This is the “Fossil Friday” post #285.  Expect this to be a somewhat regular feature of the website.  We will post any fossil pictures you send in to esconi.info@gmail.com.  Please include a short description or story.  Check the #FossilFriday Bluesky/Twitter hash tag for contributions from around the world!

---

We have a beautiful Palaeoxyris lewisi shark egg case from Mazon Creek for this week’s Fossil Friday. These egg cases are believed to have been produced by hybodont sharks.  P. lewisi was named by Jiri Zidek in 1976 in “A New Shark Egg Capsule from the Pennsylvanian of Oklahoma, and Remarks on the Chondrichthyan Egg Capsules”. 

Originally, Palaeoxyris was believed to be a plant part, maybe a seed pod.  The name palaeoxyris comes from the the flowering plant genus Xyris, which grows in swampy environments in the tropics and subtropics. For more information, see Jack Wittry’s guide on the Field Museum’s website. 

This specimen was sent in by Jeremy Zimmerman, who is one of our Field Trip chairmen. Thanks for sharing, Jeremy!