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Fossil Friday

It has been a strange week, what with trying to catch up from the holidays and all. So this post will be brief. On Monday, I posted this picture of a commonly found fossil in Arkansas, provided you look in the right places. Here were the clues.exogyra

Clue 1: It’s from the Cretaceous.

Clue 2: It’s modern day relatives are widely considered a delicacy.

Clue 3: This is no wilting lily. This creature is big and bold. It shows how twisted it is on the outside for all the world to see. Dude, that’s heavy.

Were you able to figure it out?

So for the final reveal:  Exogyra ponderosa. Allie Valtakis was able to figure out it was a mollusc, specifically a bivalve (clam), in the Order Ostreoida, Family Gryphaeidae. While mosasaurs swam the oceans and dinosaurs walked the shores, these Late Cretaceous oysters made huge oyster beds throughout the coastal waters. Like all oysters, they were filter-feeders, collecting microscopic particles of food from the water. You can find them in south-central Arkansas within several rock units, but most particularly in the Marlbrook Marl, a limy mudstone. They are known for their large, heavy, rough bottom shell with a curled, hornlike part near the hinge. The top shell is much smaller and flatter, but still a good size, something like a cap on a coffee cup, if your coffee cup was kind of bowl-shaped. They are sometimes called Devil’s toenails, but that name usually refers to a different clam called Gryphaea, an oyster that is also in the Family Gryphaeidae, but a different subfamily. If you look under a microscope at the shell, you may notice that it is very porous, giving the Family the nickname of foam or honeycomb oysters.  Some are still alive today, such as Hyotissa hyotis, the giant honeycomb oyster

E. ponderosa was one of the earliest clams of this genus that was named, by Ferdinand Roemer in 1852, a German lawyer who gave up law to study geology in Texas, thus his title as the Father of the Geology of Texas.  You can fossils of them from Texas to New Jersey and Delaware, south through Mexico and Peru.

Until next time, as Dr. Scott The Paleontologist would say, ‘Get out there, get into nature, and make your own discoveries.”

1 Comment

  1. […] part of the state, the easiest to find on the basis of quantity and size I think has to go to Exogyra ponderosa. These are Cretaceous aged oysters known for their thick shells adorned with a curled hornlike […]

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