Crocodilians of the Calvert Cliffs

[Miocene_Mason]

Hello Everyone!
Seems to be a good bit of interest in this topic, so I thought I’d make a little summary on what types of crocodilians you may find along the Calvert cliffs. Most of this information is gleaned from Dr. Robert Weems’ “Crocodilians of the Calvert Cliffs” in Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA, available freely by clicking the underlined portion. I encourage you to read that for more detail. If you have anything to add or you notice any mistakes, please let me know!

 

Thecachampsa

This genus is the only described genus along the cliffs, of which two species are described in this area. Among extant (living) creatures, it is most closely related to the false gharial. All large non-shark coprolites along the cliffs are assumed to be produced by Thecachampsa. Their vertebrae, like all reptile vertebrae, have a convex side and a concave side, making their vertebrae look like they have a ball and a socket. Their osteoderms are distinctive, with thick, blunt sections between the pits. 
 

Osteoderm associated with T. sericodon, from “Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA”

[Miocene_Mason]

T. sericodon versus T. antiquus

These two species are similar in many respects, but differ slightly both cranially and postcranially. For the purposes of this thread I will focus on teeth and context. T. antiquus teeth are much more robust with round, squat, crushing teeth and thick textured roots. T. sericodon is much more gracile by contrast, with generally thinner, piercing teeth which come with correspondingly slender and smoother roots. In addition to these differences, they also tend to occur in different strata. Below is a chart which shows where both have been found. The asterisk is T. antiquus and the crosses T. sericodon. 

 

 

 

[Miocene_Mason]

Them compared

T. sericodon examples

T. antiquus example

 

All of the above figures from “Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA”

[Miocene_Mason]

Undescribed Genus

This species is known only from the Pollock farm in Delaware, which was a Calvert formation site. It’s known from three osteoderms, one pictured below. It differs from the more robust Thecachampsa osteoderms in size and texture. It shows some similarities with a Miocene alligator species (Alligator olseni),  but the wide range of variations amongst many crocodilians makes this ID extremely tentative. Here’s the scute, and what Dr. Weems had to say. That’s a wrap for me, hope you’ve enjoyed!

USNM 540749 photo from the Smithsonian Paleobiological Database

[Miocene_Mason]

Excerpt from “Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA”

[Miocene_Mason]

@Ash here’s a more complete description of the unknown genus.

[Crocophile]

WhodamanHD, the item pictured does not resemble any crocodilian osteoderm I've ever seen in my experience working with living crocodilians and (more limited) with crocodylomorph fossils. It looks more like a turtle carapace fragment or specimen from another animal, perhaps skin of a dino.

 

Crocs have a "pitted" texture rather than the "bubbled" texture of this piece.

 

That's just my two cents.

[Miocene_Mason]

49 minutes ago, Crocophile said:

Crocs have a "pitted" texture rather than the "bubbled" texture of this piece.

The circles are concave and not convex if that’s what you mean, though the pictures can play tricks on the eye. The first one was found in association with Thecachampsa sericodon remains. The second one is one of two of its type and was IDed by Dr. Weems (a local expert in ancient Cenozoic reptiles. He identified and described many fossil turtles from this area, I doubt he would have misidentified it. Non-avian dinosaurs had been extinct for 50ish million years when these layers were deposited.
 

You can call me Mason

[Crocophile]

Understood. Thanks, Mason.