Monday, April 1, 2024

Dinosaur Tracks Found in Excavated Rocks Near Herrontown Woods

In 2023, the development of a woodlot at the corner of Van Dyke and Snowden Lane was finally begun. As heavy equipment graded the site, excavations of underlying sedimentary rock yielded a giant pile of rocks that sat for months near the road. One day, Lisa Boulanger, a Herrontown Woods neighbor with an interest in dinosaurs and geology, took a closer look at the rocks, and found several fossils, including a dinosaur footprint.

Here is her description of what she found, sent to me in an email in June. The upper Triassic is a geologic periodic that ended 200 million years ago. She said that fossils were also found in a similar excavation for the Princeton University library years ago. 
"Attached are some photos of rocks from the Prentice Woods construction site on Snowden Lane, near Herrontown Woods. Excavation for basements exposed part of the Newark Supergroup, the Passaic formation, that is from the upper Triassic. (Interestingly the same Newark formation cuts right through the center of CT, where I grew up, so the rocks are very familiar-looking.)

I split one slab and got the positive and negative of what may be a partial print from some kind of vertebrate, but it's not well-preserved enough to tell what.

I knew they were hitting some layers that had been ancient shoreline, because I found shoreline ripples in the stone.

There are also many big slabs of fossilized mud with dessication cracks, another good sign of areas that were inundated and then dried.

I found one invertebrate track, a type called Cruziana.

And then finally I found one clear print, most likely a rear foot ("pes"; the front feet are "manus"), possibly from an Atreipes.

(Of note, both Cruziana and Atreipes are what the tracks are called - it's not the name of an animal.) I just went back to the site today, and the track has been damaged, so probably not worth trying to haul it out. This rock doesn't weather well once exposed, it tends to crumble. (Note footprint to the left of the sticks on the rock in the photo below.)"

The huge pile of rocks is now gone, but we are very grateful to Lisa for sharing this photographic record of the ancient history that lay just a few feet beneath the ground near Herrontown Woods.