July 11, 2006—Meet Umoonasaurus. About the size of a sea lion, the ancient marine reptile swam the shallow waters of an inland sea that covered Australia about 115 million years ago.
Distinguished by its relatively small size and three crestlike ridges on its skull, Umoonasaurus belonged to a group of ancient meat-eating marine animals known as plesiosaurs.
"The classic analogy for a plesiosaur is a snake threaded through the body of a turtle," said Benjamin Kear, a paleontologist at the University of Adelaide and the South Australian Museum.
"Imagine a sort of compact body with four flippers, a reasonably long neck, and a tail about half [as long] coming out the other end."
Kear and his colleagues identified the new species based on fossils of 30 individuals—including seven partial skeletons—found in old collections and recent excavations.
"The beauty of a lot of the Umoonasaurus material is that it comes out of opal mines," Kear said.
"You can imagine that these are quite spectacular-looking fossils, bright blue or green. You end up with this totally opalized skeleton."
The team named their archaic reptile swimmer after Umoona, the Aboriginal name for the South Australia region where the most complete Umoonasaurus skeleton was found—with a gut full of small fish.
A study describing the species appears in the latest online edition of the journal Biology Letters.