Yalkaparidon

Beck, Robin M. D., Voss, Robert S. & Jansa, Sharon A., 2022, Craniodental Morphology And Phylogeny Of Marsupials, Bulletin of the American Museum of Natural History 2022 (457), pp. 1-353 : 339

† Yalkaparidon

SPECIES SCORED: † Yalkaparidon coheni (type species), † Yalkaparidon . sp.

GEOLOGICAL PROVENANCE OF SCORED SPECIMENS: Riversleigh Faunal Zone B, Riversleigh World Heritage Area, Queensland, Australia.

AGE OF SCORED SPECIMENS: Riversleigh Faunal Zone B is interpreted to be early Miocene, based on biostratigraphy (see above). In the absence of radiometric dates, we have assumed the entire span of the early Miocene (Aquitanian to Burdigalian; Cohen et al., 2013 [updated]) for this terminal.

ASSIGNED AGE RANGE: 23.030 –15.970 Mya.

REMARKS: † Yalkaparidon is unique among Australian fossil metatherians in that it is known from extensive craniodental material, including a well-preserved partial skull (QM F13008, the holotype of † Y. coheni ), and yet cannot be confidently referred to one of the seven extant Australian marsupial orders (Archer et al., 1988; Beck et al., 2014). This is due to its unique combination of dental features, including hypselodont first upper and lower incisors; a procumbent, gliriform lower first incisor; zalambdodont molars; and a cranial morphology that appears plesiomorphic compared with other known Australian marsupials yet also exhibits some striking apomorphic features (such as a very reduced postglenoid process, a transverse canal foramen that is posterior to the carotid foramen, and very robust and posteriorly extensive entopterygoid crests; Archer et al., 1988; Beck, 2009; Beck et al., 2014). Marshall et al. (1990) and Szalay (1994) suggested that † Yalkaparidon is a member of Diprotodontia , whereas Woodburne and Case (1996) placed it in Notoryctemorphia . However, the most detailed studies of † Yalkaparidon to date suggest that it be placed in its own order, †Yalkaparidontia (Archer et al., 1988; Beck et al., 2014). Isolated tarsals tentatively referred to † Yalkaparidon preserve apomorphic features that appear to be characteristic of australidelphians (Beck et al., 2014), and some phylogenetic analyses have placed † Yalkaparidon within Australidelphia (Beck et al., 2014; Beck et al., 2016); however, other analyses have placed † Yalkaparidon in a clade with paucituberculatans (Beck, 2017b; Zimicz and Goin, 2020), with which it shares presence of a gliriform lower first incisor.

Archer et al. (1988) described two species, both from Riversleigh: † Yalkaparidon coheni (based on specimens from Faunal Zone B) and † Y. jonesi (based on specimens from Faunal Zone C). Beck et al. (2014) examined all known material of † Yalkaparidon collected to date from Riversleigh, and identified additional specimens of † Y. coheni and other † Yalkaparidon material not identifiable to species level from one Riversleigh Faunal Zone A site (White Hunter) and multiple Faunal Zone B sites (see Beck et al., 2014: electronic supplementary material); only Faunal Zone B specimens have been used for scoring purposes here. We did not score character data from specimens of † Y. jonesi , which appears to be more derived than † Y. coheni in lacking any teeth between the enlarged procumbent anteriormost lower incisor and the tooth that Archer et al. (1988) referred to as p3 but which Beck et al. (2014) argued is m1.