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

A Phylogeny and Timescale for the Evolution of Pseudocheiridae (Marsupialia: Diprotodontia) in Australia and New Guinea

Pseudocheiridae (Marsupialia: Diprotodontia) is a family of endemic Australasian arboreal folivores, more commonly known as ringtail possums. Seventeen extant species are grouped into six genera (Pseudocheirus, Pseudochirulus, Hemibelideus, Petauroides, Pseudochirops, Petropseudes). Pseudochirops and Pseudochirulus are the only genera with representatives on New Guinea and surrounding western islands. Here, we examine phylogenetic relationships among 13 of the 17 extant pseudocheirid species based on protein-coding portions of the ApoB, BRCA1, ENAM, IRBP, Rag1, and vWF genes. Maximum parsimony, maximum likelihood, and Bayesian methods were used to estimate phylogenetic relationships. Two different relaxed molecular clock methods were used to estimate divergence times. Bayesian and maximum parsimony methods were used to reconstruct ancestral character states for geographic provenance and maximum elevation occupied. We find robust support for the monophyly of Pseudocheirinae (Pseudochirulus + Pseudocheirus), Hemibelidinae (Hemibelideus + Petauroides), and Pseudochiropsinae (Pseudochirops + Petropseudes), respectively, and for an association of Pseudocheirinae and Hemibelidinae to the exclusion of Pseudochiropsinae. Within Pseudochiropsinae, Petropseudes grouped more closely with the New Guinean Pseudochirops spp. than with the Australian Pseudochirops archeri, rendering Pseudochirops paraphyletic. New Guinean species belonging to Pseudochirops are monophyletic, as are New Guinean species belonging to Pseudochirulus. Molecular dates and ancestral reconstructions of geographic provenance combine to suggest that the ancestors of extant New Guinean Pseudochirops spp. and Pseudochirulus spp. dispersed from Australia to New Guinea ∼12.1–6.5 Ma (Pseudochirops) and ∼6.0–2.4 Ma (Pseudochirulus). Ancestral state reconstructions support the hypothesis that occupation of high elevations (>3000 m) is a derived feature that evolved on the terminal branch leading to Pseudochirops cupreus, and either evolved in the ancestor of Pseudochirulus forbesi, Pseudochirulus mayeri, and Pseudochirulus caroli, with subsequent loss in P. caroli, or evolved independently in P. mayeri and P. forbesi. Divergence times within the New Guinean Pseudochirops clade are generally coincident with the uplift of the central cordillera and other highlands. Diversification within New Guinean Pseudochirulus occurred in the Plio-Pleistocene after the establishment of the Central Range and other highlands

Australian cretaceous terrestrial faunas and floras: biostratigraphic and biogeographic implications

