Terrestrial and freshwater turtles of early cretaceous Australia

An unusual turtle fauna from Lightning Ridge, New South Wales (Albian)reveals that Australian turtles had a more extensive Mesozoic history thanpreviously indicated. Reevaluation of several primitive groups provides novelinformation on turtle evolution in the southern hemisphere.Seven turtle taxa are identified at Lightning Ridge. Two are Testudines indet. andtwo indeterminate chelid groups are evinced by isolated elements. Three newtaxa are assigned to the new family Spoochelyidae in the superfamilyMeiolanoidea.Spoochelys ormondea n. fam., gen. et sp., Sunflashemys bartondracketti n. gen.et sp. and Opalania baagiwayamba n. gen. et sp. are predominantly land-livingturtles with high-domed shells and short manus and pes. The sister-grouprelationship with the Meiolaniidae, supported by a suite of cranial and postcranialsynapomorphies, increases the stratigraphic range of the horned turtles by around~ 50 my. Primitive structures in Spoochelys (postparietal, supratemporal andinterpterygoid vacuity), occur with derived features that are variably developedacross Triassic and Jurassic turtles.Phylogenetic analysis precariously resolves the meiolanoids as sister group to aclade containing Palaeochersis and Proterochersis. Limited pleurodiranattributes suggest that meiolanoids may be pleurodiromorphs, closer to primitivepleurodires than to cryptodires. As basal ‘side-necked’ turtles, the LightningRidge meiolanoids permit first insights into cranial and postcranial progressionsin pleurodiran stem taxa. Evidence of diverse meiolanoids in Early CretaceousAustralia and ancient radiations of meiolanoid-like turtles in southern Pangea,suggest that the horned turtles are a Triassic group and that the dichotomybetween Pleurodira and Cryptodira occurred well before the Late Triassic.Early Cretaceous chelids at Lightning Ridge occur at higher palaeolatitude thanin South America. The temporal range of Australian chelids is extended by ~ 50my, demonstrating that chelids had a Jurassic history in Australia, with broaddiversifications across the polar supercontinent.The palaeoecological setting of Lightning Ridge is comprehensively describedfor the first time. Diverse invertebrates and vertebrates include terrestrial,freshwater aquatic and rare marine forms that are anomalous at this near-polarpalaeolatitude (~65-70oS). The anachronistic occurrence in Early CretaceousAustralia of distinctive radiations of ‘Triassic-type’ turtles, and other relicgroups, implies prolonged intervals of biogeographic isolation in the easternprovinces of Pangea