Early and Middle Pleistocene non-passerine bird fossils from the Thylacoleo Caves, Nullarbor Plain

Author: Elen Shute

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Shute, Elen, 2019 Early and Middle Pleistocene non-passerine bird fossils from the Thylacoleo Caves, Nullarbor Plain, Flinders University, College of Science and Engineering

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Studying the fossil record of the Pleistocene epoch (2.58 million years ago to 11,700 years ago) is key to understanding how modern ecosystems developed. The dramatic climate fluctuations of the Pleistocene have long been viewed as a major force that shaped the Australian avifauna, driving the evolution of species and sub-species of birds, and creating the distinctive regional bird assemblages seen today. Despite this, very little fossil evidence illuminates either the diversity or distribution of birds across the continent for most of the Pleistocene, and the overall effects of the Pleistocene on the Australian avifauna are difficult to assess.

The research presented here is the first study of a diverse Australian fossil landbird assemblage spanning both the Early and Middle Pleistocene, time intervals that are particularly poorly represented in the Australian fossil record. The fossils examined here come from the Thylacoleo Caves, beneath the Nullarbor Plain, Western Australia – a location of particular interest for understanding the Pleistocene ecology of southern Australia. Today, the Nullarbor is a vast, arid, treeless habitat covered by chenopod shrubs, and is noted for its low bird diversity. It is considered a major arid-habitat barrier that separates and isolates many animal taxa in the moister south-west and south-east of the continent. It has generally been inferred that the Nullarbor Plain lost its tree canopy during the Pleistocene due to increasing aridity, but the timing and processes of this transition are unclear.

Nearly 60 species of non-passerine bird were identified within the Thylacoleo Caves fossil assemblage, more than any other Australian locality of similar age. Up to 14 extinct species were identified, roughly one quarter of the total non-passerine fossil assemblage – more extinct Pleistocene species than have previously been described from the rest of the continent. The Australian avifauna may have been affected by higher rates of extinction during the Pleistocene than previously suspected. Four extinct species from the Thylacoleo Caves are formally described herein. Two of these, ground-dwelling coucals in the genus Centropus, are the world’s two largest-known cuckoo species. Two extinct megapodes, both larger than their living relatives, are also described, along with fossil megapodes from other Australian localities.

The composition of the fossil avifauna is assessed, and is used to reconstruct the Pleistocene palaeoecology of the Nullarbor Plain. The Early Pleistocene assemblage was found to contain high woodland species diversity, and includes the majority of the extinct taxa. Presence of numerous wetland taxa, including rails, charadriiforms, a duck and a stork, indicate periodic inundation, even if conditions were generally relatively arid. By contrast, the Middle Pleistocene assemblage has low diversity, includes few woodland taxa, and comprises mainly species that prefer open arid habitat similar to that of the Nullarbor Plain today. Few extinct species are present, suggesting that a majority of extinctions may have occurred between the Early and Middle Pleistocene in response to aridity-induced habitat loss.

Keywords: fossil birds, ornithology, palaeontology, palaeornithology, Pleistocene, Nullarbor, Australia

Subject: Biology thesis

Thesis type: Doctor of Philosophy
Completed: 2019
School: College of Science and Engineering
Supervisor: Professor Gavin Prideaux