New Mexico: Prehistoric Trackways

2019 March 10

The previous two postings were creatures that we found on December 4, 2018 on our way hiking to and from the Prehistoric Trackways National Monument. So, today, let’s have a look at what we found when we actually got there.

This entire part of New Mexico was evidently a section of ocean floor that, during the Permian period, was gradually elevated to a shallow, swampy sea that was ultimately cut off from the ocean. It then dried up to form the local evaporite deposits during the Triassic period. As we hiked up the dry streambed to get to the trackways site, we were starting in older seabottom sediments, with characteristic oceanic fossils like these Brachiopod shells (not really clams, but similar),


and this Ammonite (basically a type of shelled octopus),


and this sheet of what I think may be some kind of coral.


Since water runs downhill, the streambed cut up through progressively younger sediments. The first sign that we were getting into the trackways region was when we saw fossils of terrestrial plants (ferns in this case) instead of oceanic organisms.



The second sign that we were there was, of course, the actual sign. While this is a national monument, there is no visitor center or any sort of other structures. This is it.


There is also no staff or rangers, just this sign warning of dire consequences to anyone taking away or damaging anything.


There were tracks and impressions all over the place, although I suspect that the very best ones were taken away and preserved in museums rather than being left out here to weather away.

I think this first one is a dimetrodon track. The way these tracks formed, is an animal left a footprint in soft mud just before some sort of flooding event deposited a fresh layer of mud on top. Once the mud hardens into rock, it tends to break apart along the laminations between mud layers. This produces a regular “negative” footprint on the bottom part, and a “positive” cast of the footprint on the top part that is actually more the shape of the foot that made the print. I think that this one is a positive cast, which is why it sticks up from the surface instead of being a depression.


Dimetrodons were predatory animals that were distinguished by the huge fin on their backs.

Dimetrodon species2DB15.jpg
By DiBgdOwn work, CC BY-SA 4.0, Link

These other tracks were made by smaller animals, most likely amphibians similar to giant salamanders.



So, if you want to picture a shallow, tropical swamp, with a silty bottom and ferns growing up in it, being browsed by giant salamander-like things that are being preyed upon by sail-backed reptiles, then you are probably pretty close to what things looked like when these tracks were made.

Incidentally, these fossils pre-date dinosaurs. Dimetrodons and most of the big amphibians were killed in the End-Permian Mass Extinction, which was a major cataclysm of uncertain nature that happened just a few million years before the first dinosaurs evolved.

2 Responses
  1. Carole permalink
    March 10, 2019


  2. March 18, 2019

    It’s wild how many fossils you can find out there.

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