Notes from the field: Finding fossils in the Triassic rocks of Wyoming

From @VT Research

JULY 31, 2017 | Over the past week, the VT Paleobiology group, led by Drs. Michelle Stocker and Sterling Nesbitt, headed out to Wyoming to find fossil bones from the Triassic (~199 to 252 million years ago) as a part of a month-long expedition to do field work across the Midwest. The area around Lander Wyoming is home to several exposures of Triassic sedimentary rocks, exactly the kind of place you want to look to find vertebrate fossils from that time. We spent the week prospecting several localities and weren’t disappointed!

The main focus of the trip has been to uncover a large (~8 foot long) fossil phytosaur that was found in 2015 on a previous expedition. These creatures looked superficially like crocodiles but are distantly related. They had armor plating all over their bodies and long snouts filled to the brim with sharp, serrated teeth. The fossil in question lies on a ridge of exposed sedimentary rock that happens to be incredibly difficult to reach. The hike is roughly a mile from start to finish and the elevation change is over 1000 feet. We had to haul tools, personal supplies, and eventually fossils up and down this path twice a day for 6 days!

The first day on site was mostly spent scoping out the area around the phytosaur fossil which had been capped (coated in plaster and burlap to protect it) and buried at the end of the 2015 expedition. The goal for this day was to prospect for new fossils and new sites in the Chugwater formation, the formation that contains the phytosaur skeleton. We found lots of phytosaur teeth and some small fragments of miscellaneous bone from the first site that was located in 2015 but nothing new.

On the way back from the quarry, we found the bones of a horse that had died shortly before the 2015 expedition. The 2015 team dubbed it DH (dead horse) and left it to skeletonize in the desert. Two years in the elements has certainly done the trick! We collected the skull and lower jaw, the sacrum (fused pelvic vertebrae), half of the pelvis, and some of the limb bones for use as a reference in the paleobiology lab at Tech.

The first hike was a challenge but by the next day we were getting the hang of it. We arrived on site a little earlier and were able to do some more thorough prospecting in a larger area around the phytosaur fossil. A few of us found several large fossil amphibian bones in a productive layer of purplish rock near the phytosaur! These amphibians, called metoposaurids, were enormous, reaching lengths up to 6 feet. In addition to prospecting, we were able to uncover the phytosaur and begin working on excavating it further.

The team at work building plaster jackets around different parts of the phytosaur skeleton.

We spent the whole rest of the week excavating the phytosaur but it just keeps getting bigger! There’s no sign of it ending so we couldn’t get it out this trip but hey, plans change. After capping what we uncovered, the whole fossil was then buried just like last time. It’s too big to move at this point and still well encased in rock. We’ll have to come back next year!

We finished off our stay in Wyoming with some prospecting at different sites down the road from the phytosaur locality. We ended up finding a crazy new locality that’s just overflowing with fossil bones! This could be another place to quarry in the future.

Story by Alex Bradley.

 

Follow along as Paleobiogists Sterling Nesbitt and Michelle Stocker dig for dinosaurs in Summer 2017

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