1911 Encyclopædia Britannica/Cetacea
CETACEA (from the Gr. κέτος, a whale), the name of the mammalian order represented by whales, dolphins, porpoises, &c. From their fish-like form, which is manifestly merely an adaptation to their purely aquatic life, these creatures are often regarded as fishes, although they are true mammals, with warm blood, and suckle their young.
The general form is essentially fish-like, the spindle-shaped body passing anteriorly into the head without any distinct neck, and posteriorly tapering gradually towards the extremity of the tail, which is provided with a pair of lateral, pointed expansions of skin supported by fibrous tissue, called “flukes,” forming a horizontal triangular propelling organ, notched behind in the middle line. The head is generally large, in some cases attaining more than one-third the entire length; and the mouth is wide, and bounded by stiff, immobile lips. The fore-limbs are reduced to flattened paddles, encased in a continuous skin, showing no external sign of division, and without trace of nails. There are no signs of hind-limbs visible externally. The surface of the skin is smooth and glistening, and devoid of hair, although in many species there are a few bristles in the neighbourhood of the mouth which may persist through life or be present only in the young state. Immediately beneath the skin is a thick layer of fat, held together by a mesh of tissue, constituting the “blubber,” which retains the heat of the body. In nearly all species a compressed dorsal fin is present. The eye is small, and not provided with a true lacrymal apparatus. The external ear is a minute aperture in the skin situated at a short distance behind the eye. The nostrils open separately or by a single crescentic aperture, near the vertex of the head.
In the skull, the brain-case is short, broad and high, almost spherical, in fact (fig. 1). The supra-occipital bone rises upwards and forwards from the foramen magnum, to meet the frontals at the vertex, completely excluding the parietals from the upper region; and the frontals are expanded laterally to form the roof of the orbits. The nasal aperture opens upwards, and has in front of it a more or less horizontally prolonged beak, formed of the maxillae, premaxillae, vomer, and mesethmoid cartilage, extending forwards to form the upper jaw or roof of the mouth.There are no clavicles. The humerus is freely movable on the scapula at the shoulder-joint, but beyond this the articulations of the limb are imperfect; the flattened ends of the bones coming in contact, with fibrous tissue interposed, allowing of scarcely any motion. The radius and ulna are distinct, and about equally developed, and much flattened, as are all the bones of the flippers. There are four, or more commonly five, digits, and the number of the phalanges of the second and third always exceeds the normal number in mammals, sometimes considerably; they present the exceptional character of having epiphyses at both ends. The pelvis is represented by a pair of small rod-like bones placed longitudinally, suspended below and at some distance from the vertebral column at the commencement of the tail. In some species, to the outer surface of these are fixed other small bones or cartilages, the rudiments of the hind-limb.
Teeth are generally present, but exceedingly variable in number. In existing species, they are of simple, uniform character, with conical or compressed crowns and single roots, and are never preceded by milk-teeth. In the whalebone whales teeth are absent (except in the foetal condition), and the palate is provided with numerous transversely placed horny plates, forming the “whalebone.” Salivary glands are rudimentary or absent. The stomach is complex, and the intestine simple, and only in some species provided with a small caecum. The liver is little fissured, and there is no gall-bladder. The blood-vascular system is complicated by net-like expansions of both arteries and veins, or retia mirabilia, The larynx is of peculiar shape, the arytenoid cartilages and the epiglottis being elongated, and forming a tubular prolongation, which projects into the posterior nares, and when embraced by the soft palate forms a continuous passage between the nostrils and the trachea, or wind-pipe, in a more perfect manner. The brain is relatively large, round in form, with its surface divided into numerous and complex convolutions. The kidneys are deeply lobulated; the testes are abdominal; and there are no vesiculae seminales nor an os penis. The uterus is bicornuate; the placenta non-deciduate and diffuse. The two teats are placed in depressions on each side of the genital aperture. The ducts of the milk-glands are dilated during suckling into large reservoirs, into which the milk collects, and from which it is injected by the action of a muscle into the mouth of the young animal, so that sucking under water is greatly facilitated.
