Going underground: Postcranial morphology of the early miocene marsupial mole naraboryctes philcreaseri and the evolution of fossoriality in notoryctemorphians

We present the first detailed descriptions of postcranial elements of the fossil marsupial mole Naraboryctes philcreaseri (Marsupialia: Notoryctemorphia), from early Miocene freshwater limestone deposits in the Riversleigh World Heritage Area, northwestern Queensland. Qualitative functional analysis of these elements suggest that Na. philcreaseri was very well-adapted for burrowing, albeit somewhat less so than the living marsupial moles Notoryctes typhlops and N. caurinus. Quadratic discriminant analysis of limb measurements suggests that Na. philcreaseri was subterranean, and its Index of Fossorial Ability is almost identical to that of Notoryctes species, being among the highest known for any mammal. These results suggest that notoryctemorphians evolved their specialised, “mole-like” subterranean lifestyle prior to the early Miocene. Given that forested environments predominated in Australia until the middle-late Miocene, this transition to subterranean behaviour may have occurred via burrowing in forest floors, in which case fossorial mammals that live in tropical rainforests today (such as the placental golden moles Chrysospalax trevelyani and Huetia leucorhina) may represent reasonable living analogues for early notoryctemorphians. However, alternative scenarios, such as a cave-dwelling or semi-aquatic ancestry, should be considered. Phylogenetic analysis using a Bayesian total evidence dating approach places Naraboryctes as sister to Notoryctes with strong support (Bayesian posterior probability = 0.91), and indicates that Naraboryctes and Notoryctes diverged 30.3 MYA (95% HPD: 17.7-46.3 MYA). The age and known morphology of Na. philcreaseri does not preclude its being ancestral to Notoryctes. Using estimates of divergence times and ratios of nonsynonymous to synonymous substitutions per site, we infer that the nuclear gene “Retinol-binding protein 3, interstitial” (RBP3), which plays a key role in vision, became inactive in the Notoryctes lineage ~5.4 MYA (95% HPD: 4.5-6.3 MYA). This is much younger than previous published estimates, and postdates considerably the age of Na. philcreaseri, implying that RBP3 was active in this fossil taxon; hence, Na. philcreaseri may have retained a functional visual system. Our estimate for the inactivation of RBP3 in the Notoryctes lineage coincides with palaeobotanical evidence for a major increase in the abundance of grasses in Australia, which may indicate the appearance of more open environments, and hence selection pressure on notoryctemorphians to spend less time on the surface, leading to relaxed selection on RBP3. Ultimately, however, a fuller understanding of the origin and evolution of notoryctemorphians-including when and why they became “mole-like”-will require improvements in the Palaeogene fossil record of mammals in Australi

Genetic insights into the introduction history of black rats into the eastern Indian Ocean

Islands can be powerful demonstrations of how destructive invasive species can be on endemic faunas and insular ecologies. Oceanic islands in the eastern Indian Ocean have suffered dramatically from the impact of one of the world’s most destructive invasive species, the black rat, causing the loss of endemic terrestrial mammals and ongoing threats to ground-nesting birds. We use molecular genetic methods on both ancient and modern samples to establish the origins and minimum invasion frequencies of black rats on Christmas Island and the Cocos-Keeling Islands. We find that each island group had multiple incursions of black rats from diverse geographic and phylogenetic sources. Furthermore, contemporary black rat populations on these islands are highly admixed to the point of potentially obscuring their geographic sources. These hybridisation events between black rat taxa also pose potential dangers to human populations on the islands from novel disease risks. Threats of ongoing introductions from yet additional geographic sources is highlighted by genetic identifications of black rats found on ships, which provides insight into how recent ship-borne human smuggling activity to Christmas Island can negatively impact its endemic species.Vicki A. Thomson, Andrew S. Wiewel, Russell Palmer, Neil Hamilton, Dave Algar, Caitlyn Pink, Harriet Mills, Ken P. Aplin, Geoffrey Clark, Atholl Anderson, Michael B. Herrera, Steven Myers, Terry Bertozzi, Philip J. Piper, Hitoshi Suzuki, and Steve Donnella

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 new species of Varanus Merrem (Squamata: Varanidae) from the Pilbara region of Western Australia, with observations on sexual dimorphism in closely related species

Abstract not availableKenneth P. Aplin, Alison J. Fitch & Dennis J. Kin

Morphological diversity of the spermatozoon and male reproductive tract in Australian Hopping mice, genus Notomys – is it determined by sexual selection?

First published:07 April 2020Hopping mice (Genus Notomys) are a monophyletic group of Australian Old Endemic murid rodents in the Tribe Hydromyini four of which, Notomys alexis, N. mitchellii, N. fuscus and N cervinus, occur in arid or semiarid environments. Here, we compare the size and morphology of their testes, spermatozoa, accessory sex glands and external genitalia across the species, and from these data, we draw conclusions as to their likely breeding systems. We show that both wild caught and laboratory bred adult N. alexis, N. fuscus and N. mitchellii individuals have extremely small testes, but their spermatozoa vary in morphology across the species. The ventral prostate is the only large accessory sex gland present, and their glans penis has very large spines. By contrast N. cervinus individuals have significantly larger testes with their spermatozoa being less variable but generally more complex in morphology, their seminal vesicles and coagulating glands are much larger, whereas the glans penis has only small spines. Since these reproductive traits in N. cervinus are more similar to those of most other hydromyine rodents in the genus Pseudomys, they are likely to reflect the retention of the ancestral condition within the Notomys lineage whereas the divergent reproductive traits of the other species of tiny testes, variable sperm, small seminal vesicles and coagulating glands and large penile spines are probably more recently derived traits. It is suggested that N. cervinus with its relatively larger testes mass and greater abundance of sperm of more consistent morphology has retained a mating system that may potentially involve some intermale sperm competition whereas, by contrast, the reproductive anatomy of the other three Notomys species suggests that these species exhibit monogamy.W. G. Breed, X. Ding, J. Tuke, C.M. Leig