Ichthyosaurs had a very wide geographic distribution, and their fossil remains span almost the entire.... ichthyosaur fossil

Ichthyosaurs had a very wide geographic distribution, and their fossil remains span almost the entire (about 248 million to 65 million years ago); but they were most abundant and diverse during the and (248 million to 144 million years ago). Excellent fossil specimens occur in the fine-grained Early Jurassic shales of southern Germany. Several specimens are known in which the skeletal remains of small, immature ichthyosaurs are fossilized within the bodies of larger individuals, even within the birth canal. Ichthyosaurs are first known from the Triassic Period of Asia, where they began as long-bodied, undulating swimmers without many of the specializations seen in later species. Fossils from the western United States and Canada indicate that some ichthyosaurs could exceed 13 metres (43 feet) in length. The typical ichthyosaur form was fully realized by the Early Jurassic, when the like body plan suggestive of high-speed pursuit and great mobility ass Ichthyosaurs persisted i! nto Late Cretaceous times and may have been well adapted for deep diving as well as near-shore predation, but all species became extinct well before the end of the Cretaceous Period.