Whales and porpoises are found in all seas, and some dolphins and porpoises are inhabitants of the larger rivers of South America and Asia. Their organization necessitates their passing their life entirely in the water, as on land they are absolutely helpless. They have, however, to rise very frequently to the surface for the purpose of respiration; and, in relation to the upward and downward movement in the water thus necessitated, the principal instrument of motion, the tail, is expanded horizontally. The position of the nostril on the highest part of the head is important for this mode of life, as it is the only part of the body the exposure of which above the surface is absolutely necessary. Of numerous erroneous ideas connected with natural history, few are so widespread as that whales spout through their blow-holes water taken in at the mouth. But the “spouting,” or “blowing,” of whales is nothing more than the ordinary act of expiration, which, taking place at longer intervals than land-animals, is performed with a greater emphasis. The moment the animal rises to the surface it forcibly expels from its lungs the air taken in at the last inspiration, which is charged with vapour in consequence of the respiratory changes. This rapidly condensing in the cold atmosphere in which the phenomenon is often observed, forms a column of steam or spray, which has been taken for water. It happens, however, especially when the surface of the ocean is agitated into waves, that the animal commences its expiratory puff before the orifice has cleared the top of the water, some of which may thus be driven upwards with the blast, tending to complete the illusion. From photographs of spouting rorquals, it appears that the height and volume of the “spout” of all the species is much less than was supposed to be the case by the older observers; even that of the huge “sulphur-bottom” (Balaenoptera sibbaldi) averaging only about 14 ft. in height, although it may occasionally reach 20 ft.
As regards their powers of hearing, the capacity of cetaceans for receiving (and acting upon) sound-waves is demonstrated by the practice of shouting on the part of the fishermen when engaged in driving a shoal of porpoises or black-fish into shallow water, for the purpose of frightening their intended victims. As regards the possession of a voice by cetaceans, it is stated that one species, the “buckelwal” of the Germans, utters during the breeding-season a prolonged scream, comparable to the scream of a steam-siren, and embracing the whole musical scale, from base to treble. In respect of anatomical considerations, it is true that the external ear is much reduced, the “pinna” being absent, and the tube or “meatus” of very small calibre. On the other hand, the internal auditory organs are developed on the plan of those of ordinary mammals, but display certain peculiar modifications (notably the remarkable shell-like form of the tympanic bone) for intensifying and strengthening the sound-waves as they are received from the water. It seems, therefore, perfectly evident that whales must hear when in the water. This inference is confirmed by the comparatively small development of the other sense-organs. The eye, for instance, is very small, and can be of little use even at the comparatively small depths to which whales are now believed to descend. Again, the sense of smell, judging from the rudimentary condition of the olfactory organs, must be in abeyance; and whales have no sense-organs comparable to the lateral-line-system of fishes. Consequently, it would seem that when below the surface of the water they must depend chiefly upon the sense of hearing. Probably this sense is so highly developed as to enable the animals, in the midst of the vibrations made by the screw-like movements of the tail, or flukes, to distinguish the sound (or the vibrations) made by the impact of water against rocks, even in a dead calm, and, in the case of piscivorous species, to recognize by the pulse in the water the presence of a shoal of fish. Failing this explanation, it is difficult to imagine how whales can find their way about in the semi-darkness, and avoid collisions with rocks and rock-bound coasts.
In the Christiania Nyt Magazin for Naturvidenskaberne, vol. xxxviii., Dr G. Guldberg has published some observations on the body-temperature of the Cetacea, in which he shows how extremely imperfect is our knowledge of this subject. As he remarks, it is a matter of extreme difficulty to obtain the temperature of living cetaceans, although this has been taken in the case of a white-whale and a dolphin, which some years ago were kept in confinement in a pond in the United States. With the larger whales such a mode of procedure is, however, obviously quite impracticable, and we have, accordingly, to rely on post-mortem observations. The layer of blubber by which all cetaceans are protected from cold renders the post-mortem refrigeration of the blood a much slower process than in most mammals, so that such observations have a much higher value than might at first be supposed to be the case. Indeed, the blood-temperature of a specimen of Sibbald’s rorqual three days after death still stood at 34° C. The various observations that have been taken have afforded the following results in individual cases: Sperm-whale, 40° C.; Greenland right-whale, 38.8° C.; porpoise, 35.6° C.; liver of a second individual, 37.8° C.; common rorqual, 35.4° C.; dolphin, 35.6° C. The average blood-temperature of man is 37° C., and that of other mammals 39° C.; while that of birds is 42 C. The record of 40° C. in the case of the sperm-whale seems to indicate that at least some cetaceans have a relatively high temperature.
