Author: Arthur Crichton
Crichton, Arthur, 2025 Pwerte Marnte Marnte: Characterising an Oligocene Vertebrate Fauna of Central Australia, Flinders University, College of Science and Engineering
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The terrestrial vertebrate fauna of Australia is unique, but our view of how this came to be is markedly incomplete due to large gaps in the Cenozoic (66 Ma to present) fossil record. In particular, the evolutionary origins of the marsupial groups are obscured by a 30-Myr gap, from the early Eocene to the late Oligocene (c. 55–25 Ma). Any land-mammal-bearing site from Australia that may fall within this window is therefore of considerable interest for evolutionary and biochronological understanding. It has been suggested that one fairly recently discovered mammal-bearing deposit, near Pwerte Marnte Marnte in the southern Northern Territory, may be the oldest known from the Oligocene strata of Australia, possibly representative of an as-yet-unnamed land mammal age. The primary aims of this thesis were to determine the diversity and relative age of Pwerte Marnte Marnte assemblage, to better characterise terrestrial vertebrate diversity from the earlier part of the Oligocene fossil record of Australia. To achieve this, over two tonnes of fossiliferous conglomerate was processed during 2020–2024, yielding over 600 identifiable vertebrate fossils. Systematic assessment of this material allowed at least 35 vertebrate taxa to be recognised (21–22 marsupials, 10 birds and 4–5 reptiles), tripling the number reported in a preliminary assessment, and making the Pwerte Marnte Marnte assemblage among the most diverse Australian faunas of nominally late-Oligocene age. Giant flightless birds predominate, both in body size and relative abundance. Large-bodied marsupials are represented primarily by archaic herbivores of the suborder Vombatiformes: i.e., ilariids, mukupirnids, ?wynyardiids and phascolarctids. Kangaroos are represented by four small-bodied hypsiprymnodontid-like forms. Diprotodontoids are rare and balbarid kangaroos are absent. The predatory guild comprises two species of crocodylian, a madtsoiid, a raptor, and diminutive species of thylacinid and thylacoleonid. In this thesis, six demonstrably new diprotodontian marsupials are described: an ektopodontid, mukupirnid, ?phascolarctid, ilariid, ?wynyardiid, and ?petauroid. The former four taxa were the focus of targeted phylogenetic and palaeoecological investigations. Palaeoecological reconstructions based on inferred habitat preferences suggests a well-wooded palaeoenvironment at Pwerte Marnte Marnte.
To standardise the Australian Land mammal age scheme with those of other continents, assemblages nominally ascribed to the late Oligocene through Late Miocene were biochronologically categorised into a genus-level timescale. The Pwerte Marnte Marnte assemblage is resolved within the Etadunnan(G). Whether it is the oldest of Etadunnan(G) assemblages remains to be confirmed, though several lines of faunal evidence corroborate this hypothesis. Regardless, the substantial increase in marsupial diversity afforded by the assemblage accentuates the scale of latest Oligocene turnover that defines the Etadunnan(G)–Wipajirian(G) boundary (24.7–24.5 Ma under current age schemes). Turnover is greatest among terrestrial marsupial herbivores (vombatomorphians and macropodoids). We suggest that nominally late-Oligocene-age Wipajirian(G) assemblages may sit closer to the Oligocene–Miocene boundary or within the earliest Miocene, and that this latest Oligocene turnover may have been caused by a reduction in water availability.
Keywords: Pwerte Marnte Marnte, late Oligocene, palaeontology, marsupials, Vombatomorphia, Vombatiformes, fossil, biochronology
Subject: Archaeology thesis
Thesis type: Doctor of Philosophy
Completed: 2025
School: College of Science and Engineering
Supervisor: Gavin Prideaux