A new Early–Middle Miocene phalangerid (Marsupialia: Phalangeridae) from the Riversleigh World Heritage Area, Boodjamulla (Lawn Hill) National Park, northwestern Queensland

Abstract

Archerus johntoniae represents a new genus and species of phalangerid possum from the Early to Middle Miocene of the Riversleigh World Heritage Area, northwestern Queensland. The new taxon is the tenth extinct phalangerid species to be described and is the seventh species recognized from the diverse Riversleigh fossil assemblages. A. johntoniae has its closest morphometric affinities (such as relatively short molars, narrow premolars, an anteriorly narrow upper first molar, and posteriorly narrow fourth molars) with trichosurine and stem phalangerids. Morphologically, A. johntoniae has similarities to phalangerines and trichosurines, but is most dissimilar to other fossil phalangerids. The new species is one of the smallest (ca 1.3 kg) phalangerids known and may have occupied Early and Middle Miocene frugivorous/insectivorous niches demarcated from other phalangerids by body size and diet. A. johntoniae is one of a minority of Riversleigh species to have survived a significant decline in marsupial diversity associated with a rapid spike in global temperature at the Middle Miocene Climatic Optimum.

Troy Myers [[email protected]], Earth and Sustainability Science Research Centre, School of Biological, Earth & Environmental Sciences, UNSW Sydney, NSW 2052, Australia; Kirsten Crosby [[email protected]], GHD Group Pty Ltd, Level 15, 133 Castlereagh St, Sydney, NSW, 2000 (currently), School of Biological, Earth & Environmental Sciences, UNSW Sydney, NSW 2052, Australia.

Keywords:

• Neogene
• possums
• brushtail
• Trichosurinae
• Middle Miocene Climatic Optimum (MMCO)

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Beck et al. (2022) postulate that the kinked buccal crest in phalangeroids may not be homologous with the cristid obliqua. The specimens examined herein provide only equivocal data (i.e., rarely present, very minor ridglets extending from the buccal cuspids, that may be crenulations) regarding a plesiomorphic, more lingually placed crest. We therefore follow Beck et al. (2022) in referring to the kinked crest as the cristid obliqua, in the absence of more compelling data.

2 Beck et al. (2022) proposed that the buccal cusps on the protoloph and metaloph are stylar cusps B and D respectively. Consequently, the neoparaconule and neometaconule present in some phalangerids (e.g., Eocuscus sarastamppi Case, Meredith & Person, 2008) would be the reduced paracone and metacone, which were eventually incorporated into the lophs of more derived taxa. Although the argument is compelling, we have decided herein to adopt the traditional nomenclature and assume that the buccal cusps are homologous to the paracone and metacone, until further evidence is forthcoming.

Additional information

Funding

Support for our research has come from the Australian Research Council [DP170101420 grants to Professors M. Archer and S. J. Hand]; the University of New South Wales; P. Creaser and the CREATE Fund; the Queensland Parks and Wildlife Service; Environment Australia; the Queensland Museum; the Riversleigh Society Inc.; Outback at Isa; Mount Isa City Council; the Waanyi people of northwestern Queensland; and private supporters including D. and A. Jeanes, K. and M. Pettit, E. Clark, M. Beavis, M. Dickson and the Rackham family including Alan Snr, Alan Jnr, Kerry and Dale. Highly skilled fossil preparation was undertaken by Dr Anna Gillespie. Assistance in the field has come from many hundreds of volunteers as well as staff and postgraduate students at the University of New South Wales.