With the possible exception of one West African dolphin, all the Cetacea are predaceous, subsisting on living animal food of some kind. One kind alone (Orca) eats other warm-blooded animals, as seals, and even members of its own order, both large and small. Many feed on fish, others on small floating crustaceans, pteropods and jelly-fishes, while the principal staple of the food of many is constituted by cuttle-fishes and squids. In size cetaceans vary much, some of the smaller dolphins scarcely exceeding 4 ft. in length, while whales are the most colossal of all animals. It is true that many statements of their bulk are exaggerated, but the actual dimensions of the larger species exceed those of all other animals, not even excluding the extinct dinosaurian reptiles. With some exceptions, cetaceans are generally timid, inoffensive animals, active in their movements and affectionate in their disposition towards one another, especially the mother towards the young, of which there is usually but one, or at most two at a time. They are generally gregarious, swimming in herds or “schools,” sometimes amounting to many thousands in number; though some species are met with either singly or in pairs.
Commercially these animals are of importance on account of the oil yielded by the blubber of all of them; while whalebone, spermaceti and ambergris are still more valuable products yielded by certain species. Within the last few years whalebone has been sold in America for £2900 per ton, while it is also asserted that £3000 per ton has been paid for two and a quarter tons at Aberdeen, although there seems to be some degree of doubt attaching to the statement. Soon after the middle of the last century, the price of this commodity was as low as £150 per ton, but, according to Mr Frank Buckland, it suddenly leapt up to £620 with the introduction of “crinoline” into ladies’ costume, and it has apparently been on the rise ever since. Ambergris, which is very largely used in perfumery, is solely a product of the sperm-whale, and appears to be a kind of biliary calculus. It generally contains a number of the horny beaks of the cuttle-fishes and squids upon which these whales chiefly feed. Its market-price is subject to considerable variation, but from £3 to £4 per oz. is the usual average for samples of good quality. In 1898 a merchant in Mincing Lane was the owner of a lump of ambergris weighing 270 ℔, which was sold in Paris for about 85 s. per oz., or £18,360.
Whalebone Whales.—Existing Cetacea are divisible into two sections, or suborders, the relationships of which are by no means clearly apparent. The first section is that of the whalebone whales, or Mystacoceti, in which no functional teeth are developed, although there are tooth-germs during foetal life. The palate is furnished with plates of baleen or whalebone; the skull is symmetrical; and the nasal bones form a roof to the nasal passages, which are directed upwards and forwards. The maxilla is produced in front of, but not over, the orbital process of the frontal. The lacrymal is small and distinct from the jugal. The tympanic is welded with the periotic, which is attached to the base of the skull by two strong diverging processes. The olfactory organ is distinctly developed. The two halves of the lower jaw are arched outwards, their anterior ends meeting at an angle, and connected by fibrous tissue without any symphysis. All the ribs at their upper extremity articulate only with the transverse processes of the vertebrae; their capitular processes when present not articulating directly with the bodies of the vertebrae. The sternum is composed of a single piece, and articulates only with a single pair of ribs; and there are no ossified sternal ribs. External openings of nostrils distinct from each other, longitudinal. A short conical caecum.
