Umoonasaurus  Umoonasaurus is an extinct genus of plesiosaur belonging to the family Leptocleididae. This genus lived approximately 115 million years ago (Aptian-Albian) in shallow seas covering parts of what is now Australia. It was a relatively small animal around 2.5 m (8 ft) long. An identifying trait of "Umoonasaurus" is three crest-ridges on its skull. The holotype of "Umoonasaurus demoscyllus" is AM F99374 is an opalized skeleton that has been nicknamed "Eric". It was discovered in the Zorba Extension Opal Field near the town of Coober Pedy, and is very well preserved, representing the most complete opalized fossil of a vertebrate known. 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 also 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. The generic name is a combination of the Antakirinja name for the Coober Pedy region, "Umoona", and the Greek word "sauros", meaning "lizard." The specific name comes from the Greek words and , meaning "of the people" and "sea monster," respectively. The specific name refers to the public donations given to acquire the holotype. "Umoonasaurus" is a small plesiosaur, a four-flippered marine reptile. The holotype is estimated to have been long, while the juvenile specimen SAM P15980 was only long at maximum. "Umoonasaurus" is unusual in possessing a combination of primitive and derived characters. "Umoonasaurus" had a small, triangular skull with a length of and a width of . A tall, narrow crest is present along the middle of the anterior end of the skull. Two other ridges are present above the orbits. The premaxilla bears a dental rosette with five tooth sockets. These would have held long, sharp teeth.