Karen H. Black

Current status of species-level representation in faunas from selected fossil localities in the Riversleigh World Heritage Area, northwestern Queensland

Current lists of species-level representation in faunas from 80 Cenozoic fossil localities at the Riversleigh World Heritage Area have been compiled by review of recorded occurrences of taxa obtained from both published and unpublished sources. More than 290 species-level taxa are represented, comprising mammals, amphibians, reptiles, birds, fishes, molluscs and crustaceans. The data are presented for the purpose of ongoing palaeoecological and biochronological studies.

The Rise of Australian Marsupials: A Synopsis of Biostratigraphic, Phylogenetic, Palaeoecologic and Palaeobiogeographic Understanding

The origins, evolution and palaeodiversity of Australia’s unique marsupial fauna are reviewed. Australia’s marsupial fauna is both taxonomically and ecologically diverse comprising four extant orders (Dasyuromorphia, Peramelemorphia, Notoryctemorphia and Diprotodontia) and one extinct order (Yalkaparidontia). Molecular divergence dates estimate a Palaeocene origin for the Australian marsupial orders yet ordinal differentiation is obscured by significant gaps in the fossil record with a single terrestrial mammal-bearing deposit known between the late Cretaceous and the late Oligocene. This deposit, the 55 million-year-old early Eocene Tingamarra Local Fauna of southeastern Queensland, contains Australia’s oldest marsupial (Superorder Australidelphia) as well as taxa tentatively interpreted to represent South American groups (Order Polydolopimorphia). Palaeobiogeographic hypotheses regarding the distribution and interordinal relationships of Australian and South American marsupials are discussed. Dasyuromorphia and Peramelemorphia were possibly also present in the early Eocene, Diprotodontia in at least the late Oligocene and Notoryctemorphia and Yalkaparidontia in the early Miocene. Palaeobiodiversity was highest during the early to middle Miocene as evidenced by a spectacular array of marsupial groups in the rainforest assemblages of the Riversleigh World Heritage Area. The onset of icehouse conditions during the middle Miocene saw significant faunal turnover with loss of many archaic groups and the emergence of a range of modern lineages. Few deposits of late Miocene age are known. Development of Australia’s first grasslands and arid habitats occurred in the Pliocene, accompanied by an explosive radiation of grazing kangaroos. The Pleistocene was characterised by severe and unpredictable climatic conditions and the extinction of the Australian megafauna. Lowered sea levels allowed faunal interchange between mainland Australia and neighbouring New Guinea as well as the arrival of the first humans. Resolution of the role of humans and/or climate change in megafaunal extinction requires more precise dating of late Pleistocene deposits. We reflect on the predictive power of the fossil record to enhance understanding of the effects of climate change and humans on the future of the Australian marsupial fauna.

Revision in the Diprotodontid Marsupial Genus Neohelos: Systematics and Biostratigraphy

Neohelos is a geographically and temporally widespread genus of Cenozoic diprotodontid marsupials commonly used to biocorrelate otherwise undated Australian fossil deposits. Here, we revise the genus and describe two new species from the Riversleigh World Heritage Area of northwestern Queensland. Neohelos solus sp. nov. is a small, relatively abundant, plesiomorphic form, while the rarer, larger Neohelos davidridei sp. nov. is the most derived species of the genus with an upper premolar morphology that is structurally antecedant to members of the Late Miocene genus Kolopsis. Additional material of Neohelos tirarensis and Neohelos stirtoni is described. A chronological morphocline is evidenced by a gradual change in morphology accompanied by an increase in size from Ne. tirarensis through Ne. stirtoni to Ne. davidridei, and is generally consistent with the biostratigraphic distribution of Neohelos species throughout Riversleighs faunal zones A to D. Stage of evolution biocorrelation of Neohelos species confirms that some of Riversleighs Faunal Zone A deposits are Late Oligocene in age and predate the Wipajiri Formation of South Australia. Strong faunal correlations exist between Riversleighs topographically low to middle Faunal Zone C deposits and the Northern Territorys Middle Miocene Bullock Creek Local Fauna. The presence of the highly derived N. davidridei in the Jaw Junction Local Fauna of Riversleighs Upper Faunal Zone C suggests a later Middle Miocene (post-Bullock Creek) age for this deposit.

