39–45% of the vertebral column (compared to 33% in other mysticetes). Each thoracic vertebrae has a pair of huge wing-like transverse processes, many of which overlap. The dorsal end of the ribs are remarkably thin and almost fail to make contact with the transverse processes. The reduced tail (or sacrocaudal region) features a vestigial pelvis and small chevron bones. The flippers have four digits. The lungs and heart are relatively small, which suggests that the pygmy right whale is not a deep diver. The larynx is reported to be different from any other cetacean. Like other mysticetes, the pygmy right whale has a large laryngeal sac, but in contrast to other mysticetes, this sac is positioned on the right side of the midline in the pygmy right. The presence of this laryngeal sac can possibly be the explanation for the long thorax and flattened ribs, but the peculiar ribs have led to multiple speculations as to their origin. Behavior and ecology Analysis of the stomach contents of dead pygmy right whales indicates that it feeds on copepods and euphausiids (krill). The social and mating structures are unknown. The whale is typically seen alone or in pairs, sometimes associated with other cetaceans (including dolphins, pilot whales, minke whales, and once a sei whale cow and calf). Occasionally larger groups are seen — in 2001 a group of 14 were seen at 46°S in the South Pacific about 450 km southeast of New Zealand, while in 1992 a group of about 80 individuals were seen southwest of Cape Leeuwin and another group of over 100 individuals were sighted in June 2007 about southwest of Portland, Victoria. The flukes, blubber, and baleen plates of a pygmy right whale calf were found in 7.47 m (24.5 ft) killer whale caught by whalers off South Africa. Population and distribution The pygmy right whale is among the least studied cetaceans; until 2008, fewer than 25 sightings of the species had been made at sea. The species lives in the Southern Hemisphere and is believed to be circumpolar, living in a band from about 30°S to 55°S in areas with surface water temperatures between . Individuals have been found on the coasts of Chile, Tierra del Fuego, Namibia, South Africa, Australia and New Zealand. One group may be a year-round resident off Tasmania. The total population is unknown. There is an extralimital stranding record in the Northern