When in the foetal state these whales have numerous minute teeth lying in the dental groove of both upper and lower jaws. They are best developed about the middle of foetal life, after which they are absorbed, and no trace of them remains at the time of birth. The whalebone does not make its appearance until after birth; and consists of a series of flattened horny plates, between three and four hundred in number, on each side of the palate, with a bare interval along the middle line. The plates are placed transversely to the long axis of the palate, with short intervals between them. Each plate or blade is somewhat triangular in form, with the base attached to the palate and the apex hanging downwards. The outer edge of the blade is hard and smooth, but the inner edge and apex fray out into long bristly fibres, so that the roof of the whale’s mouth looks as if covered with hair, as described by Aristotle. At the inner edge of each principal blade are two or three much smaller or subsidiary blades. The principal blades are longest near the middle of the series, and gradually diminish towards the front and back of the mouth. The horny plates grow from a fibrous and vascular matrix, which covers the palatal surface of the maxillae, and sends out plate-like processes, one of which penetrates the base of each blade. Moreover, the free edges of these processes are covered with long vascular thread-like papillae, one of which forms the central axis of each of the hair-like fibres mainly composing the blade. A transverse section of fresh whalebone shows that it is made up of numbers of these soft vascular papillae, circular in outline, and surrounded by concentrically arranged epidermic cells, the whole bound together by other epidermic cells, that constitute the smooth (so-called “enamel”) surface of the blade, which, disintegrating at the free edge, allows the individual fibres to become loose and assume a hair-like appearance.
Whalebone really consists of modified papillae of the mucous membrane of the mouth, with an excessive and horny epithelial development. The blades are supported and bound together for a certain distance from their base, by a mass of less hardened epithelium, secreted by the surface of the palatal membrane or matrix of the whalebone in the intervals of the plate-like processes. This is the “gum” of the whalers. Whalebone varies much in colour in different species; in some it is almost jet black, in others slate colour, horn colour, yellow, or even creamy-white. In some descriptions the blades are variegated with longitudinal stripes of different hues. It differs also greatly in other respects, being short, thick, coarse, and stiff in some cases, and greatly elongated and highly elastic in those species in which it has attained its fullest development. Its function is to strain the water from the small marine molluscs, crustaceans, or fish upon which the whales subsist. In feeding, whales fill the immense mouth with water containing shoals of these small creatures, and then, on closing the jaws and raising the tongue, so as to diminish the cavity of the mouth, the water streams out through the narrow intervals between the hairy fringe of the whalebone blades, and escapes through the lips, leaving the living prey to be swallowed.
Although sometimes divided into two families, Balaenidae and Balaenopteridae, whalebone-whales are best included in a single family group under the former name. The typical members of this family are the so-called right-whales, forming the genus Balaena, in which there are no folds on the throat and chest, and no back-fin; while the cervical vertebrae are fused into a single mass. The flippers are short and broad, with five digits; the head is very large and the whalebone very long and narrow, highly elastic and black; while the scapula is high, with a distinct coracoid and coronoid process. This genus contains the well-known Greenland right-whale (B. mysticetus) of the Arctic seas, the whalebone and oil of which are so much valued in commerce, and also other whales, distinguished by having the head somewhat smaller in proportion to the body, with shorter whalebone and a larger number of vertebrae. These inhabit the temperate seas of both northern and southern hemispheres, and have been divided into species in accordance with their geographical distribution, such as B. biscayensis of the North Atlantic, B. japonica of the North Pacific, B. australis of the South Atlantic, and B. antipodarum and novae-zelandiae of the South Pacific; but the differences between them are so small that they may probably be regarded as races of a single species, the black whale (B. australis). On the head these whales carry a peculiar structure which is known to whalers as the “bonnet.” This is a large horny excrescence, worn into hollows like a much-denuded piece of limestone rock, growing probably in the neighbourhood of the blow-hole. More than one theory has been suggested to account for its presence. One suggestion is that it indicates the descent of whales from rhinoceros-like mammals; another that this species of whale is in the habit of rubbing against rocks in order to free itself from barnacles, and thus produces a kind of corn—although why on the nose alone is not stated. Dr W. G. Ridewood, however, considers that the structure is due to the fact that the horny layers which are produced all over the skin are not shed on this particular spot.
The pigmy whale (Neobalaena marginata) represents a genus agreeing with the right-whales in the absence of throat-flutings, and with the rorquals in the presence of a dorsal fin. The cervical vertebrae are united, and there are only 43 vertebrae altogether. The flippers are small, narrow, and with only four digits. The ribs remarkably expanded and flattened; the scapula low and broad, with completely developed acromion and coracoid processes. The whalebone is long, slender, elastic and white. The species which inhabits the South American, Australian and New Zealand seas is the smallest of the whalebone-whales, being not more than 20 ft. in length.
