On top of the Alcova Limestone lies the Jelm. On Muddy Mountain most of the Jelm has weathered away – indeed, it’s because the Alcova Limestone serves as a protective capstone that a similar fate hasn’t befallen the Red Peaks – but good outcrops can be seen at Alcova. It consists of red beds alternating with white layers of sandstone – the Jelm always reminds me of a candy cane. The sandstone layers represent river channels, dumping their load of sand on the streambeds as they crisscrossed their way across the flat, brick-red plains of Triassic Wyoming.
Very few fossils have been found in the lower Chugwater — the seasonally arid, barren sandy plains weren’t the easiest place to make a living, and the harsh, oxidizing chemistry of the Chugwater soils didn’t preserve bones well. Nevertheless, there are a few clues. Fossil footprints have been found, which might have been made by a rhynchosaur. If you’ve never seen one, it looked kind of like a cross between a pig and an iguana, with a face like a staple-puller. Teeth have also been found, probably from crocodile-like reptiles.
At a few localities in Wyoming, there is one more member on top of the Jelm: the Popo Agie – believe it or not, that’s pronounced poe-POE-zhia. This is the one layer of the Chugwater in which abundant fossils have been found. One of the oddest is Buettneria, a flat-headed beast that looked like a salamander blown up to the size of a small alligator. Its eyes and nostrils were on top of its head so, like an alligator, it might have hidden just under the surface of the water waiting to ambush unwary animals as they came down to the water’s edge. Remember that Wyoming’s first dinosaur, little Agialopous, was only the size of a dog so it could very well have been on Buettneria’s menu from time to time.
As impressive as Buettneria was, it wasn’t the undisputed king of Triassic Wyoming. That title goes to Heptasuchus, a terrestrial reptile a bit like a long-legged crocodile with a head over 60 cm long. Its bladed, knife-edged teeth would have made short work of almost any prey animal it came across. One exception would have been the Desmatosuchus. This was another somewhat crocodile-like reptile, but with peg-like teeth for eating plants and an upturned, pig-like snout. Desmatosuchus was covered in bony armor plates, so any Heptasuchus foolish enough to bite one would have just ended up with broken teeth.
So, what modern habitats provide a good analog for the world of the Wyoming Triassic? Near the watercourses, there would have been strips of seasonally dry, open canopy forest, much like the tropical dry forests of East India. The Chugwater hasn’t produced much in the way of plant fossils, but contemporary fossil floras from the Petrified Forest in Arizona suggest that there would have been star ferns, seed ferns, conifers, and plants related to modern horsetails and cycads.
What about the arid lands far away from the watercourses? In these areas, there would have been no plants, no animals, no streams – just acres and acres of dry red rock, red sand and red dust stretching from one horizon to the other. In other words, just about exactly like the planet Mars!
As impressive as Buettneria was, it wasn’t the undisputed king of Triassic Wyoming. That title goes to Heptasuchus, a terrestrial reptile a bit like a long-legged crocodile with a head over 60 centimeters long.