Nonmarine Cretaceous sediments representing fluvial/lacustrine deposits occur in 22 of Australia's 23 Mesozoic depositional basins. They are associated with open to marginal marine sediments whose enclosed planktic faunas and floras provide tie points to the Tethyan and European stages. Integration of marine and nonmarine sequences has been effected through spore-pollen biostratigraphies which in turn are linked to macroplant zones, vertebrate ranges and radiometric dates. This evidence is reviewed and it is concluded that the C. hughesii-P. pannosus spore-pollen Zones define Aptian to Albian ages and that their zonal boundaries are isochronous across Australia; the P. mawsonii-F. longus spore-pollen Zones in south-eastern Australia are datable as Turonian-Maastrichtian. However, evidence for a Cenomanian age for the intervening A. distocarinatus Zone is not indubitable. Also, the position of the Jurassic-Cretaceous boundary and the temporal significance of several index taxa of the ?latest Jurassic-Barremian C. australiensis-F. wonthaggiensis Zones in eastern Australia and the B. eneabbaensis-lower B. limbatus Zones in Western Australia is not certain. Isochronous incomings of individual spore-pollen taxa on a regional scale relate to the mode of dispersal of the source plant, and to the distribution of environments suitable for dispersal. For the Aptian-Albian, when Australia was inundated by shallow seas and lake/river systems that fed into them, several index taxa sourced from aquatic and strandline plants appear to have temporal significance. By contrast, anemophilous pollen are stratigraphically useful and temporally significant in the Turonian-Maastrichtian of south-eastern Australia. Throughout the Cretaceous, Australia supported a succession of coniferous forests. Early Cretaceous podocarp/araucarian/Ginkgo canopy associations were modified in the Late Cretaceous by the loss of Ginkgo and the introduction of rainforest Proteaceae and Nothofagus. Regional variations in the vegetation reflect topographic, edaphic and climatic variations between the disparate sedimentary basins. Floral migration within Australia and between associated land masses occurred in a step-wise fashion, and was mostly west to east. Two dinosaur faunas are recognized: one, in the Aptian-early Albian of Victoria, consists of small ornithopods and theropods; and the other, in the middle Albian-Cenomanian of Queensland, comprises ankylosaurs, sauropods and theropods. The Victorian herbivorous dinosaurs were low feeders and probably shared a single mode of feeding, whereas those from Queensland may have had several feeding modes and fed up to 6 m from the ground. The small ornithopods, mostly from Victoria, were hypsilophodontians with grinding dentitions; their food source may have been lycopods or diaspores of podocarps and Ginkgo. Ankylosaurs seem to have preferred soft vegetation, some possibly aquatic. The Queensland sauropods may have fed on living and dead vegetation, perhaps including fleshy seeds of podocarps/taxads and gleicheniaceous ferns that apparently proliferated in the region. The lungfish had grinding toothplates and were probably omnivorous like extant Neoceratodus forsteri. Victorian faunas contain several relicts including the youngest known temnospondyl, the theropod Allosaurus, the lungfish Ceratodus avus, and the freshwater mussel Mesohydridella ipsviciensis. Australian earliest Cretaceous climates were temperate with cool temperatures (0-12°C) and high precipitation levels (750-1150 mm/year) in southern regions where winter freezing may have occurred during the Aptian. A warming trend during the Albian is indicated by land vegetation and verified by isotope palaeotemperatures (12-16°C) from the marine realm. Cool to warm temperate climates prevailed in the south-east during Turonian-Maastrichtian times; sea water temperatures were 16-28°C, and the vegetation is indicative of high humidities

Invictokoala monticola gen. et sp. nov. (Phascolarctidae, Marsupialia), a Pleistocene plesiomorphic koala holdover from Oligocene ancestor

Koalas (Phascolarctidae) are uncommon elements within the Australian fossil record. The earliest representatives are recorded from late Oligocene rainforest assemblages of central Australia. In contrast, the extant Koala Phascolarctos cinereus Blainville, 1816 (the only surviving member of a once diverse family) is found only in eastern Australian open woodlands. Extinction of koalas from rainforests was previously thought to have occurred after the middle Miocene. Recent systematic cave excavations at Mt. Etna, central eastern Queensland, Australia, have revealed several remarkable new middle Pleistocene vertebrate assemblages that are dominated by rainforest-adapted taxa. Within one of the deposits, we have identified a new, but archaic, genus and species of koala. Invictokoala monticola gen. et sp. nov. shares affinities with the most plesiomorphic member of the family, Madakoala Woodburne et al., 1987 (late Oligocene), but is distinguished by possessing higher-crowned upper molars, with a tricsupate (rather than linear) paraconule on M2 (autapomorphic condition within koalas), closely positioned stylar cusps, and better-developed posterior cingulae. Thus, not only does I. monticola represent a 'holdover' from an Oligocene ancestor, but the Madakoala-Invictokoala stem represents a 'ghost' lineage within the Phascolarctidae, with no representatives known between the late Oligocene and middle Pleistocene. Previously, it was thought that the post-middle Miocene loss of koalas from rainforests may have been a result of a co-evolved dependence of koalas to open eucalypt woodlands, and/or competitive exclusion with koala-like rainforest-adapted ringtail possums. However, the inferred diet of middle Pleistocene I. monticola (i.e. non-Eucalyptus) and coeval occurrence with numerous rainforest-adapted ringtail possums does not support that hypothesis. It appears more likely that koalas had always been closely associated with rainforests, at least until the late Quaternary extinction of I. monticola. Generally, the paucity of rainforest faunal assemblages, and specifically, records of fossil koalas through the late Cenozoic drastically limits our understanding of their evolution