In its Northern Hemisphere environment, Grey Squirrels weigh 400–500 g (although specimens up to 800 g have been reported), have a total length of about 460 mm including a tail of about 215 mm (Barkalow & Shorten 1973; Tittensor 1977). Victorian specimens from the Ballarat colony were generally close to these dimensions (Seebeck 1984).
Palm Squirrels are much smaller. Adults weigh about 135 g, but may reach nearly 200 g (Wright 1972). Watts & Aslin (1981) quote size as total length 250–270 mm and tail length 110–120 mm. Nine live animals measured by Scanlan, Gorton & Pearsall (1978) averaged 243 mm (range 200–300 mm) and a specimen in the Western Australian Museum has a total length of 292 mm.
Both species have conventional small mammal skeletal systems, although the ankles, as in all tree-squirrels, display extraordinary rotational capabilities, an adaptation for arboreality. Dentition in the sciurids (Fig. 46.2) differs from that of Australian native and introduced rodents (Family Muridae) by the presence of premolars, which are simple or molariform. The skulls are distinguished from those of murids by the presence of a pronounced supra-orbital spine and a small infraorbital foramen which is rounded, never slit-like. The tibia and fibula are separate. Sharp, curved, non-retractable claws aid in climbing.
Figure 46.2 The skull (A-F), in dorsal, lateral and ventral view, and lateral view of the mandible (G, H) of squirrels. A, C, E, G, the American Grey Squirrel, Sciurus carolinensis, and the Northern Palm Squirrel, Funambulus
pennanti. (© ABRS)