First Eocene bat from Australia
Remains of a bat, Australonycteris clarkae, gen. et sp. nov., are reported from freshwater clays radiometrically dated at 54.6 million years old in southeastern Queensland, Australia. It is the oldest bat yet recorded for the Southern Hemisphere and one of the world's oldest. Previously, the earliest records for bats came from the Northern Hemisphere and were of Sparnacian age in Europe, Wasatchian in North America, and late early Eocene in North Africa. The North American Wyonycteris chalix, originally described as a latest Paleocene bat and as such the world's oldest, is re-examined. Its lack of key bat synapomorphies and overall morphology do not support the claim that it is a bat. Early bats probably entered Australia via Asia rather than South America, although their appearance in Australia predates the final breakup of Gondwana. The Australian fossils described here (a lower molar, upper premolar, edentulous dentary fragment, and part of a periotic) may corroborate the hypothesis that modern bat groups evolved from isolated immigrant archaic bats somewhere in the Southern Hemisphere in the early Eocene.