Page:EB1911 - Volume 05.djvu/810

 The porpoise, which is so common in British waters and the Atlantic, seldom enters the Mediterranean, and apparently never resides there. There is, however, a porpoise in the Black Sea, which, according to Dr O. Abel, is entitled to rank as a distinct species, with the name of Phocaena relicta. This Black Sea porpoise is readily distinguished from the Atlantic species by the contour of the profile of the head, which, in place of forming a continuous curve from the muzzle to what represents the neck, has a marked prominence above the angle of the mouth, followed by an equally marked depression. The teeth are also different in form and number. The absence of porpoises from the Mediterranean is explained by Dr Abel on account of the greater saltness of that sea as compared with the ocean in general; his idea being that these cetaceans are near akin to fresh-water members of the group, and therefore unsuited to withstand an excessively saline medium. From the Taman Peninsula, on the north shore of the Black Sea, the same writer has described an extinct type of ancestral porpoise, under the name of Palaeophocaena andrussowi. Another species is the wholly black P. spinipennis, typically from South America. Black is also the hue of the Indian porpoise (Neophocaena phocaenoides), which wants a dorsal fin, and has eighteen pairs of teeth rather larger than those of the ordinary porpoise. (See .)

Next comes the Indo-Malay genus Orcella, in which the $12⁄12$ to $14⁄14$, small, conical teeth are pointed, rather closely set, and occupy nearly the whole length of the rostrum. Skull sub-globular, high. Rostrum nearly equal in length to the cranial portion of the skull, tapering. Flippers of moderate size, not elongated, but somewhat pointed, with all the bones of the digits broader than long, except the first phalanges of the index and third fingers. Head globular in front. Dorsal fin rather small, placed behind the middle of the body. Two species, both of small size—O. brevirostris, from the Bay of Bengal, and O. fluminalis, from the Irrawaddy river, from 300 to 900 m. from the sea.

In the grampus, or killer, Orca gladiator (or O. orca) the teeth form about twenty pairs, above and below, occupying nearly the whole length of the rostrum, very large and stout, with conical recurved crowns and large roots, expanded laterally and flattened, or rather hollowed, on the anterior and posterior surfaces. Rostrum about equal in length to the cranial part of the skull, broad and flattened above, rounded in front; premaxillae broad and rather concave in front of the nostrils, contracted at the middle of the rostrum, and expanding again towards the apex. Vertebrae: C 7, D 11-12, L 10, Ca 23; total 51 or 52; bodies of the first and second and sometimes the third cervical vertebrae united; the rest free. Flippers very large, ovate, nearly as broad as long, with all the phalanges and metacarpals broader than long. General form of body robust. Face short and rounded. Dorsal fin near the middle of the back, very high and pointed. See.

The lesser killer or black killer, Pseudorca crassidens, has its $8-12⁄8-12$ teeth confined to the anterior half of the rostrum and corresponding part of the lower jaw; they are small, conical, curved and sharp-pointed when unworn, but sometimes deciduous in old age. Skull broad and depressed; with the rostrum and cranial portions about equal in length. Upper surface of rostrum broad and flat. Premaxillae concave in front of the nostrils, as wide at the middle of the rostrum as at the base, and nearly or completely concealing the maxillae in the anterior half of this region. Vertebrae: C 7, D 11, L 12-14, Ca 28-29; total 58 or 59. Bodies of the anterior five or six cervical vertebrae united. Length of the bodies of the lumbar and anterior caudal vertebrae about equal to their width. Flippers very long and narrow, with the second digit the longest, and having as many as 12 or 13 phalanges, the third shorter (with 9 phalanges), the first, fourth and fifth very short. Fore part of the head round, in consequence of the great development of a cushion of fat, placed on the rostrum of the skull in front of the blow-hole. Dorsal fin low and triangular, the length of its base considerably exceeding its vertical height.

Next comes the ca’ing whale, or black-fish (Globicephalus melas), with about ten pairs of upper and lower teeth. Cranial and dental characters generally like those of Orca, except that the roots of the teeth are cylindrical. Vertebrae: C 7, D 10, L 9, Ca 24; total 50; first to sixth or seventh cervical vertebrae united; bodies of the lumbar vertebrae distinguished from those of the preceding genera by being more elongated, the length being to the width as 3 to 2. Flippers of moderate size, narrow and pointed. Dorsal fin situated near the middle of the back, of moderate size, and sickle-shaped. Head in front of the blow-hole high, and compressed anteriorly, the snout truncated. See.

