Morphological variation within an individual Pleistocene Diprotodon optatum Owen, 1838 (Diprotodontinae; Marsupialia): implications for taxonomy within diprotodontoids

A comprehensive understanding of morphological and morphometrical variation for systematically important characters is a prerequisite for reliable taxonomic analyses of extinct morphospecies. However, perception of such variation is commonly limited due to a paucity of fossil material that forms the basis of such analyses. Here we report a new record of Pleistocene Diprotodon optatum Owen, 1838 (Diprotodontoidea) represented by near-complete upper tooth rows that exhibit a high degree of individual variation within systematically important upper premolars. The individual possesses features (e.g. development of parastyle, anterocristae and anterior longitudinal groove) that are considered to be close to the polar extremes of premolar variation within the morphospecies, but occurring on either side of the palate. Although such morphologies were previously recognized on the basis of isolated specimens, they have never been observed as having occurred on either side of the tooth row within a single indvidual....