First Crania and Assessment of Species Boundaries in Nimbadon (Marsupialia: Diprotodontidae) from the Middle Miocene of Australia

Abstract Abundant, exceptionally well-preserved cranial material of the zygomaturine diprotodontid Nimbadon lavarackorum is described from AL90 site, a middle Miocene deposit in the Riversleigh World Heritage Area, Queensland, Australia. The material has enabled a comprehensive assessment of the expected level of morphological variation within a fossil marsupial species from a single locality, thus forming a benchmark for determining species boundaries in extinct marsupials. Variation is assessed by quantitative and qualitative means. Univariate analyses of N. lavarackorum cranial and dental dimensions indicate low coefficients of variation consistent with expected values for single species populations. Conversely, qualitative analyses indicate high levels of morphological variation, particularly in structures previously deemed phylogenetically significant, such as the upper third premolar. Some cranial variation may be due to sexual dimorphism or ontogeny but there appears to be a high degree of intraspecific morphological variation. Features once regarded to distinguish N. whitelawi from the type species fall within the boundaries of that intraspecific variation and N. whitelawi is herein regarded as a junior synonym of N. lavarackorum. Comparison with morphological variation in the Miocene diprotodontid Neohelos stirtoni suggests that N. lavarackorum was a less variable species overall, reflecting differences between the taxa in body size, home range, and habitat preference and stability. Nimbadon lavarackorum was a relatively small (75–120 kg), possibly gregarious browsing species probably restricted to closed-forest habitats.

Ngapakaldia bonythoni (Marsupialia, Diprotodontidae): new material from Riversleigh, northwestern Queensland, and a reassessment of the genus Bematherium

Ngapakaldia bonythoni has been recognized in several Oligo-Miocene deposits at Riversleigh, thus extending the known temporal and geographic range of the species. The excellent state of preservation of the Riversleigh material has enabled a description of diagnostic features of the palate, dentary and dentition previously not possible from the badly fractured holotype. In light of this new material, a reanalysis of the single known dentary of Bematherium angulum from Riversleighs Site C (Tedford 1967), suggests B. angulum is a junior synonym of N. bonythoni, a relationship first proposed tentatively by Archer (1984). Few morphological differences (apart from size) distinguish N. bonythoni from its smaller congeneric N. tedfordi. Despite this similarity in form, the abundance of N. bonythoni, and the absence of any smaller forms such as N. tedfordi at Riversleigh, supports the recognition of two distinct species in Ngapakaldia. The shared presence of Ngapakaldia bonythoni in several Faunal Zone A local faunas at Riversleigh, and the Ngapakaldi Local Fauna (Zone C) of the Etadunna Formation, lends further support to a late Oligocene age for these deposits.

Descriptions of koala fossils from the Miocene of Riversleigh, northwestern Queensland and implications for Litokoala (Marsupialia, Phascolarctidae)

Louys, J., Black, K., Archer, M., Hand, S.J. & Godthelp, H., June, 2007. Descriptions of koala fossils from the Miocene of Riversleigh, northwestern Queensland and implications for Litokoala (Marsupialia, Phascolarctidae). Alcheringa 31, 99‐110. ISSN 0311-5518. Litokoala is revised on the basis of new material from the early to middle Miocene deposits of Riversleigh. A new species of Litokoala is described from the System B Outasite Local Fauna. Litokoala garyjohnstoni sp. nov. possesses a unique combination of both plesiomorphic and apomorphic dental features, making its phylogenetic position within Litokoala difficult to interpret. In some aspects of dental morphology, L. garyjohnstoni is convergent on the early Miocene phascolarctid Nimiokoala greystanesi Black & Archer, 1997. The dentition of a partial skull of Litokoala from Jims Carousel Site, System C is also described. On the basis of this dentition, it is suggested that the morphological variation between L. kutjamarpensis Stirton, 1967 and L. kanunkaensis Springer, 1987 does not warrant specific distinction, the latter being the junior synonym.

Earliest modern bandicoot and bilby (Marsupialia, Peramelidae and Thylacomyidae) from the Miocene of the Riversleigh World Heritage Area, northwestern Queensland, Australia

ABSTRACT Recent molecular phylogenies of peramelemorphians suggest that thylacomyids (bilbies) and peramelids (modern bandicoots) diversified sometime in the late Oligocene or early Miocene. Until now, however, the earliest fossil evidence of thylacomyids and peramelids was from the Australian Pliocene. Here we describe the oldest peramelid and thylacomyid from the middle Miocene of the Riversleigh World Heritage Area, northwestern Queensland. The peramelid, Crash bandicoot, gen. et sp. nov., is represented by a single maxilla containing M1–3 that exhibits peramelid synapomorphies, including development of a metaconular hypocone, an incomplete centrocrista, and well-developed anterior cingulum. The thylacomyid, Liyamayi dayi, gen. et sp. nov., is represented by M2 and m1, which show thylacomyid synapomorphies including a conical entoconid, a conical stylar cusp B (StB) and StD, and reduced distance between the metastyle and StD. The results of our phylogenetic analysis indicate that both species are part of crown-group Peramelemorphia

First comprehensive analysis of cranial ontogeny in a fossil marsupial—from a 15-million-year-old cave deposit in northern Australia

