A Porpoise, Australophocaena dioptrica, Previously Identified As Phocoena spinipinnis, From Heard Island

Guiler, Burton and Gales (1987) reported a cranium (Tasmanian Museum No. A141 1) they identified as belonging to Burmeister’s porpoise, Phocoena spinipinnis Burmeister, 1865 from Heard Island (53°S 73°30’E). They noted that P. spinipinnis was previously known only from the cold-temperate coastal waters of South America and claimed that this cranium was evidence that the species has a much wider distribution than previously known. We have examined the photographs and details of their specimen and re-identify it here as Australophocaena dioptrica (Lahille, 1912) (family Phocoenidae). Barnes (1985) listed several features that distinguish the skulls of species within the subfamily Phocoenoidinae (including A. dioptrica) from those species within the Phocoeninae (including Phocoena spp.). Features that distinguish A. dioptrica from P. spinipinnis, dearly visible in the published photographs of the cranium from Heard Island, include: a relatively small, oval-shaped temporal fossa; an elevated, high-vaulted braincase that slopes abruptly onto the narial region; relatively large, high and convex premaxillary bosses; dorso-ventrally expanded zygomatic process of the squamosal; short and antetoposteriorly expanded postorbital process of the fronds; and maxillae extendmg nearly to the dorsal margin of the supraoccipital on the top of the skull. In all these features, the Heard Island specimen conforms with those of A. dioptrica. Crania of A. dioptrica have been illustrated by Hamilton (1941), Norris and McFarland (1958), Brownell (1975), Fordyce et al. (1984), and Barnes (1985). Crania of P. spinipinnis have been illustrated by Norris and McFarland (1958) and Brownell and Praderi (1984).

Paleoclimates in Southwestern Tasmania during the Last 13,000 Years

Plant-sociological and climatic classification of the Australian Nothofagus cunninghamii rain forest provides the basis for a new, semiquantitative approach to interpretations of late-Quaternary paleoclimates from four pollen sequences in southwestern Tasmania. Varying proportions of rain-forest pollen types in the records were related to different modern rain-forest alliances and their specifc climatic regimes, such as Eastern Rain Forest, Leatherwood Rain Forest, and sclerophyllous, Subalpine Rain Forest. According to this interpretation, early Holocene climates were characterized by 1,600 mm annual precipitation and 10°C annual temperature, conditions substantially warmer and drier than previously thought. Maximum precipitation levels of 2,500 mm annually were not reached until 8,000 years B.P. A short-term cooling episode between 6,000 and 5,000 years B.P. led to the establishment of modern rain-forest distribution in western Tasmania, characterized either by a precipitation gradient steeper than before, or by greater climatic variability. To interpret paleoclimates from before 12,000 years B. P., when non-arboreal environments dominated in western Tasmanian bollen records, various modern treeless environments were studied in search for analogs. Contrary to earlier interpretations, late-glacial environments were not alpine tundra with a treeline at modern sea level, but steppe, with marshes or shallow lakes instead of the modern lakes. Climate was characterized by 50% less precipitation than today, resulting in substantial summer droughts. To explain such drastic precipitation decrease, the westerlies that dominate Tasmanian climate today must have been shifted polewards. This suggestion is supported by climate models that take Milankovitch-type insolation differences into account as well as sea-surface temperatures. Paleolimnological information based on diatom analyses support the general paleoclimatic reassessment.