Tuesday, June 9, 2009

Fossil of the week: 6/9/09

Let's talk big fish this week!

Ichthyodectid fish are amongst the most common fish found in the Niobrara chalk. The genera Prosaurodon, Saurodon, Saurocephalus, Gillicus, Ichthyodectes and the giant Xiphactinus are all found at various stratigraphic levels. Fish have very delicate skulls, however many times they are recovered articulated. It is impossible to disassemble these skulls without damaging them, so we usually prepare them in profile view. Sometimes they are disarticluated, looking like they reenacted the final scene from "Jaws 3D". These scattered skulls enable us to reassemble the pieces and take out some of the crushing distortion from 82-86 million years of burial.

The photo is of a specimen of Saurodon leanus named "Tony" that I discovered in Logan County, Kansas in October of 2006. Stratigraphically we're at about marker unit 18, so fairly high in the chalk, nearing the Pierre Shale contact. This is one of the more rare fish in the chalk, caricterized by it's long eel-like body and distinctive chin spike. As you can see, the bones of the skull have blown all apart, making this specimen a great candidate for molding and 3d reconstruction. No one is quite sure what the spike is used for, my guess is probing into the bottom muds of the western interior seaway looking for soft bodied invertebrates (such as worms) to eat. Hopefully we'll find more specimens in the future that may include stomach contents.


  1. Pretty cool fish, I didn't know that they had that weird projecting lower jaw with a spike at the end, very bizarre.

  2. We discussed that chin spike once in the Marine Reptiles Forum. The consesnus wass "I dunno, it's a weird fish". Here's the thread. http://www.plesiosaur.com/forum/index.php?topic=195.0

    Also, anone interested in the critters of the Niobrara, reptiles or not, really should consider joining and contributing.