Phascolarctos sp.

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 : 43-44

Phascolarctos sp.

Figs 3B , 4A

Referred material. QMF52288, isolated LM 2, QML1384 ( Unit “L.U.”; Elephant Hole Cave ), Mt. Etna , central eastern Queensland, Australia (Middle Pleistocene; Table 1)

Description. LM 2 with anterior portion missing; tooth trapezoidal in occlusal outline, tapering posteriorly; protocone and paracone sub-equal in height, slightly taller than metacone and metaconule, neometaconule shortest cusp; protocone most anterior cusp forming anterolingual corner of tooth; paracone transverse, slightly posterior to protocone, forming anterobuccal margin of tooth; metacone directly posterior to paracone forming posterobuccal corner of tooth; metaconule posterobuccal to protocone, transverse to metacone, forming posterolingual corner of tooth; postprotocrista well developed, descends posterobuccally from apex of protocone to meet with premetaconulecrista; cristae on paracone missing; rib descends posteriorly from apex of paracone to mid-crown basin; premetacrista well developed, descends anterobuccally from apex of metacone, terminating at stylar cusp D; postmetacrista well defined, descends posterobuccally from apex of metacone; posterolingual crista weakly-expressed descending from metacone apex to posterolingual base of metacone; neometaconule small, distinct at anterolingual base of metacone; premetaconulecrista well developed, descends anterobuccally from apex of metaconule terminating at midcrown basin; postmetaconulecrista well developed, descends posterobuccally from apex of metaconule, with inflexion at posterior cingulum; lingual cingulum moderately developed at base of crown between protocone and metaconule; posterior cingulum well defined, descends from inflexion with postmetaconulecrista, terminating at posterobuccal corner of tooth near stylar cusp E; metacone buccal ridge small, descends posteriorly from stylar cusp D, terminating at posterobuccal corner of tooth; molar enamel heavily crenulated.

Remarks. QMF52288 is regarded as an M 2 due to its trapezoidal occlusal outline that tapers posteriorly and by its possession of a relatively small neometaconule, identical to that of M 2 in other species of Phascolarctos . QMF52288 is significantly larger than corresponding teeth of Koobor , Madakoala , Perikoala , Nimiokoala and Litokoala , and Ph. cinereus . However, the tooth is morphologically similar to other species of Phascolarctos . In comparison to Ph. stirtoni , the posterior cingula is relatively smaller, molar enamel is less crenulated (although that feature may be slightly variable judging from variation expressed in large samples of modern Ph. cinereus ), and the tooth is smaller overall ( Fig. 3B ). However, judging by the range of morphometrical variation exhibited in modern Ph. cinereus ( Fig. 3B ), QMF52288 could easily fall within the lower size range of Ph. stirtoni . QMF52288 is somewhat similar in morphology to extant Ph. cinereus . However, it is larger and falls outside the morphometrical range of variation of modern populations ( Fig. 3B ). Pledge (1987) suggested that Ph. maris (a species questionable distinct from Ph. stirtoni ; see Black, 1999) is intermediate in size between the smaller Ph. cinereus and larger Ph. stirtoni . Thus, QMF52288 potentially represents Ph. maris . However, it is not possible to compare QMF52288 to Ph. maris (nor to the significantly larger Cundokoala (?Ph.) yorkensis ) as corresponding teeth are unknown in those species.

Figures

Fig. 3. Morphometrics of fossil koala specimens. (A) Depth versus width of dentaries of modern Phascolarctos cinereus from eastern Queensland (Appendix), fossil Cundokoala (?Ph.) yorkensis (SAMP24904) from Corra Lynn Cave (South Australia), and phascolarctid gen et. sp. indet (QMF52287) from Chinchilla, eastern Australia. Note that the depth of the Chinchilla koala dentary is a minimum measurement because the specimen is broken along the alveolar border (Fig. 2). (B) Anterior versus posterior width of Phascolarctos spp. M2 (See Appendix for list of modern Ph. cinereus specimens examined).

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.