Smallbodied Omnivores

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In contrast to the miniature flower specialists, petaurids are larger in size and apparently less dependent on nectar and pollen. Perhaps the most primatelike member of the family is the Leadbeater's possum, Gymnobelideus lead-beateri, which is restricted to moist eucalypt forests in mountains of southern Australia. Gymnobelideus was believed to be extinct for many decades, until it was rediscovered in the wild in the 1960s (Smith, 1984a). Gymnobelideus weighs between 100 and 170 g, so it is within the size range of the ecologically similar cheirogaleids; it looks superficially like a South Australian version of Madagascar's Phaner (Figure 5). It is quite prosimian-like in appearance, with a short face, large and moderately convergent orbits, black facial markings and a dorsal stripe, with grasping hands and feet. Unlike many phalangeroids, it lacks both a gliding membrane and a prehensile tail. The species is noctur-

Figure 5. Comparison between the possum Gymnobelideus (A) and the primate Phaner (B). Photograph (A) by A. Smith; photograph (B) by R. Mittermeier reproduced with his permission.

Figure 5. Comparison between the possum Gymnobelideus (A) and the primate Phaner (B). Photograph (A) by A. Smith; photograph (B) by R. Mittermeier reproduced with his permission.

nal, and is an agile arborealist, capable of making leaps of a meter or more in distance. The diet is very similar to those of cheirogaleids, consisting of insects, tree exudates, flower products, and even secretions of homopteran insects, as also observed in Phaner and Mirza (Hladik et al., 1980; Pages, 1980; Smith and Ganzhorn, 1996; Smith, 1984c, 1984d; Sussman, 1999; Wright and Martin, 1995). Gymnobelideus resembles the primates Callithrix, Cebuella, and Phaner in gouging or scraping tree trunks to generate the flow of exudates (Charles-Dominique and Petter, 1980). The arthropod prey of Gymnobelideus consists of tree crickets, beetles, moths, and spiders (Lee and Cockburn, 1985). In addition, these marsupials feed on manna (a carbohydrate exudate from eucaplypt leaves). Among phalangeroids, Gymnobelideus is one of the best overall matches ecomorphologically to the primitive primate Mirza, the exudate specialist Phaner, and the primate-like didelphid Caluromys.

The other nongliding genus in Petauridae is Dactylopsila, which has already gained fame in comparison to primates by sharing a specialized feeding adaptation with the Malagasy aye-aye, Daubentonia (Cartmill, 1974b; Rand, 1937). Both taxa have enlarged incisors for gouging wood, which they utilize to open the tunnels of wood-boring larvae, and an elongated finger on the hand tipped with a hooked nail, which they use to ream out beetle larvae. Both tap the wood with their forefeet, apparently using auditory clues to detect subsurface features (Erickson, 1995). The small-bodied Dactylopsila is even more similar in size and shape to the extinct apatemyids than it is to the much larger Daubentonia; apatemyids were a very successful group of arboreal Eocene mammals widespread in North America and Europe (Koenigswald, 1987). It has been pointed out that Madagascar, Australasia, and the Eocene all lack woodpeckers (Picidae), birds that specialize on wood-boring larvae on most landmasses today (Cartmill, 1974b; Koenigswald, 1987). Dactylopsila is reported to be a frenetic, extremely quick and active arborealist, quite a contrast to the more deliberate, heavy Daubentonia. In addition to its wood-boring activities, Dactylopsila breaks into the nests of eusocial insects (Smith, 1982b), and also feeds on crickets, spiders, and other arthropods (Lee and Cockburn, 1985). Dactylopsila shows greater orbital convergence than phalangerids proper (Cartmill, 1972). In the future, research should investigate the extent to which the adaptations of Dactylopsila match primate attributes aside from the aye-aye parallels.

The gliding petaurids (Petaurus), such as the sugar glider (P. breviceps), have been noted by many zoologists to be reminiscent of primates. The larger-bodied and more folivorous species, such as P. australis (up to 700 g), are much more heavily clawed than is the small species, P. breviceps (100-160 g), which has more primate-like hands. This difference presumably indicates that the larger forms are utilizing thicker, supportive branches and trunks that exceed the grasping diameter of their hands. P. breviceps also differs from its larger congeners in having a flatter, primate-like face (reflected in the species name), and it apparently exhibits more orbital convergence than the larger forms (Figure 6). P. breviceps resembles some cheirogaleid and galagine primates in having a diet consisting of insects, fruit, tree exudates, and homopteran secretions (Henry and Suckling, 1984; Smith, 1982a). In a fine display of visually directed predation, P. breviceps has been observed to leap at and catch moths in flight (Nowak and Paradiso, 1983). Members of the genus

Placental Mammals Examples

Figure 6. The possum Petaurus norfolcensis (A), one of the larger species of gliding petaurids, compared to Galago moholi (B), a small galagine. Photograph (A) by E. Beaton, www.estherbeaton.com; photograph (B) T. Rasmussen.

Figure 6. The possum Petaurus norfolcensis (A), one of the larger species of gliding petaurids, compared to Galago moholi (B), a small galagine. Photograph (A) by E. Beaton, www.estherbeaton.com; photograph (B) T. Rasmussen.

communicate chemically using well-developed scent glands, and vocally by using a diversity of calls (Goldingay, 1992). P. breviceps nests gregariously in apparent kin groups of up to about seven individuals. Its life history is also similar to that of small-bodied prosimians, producing one litter per year of one or two offspring, which grow up fairly slowly. The young are independent at three months and disperse by about 10 months of age.

Gymnobelideus, Dactylopsila, and Petaurus have the highest encephaliza-tion quotients of any marsupials, a final important parallelism with primates (Lee and Cockburn, 1985; Nelson and Stephan, 1982).

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