Was the Oligo‐Miocene Australian metatherian Yalkaparidon a ‘mammalian woodpecker’?

One of the most striking examples of convergent evolution within mammals is the suite of anatomical specializations shared by the primate Daubentonia of Madagascar and the marsupial Dactylopsila of Australia and New Guinea. Having last shared a common ancestor over 125 million years ago, these two genera have independently evolved extremely similar adaptations for feeding on xylophagous (wood-boring) insect larvae. These include enlarged incisors to gouge holes in wood, cranial modifications to strengthen the skull against the stresses generated by wood gouging and elongate manual digits that are used as probes to extract the larvae. Elsewhere in the world, the same ecological niche is filled by birds (woodpeckers or morphologically convergent forms) that use their beaks for wood gouging. An extinct group of eutherian mammals, the apatemyids, exhibit very similar craniodental and postcranial adaptations to Daubentonia and Dactylopsila and presumably also occupied the woodpecker niche. A qualitative analysis of characters of the skull and dentition of the enigmatic Oligo-Miocene Australian metatherian Yalkaparidon – specifically its combination of very large, open-rooted incisors, zalambdodont molars and features to strengthen the skull against rostral bending – supports the hypothesis that it is probably a fourth 'mammalian woodpecker'. Discovery of the (as yet unknown) manus of Yalkaparidon will test this hypothesis by revealing whether any of its digits are elongate.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 1–17.     

NEW AUSTRALIAN OLIGOCENE TO MIOCENE RINGTAIL POSSUMS (PSEUDOCHEIRIDAE) AND REVISION OF THE GENUS MARLU

Abstract:  Four genera of extinct ringtail possums have been reported from Australian Oligocene to Miocene sediments since 1987. The genus Marlu was described from two species, M. kutjamarpensis and M. praecursor (Woodburne, Tedford and Archer), from the Miocene Kutjamarpu Local Fauna (Leaf Locality) and late Oligocene Wadikali Local Fauna respectively, of northern South Australia. New fossil material referable to this genus has been collected from the Leaf Locality and the Oligocene to Miocene Riversleigh World Heritage Area in northwest Queensland. Three new species, Marlu karya sp. nov. from middle Miocene Riversleigh local faunas and Marlu syke sp. nov. and Marlu ampelos sp. nov. from the Leaf Locality as well as early to middle Miocene Riversleigh local faunas are described. A revision and rediagnosis of the genus and published species are made following the re-examination of referred material in conjunction with the new material. Marlu is characterized by simple dentition and synapomorphies with extant pseudocheirids such as a conjoined postmetacristid and preentocristid on m1 and the loss of the entostylid ridge. New material from middle Miocene Riversleigh deposits has been referred to M. kutjamarpensis , extending the known distribution and age of that species. Re-examination of M. praecursor has revealed the presence of a small m1 entostylid ridge, contributing further to differences between M. praecursor and all other Marlu species and raising the possibility that Marlu is paraphyletic. The new material does not contradict a sister group relationship between ' Marlu ' (excluding M. praecursor ) and the Pliocene–Pleistocene genus Pseudokoala. Homology of the pseudocheirid m1 protostylid identified in species of Paljara , Pildra and Marlu with that observed in extant species is reconsidered. The 'protostylid' of the extinct genera is herein described as the buccal stylid.     

Australia's first fossil marsupial mole (Notoryctemorphia) resolves controversies about their evolution and palaeoenvironmental origins

Fossils of a marsupial mole (Marsupialia, Notoryctemorphia, Notoryctidae) are described from early Miocene deposits in the Riversleigh World Heritage Area, northwestern Queensland, Australia. These represent the first unequivocal fossil record of the order Notoryctemorphia, the two living species of which are among the world's most specialized and bizarre mammals, but which are also convergent on certain fossorial placental mammals (most notably chrysochlorid golden moles). The fossil remains are genuinely 'transitional', documenting an intermediate stage in the acquisition of a number of specializations and showing that one of these-the dental morphology known as zalambdodonty-was acquired via a different evolutionary pathway than in placentals. They, thus, document a clear case of evolutionary convergence (rather than parallelism) between only distantly related and geographically isolated mammalian lineages-marsupial moles on the island continent of Australia and placental moles on most other, at least intermittently connected continents. In contrast to earlier presumptions about a relationship between the highly specialized body form of the blind, earless, burrowing marsupial moles and desert habitats, it is now clear that archaic burrowing marsupial moles were adapted to and probably originated in wet forest palaeoenvironments, preadapting them to movement through drier soils in the xeric environments of Australia that developed during the Neogene.     