In contrast to the preceding is the great grey whale (Rachianectes glaucus) of the North Pacific, which combines the relatively small head, elongated shape, and narrow flippers of the fin-whales, with the smooth throat and absence of a back-fin distinctive of the right-whales. The whalebone is shorter and coarser than in any other species. In the skeleton the cervical vertebrae are free, and the first two ribs on each side expanded and united to form a large bony shield. In the humpback-whale (Megaptera longimana or boops) the head is of moderate size, the whalebone-plates are short and wide, and the cervical vertebrae free. The skin of the throat is fluted so as to form an expansible pouch; there is a low back-fin; and the flippers, which have four digits each, are extremely long, equalling about one-fourth the total length of the animal. The acromion and coracoid processes of the scapula are rudimentary. See Humpback-Whale.
The right-whales are built for cruising slowly about in search of the shoals of small floating invertebrates which form their food, and are consequently broad in beam, with a float-shaped body and immovable neck. The humpback is of somewhat similar build, but with a smaller head, and probably attains considerable speed owing to the length of its flippers. The finners, or rorquals (Balaenoptera), which prey largely on fish, are built entirely for speed, and are the ocean greyhounds of the group. Their bodies are consequently long and attenuated, and their necks are partially mobile; while they are furnished with capacious pouches for storing their food. They chiefly differ from the humpback by the smaller head, long and slender build, small, narrow, and pointed flippers, each containing four digits, and the large acromion and coracoid processes to the low and broad scapula. Rorquals are found in almost every sea. Among them are the most gigantic of all animals, B. sibbaldi, which attains the length of 80 ft., and the small B. rostrata, which does not exceed 30. There are certainly four distinct modifications of this genus, represented by the two just mentioned, and by B. musculus and B. borealis, all inhabitants of British seas, but the question whether almost identical forms found in the Indian, Southern and Pacific Oceans are to be regarded as specifically identical or as distinct awaits future researches, although some of these have already received distinct names. See Rorqual.
In the report on the zoology of the “Discovery” expedition, published in 1907 by the British Museum, E. A. Wilson describes a whale frequenting the fringe of the Antarctic ice which indicates a new generic type. Mainly black in colour, these whales measure about 20 or 30 ft. in length, and have a tall dorsal fin like that of a killer.
Toothed Whales.—-The second suborder is represented by the toothed whales, or Odontoceti, in which there is no whalebone, and teeth, generally numerous, though sometimes reduced to a single pair, and occasionally wanting, are normally developed. Unlike that of the whalebone-whales, the upper surface of the skull is more or less unsymmetrical. The nasal bones are in the form of nodules or flattened plates, applied closely to the frontals, and not forming any part of the roof to the nasal passage, which is directed upwards and backwards. The olfactory organ is rudimentary or absent. Hinder end of the maxilla expanded and covering the greater part of the orbital plate of the frontal bone. Lacrymal bone either inseparable from the jugal, or, if distinct, large, and forming part of the roof of the orbit. Tympanic bone not welded with the periotic, which is usually only attached to the rest of the skull by ligament. Two halves of the lower jaw nearly straight, expanded in height posteriorly, with a wide funnel-shaped aperture to the dental canal, and coming in contact in front by a flat surface of variable length, but constituting a symphysis. Several of the anterior ribs with well-developed capitular processes, which articulate with the bodies of the vertebrae. Sternum almost always composed of several pieces, placed one behind the other, with which several pairs of ribs are connected by well-developed cartilaginous or ossified sternal ribs. External respiratory aperture single, the two nostrils uniting before they reach the surface, usually in the form of a transverse sub-crescentic valvular aperture, situated on the top of the head. Flippers with five digits, though the first and fifth are usually little developed. No caecum, except in Platanista.
The first family, Physeteridae, is typified by the sperm-whale, and characterized by the absence of functional teeth in the upper jaw; the lower teeth being various, and often much reduced in number. Bones of the skull raised so as to form an elevated prominence or crest behind the nostrils. Pterygoid bones thick, produced backwards, meeting in the middle line, and not involuted to form the outer wall of the post-palatine air-sinuses, but simply hollowed on their outer side. Transverse processes of the arches of the dorsal vertebrae, to which the tubercles of the ribs are attached, ceasing abruptly near the end of the series, and replaced by processes on the body at a lower level, and serially homologous anteriorly with the heads of the ribs, and posteriorly with the transverse processes of the lumbar vertebrae. Costal cartilages not ossified.
