New Mexico Museum of Natural History and Science

Ammonites nearly went extinct at the end of the Triassic. Only one genus survived into the Jurassic, giving rise to the diversity of ammonites that swam the Jurassic and Cretaceous seas. Triassic ammonites were diverse and most had complex shell shapes and ornamentation, unlike the smooth-shelled ammonite (Psiloceras) that survived the extinction.

Ammonite fossils collected and donated by Jim Jenks

Photos taken by David Baccadutre

Ammonite illustration by Mary Sundstrom