Phascolarctos, Blainville, 1816

Price, Gilbert J., Zhao, Jian-xin, Feng, Yue-xing & Hocknull, Scott A., 2009, New Records of Plio-Pleistocene Koalas from Australia: Palaeoecological and Taxonomic Implications, Records of the Australian Museum 61 (1), pp. 39-48 : 44

Phascolarctos ? stirtoni

Figs 4B, C

Referred material. QMF52289, isolated RM 1 , 2 or 3 fragment, QML7, Chinchilla , southeast Queensland, Australia (Middle Pliocene) ; QMF52290 isolated RM 2 fragment, QML1420 Marmor Quarry , central eastern Queensland, Australia (Middle Pleistocene; Table 1) .

Description. RM 1, 2 or 3, description based on QMF52289: Metacone only major cusp preserved, very large, worn; postmetacrista moderately developed, descends apex of metacone posterobuccally to small stylar cusp E; buccal crest small but distinct, directed anteriorly from stylar cusp E, slightly ascending buccal margin of tooth; posterior cingulum large, worn; molar enamel crenulated at posterolingual base of metacone.

RM 2, description based on QMF52290: Protocone only major cusp preserved; preprotocrista well developed, descends anterobuccally to lingual portion of anterior cingulum; postprotocrista descends posterobuccally to base of protocone; rib descends protocone between pre- and postprotocristae, well developed; anterior fossette well developed at anterior base of protocone; lingual cingulum well developed, extending along lingual margin at base of protocone, ascending and terminating at lingual corner of tooth; molar enamel crenulated on all sides of protocone.

Remarks. The wear pattern on the posterior margin of the metacone molar fragment (QMF52289) is consistent with wear from abrasion with a succeeding tooth whilst still in the maxilla. This suggests that the specimen represents either an M 1, 2 or M 3, rather than an M 4 (the most posterior tooth in phascolarctids). On the basis of molar morphology, the teeth are referable to Phascolarctos due to: (a) their well-developed molar crenulations; (b) minor degree of development of stylar cusps and associated stylar shelf (QMF52289); (c) welldeveloped lingual cingulum (QMF52290); and (d) being higher-crowned than all other phascolarctids (excepting Cundokoala (?Ph.) yorkensis ). Morphometrically, both teeth are larger than corresponding teeth of Ph. cinereus , but are smaller than corresponding teeth of C. (?Ph.) yorkensis . The protocone fragment (QMF52290) is morphologically similar to the corresponding M 2 of Ph. stirtoni , particularly in the development of the anterior fossette at the base of the protocone, and the anterolingual extension of the lingual cingulum. The metacone fragment (QMF52289) lacks a welldeveloped stylar shelf as exhibited in C. (?Ph.) yorkensis , and in that respect, closely resembles the condition exhibited in Ph. stirtoni . Corresponding teeth of Ph. maris and C. (?Ph.) yorkensis are either not known or are poorly represented, thus, preventing further comparison to the material described here. However, the molar fragments described here are similar in size to Ph. stirtoni , a species that is intermediate in size between Ph. maris and C. (?Ph.) yorkensis ( Pledge, 1987, 1992). Thus, QMF52289 and QMF52290 are unlikely to be referable to those poorly known taxa. The fragmentary nature of the material precludes additional comparison to Ph. stirtoni .

Figures

Fig. 4. Photographs of fossil koala teeth from eastern Australia. (A) QMF52288, LM2 of Phascolarctos sp., site QML1384, Mt. Etna. (B) QMF52289, RM1, 2 or 3 metacone fragment of Ph.?stirtoni, Chinchilla. (C) QMF52290, RM2 protocone fragment of Ph.?stirtoni, Marmor.