An unusual turtle fauna from Lightning Ridge, New South Wales (Albian) reveals that Australian turtles had a more extensive Mesozoic history than previously indicated. Reevaluation of several primitive groups provides novel information on turtle evolution in the southern hemisphere. Seven turtle taxa are identified at Lightning Ridge. Two are Testudines indet. and two indeterminate chelid groups are evinced by isolated elements. Three new taxa are assigned to the new family Spoochelyidae in the superfamily Meiolanoidea. Spoochelys ormondea n. fam., gen. et sp., Sunflashemys bartondracketti n. gen. et sp. and Opalania baagiwayamba n. gen. et sp. are predominantly land-living turtles with high-domed shells and short manus and pes. The sister-group relationship with the Meiolaniidae, supported by a suite of cranial and postcranial synapomorphies, increases the stratigraphic range of the horned turtles by around ~ 50 my. Primitive structures in Spoochelys (postparietal, supratemporal and interpterygoid vacuity), occur with derived features that are variably developed across Triassic and Jurassic turtles. Phylogenetic analysis precariously resolves the meiolanoids as sister group to a clade containing Palaeochersis and Proterochersis. Limited pleurodiran attributes suggest that meiolanoids may be pleurodiromorphs, closer to primitive pleurodires than to cryptodires. As basal side-necked turtles, the Lightning Ridge meiolanoids permit first insights into cranial and postcranial progressions in pleurodiran stem taxa. Evidence of diverse meiolanoids in Early Cretaceous Australia and ancient radiations of meiolanoid-like turtles in southern Pangea, suggest that the horned turtles are a Triassic group and that the dichotomy between Pleurodira and Cryptodira occurred well before the Late Triassic. Early Cretaceous chelids at Lightning Ridge occur at higher palaeolatitude than in South America. The temporal range of Australian chelids is extended by ~ 50 my, demonstrating that chelids had a Jurassic history in Australia, with broad diversifications across the polar supercontinent. The palaeoecological setting of Lightning Ridge is comprehensively described for the first time. Diverse invertebrates and vertebrates include terrestrial, freshwater aquatic and rare marine forms that are anomalous at this near-polar palaeolatitude (~65-70oS). The anachronistic occurrence in Early Cretaceous Australia of distinctive radiations of Triassic-type turtles, and other relic groups, implies prolonged intervals of biogeographic isolation in the eastern provinces of Pangea.
| Identifer | oai:union.ndltd.org:ADTP/272522 |
| Date | January 2009 |
| Creators | Smith, Elizabeth T, Biological, Earth & Environmental Sciences, Faculty of Science, UNSW |
| Publisher | Awarded By:University of New South Wales. Biological, Earth & Environmental Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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