Abstract

(…) Neophocaena phocaenoides is the only member of the family Phocoenidae without a dorsal fin (Fig. I ). In its place is a low, geographically-variable dorsal ridge (sometimes inappropriately called a “groove”) covered with lines of small tubercles running along the back. The body is relatively more slender than that of other phocoenids. Unlike other porpoises , which all have sloping foreheads, the forehead of adult finless porpoises is very steep. The skull (Fig. 2) is relatively small and the rostrum is broader and less pointed than in other phocoenids (Kasuya 1999). Condylobasal length of adults ranges from 181 to 251 mm (n = 218 – Jefferson 2002), which is shorter than in Phocoena spinipinnis (270-297 mm-Brownell and Clapham 1999a), Phocoena dioptrica (279- 324 mm-Brownell and Clapham I999b), and Phocoenoides dalli (309- 340 mm-Houck and Jefferson 1999; Jefferson 1988). Tooth counts of Neophocaena range from 15 to 22 in both upper and lower jaws (Jefferson 2002). Although some overlap occurs, finless porpoise tooth counts are generally lower than in Phocoena phocoena (21- 29- Read 1999) and Phocoenoides dalli (21-28-Houck and Jefferson 1999). Antorbital notches are relatively deep (> 2 mm) in this species, but in other species of phocoenids are absent or < 2 mm deep (T. A. Jefferson, in litt.). Morphology of tympano-periotic bones differs from that of other members of Phocoenidae in height of tympanic bulla , thickness of periotic, and diameter of the cochlea r portion (Kasuya 1973). (...)