumble into black powder almost as easily. Following up on earlier experiments painting with mud from other fossil sites*, I thought it might be worth trying a few sketches with Triassic charcoal. The charcoal was far from “artist-grade”, but I managed to (literally) scratch out the little scorched Triassic landscape shown above, and the snaggle-toothed phytosaur depicted below:
*Wish I could say that I came up with this idea all by myself, but I ripped it off was inspired to try it after seeing Alexis Rockman’s studies painted with sediments from the Burgess Shale and Karoo Basin. Lithographs based on some of his paintings with LaBrea tar can be seen online here.
Phytosaurs are by far the most common fossils found at the Snyder Quarry. Exactly why this is so is a matter of some conjecture, but during my time there, the crew pulled out several bones that most likely belonged to these ancient archosaurs, who developed what we would call a crocodile style long before the ancestors of today’s crocs picked up the habit. Back at camp, with phytosaurs still on the brain, I pulled out a pen and sketched up this brute:
Phytosaurs definitely loom large in my immediate future. Although this entry wraps up this series of posts about my visit to the Snyder Quarry, there will certainly be more about these and other Triassic reptiles to share within the coming months.
Further reading:
Zeigler, K. E., Heckert, A. B., and Lucas, S. G., eds. 2003. Paleontology and Geology of the Upper Triassic (Revueltian) Snyder Quarry, New Mexico. New Mexico Museum of Natural History and Science Bulletin 24.
The whole bulletin is full of papers on the Quarry, but this paper aptly summarizes the evidence for a Triassic wildfire:
Zeigler, K. E. 2003. Taphonomic analysis of the Snyder Quarry: a fire-related Upper Triassic vertebrate fossil assemblage from north-central New Mexico. NMMNHS Bulletin 24, pp. 49–62.
And poking around on Google, I found this post on the Snyder Quarry wildfires at Science, AntiScience and Geology.
—Matt Celeskey.
File under: Reptiles, The Day Job, Triassic.
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