Abstract
A new specimen of the bizarrely specialised Malleodectes mirabilis from middle Miocene deposits in the Riversleigh World Heritage Area provides the first and only information about the molar dentition of this strange group of extinct marsupials. Apart from striking autapomorphies such as the enormous P3, other dental features such as stylar cusp D being larger than B suggest it belongs in the Order Dasyuromorphia. Phylogenetic analysis of 62 craniodental characters places Malleodectes within Dasyuromorphia albeit with weak support and without indication of specific relationships to any of the three established families (Dasyuridae, Myrmecobiidae and Thylacinidae). Accordingly we have allocated Malleodectes to the new family, Malleodectidae. Some features suggest potential links to previously named dasyuromorphians from Riversleigh (e.g., Ganbulanyi) but these are too poorly known to test this possibility. Although the original interpretation of a steeply declining molar row in Malleodectes can be rejected, it continues to seem likely that malleodectids specialised on snails but probably also consumed a wider range of prey items including small vertebrates. Whatever their actual diet, malleodectids appear to have filled a niche in Australia’s rainforests that has not been occupied by any other mammal group anywhere in the world from the Miocene onwards.
Highlights
Until recently, all known dasyuromorphians have been comfortably accommodated into one of three families: Dasyuridae, Thylacinidae and Myrmecobiidae, with the interrelationships of these clades the subject of long-standing controversy[1,2,3,4,5,6]
Wroe[7,8] and Godthelp et al.[9] further argued that some fossil dasyuromorphian-like taxa do not preserve sufficient features to enable them to be placed with confidence in Dasyuromorphia, or even the cohort clade Australidelphia
The practical path in palaeontology involving fragmentary fossils is tentative allocation based on the range of morphology exhibited by crown group clades
Summary
All known dasyuromorphians have been comfortably accommodated into one of three families: Dasyuridae, Thylacinidae and Myrmecobiidae, with the interrelationships of these clades the subject of long-standing controversy[1,2,3,4,5,6]. Recent discoveries being made in the Oligo-Miocene deposits of the Riversleigh World Heritage Area in NW Queensland have resulted in publication of a series of anomalous carnivorous taxa that do not fit comfortably within any of the three known dasyuromorphian families. In most cases these have been published as new genera with uncertain familial position. Assignment of these two teeth to the same dasyurid taxon was based on apparent ‘bone-cracking’ (i.e., bone-crushing) adaptations and at least partial resemblance of both teeth to those of species of Sarcophilus
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