Kear, B.P., Schroeder, N.I. & Lee, M.S.Y. (2006) An archaic crested plesiosaur in opal from the Lower Cretaceous high-latitude deposits of Australia. Proceedings of the Royal Society B: Biology Letters. FirstCite Early Online Publishing.

Abstract: \\\\\\\"_Umoonasaurus demoscyllus_ gen. et sp. nov. is a new small-bodied (approx. 2.5m) pliosauroid plesiosaur from the Lower Cretaceous (Aptian-Albian) of southern Australia. It is represented by several partial skeletons (one with a near complete skull is the most complete opalized vertebrate fossil yet known), and is unique in having large crests on the skull midline and above the orbits. _Umoonasaurus_ is surprisingly archaic despite its relatively late age (approx. 115Myr ago) - being simultaneously the most basal (primitive) and last surviving rhomaleosaurid. Notably, it lacks the ‘pliosauromorph’ features (large head, short neck, gigantism) typically characterizing many more derived Jurassic rhomaleosaurids; thus, reinforcing the suspected convergent evolution of the ‘pliosauromorph’ hypercarnivore body plan. _Umoonasaurus_ inhabited an Early Cretaceous high-latitude (approx. 70°S) inland seaway subject to seasonally near-freezing climatic conditions. This extreme environment supported a diverse range of plesiosaur taxa, suggesting that these marine reptiles might have possessed adaptations (e.g. heightened metabolic levels) to cope with cold-water temperatures. Indeed, survival of ancient endemic lineages such as _Umoonasaurus_ is a common phenomenon in Australian Cretaceous vertebrate assemblages and might have been facilitated by isolation in low-temperature high-latitude regions.\\\\\\\"

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