New genus of primitive wombat (Vombatidae, Marsupialia) from Miocene deposits in the Riversleigh World Heritage Area (Queensland, Australia)

Abstract

Brewer, Philippa, Archer, Michael, Hand, Suzanne J., and Abel, Richard. 2015 A new genus of primitive wombat, described here, is the most complete early wombat found. Two partial maxillae, as well as isolated teeth, were found within the Riversleigh World Heritage Area in northwestern Queensland, Australia. Previous to this, only a single species of wombat (Rhizophascolonus crowcrofti) was known from deposits older than 10 Ma, despite an estimated divergence date of 40 Ma between wombats and their closest living relative, the koala. We performed a phylogenetic analysis incorporating the new taxon and using dental, cranial and postcranial characters as well as multiple outgroups in order to control for the diverse specialisations of closely related families and the continuing problem of recognising homologies within these groups. The results indicate a sister relationship between the new taxon and R. crowcrofti relative to all other wombats. Based on detailed comparisons between the cheek teeth of wombats, we propose a model which explains the observed differences in cheek tooth form and function in this group. If this model is correct, it could be used to map morphology against diet, and potentially climate.Brewer, Philippa. Department of Earth Sciences, Natural History Museum, London SW7 5BD. p.brewer@nhm.ac.uk Archer, Michael.

A new species of Miocene wombat (Marsupialia, Vombatiformes) from Riversleigh, Queensland, Australia, and implications for the evolutionary history of the Vombatidae

“…Regardless, the P3 cusp morphology for R. ngangaba and V. ursinus and L. latifrons show many differences ( Figure 13), and identifying homologous cusps between these taxa and other Vombatiformes is challenging. P3 of R. ngangaba is most similar to that of N. boodjamullensis (Brewer et al, 2015). Interestingly, the pattern of enamel around the perimeter of the adult teeth of R. ngangaba, N. boodjamullensis, and species of Warendja is similar and contrasts to that of V. ursinus, L. latifrons, P. gigas, S. medius, and R. magna, where it is most extensive on the lingual surface, not the buccal.…”

“…On some specimens (QM F209494 and QM F57963), the anterolingual root is twisted over the posterior root away from the occlusal surface. This is interpreted to be a feature more commonly seen at the anterior of the tooth row (Brewer et al, 2015), due to individual variation or possibly due to impacted growth.…”

“…A phylogenetic analysis was performed using three outgroups: one representative of each of the two vombatiform families which are consistently shown to be more plesiomorphic than wombats i.e., Phascolarctidae and Thylacoleonidae (e.g., Black et al, 2012a;Brewer et al, 2015), and a bandicoot, considered plesiomorphic relative to Diprotodontia (e.g., Beck 2008) and with a relatively unspecialised tooth morphology in comparison to notoryctemorphians and dasyuromorphians. Species selected were based on availability of relatively complete specimens and their phylogenetic position within their respective families.…”

“…Molecular clock estimates suggest they diverged from phascolarctids (the family that includes their closest living relative, the koala) around 40 Ma (Beck, 2008), but they do not appear in the fossil record until the early Miocene (Brewer et al, 2015). Two monotypic genera of vombatids have been described from early Miocene (Nimbavombatus boodjamullensis; Brewer et al, 2015) and early/middle Miocene (Rhizophascolonus crowcrofti; Stirton et al, 1967;Brewer et al, 2008;Black et al 2012) deposits, respectively. Following this, we see a single species in the late Miocene (Warendja encorensis; Brewer et al, 2007), and then a radiation of taxa in the Plio-Pleistocene (Murray, 1998).…”

“…Four additional specimens from Riversleigh are recognised here (QM F57960, QM F57961, QM F57962, and QM F12452; Figure 6). QM F57961 and QM F57962 are interpreted to be m2 or m3s based on the similar size of the moieties (length and width) and the relatively wide dentine tracts on anterior and posterior surfaces (Brewer et al, , 2015. QM F57960 and QM F12452 have a narrow dentine tract on the posterior surface, which may indicate that they are m3 or m4s.…”