Umoonasaurus

Umoonasaurus is an extinct genus of plesiosaur belonging to the family Leptocleididae. This genus lived approximately 115 million years ago during the Early Cretaceous period (Aptian-Albian stages), in shallow seas covering parts of what is now Australia. It was a relatively small animal around long. An identifying trait of Umoonasaurus is the presence of three crest-ridges on its skull.

==Discovery and naming== The holotype of Umoonasaurus demoscyllus is AM F99374 (nicknamed "Eric"), representing the most complete opalized fossil of a vertebrate known. Discovered by the local miners of the Zorba Extension Opal Field near the town of Coober Pedy, the chairman of the company Comrealty ("Mr. Sid Londish") bought the specimen in 1988, and later agreed to donate it to the Australian Museum where it was prepared during September of the same year. Other specimens have also been referred to this species. SAM P2381, discovered in the Andamooka opal fields, is another opalized specimen. SAM 31050 was discovered in the Curdimurka area near Lake Eyre, and SAM P410550, a juvenile specimen, comes from the Neales River region, near the town of Oodnadatta. Another juvenile specimen, SAM P15980, was later referred to this species. All known specimens come from the Bulldog Shale in South Australia, although material very similar to Umoonasaurus has been found in the Darwin Formation in the Northern Territory.