ABSTRACT We present the first detailed account of cranial ontogeny in a fossil marsupial. An exceptionally well-preserved ontogenetic sample representing 26 individuals of Nimbadon lavarackorum (Diprotodontidae, Zygomaturinae) is described from a 15 million-year-old cave deposit in the Riversleigh World Heritage Area, Queensland. Based on comparison with one of N. lavarackomrris closest living relatives, the common wombat (Vombatus ursinus), the N. lavarackorum sample represents developmental stages spanning suckling pouch young through to elderly adults. In addition to documenting ontogenetic changes, reduced major axis regression analyses of 14 cranial and seven mandibular measurements were used to analyze allometric growth. Early growth patterns in the cranium are comparable to those of other marsupials such that the bones of the facial portion of the cranium develop precociously compared with those of the neurocranium. Most differences between adult and juvenile crania result from reorganization of structures associated with the cranio-mandibular joint and the developing dentition and strengthening of areas for insertion of the muscles of mastication. These changes reflect the transition from a purely suckling function to one focused on mastication of leaves. The sample also provides a unique view into the development of the extraordinarily complex endocranial sinuses characteristic of diprotodontid marsupials.

Herds Overhead: Nimbadon lavarackorum (Diprotodontidae), Heavyweight Marsupial Herbivores in the Miocene Forests of Australia

The marsupial family Diprotodontidae (Diprotodontia, Vombatiformes) is a group of extinct large-bodied (60–2500 kg) wombat-like herbivores that were common and geographically widespread in Cenozoic fossil deposits of Australia and New Guinea. Typically they are regarded to be gregarious, terrestrial quadrupeds and have been likened in body form among placental groups to sheep, rhinoceros and hippopotami. Arguably, one of the best represented species is the zygomaturine diprotodontid Nimbadon lavarackorum which is known from exceptionally well-preserved cranial and postcranial material from the middle Miocene cave deposit AL90, in the Riversleigh World Heritage Area, northwestern Queensland. Here we describe and functionally analyse the appendicular skeleton of Nimbadon lavarackorum and reveal a far more unique lifestyle for this plesiomorphic and smallest of diprotodontids. Striking similarities are evident between the skeleton of Nimbadon and that of the extant arboreal koala Phascolarctos cinereus, including the powerfully built forelimbs, highly mobile shoulder and elbow joints, proportionately large manus and pes (both with a semi-opposable digit I) and exceedingly large, recurved and laterally compressed claws. Combined with the unique (among australidelphians) proportionately shortened hindlimbs of Nimbadon, these features suggest adept climbing ability, probable suspensory behaviour, and an arboreal lifestyle. At approximately 70 kg, Nimbadon is the largest herbivorous mammal to have occupied the forest canopies of Australia - an ecological niche that is no longer occupied in any Australian ecosystem and one that further expands the already significant niche diversity displayed by marsupials during the Cenozoic.

Understanding morphological variation in the extant koala as a framework for identification of species boundaries in extinct koalas (Phascolarctidae; Marsupialia)

We document morphological variation (both geographical and sexual) in the dentition of the extant koala, Phascolarctos cinereus, in order to facilitate discrimination of species boundaries in extinct phascolarctids. Considerable variation is evident in dental structures previously used to diagnose several phascolarctid fossil species. Consistent patterns of morphological variation are not evident between sexes or geographic regions, with variation as great between samples as within them. Metric variation is evident between the sexes in upper molar dimensions with Victorian (southern) males significantly larger than Victorian females, although this is not reflected in lower molar dimensions or in the Queensland (northern) sample. Male koalas from southern populations generally display significantly larger molars than their northern counterparts; however this trend is not evident in female upper molar dimensions. In both males and females, some, but not all, lower molar dimensions are larger in southern populations than northern. In light of these results, a systematic revision of species of Litokoala suggests L. ‘dicktedfordi’ is a junior synonym of L. kutjamarpensis, and the poorly known L. thurmerae is regarded to be a nomen dubium. Further, we describe a partial cranium of a new species of koala from Early Miocene sediments in the Riversleigh World Heritage Area, northern Australia. Litokoala dicksmithi sp. nov. is the fifth koala species recorded from the diverse rainforest assemblages of Riversleigh and the third species referred to the Oligo-Miocene genus Litokoala. Aspects of cranial morphology, including a shortened robust rostrum and broad, irregular nasal aperture, confirm placement of Litokoala as sister taxon to the modern genus Phascolarctos. Relatively large orbits and small body size suggest the possibility that L. dicksmithi was nocturnal, had enhanced visual acuity, and was a more agile arboreal species than the relatively sedentary extant koala. http://zoobank.org/urn:lsid:zoobank.org:pub:EE5D13C1-47BB-4432-B281-16398A1781E1