Litokoala

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 : 326-327

† Litokoala

SPECIES SCORED: † Litokoala kutjamarpensis (type species), † L. dicksmithi.

GEOLOGICAL PROVENANCE OF SCORED SPECIMENS: UCR Locality RV-8453 (Kanunka North Local Fauna), Etadunna Formation, Lake Kanunka, South Australia, Australia († L. kutjamarpensis); Jim’s Carousel, Henk’s Hollow, Dwornamor, and Gotham sites (Riversleigh Faunal Zone C), Riversleigh World Heritage Area, Queensland, Australia († L. kutjamarpensis); Ross Scott-Orr Site (Riversleigh Faunal Zone B), Riversleigh World Heritage Area, Queensland, Australia († L. dicksmithi).

AGE OF SCORED SPECIMENS: Based on the paleomagnetic data of Woodburne et al. (1994), Metzger and Retallack (2010) estimated the Etadunna Formation to span 26.1–23.6 Mya. Riversleigh Faunal Zone B and C are interpreted to be early and middle Miocene, respectively, based on biostratigraphy (see above), but only Ross ScottOrr (RSO) Site has a radiometric date, of 16.24– 16.86 Mya (Woodhead et al., 2014). We conservatively assign an age range of the entire late Oligocene to middle Miocene (Chattian to Serravalian; Cohen et al., 2013 [updated]) for this taxon.

ASSIGNED AGE RANGE: 27.820 –11.630 Mya.

REMARKS: † Litokoala is one of only two fossil phascolarctids known from relatively complete craniodental material (Louys et al., 2009; Black et al., 2014a), but its taxonomic history is complex and remains controversial. † Litokoala kutjamarpensis was described by Stirton et al. (1967a) based on a single M1 from the Kutjamarpu Local Fauna, Wipajiri Formation, Lake Ngapakaldi, South Australia. Springer (1987) then described a second species, † L. kanunkaensis, based on two isolated lower molars and two partial upper molars from the Kanunka North Local Fauna, Etadunna Formation, Lake Kanunka, South Australia. Black and Archer (1997b) subsequently referred several phascolarctid dental specimens from a number of Riversleigh Faunal Zone C sites to † L. kanunkaensis. However, based on study of the dentition of a new, well-preserved partial cranium (QM F51382 ) from the Riversleigh Faunal Zone C JC Site, Louys et al. (2007) concluded that † L. kanunkaensis is a junior synonym of † L. kutjamarpensis. Louys et al. (2007) also named a new species, † L. garyjohnstoni, based on a partial maxilla and isolated M4 from the Riversleigh Faunal Zone B Outasite Site. Louys et al. (2009) subsequently gave a detailed description of the cranial morphology of QM F51382 , which they maintained represents † L. kutjamarpensis.

Pledge (2010), however, retained † L. kanunkaensis as a separate species for the isolated molars from the Kanunka North Local Fauna described by Springer (1987), referred the Riversleigh Faunal Zone C specimens (including QM F51382 ) to a new species, † L. dicktedfordi, and named a further species, † L. thurmerae, based on an isolated M3 from the?late Oligocene Ngama Local Fauna, Lake Palankarinna, South Australia. Thus, Pledge (2010) recognized five species: † L. kutjamarpensis (Kutjamarpu Local Fauna;?early or middle Miocene), † L. kanunkaensis (Kanunka North Local Fauna;?late Oligocene), † L. garyjohnstoni (Riversleigh Faunal Zone B;?early Miocene), † L. dicktedfordi (Riversleigh Faunal Zone C;?middle Miocene), and † L. thurmerae (Ngama Local Fauna;?late Oligocene). Most recently, Black et al. (2014a, 2014b) reaffirmed that † L. kanunkaensis (including the Riversleigh Faunal Zone C species referred to † L. dicktedfordi by Pledge, 2010) is a junior synonym of † L. kutjamarpensis, considered † L. thurmerae to be a nomen dubium, and named yet another new species, † L. dicksmithi, based on a well-preserved rostral fragment (QM F54567 ). Here we follow the taxonomy of Louys et al. (2007, 2009) and Black et al. (2014a, 2014b), who recognized only two species within the genus: the type species, † Litokoala kutjamarpensis, and † L. dicksmithi.

We scored our † Litokoala terminal based on specimens of † L. kutjamarpensis from both the Kanunka North Local Fauna and Riversleigh Faunal Zone C sites, and also on the only known specimen (QM F54567 ) of † L. dicksmithi. Based on this material, † Litokoala appears to have lacked masticatory specializations seen in Phascolarctos (Louys et al., 2009) . In addition, estimated body masses for † Litokoala species (2.4–4.6 kg; Black et al., 2014a; 2014b) are considerably less than those of P. cinereus (4.1–13.5 kg; Martin et al., 2008). Nevertheless, phylogenetic analyses of vombatiform relationships based on 71 craniodental characters by Black et al. (2012a) supported a sister-group relationship between † Litokoala and Phascolarctos to the exclusion of the other currently named fossil phascolarctid genera, and Beck et al. (2020 fig. 5) found † Litokoala to be paraphyletic with respect to Phascolarctos , with † L. kutjamarpensis and Phascolarctos forming a clade to the exclusion of † L. dicksmithi. However, an undescribed new genus and species of phascolarctid from the Riversleigh Faunal Zone D Encore Site, previously identified as Phascolarctos sp. by Myers et al. (2001), may be more closely related to the living genus than is † Litokoala (Black et al., 2014b) .