The first group, or Physeterinae, includes the sperm-whale itself and is characterized by the presence of a full series of lower teeth, which are set in a groove in place of sockets, the groove being imperfectly divided by partial septa, and the teeth held in place by the strong, fibrous gum. No distinct lacrymal bone. Skull strikingly asymmetrical in the region of the nasal apertures, in consequence of the left opening greatly exceeding the right in size.
In the sperm-whale (Physeter macrocephalus) the upper teeth are apparently of uncertain number, rudimentary and functionless, being embedded in the gum. Lower jaw with from 20 to 25 teeth on each side, stout, conical, recurved and pointed at the apex until they are worn, without enamel. Upper surface of the skull concave; its posterior and lateral edges raised into a very high and greatly compressed semicircular crest or wall (fig. 2). Zygomatic processes of jugal bones thick and massive. Muzzle greatly elongated, broad at the base, and gradually tapering to the apex. Lower jaw exceedingly long and narrow, the symphysis being more than half the length. Vertebrae: C 7, D 11, L 8, Ca 24; total 50. Atlas, or first vertebra, free; all the other cervical vertebrae united by their bodies and spines into a single mass. Eleventh pair of ribs rudimentary. Head about one-third the length of the body; very massive, high and truncated, and rather compressed in front; owing its huge size and form mainly to the accumulation of a mass of fatty tissue filling the large hollow on the upper surface of the skull and overlying the long muzzle. The single blow-hole is longitudinal, slightly S-shaped, and placed at the upper and anterior extremity of the head to the left side of the middle line. The opening of the mouth is on the under side of the head, considerably behind the end of the snout. Flippers short, broad and truncated. Dorsal fin represented by a low protuberance. See Sperm-Whale.
|Fig. 2.—Skull of Sperm-Whale (Physeter macrocephalus).|
In the lesser or pigmy sperm-whale (Cogia breviceps) there may be a pair of rudimentary teeth in the upper jaw, while on each side of the lower jaw there are from 9 to 12 rather long, slender, pointed and curved teeth, with a coating of enamel. Upper surface of the skull concave, with thick, raised, posterior and lateral margins, massive and rounded at their anterior terminations above the orbits. Muzzle not longer than the cranial position of the skull, broad at the base, and rapidly tapering to the apex. Zygomatic process of the jugal rod-like. Lower jaw with symphysis less than half its length. Vertebrae: C 7, D 13 or 14, L and Ca 30; total 50 or 51. All the cervical vertebrae united by their bodies and arches. The head is about one-sixth of the length of the body, and obtusely pointed in front; the mouth small and placed far below the apex of the snout; the blow-hole crescentic, and placed obliquely on the crown of the head in advance of the eyes and to the left of the middle line; while the flippers are bluntly sickle-shaped, and the back-fin triangular. This species attains a length of from 9 to 13 ft.
|Fig. 3.—Bottle-nose (Hyperoödon rostratus). From a specimen taken off the coast of Scotland, 1882.|
The typical representative of the beaked whales is Ziphius cuvieri, in which there is a single conical tooth of moderate size on each side close to the anterior extremity of the lower jaw, directed forwards and upwards. Skull with the premaxillae immediately in front and at the sides of the nostrils expanded, hollowed, with elevated lateral margins, the posterior ends rising to the vertex and curving forwards, the right being considerably more developed than the left. The conjoint nasals form a pronounced symmetrical eminence at the top of the skull, projecting forwards over the nostrils, flat above, prominent and rounded in the middle line in front, and separated by a notch on each side from the premaxillae. Preorbital notch not distinct. Rostrum (seen from above) triangular, tapering from the base to the apex; upper and outer edges of maxillae at base of rostrum raised into low roughened tuberosities. Mesethmoid cartilage densely ossified in adult age, and coalescing with the surrounding bones of the rostrum. Vertebrae: C 7, D 10, L 10, Ca 22; total 49. The three anterior cervical vertebrae united, the rest free.
