likely the temnospondyls inhabited the freshwater systems of polar Australia until the Bonarelli Event in the Middle Cretaceous around 100 mya increased temperatures and allowed neosuchians to inhabit Antarctica. These neosuchians, at an adult size of no more than in length, likely led to the extinction of the temnospondyls in tandem with more-developed ray-finned fish which perhaps targeted their larvae. The migration of neosuchians into the region suggests that average winter temperatures were greater than , with an average annual temperature of more than . However, polar neosuchians are only known from an almost complete skeleton of Isisfordia, and other neosuchian remains are of undetermined species. Plesiosaurs inhabited freshwater river and estuary systems, given the locations of their remains, probably colonizing Australia in the Early to Middle Jurassic. Their remains, mainly teeth, have been documented from southeastern Australia deriving from the Late Cretaceous, though they were never described as the remains are too sparse to do so. The teeth share some affinity with pliosaurs, notably the rhomaleosaurids and Leptocleidus, which died out in the Early Cretaceous, indicating the polar freshwater systems may have been a refuge for the pliosaurs of the Cretaceous. In contrast to modern marine reptiles, these South Polar plesiosaurs probably had a better tolerance of colder waters. Oceans Early to Middle Cretaceous marine reptile remains of South Australia include five families of plesiosaurs–Cryptoclididae, Elasmosauridae, Polycotylidae, Rhomaleosauridae, and Pliosauridae–and the ichthyosaur family Ophthalmosauridae. The discovery of several juvenile plesiosaur remains suggest they used the nutrient-rich waters of the coast as sheltered calving grounds, the cold deterring predators such as sharks. Most of the plesiosaurs discovered had a cosmopolitan distribution, however endemic forms existed there such as Opallionectes and a possible new species of cryptoclidid. A dubious species of elasmosaurid Woolungasaurus, was named in 1928, one of the earliest description of an Australian marine reptile. Several mollusc, gastropod, ammonite, bony fish, chimaerid, and squid-like belemnite remains have been recovered as well. The coastal area may have experienced winter freezing, and these reptiles, in response, may have migrated north during the winter, had a more active metabolism than tropical reptiles, have hibernated in freshwater areas much like the modern day American alligator (Alligator mississippiensis), or have been endothermic similar to modern day leatherback sea turtles (Dermochelys coriacea). The lower number of plesiosaurs and higher number of ichthyosaurs and sea turtles in more northerly areas of Australia indicates a preference for