Understanding morphological variation in the extant koala as a framework for identification of species boundaries in extinct koalas (Phascolarctidae; Marsupialia)

Abstract

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 n. sp. 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.

Description of new cranial material of Propalorchestes (Marsupialia: Palorchestidae) from the Middle Miocene Camfield Beds, Northern Territory, Australia

“…Without a substantial data set, variation within any given population between geographical regions, or over substantial periods of time, is difficult to define for fossil taxa. Regarding extant Vombatiformes, Black et al (2014) detailed modern koala dental variation and related it to fossil taxa. Sharp and Trusler (2015) provide a brief summary of the morphological variation seen in the wombat genera Vombatus and Lasiorhinus.…”

Middle Miocene origins for tough-browse dietary specialisations in the koala (Marsupialia, Phascolarctidae) evolutionary tree: description of a new genus and species from the Riversleigh World Heritage Area

“…nov. is described here on the basis of a single first lower molar (M 1 ) from a middle Miocene deposit, Jim's Jaw Site. Despite the relative scarcity of material, M 1 has previously been demonstrated to hold considerable taxonomic and phylogenetic significance within Phascolarctidae (Black et al, 2012a(Black et al, , 2014a(Black et al, , 2014b. Consequently, Stelakoala riversleighensis is shown here to represent a significant stage in the evolution of this iconic and once diverse group of Australian marsupials.…”

“…Taxonomically valid phascolarctid species are those identified by Black et al (2014b). Reference to Litokoala kutjamarpensis is sensu Louys et al (2007) and Black et al (2014a). Biostratigraphic nomenclature follows Archer et al (1994Archer et al ( , 1997b, Creaser 1997 andTravouillon et al (2006).…”

“…2B-C), giving the appearance of a 'twinned' entoconid similar to that found in Phascolarctos. Also as in Phascolarctos spp., moderate depressions occupy the lingual face of the entoconid between the lingual ribs and the preentocristid (anterolingually) and postentocristid (posterolingually) (see entoconid lingual shelf of Black et al 2014a; fig. 2).…”

“…Nimiokoala greystanesi Black and Archer, 1997, Litokoala kutjamarpensis and Litokoala dicksmithi Black, Louys and Price, 2014a), most specimens comprise isolated teeth or, at best, partial dentitions. Stelakoala riversleighensis gen. et sp.…”