Chelid Turtles (Pleurodira, Chelidae) from the Miocene Camfield Beds, Northern Territory of Australia, with a Description of a New Genus and Species

Abstract

The Bullock Creek Local Fauna (mid Miocene Camfield Beds, Northern Territory of Australia) contains five or possibly six species of chelid turtles (Pleurodira: Chelidae), though only one form is sufficiently represented to be named. Birlimarr gaffneyi gen. et sp. nov. is a small (carapace length: 160 mm), shortnecked species represented by a complete skeleton. A phylogenetic analysis of cranial and shell characters resolves the new genus as quite derived amongst Australian short-necked chelids, the plesiomorphic sister taxon to a clade composed of Emydura plus an Elseya dentata 'generic group'. Three other forms are diagnosed on shell material to genus or suprageneric level: a large (carapace length ca. 440 mm) shortnecked form is designated gen. aff. Emydura/Elseya sp. indet. and two long-necked forms are designated Chelodina sp. A and sp. B. Additional shell material indicates a fifth and possibly a sixth chelid species is present in the assemblage, but the lower level affinities of these forms cannot be determined. The Emydura/Elseya form is similar but not identical to previously described 'Emydura ' material from the Miocene of South Australia (Wipajiri and Namba Formations), while a previously described carapace from the Miocene of western Queensland (Carl Creek Limestone) may represent a species of Birlimarr gen. nov. The Carl Creek Limestone and Camfield Beds assemblages are similarly diverse, approximating the maximum sympatric diversity recorded in extant assemblages: palaeoenvironmental conditions at these two Miocene localities thus appear to have been optimal for chelid diversity. Many of the Camfield Beds specimens show evidence of predation by crocodiles.