Risso’s dolphin, Grampus griseus, represents another genus, characterized by the absence of teeth in the upper and the small number of these in the lower jaw (3 to 7 on each side, and confined to the region of the symphysis). Vertebrae: C 7, D 12, L 19, Ca 30; total 68. General external characters much as in Globicephalus, but the fore part of the head less rounded, and the flippers less elongated. G. griseus is about 13 ft. long, and remarkable for its great variability of colour. It has been found, though rarely, in the North Atlantic and Mediterranean.

The common dolphin (Delphinus delphis) is the typical representative of a large group of relatively small species, some of which are wholly marine, while others are more or less completely fluviatile. They are divided into a number of genera, such as Prodelphinus, Steno, Lagenorhynchus, Cephalorhynchus, Tursiops, &c., best distinguished from one another by the number and size of the teeth, the form and relations of the bones on the hinder part of the palate, the length of the beak and of the union of the two halves of the lower jaw, and the number of vertebrae. For the distinctive characters of these genera the reader may refer to one of the works mentioned below; and it must suffice to state that, collectively, all these dolphins are characterized by the following features. The teeth are numerous in both jaws, and more than $20⁄20$ in number, occupying nearly the whole length of the rostrum, and small, close-set, conical, pointed and slightly curved. Rostrum more or less elongated, and pointed in front, usually considerably longer than the cranial portion of the skull. Vertebrae: C 7, D 12-14, L and Ca variable; total 51 to 90. Flippers of moderate size, narrow, pointed, somewhat sickle-shaped, with the first digit rudimentary, the second longest, third nearly equal, and the fourth and fifth extremely short. Externally the head shows a distinct beak or pointed snout, marked off from the antenasal fatty elevation by a V-shaped groove. Dorsal fin rather large, triangular or sickle-shaped, rarely wanting. A curiously marked brown and white species, perhaps referable to Lagenorhynchus is found on the fringe of the Antarctic ice (see report on the zoology of the “Discovery,” published in 1907 by the British Museum). See.

Extinct Cetacea.

At present we are totally in the dark as to the origin of the whalebone-whales, not being even assured that they are derived from the same stock as the toothed whales. It is noteworthy, however, that some of the fossil representatives of the latter have nasal bones of a type recalling those of the former. Such fossil whalebone-whales as are known occur in Pliocene, and Miocene formations are either referable to existing genera, or to more or less nearly related extinct ones, such as Plesiocetus, Herpetocetus and Cetotherium.

The toothed whales, on the other hand, are very largely represented in a fossil state, reaching as low in the geological series as the upper Cretaceous. Many of these present much more generalized characters than their modern representatives, while others indicate apparently a transition towards the still more primitive zeuglodonts, which, as will be shown later, are themselves derived from the creodont Carnivora. In the Pliocene deposits of Belgium and England are preserved the teeth and other remains of a number of cetaceans, such as Physodon, Encetus, Dinoziphius, Hoplocetus, Balaenodon and Scaldicetus, more or less nearly related to the sperm-whale, but presenting several primitive characters. A complete skull of a member of this group from the Tertiary deposits of Patagonia, at first referred to Physodon, but subsequently to Scaldicetus, has a full series of enamelled teeth in the upper jaw; and it is probable that the same was the case in other forms. This entails either a modification of the definition of the Physeteridae as given above, or the creation of a separate family for these primitive sperm-whales. In other cases, however, as in the Miocene Prophyseter and Placoziphius, the anterior portion or the whole of the upper jaw had already become toothless; and these forms are regarded as indicating the descent of the sperm-whales from the under-mentioned Squalodon. The beaked whales, again, are believed to be independently descended from the latter type, Berardius being traced into the Miocene Mioziphius, Anoplonassa and Palaeoziphius, the last of which shows signs in its dentition of approximating to the complicated tooth-structure of the squalodonts.

Another line of descent from the latter, apparently culminating in the modern Platanistidae, is represented by the family