A NEW HIPPOSIDERID GENUS (MICROCHIROPTERA) FROM AN EARLY MIOCENE BAT COMMUNITY IN AUSTRALIA

Abstract:  A new genus and species of hipposiderid bat is described from an early Miocene cave deposit (Bitesantennary Site) in the Riversleigh World Heritage fossil property, northern Australia. Eight hipposiderid genera are now recorded from Riversleigh's Miocene sediments: Hipposideros , Brachipposideros, Rhinonycteris , Riversleigha, Xenorhinos , Miophyllorhina , Archerops and Brevipalatus gen. nov. The new taxon appears to be most closely related to Australian endemic Rhinonycteris and Brachipposideros species, but its autapomorphically very short palate distinguishes it from other members of this relatively plesiomorphic group. It is one of eight hipposiderid species recovered from the Bitesantennary Site deposit, and one of 11 recorded from Riversleigh's early Miocene sediments. Compared with modern bat faunas, the early Miocene Riversleigh bat community differs strikingly in its high hipposiderid diversity but may differ less in its overall trophic structure.     

Mid-Tertiary elapid snakes (Squamata, Colubroidea) from Riversleigh, northern Australia: early steps in a continent-wide adaptive radiation

Vertebral and cranial remains of elapid snakes have been collected from fossil assemblages at Riversleigh, north-west Queensland, Australia; most are Miocene but one may be late Oligocene and another as young as Pliocene. The oldest specimen (probably the oldest elapid yet known anywhere) is a vertebra that can be referred provisionally to the extant taxon Laticauda (Hydrophiinae, sensu Slowinski and Keogh, 2000), implying that the basal divergences among Australasian hydrophiine lineages had occurred by the early Miocene, in contrast to most previous estimates for the age of this geographically isolated adaptive radiation. Associated vertebrae and jaw elements from a Late Miocene deposit are described as Incongruelaps iteratus nov. gen. et sp., which has a unique combination of unusual derived characters otherwise found separately in several extant hydrophiine taxa that are only distantly related. Associated vertebrae from other sites, and two parietals from a possibly Pliocene deposit, suggest the presence of several other taxa distinct from extant forms, but the amount of material (and knowledge of variation in extant taxa) is currently insufficient to diagnose these forms. The Tertiary elapids of Riversleigh thus appear to be relatively diverse taxonomically, but low in abundance and, with one exception, not referable to extant taxa below the level of Hydrophiinae. This implies that the present diversity of hydrophiine elapids (31 recognized terrestrial genera, and approximately 16 marine) represents the result of substantial extinction as well as the “cone of increasing diversity” that could be inferred from phylogenetic studies on extant forms.     

Hammer-toothed 'marsupial skinks' from the Australian Cenozoic

Extinct species of Malleodectes gen. nov. from Middle to Late Miocene deposits of the Riversleigh World Heritage Area, northwestern Queensland, Australia are enigmatic, highly specialized, probably snail-eating marsupials. Dentally, they closely resemble a bizarre group of living heterodont, wet forest scincid lizards from Australia (Cyclodomorphus) that may well have outcompeted them as snail-eaters when the closed forests of central Australia began to decline. Although there are scincids known from the same Miocene deposits at Riversleigh, these are relatively plesiomorphic, generalized feeders. This appears to be the most striking example known of dental convergence and possible competition between a mammal and a lizard, which in the long run worked out better for the lizards.     

The Calcaneum—On the Heels of Marsupial Locomotion

The potential for making functional interpretations from a single postcranial element for marsupials was investigated through morphometric analysis of the calcanea of 61 extant species from Australia and New Guinea. Extant species were grouped into locomotor categories and a canonical variates analysis was carried out on measurements of their calcanea. A relationship between measurements of the calcanea and the locomotor behavior of species was found, allowing for prediction of locomotor behavior from calcaneum morphometrics. This was applied to fossil marsupial taxa, from early–late Miocene/?Pliocene deposits at Riversleigh, in an attempt to determine their locomotor behavior. Hopping (saltatorial) taxa are distinguished from quadruped terrestrial taxa and taxa capable of climbing (arboreal and scansorial) by their relatively longer tuber calcis and wider calcaneal head, by their dorso-ventrally thicker calcaneal head, and by their calcaneocuboid facet being less steeply angled antero-posteriorly. Taxa capable of climbing are distinguished from quadruped terrestrial taxa by their shorter tuber calcis relative to the calcaneal head and by their smaller calcaneo-astragalar facet. The locomotor categories distinguished in this study (arboreal/scansorial, quadruped terrestrial, and saltatorial) highlight differences between species in their use of available substrates and thus are informative with regards to the structural components of their habitat. The results of this analysis can be used, in combination with other data, to make inferences about the habitats of paleocommunities at Riversleigh through the Miocene. The calcaneum is a dense and very robust element and, therefore, has a good chance of being preserved. This method provides a quick and easy way of inferring locomotion and has a wide potential for application to many fossil deposits because it requires only a single element.