November 04, 2014

Digging for fossils in the Petrified Forest

By Tom Kaye

The sky was crystal clear as my wife Carol and I geared up for our first day “on expedition” at Petrified Forest National Park in northern Arizona. This trip was particularly exciting for us because Petrified Forest had recently acquired a huge new tract of land and we, along with several colleagues from the Burke Museum, were the first team going in to look for fossils!

Specifically, we were looking for fossils of huge predators from 210 million years ago during the Triassic Period. We knew that most of the fossils we found would belong to extinct groups known as aetosaurs and phytosaurs. The former sported armor plates and foot-long spikes to ward off attacks. The latter were the Triassic equivalent of crocodiles: aquatic predators that you didn’t want to mess with.

Hunting for fossils isn’t as glamorous as it’s cracked up to be. It was never less than 100 degrees on the desert floor thanks to the sun’s reflection. We wore SPF 50 sunblock made for children so it didn’t sting when the sweat runs in your eyes. We were almost never in sight of anyone else. And the best fossils are ALWAYS the farthest from the truck.

So, I hope you enjoy the pictures and know that you’re getting the best parts of the trip right here!

This is the “badlands,” appropriately named by the early settlers because nothing would grow there. However, this is prime hunting ground for fossils from long-dead animals. The dirt erodes down the hillsides oftentimes exposing fossils. This erosion causes some fossils to break up and go down the hill, so we were on the lookout for “bone trails” where we’d follow a trail to hopefully find the remainder of the skeleton sticking out of the ground. 

I found the leg bone from a phytosaur just sitting in pieces on the desert floor. This is a 215-million-year-old crocodile-like reptile. This guy was probably more than 15 feet long. 

A tooth from a phytosaur. Definitely someone you would not want to mess with!

This is the largest petrified log we saw in the park. It was probably
larger, but most of the outer layers have fallen away.

This is an "ice" rock. Not a formal name but appropriate. This happens when a crack forms in the ground and then minerals fill it in. The dirt erodes away leaving the mineral on the surface.

On first look you might think this is a fossil snake but it’s actually a fossil root!

This photo shows me crawling into a sinkhole to get some shade.
This is where the rattlesnakes hang out during the day and is not advised.

See the dark markings at an angle? They are called "cross bedded sandstones" and tell us the direction the water was flowing in the stream 215 million years ago. In this case, it flowed from right to left. Putting together many of these can help map how the rivers flowed in this area in ancient times.

A desert waterfall. It’s pretty even without water.

The GPS tracker showing where Carol and I walked through rough desert terrain over the 10 days—more than 50 miles combined! Yellow line = 1 mile. The average elevation change per day was 500 feet over hillsides completely covered with marble-sized gravel. Everyone on the team went down the hill on his or her backside at least once during this trip.

The Burke Museum team looking very happy after 10 days in the field. Front row, left to right: Dr. Christian Sidor, my friend and colleague who is the curator of vertebrate paleontology at the Burke Museum, Jackie L. starting her PhD this year and way stronger than she looks, Chuck B. working on his PhD at the Burke, and as always, they put the old people in the back.

In the end, our most exciting find was a bone bed containing fossils of a rare “dinosaur mimic” beaked reptile called a shuvosaurid. Despite walking on two legs, this animal is more closely related to crocodiles than dinosaurs! Over a two-day period we must of have collected more than a hundred pieces of small bone, not much bigger than a finger, as we scoured the desert surface. We then quarried out a large block of the bone bed for further examination.

The block of bone bed is now in the Burke’s fossil lab, where the bones can be carefully extracted under a microscope. We estimate that there are more than 100 bones in this block, so stay tuned for more fossil discoveries!


Tom Kaye is a research associate in the Burke Museum's vertebrate paleontology collections. 

Mark your calendars! Dino Day is coming up on Saturday, March 7, 2015!