An Ichthyosaur Jaw Bone

a fossilized jawbone and tooth of an ichthyosaur
(Natural History Museum of Utah)

During the Triassic, Jurassic, and Cretaceous periods, when dinosaurs reigned on land, sea reptiles like ichthyosaurs lived in the ocean. This is a Shonisaurus popularis fossil collected from Berlin Ichthyosaur State Park in Nevada. Fossils like this one helped scientists learn about ichthyosaur parenting behavior, including evidence that ichthyosaur mothers congregated in specific nursery habitats to birth and rear their young.