Vertebrate palaeontology of Australasia
The presence of Dromornithidae in the Australian Cenozoic fossil record was first reported in 1872, yet although eight species and hundreds of specimens are known, key information on their morphology remains elusive. This is especially so for their skulls, which contributes to a lack of resolution regarding their relationships within Galloanserae. The skull of the Pleistocene dromornithid, Genyornis newtoni, was initially described in 1913. Additional fossils of this species have since been discovered and understanding of avian skull osteology, arthrology, and myological correlates has greatly advanced. Here we present a complete redescription of the skull of Genyornis newtoni, updating knowledge on its morphology, soft-tissue correlates, and palaeobiology. We explore the diversity within Dromornithidae and make comprehensive comparisons to fossil and extant galloanserans. Furthermore, we expand on the homologies of skull muscles, especially regarding the jaw adductors and address the conflicting and unstable placement of dromornithids within Galloanserae. Findings support generic distinction of Genyornis newtoni, and do not support the close association of Dromornithidae and Gastornithidae. We thus recommend removal of the dromornithids from the Gastornithiformes. Considering character polarities, the results of our phylogenetic analyses, and palaeogeography, our findings instead support the alternative hypotheses, of dromornithids within, or close to, the Suborder Anhimae with Anseriformes.
Diprotodontians are the morphologically and ecologically most diverse order of marsupials. However, an approximately 30-million-year gap in the Australian terrestrial vertebrate fossil record means that the first half of diprotodontian evolution is unknown. Fossil taxa from immediately either side of this gap are therefore critical for reconstructing the early evolution of the order. Here we report the likely oldest-known koala relatives (Phascolarctidae), from the late Oligocene Pwerte Marnte Marnte Local Fauna (central Australia). These include coeval species of Madakoala and Nimiokoala, as well as a new probable koala (?Phascolarctidae). The new taxon, Lumakoala blackae gen. et sp. nov., was comparable in size to the smallest-known phascolarctids, with body-mass estimates of 2.2-2.6 kg. Its bunoselenodont upper molars retain the primitive metatherian condition of a continuous centrocrista, and distinct stylar cusps B and D which lacked occlusion with the hypoconid. This structural arrangement: (1) suggests a morphocline within Phascolarctidae from bunoselenodonty to selenodonty; and (2) better clarifies the evolutionary transitions between molar morphologies within Vombatomorphia. We hypothesize that the molar form of Lumakoala blackae approximates the ancestral condition of the suborder Vombatiformes. Furthermore, it provides a plausible link between diprotodontians and the putative polydolopimorphians Chulpasia jimthorselli and Thylacotinga bartholomaii from the early Eocene Tingamarra Local Fauna (eastern Australia), which we infer as having molar morphologies consistent with stem diprotodontians.
Faunal turnover in Indo-Australia across Wallace's Line is one of the most recognizable patterns in biogeography and has catalyzed debate about the role of evolutionary and geoclimatic history in biotic interchanges. Here, analysis of more than 20,000 vertebrate species with a model of geoclimate and biological diversification shows that broad precipitation tolerance and dispersal ability were key for exchange across the deep-time precipitation gradient spanning the region. Sundanian (Southeast Asian) lineages evolved in a climate similar to the humid "stepping stones" of Wallacea, facilitating colonization of the Sahulian (Australian) continental shelf. By contrast, Sahulian lineages predominantly evolved in drier conditions, hampering establishment in Sunda and shaping faunal distinctiveness. We demonstrate how the history of adaptation to past environmental conditions shapes asymmetrical colonization and global biogeographic structure.
The taxa found in an Eocene deposit, near Murgon, Queensland, the only pre-Oligocene Paleogene site recording a terrestrial vertebrate fauna from Australia, are very significant for the insight they provide concerning the evolution of the Australian biota. Here we resolve the identity of fossils previously referred to the Graculavidae, waterbirds of then unresolved affinities. We taxonomically describe the first bird to be named from this fauna, Murgonornis archeri gen. et sp. nov., Presbyornithidae. Our findings reveal that presbyornithids were widespread globally in the earliest Eocene, and that this family had a history on Australia from at least 55 Ma until ca. 24 Ma, when they disappear from the fossil record.
