Poebrotherium sp. jaw section from the Brule formation

Back during the Oligocene period there were lots of weird mammals running around that would evetually evolve into the modern forms we know today. One of these was Poebrotherium sp. which roamed the plains of the upper Midwest US. It's remains are found in the Brule formation which is a sub-unit of the famous White River formation.  Poebrotherium sp. was about the size of sheep but was more closely related to camels and llamas. According to Wikipedia, Poebrotherium sp. was a grass eater and was the equivalent of the modern gazelle or deer. The specimen below was one that I purchased primarily for the color of the jaw bone which looks like a nice piece of marble.

The Brule formation is a sub unit within the White River formation and was deposited roughly 32 mya during the Oligocene (Rupelian stage). This specimen was found on private land in Nebraska.

Rhynchosauroides sp. swim traces from the Newark Supergroup

Today I have a fossil trackway to show you. This is more properly called an Ichnofossil as the body of the animal is not present. On this piece of shale are what appear to be scratch marks. I lost the original tag that came with the specimen but I recall that they were traces from swimming. An inquiry to the Fossil Forum website and the hive mind came up with Rhynchosauroides sp. as the name of the traces.  These represent a primitive reptile that was swimming in a pond or pool near a river. The creature floated in the water but it was shallow enough that it's claws grazed the sediment below and left traces. The pond may have been temporary and subject to frequent flooding as the substrate was firm enough to preserve the initial traces before they washed away, and then get buried with a new layer of sediment.   As I mentioned before, I lost the original tag but I believe this was Triassic aged and came from the rocks of the Newark Supergroup in Pennsylvania.  These rocks were originally laid down in a rift valley as the super continent Pangea was breaking up.

Edestus heinrichi tooth and jaw section from Illinois

Below are pictures of a rare shark tooth and jaw section from a bizarre shark called Edestus heinrichi. It was called the "Scissor tooth" shark because reconstructions of it have long jaws sticking out from the face of the shark with teeth lining them. Envision them like a large pair of pinking shears on the body of a shark where the mouth would be. The jaws of these odd group of fish never shed their teeth and just continued to grow outward. Each tooth was rooted in a chunk of cartilage and would stack on the previous piece of cartilage. In this way the shark had a mouth full of teeth at all times.

Edestus was related to a group of sharks that have modern representatives in the Ratfish (Chimaera) and are better represented by the whorl tooth possessing Helicoprion. Both Edestus and Helicoprion lived during the end of the Carboniferous period (upper Pennsylvanian stage). The fossil below was among many found by coal miners in Illinois. Why was it found in a coal mine when it was shark that lived in water? Edestus lived and died in brackish waters in between growth of the coal swamps. As the coal was removed in the mine these non coal bearing rocks were exposed with some of them being marine in origin.

The specimen I own has just a single tooth in a piece of the jaw. There are some terrific examples of more complete jaw sections on the web like this group of pictures from the Illinois state Museum.  This thread on the Fossil Forum has pictures of some nice specimens in other people's collections.