|Fig. 4.—Sowerby’s Beaked Whale (Mesoplodon bidens).|
In the numerous species of the allied genus Mesoplodon there is a much-compressed and pointed tooth in each half of the lower jaw, variously situated, but generally at some distance behind the apex; its point directed upwards, and often somewhat backwards, occasionally developed to a great size. In the skull the region round the nostrils is as in Hyperoödon, except that the nasals are narrow and more sunk between the upper ends of the premaxillae; like those of Hyperoödon, they are concave in the middle line in front and above. No maxillary tuberosities. Preorbital notch not very distinct. Rostrum long and narrow. Mesethmoid in the adult ossified in its entire length, and coalescing with the surrounding bones. Vertebrae: C 7, D 10, L 10 or 11, Ca 19 or 20; total 46 to 48. Two or three anterior cervicals united, the rest usually free.
|Fig. 5.—Skull of a Beaked Whale (Mesoplodon densirostris).|
Though varying in form, the lower teeth of the different members of this genus agree in their essential structure, having a small and pointed enamel-covered crown, composed of dentine, which, instead of surmounting a root of the ordinary character, is raised upon a solid mass of osteo-dentine, the continuous growth of which greatly alters the form and general appearance of the tooth as age advances, as in the case of M. layardi, where the long, narrow, flat, strap-like teeth, curving inwards at their extremities, meet over the rostrum, and interfere with the movements of the jaw. In one species (M. grayi) a row of minute, conical, pointed teeth, like those of ordinary Dolphins, 17 to 19 in number, is present even in the adults, on each side of the middle part of the upper jaw, but embedded by their roots only in the gum, and not in bony sockets. This, with the frequent presence of rudimentary teeth in other species of this genus, indicates that the beaked whales are derived from ancestral forms with teeth of normal character in both jaws. The species are distributed in both northern and southern hemispheres, but most frequent in the latter. Among them are M. bidens, M. europaeas, M. densirostris, M. layardi, M. grayi and M. hectori; but there is still much to be learned with regard to their characters and distribution. This group was abundant in the Pliocene age, as attested by the frequency with which the imperishable long, cylindrical rostrum of the skull, of more than ivory denseness, is found among the rolled and waterworn animal remains which compose the “bone-bed” at the base of the Red Crag of Suffolk.
Finally, in Arnoux’s beaked whale (Berardius arnouxi), of New Zealand, which grows to a length of 30 ft., there are two moderate-sized, compressed, pointed teeth, on each side of the symphysis of the lower jaw, with their summits directed forwards, the anterior being the larger of the two and close to the front of the jaw. Upper ends of the premaxillae nearly symmetrical, moderately elevated, slightly expanded, and not curved forward over the nostrils. Nasals broad, massive and rounded, of nearly equal size, forming the vertex of the skull, flattened in front, most prominent in the middle line. Preorbital notch distinct. Rostrum long and narrow. Mesethmoid partially ossified. Small rough eminences on the outer edge of the upper surface of the maxillae at base of rostrum. Vertebrae: C 7, D 10, L 12, Ca 19; total 48. The three anterior cervicals welded, the rest free and well developed. Apparently this whale has the power of thrusting its teeth up and down, exposing them to view when attacked.
|Fig. 6.—The Susu, or Ganges Dolphin (Platanista gangetica).|
In a family by themselves—the Platinistidae—are placed three cetaceans which differ from the members of the preceding and the following groups in the mode of articulation of the ribs with the vertebrae, as the tubercular and capitular articulations, distinct at the commencement of the series, gradually blend together, as in most mammals. The cervical vertebrae are all free. The lacrymal bone is not distinct from the jugal. The jaws are long and narrow, with numerous teeth in both; the symphysis of the lower one exceeding half its length. Externally the head is divided from the body by a slightly constricted neck. Pectoral limbs broad and truncated. Dorsal fin small or obsolete. In habits these dolphins are fluviatile or estuarine. In the Indian susu, or Ganges dolphin (Platanista gangetica), the teeth number about 30 on each side, are set near together, are rather large, cylindrical, and sharp-pointed in the young, but in old animals acquire a large laterally compressed base, which in the posterior part of the series becomes irregularly divided into roots. As the conical enamel-covered crown wears away, the teeth of the young and old animals have a totally different appearance. The beak and tooth-bearing portion of the lower jaw are so narrow that the teeth of the two sides are almost in contact. Maxillae supporting large, incurved, compressed bony crests, which overarch the nostrils and base of the rostrum, and almost meet in the middle line above. Orbits very small and eyes rudimentary, without crystalline lens. Blow-hole longitudinal, linear. Vertebrae: C 7, D 11, L 8, Ca 25; total 51. A small caecum. No pelvic bones. Dorsal fin represented by a low ridge.
