All about fossils: Brachychampsa or Leidyosuchus?

I got this crocodile jaw from Judith River formation in Montana, which means it is about 80 million years old (late Cretaceous age). But we did not know what crocodile species it belonged to. I did some research.

I compared the teeth in the jaw to a black crocodile tooth I found on fossil beach in Maryland. They were the same size! Conclusion: crocodiles they came from were the same size! The tooth from Maryland is on the left in the photo below:

I measured the jaw piece. It was 7cm (a bit shorter than 3 inches). I compared it to the jaw size of 3 crocodiles/alligators found in Judith River formation. They were: Deinosuchus, Leidyosuchus, and Brachychampsa.

According to my research, if my jaw piece came from Deinosuchus, it would have been almost ONE FOOT long! So, it definitely was not from Deinosuchus. Those crocodiles were almost 40 feet long, and ate large dinosaurs and sea turtles. What a pity!!! I wish my jaw piece was from the giant and scary Deinosuchus.

So, the jaw piece came from Leidyosuchus or Brachychampsa, which were about the same size of about 2m (6-7 feet). But which one?????

We looked closer at the jaw piece. I noticed that something was not right. The jaw had a strange dent on the side, with smooth bone instead of rough surface where the bones were broken. So, that dent must be the turn/shape of the jaw.

I also noticed that on the other side, there was another dent, also with smooth surface. What could it be?

I looked at the jaws of the two crocodiles more closely.

BINGO! This piece came from front part of the upper jaw, and the second dent is the….. NOSTRIL!

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Brachychampsa’s jaw looks like an arch, it does not have dents. Brachychampsa’s teeth are about the same size and around the same distance from each other. But my jaw piece had teeth of different sizes and in groups of 3 and 2 teeth, with a space in between. It also had a turn (the first dent). That seemed like the place in Leydyosuchus’ jaw where the lower teeth come out on top. It makes the jaw look a bit like number 8.

CONCLUSION: this is definitely a piece of jaw from a Leidyosuhus.

See how well it fits the picture of the real Leidyosuchus jaw from a museum:

Here are some other crocodilian fossils that I found on the beach in Maryland (Potomac river Nanjemoy formation is from middle Eocene, about 45 million years ago).