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

Abstract

Additional material referable to Propalorchestes novaculacephalus from the middle Miocene Camfield Beds is described. A cranium prepared in 1999-2000 from material collected on the T. H. Rich expedition of 1981 represents the most complete skull of the genus found to date. The detailed preservation of the previously unknown rostral anatomy supports the hypothesis that Propalorchestes possessed retracted nasal morphology. Cheek teeth from the skull and an additional isolated mandibular fragment from the same site, adds to the dental record for the genus. It further supports the intermediate condition of the molar morphology between the fully bilophodont Palorchestes and the subselenodont/ semilophodont wynyardiid morphologies. The highly retracted nasal morphology and corresponding mandibular features demonstrate an advanced and highly derived condition in contrast to the plesiomorphic features previously described for the basicranium. In comparison to the generalized rostral anatomy of the sister group, the early to middle Miocene Diprotodontidae, this more complete record of Propalorchestes cranial morpholgy, suggests a significantly earlier origin for the highly derived facial anatomy in the Palorchestidae.

The extraordinary osteology and functional morphology of the limbs in Palorchestidae, a family of strange extinct marsupial giants

“…The preceding descriptions depict a morphocline within the palorchestid lineage toward the highly derived forelimb seen in the largest and latest species Palorchestes azael . Prior analyses of the cranial morphology of the group have recognised that their apomorphic cranial characteristics were already well-established in the smaller, earliest-known species and that the origin of their specialised rostrum was not associated with increasing body size [28, 36, 37, 68]. Here we demonstrate that specialisation of the postcrania was delayed relative to the skull, and may indeed have been linked to increasing body size.…”

“…parvus may have been sympatric at the Buchan site (Table 2), the body size disparity we have shown between the species is interesting. Trusler and Sharp [37] note that the coexistence of palorchestid species at various periods in their evolutionary past–particularly during the Pleistocene–shows that smaller species were able to persist in the same environmental conditions in which their close relatives achieved gigantism. While P .…”

“…Recent discovery of new fossils and subsequent re-examination of all known palorchestid cranial material have challenged this longstanding tapir analogy, omitting the hypothesised proboscis in favour of a sensitive prehensile lip accompanied by a long protrusible tongue [36]. Whatever its fleshy appearance, this unique rostral morphology was already evident in the earliest-known palorchestid crania, indicating early cranial specialisation at some point after their divergence from the Diprotodontidae [28, 37].…”

Low elbow mobility indicates unique forelimb posture and function in a giant extinct marsupial

“…This suggests that Palorchestes azael was experiencing strong constraints preventing their forelimb from undergoing the postural shifts associated with optimal locomotion at large body sizes. Most likely this was due to their dependence on the forelimb for food acquisition, a habit which appears to have persisted throughout their lineage given the consistency of specialised palorchestid craniodental and postcranial morphologies since the early Miocene (Richards et al, 2019; Trusler & Sharp, 2016). We suggest this forelimb anatomy may have been used either in scratch digging or, perhaps more likely, bipedal browsing—a functional niche unrepresented among living mammals (Coombs, 1983).…”

Craniodental morphology and phylogeny of marsupials

“…Bartholomai (1978), the superfamily †Diprotodontoidea is currently considered as comprising the families †Diprotodontidae and †Palorchestidae (see also Archer, 1984c;Archer et al, 1999;Long et al, 2002;Archer and Hand, 2006;Black et al, 2012b). We have not included any palorchestids (the so-called "marsupial tapirs"; Bartholomai, 1978;Archer, 1984c;Flannery and Archer, 1985;Murray, 1986;Murray, 1990;Archer et al, 1999;Long et al, 2002;Archer and Hand, 2006;Black, 2006;Mackness, 2008;Black et al, 2012b;Trusler, 2016;Trusler and Sharp, 2016;Richards et al, 2019) as terminals here, so we cannot distinguish between craniodental apomorphies for †Diprotodontoidea and those for †Diprotodontidae; however, future inclusion of palorchestids should reveal which apomorphies apply to †Diprotodontidea, and which are specific to †Diprotodontidae.…”