A pregnant ichthyosaur that died about 180 million years ago still has the remains of between six and eight of its small embryos within its ribs.
Ichthyosaurs are dolphin-like reptiles that lived during the Early Jurassic. They are often mistaken as aquatic dinosaurs but appeared before the first dinosaurs evolved. These aquatic reptiles gave birth to live young instead of laying eggs. They fed on other reptiles, fish, and marine invertebrate.
Although fossils of these prehistoric creatures are quite commonly found in the United Kingdom, only five specimens from Britain have so far been found with embryos.
The new specimen was collected about eight years ago from near Whitby in North Yorkshire, England. The specimen currently has the most number of embryos among embryo-bearing ichthyosaurs. It is also the first time that reptilian embryos from the Jurassic period were found in Yorkshire.
Youngest Of British Embryo-bearing Ichthyosaur Specimens
The specimen is also the youngest of British embryo-bearing specimens. Others that were found in England are estimated to be between 200 and 190 million years old. The Whitby specimen hails from the Toarcian Stage of the Jurassic, which means it is around 180 million-year-old.
"It represents the geologically-youngest occurrence of ichthyosaur embryos thus far recorded from the UK and the first such occurrence to be reported from Yorkshire," University of Manchester researchers Dean Lomax and Mike Boyd reported in the Proceedings of the Yorkshire Geological Society on April 4.
Six To Eight Embryos
The researchers said that they have considered the idea of the tiny remains as stomach contents. It is unlikely, however, that the creature would swallow between six and eight newborn or aborted ichthyosaurs all at the same time.
The embryos do not also show erosions from the stomach acids and are neither associated with stomach contents commonly found in ichthyosaurs that lived in the Early Jurassic.
The specimen, a small boulder that was cut in half and polished, is featured at the Yorkshire's Jurassic World. Its display incorporates a technology that reveals the embryos and explains the significance of the discovery.
The discoveries of ichthyosaur fossils help shed light on what happened in prehistory. A 2016 study of an early species of ichthyosaur called Sclerocormus parviceps, for instance, showed that evolution after the worst mass extinction event that wiped out 96 percent of marine species occurred fast.
Researchers found that the ichthyosaurs and their relatives rapidly evolved and diversified within the first million years of their evolution during the early Triassic.