Trevor H. Worthy [trevor.worthy@flinders.edu.au], College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide 5001, SA, Australia; Vanesa L. De Pietri [vanesa.depietri@canterbury.ac.nz], University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand; R. Paul Scofield [pscofield@canterburymuseum.com], Canterbury Museum, 11 Rolleston Avenue, Christchurch 8013, New Zealand; Suzanne J. Hand [s.hand@unsw.edu.au], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
The late Oligocene taxa Marada arcanum and Mukupirna nambensis (Diprotodontia, Vombatiformes) are the only known representatives of the families Maradidae and Mukupirnidae, respectively. Mukupirna nambensis was described from a partial skeleton, including a cranium but no dentary, and reconstructed as the sister taxon to Vombatidae (wombats). By contrast, Ma. arcanum is known only from a single dentary, preventing direct comparison between the two. Here, we describe a new species, Mu. fortidentata sp. nov., based on craniodental and postcranial specimens from the Oligocene Pwerte Marnte Marnte Local Fauna, Northern Territory, Australia. Phylogenetic analysis of Vombatiformes, using 124 craniodental and 20 postcranial characters, places these three species within Vombatoidea, wherein Marada arcanum is sister to species of Mukupirna + Vombatidae. Mukupirna fortidentata sp. nov. does not share any robust synapomorphies of the dentary with Ma. arcanum that would support placing them together in a clade to the exclusion of Vombatidae. We therefore maintain separation of the families Mukupirnidae and Maradidae. From a functional perspective, the craniodental specimens of Mu. fortidentata sp. nov. reveal a suite of morphological traits that are unusual among vombatiforms, which we interpret as adaptations for acquiring and processing hard plant material. These include: a short, broad rostrum; large, robust, steeply upturned incisors; and a steep, anteroposteriorly decreasing gradient in cheek tooth size. The dental specimens of Mu. fortidentata sp. nov. also assist in the identification of two further allied taxa: an early vombatid from the younger late Oligocene Tarkarooloo Local Fauna, South Australia; and a possible vombatoid from the earliest Miocene Geilston Bay Local Fauna, Tasmania. The Tarkarooloo Local Fauna taxon indicates that vombatids diverged from other vombatoids prior to 24 million years ago.
Arthur I. Crichton [arthur.crichton@flinders.edu.au], College of Science and Engineering, Flinders University, Bedford Park, Adelaide, 5042, South Australia;
Trevor H. Worthy [trevor.worthy@flinders.edu.au], Aaron B. Camens [aaron.camens@flinders.edu.au], Adam Yates [Adamm.Yates@magnt.net.au] Museum and Art Gallery of the Northern Territory, Alice Springs 0870, Northern Territory, Alice Springs, 0870 Australia;
Aidan M. C. Couzens [acouzens@ucla.edu], Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA;
Gavin J. Prideaux [gavin.prideaux@flinders.edu.au], Flinders University School of Biological Sciences, Palaeontology, Adelaide, 5001 Australia.
The Ektopodontidae are an enigmatic group of phalangeroid marsupials known from the late Oligocene to the Early Pleistocene of Australia. Although represented to date only by isolated teeth and several partial dentaries and maxillae, their highly distinctive dental morphology has allowed three genera and nine species to be distinguished. Here, we describe possibly the geologically oldest ektopodontid, Chunia pledgei sp. nov., from the Oligocene Pwerte Marnte Marnte fossil locality of central Australia. Phylogenetic analyses of Phalangeroidea, using 80 primarily dental characters framed by a molecular scaffold, support placement of the new taxon in the genus Chunia. The analyses failed to recover species of the genus Durudawiri in a monophyletic Miralinidae, indicating that they require systematic review. We also transfer the purported basal phalangerid Eocuscus sarastamppi to Miralinidae (Miralina sarastamppi comb. nov.). Additionally, the M1 specimens used to describe the Early to Middle Miocene miralinid genus Barguru, and three species therein, are re-identified as deciduous third premolars from early macropodoids. These findings imply that the Miralinidae are known only from the late Oligocene, whereas the oldest named phalangerids are from the Early Miocene. From a functional consideration of ektopodontid dental morphology, we infer support for prior suggestions of a granivorous and/or frugivorous diet for them. The relative stage-of-evolution expressed by the new taxon is comparable to those in the lower faunal zones of the Namba and Etadunna formations, which supports a late Oligocene age for the Pwerte Marnte Marnte assemblage.
Our understanding of the biology of the extinct pig-footed bandicoots (Chaeropus) has been substantially revised over the past two decades by both molecular and morphological research. Resolving the systematic and temporal contexts of Chaeropus evolution has relied heavily on sequencing DNA from century-old specimens. We have used sliding window BLASTs and phylogeny reconstruction, as well as cumulative likelihood and apomorphy distributions, to identify contamination in sequences from both species of pig-footed bandicoot. The sources of non-target DNA that were identified range from other bandicoot species to a bird—emphasizing the importance of sequence authentication for historical museum specimens, as has become standard for ancient DNA studies. Upon excluding the putatively contaminated fragments, Chaeropus was resolved as the sister to all other bandicoots (Peramelidae), to the exclusion of bilbies (Macrotis). The estimated divergence time between the two Chaeropus species also decreases in better agreement with the fossil record. This study provides evolutionary context for testing hypotheses on the ecological transition of pig-footed bandicoots from semi-fossorial omnivores towards cursorial grazers, which in turn may represent the only breach of deeply conserved ecospace partitioning between modern Australo-Papuan marsupial orders.
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