Wyulda squamicaudata, Alexander, 1918

CROSBY, KIRSTEN & NORRIS, CHRISTOPHER A., 2003, Periotic Morphology in the Trichosurin Possums Strigocuscus celebensis and Wyulda squamicaudata (Diprotodontia, Phalangeridae) and a Revised Diagnosis of the Tribe Trichosurini, American Museum Novitates 3414, pp. 1-16 : 1-2

celebensis and the scaly­tailed possum Wyul­ da squamicaudata are small to medium­size

members of the marsupial family Phalangeridae . Both species bear a superficial resemblance to members of the most diverse and abundant group of phalangerids, the true cuscuses of the genus Phalanger . In the case of

1 Graduate Student, School of Biological Sciences, University of New South Wales, Sydney, Australia, e­mail: [e-mail].

2 Curatorial Associate, Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History, e­mail: [e-mail]. Present address: Division of Paleontology, American Museum of Natural History.

Copyright © American Museum of Natural History 2003

ISSN 0003­0082

S. celebensis this similarity led to inclusion of the species in Phalanger (e.g., Tate, 1945), a situation which prevailed as the accepted taxonomy until comparatively recently. By contrast, Wyulda has always been recognized as a distinct taxon, with craniodental characters that indicate a close affinity to the brushtailed possums of the genus Trichosurus .

The division of the Phalangeridae into two groups, the monogeneric cuscuses and the two genera of possums, remained unchallenged until the phylogenetic revision of Flannery et al. (1987), who proposed that cuscuses were paraphyletic with respect to the possums. The Phalangeridae were divid­ ed into two subfamilies, the Ailuropinae, containing a single species Ailurops ursinus , and the Phalangerinae, containing all the remaining species of phalangerid. The Phalangerinae were divided into a further two groups: the tribes Phalangerini and Trichosurini . Flannery et al. (1987) resurrected the generic name Strigocuscus from synonymy within Phalanger and placed the genus within the Trichosurini , along with Wyulda and Trichosurus . As originally defined by Flannery et al., Strigocuscus contained four species formerly included within Phalanger : S. celebensis , S. gymnotis , S. ornatus , and S. rothschildi . A fifth taxon, S. mimicus , was raised from subspecific status within Phalanger orientalis . Subsequent studies have removed all species but S. celebensis from within the group and added a new species, S. pelengensis ( George, 1987; Springer et al., 1990; Norris, 1992; Flannery, 1994; Hamilton and Springer, 1999), previously a subspecies of S. celebensis ( Tate, 1945) . The generic placement of this taxon is still under debate.

A study by Norris (1994) described the periotic bones of various phalangerid species and categorized three periotic morphologies which more or less corresponded to the divisions originally proposed by Flannery et al. (1987), together with the narrower definition of Strigocuscus made by later authors. Norris only studied one trichosurin periotic in detail, that of Trichosurus vulpecula . No loose periotic of either S. celebensis or W. squamicaudata was available for examination.

The fact that periotic morphology in phal­ angerids corresponded so closely to the phylogenetic divisions created by analysis of a broad character set of morphological and molecular characters suggested that a study of this region in specimens of fossil phalangerids from Tertiary deposits at Riversleigh, Australia, might provide insights into the early evolution and diversification of the group. In superficial morphology, the Riversleigh species appear to be trichosurin. However, they also possess a number of cranial characters that are plesiomorphic for phalangerids as a whole. Flannery et al. (1987) hinted at this in their list of synapomorphies for the trichosurins, where they noted that the Riversleigh species Trichosurus dicksoni exhibited the plesiomorphic state for some characters. A comparison of the periotic of this species and of Strigocuscus reidi , also from Riversleigh, showed a very different morphology than that of T. vulpecula , as discussed by Norris (1994). In fact, examination of these, and other, extinct taxa from Riversleigh suggest that a much broader range of periotic morphologies may be present within the group than is apparent from its extant members. Since other craniodental characters of these fossil species suggest that the majority of them have trichosurin affinities (K.C., in prep.), a broader knowledge of the periotic anatomy of the living trichosurins is required. To this end, periotics of Strigocuscus celebensis and Wyulda squamicaudata were dissected from skulls housed in the Department of Mammalogy at the American Museum of Natural History (AMNH) and studied in detail.