|Fig. 7.—River Plate Dolphin (Stenodelphis blainvillei).|
The second genus is represented by Inia geoffroyi, of the Amazon, in which the teeth vary from 26 to 33 pairs in each jaw; those at the posterior part with a distinct tubercle at the inner side of the base of the crown. Vertebrae: C 7, D 13, L 3, Ca 18; total 41. Transverse processes of lumbar vertebrae very broad. Sternum short and broad, and consisting of a single segment only. Dorsal fin a mere ridge. The long cylindrical rostrum externally furnished with scattered, stout and crisp hairs. The third type is Stenodelphis blainvillei, the River Plate dolphin, a small brown species (fig. 7), with from 50 to 60 pairs of teeth in each jaw, furnished with a cingulum at the base of the crown. Jaws very long and slender. Vertebrae: C 7, D 10, L 5, Ca 19; total 41. Transverse processes of the lumbar vertebrae extremely broad. Sternum elongated, composed of two segments, with four sternal ribs attached. Dorsal fin rather small, triangular, pointed. Blow-hole transverse. In several respects this species connects the two preceding ones with the Delphinidae (see Dolphin).
|Fig. 8.—Upper surface of the Skull of male Narwhal (Monodon monoceros), with the whole of both teeth exposed by removal of the upper wall of their alveolar cavities.|
The last family of existing cetaceans is the above-mentioned Delphinidae, which includes the true dolphins, porpoises, grampuses and their relatives. As a rule there are numerous teeth in both jaws; and the pterygoid bones of the skull are short, thin and involuted to form with a process of the palate bone the outer wall of the post-palatine air-sinus. Symphysis of lower jaw short, or moderate, never exceeding one-third the length of the jaw. Lacrymal bone not distinct from the jugal. Transverse processes of the dorsal vertebrae gradually transferred from the arches to the bodies of the vertebrae without any sudden break, and becoming posteriorly continuous serially with the transverse processes of the lumbar vertebrae. Anterior ribs attached to the transverse process by the tubercle, and to the body of the vertebra by the head; the latter attachment lost in the posterior ribs. Sternal ribs ossified. The blow-hole is transverse, crescentic, with the horns of the crescent pointing forwards.
First on the long list is the narwhal, Monodon monoceros, in which, apart from some irregular rudimentary teeth, the dentition is reduced to a single pair of teeth which lie horizontally in the maxilla, and in the female remain permanently concealed within the socket, so that this sex is practically toothless, while in the male (fig. 8), the right tooth usually remains similarly concealed while the left is immensely developed, attaining a length equal to more than half that of the entire animal, projecting horizontally from the head in the form of a cylindrical, or slightly tapering, pointed tusk, without enamel, and with the surface marked by spiral grooves and ridges, running in a sinistral direction. Vertebrae: C 7, D 11, L 6, Ca 26; total 50. Cervical region comparatively long, and all the vertebrae distinct, or with irregular unions towards the middle of the series, the atlas and axis being usually free. Flipper small, short and broad, with the second and third digits nearly equal, the fourth slightly shorter. No dorsal fin. See Narwhal.
Closely allied is the beluga or white-whale (Delphinapterus leucas), of the Arctic seas, in which, however, there are from eight to ten pairs of teeth in each jaw, occupying the anterior three-fourths of the rostrum and corresponding portion of the lower jaw, rather small, conical, and pointed when unworn, but usually become obliquely truncated, separated by intervals considerably wider than the diameter of the tooth, and implanted obliquely, the crowns inclining forwards especially in the upper jaw. Skull rather narrow and elongated, depressed. Premaxillae convex in front of the nostrils. Rostrum about equal in length to the cranial portion of the skull, triangular, broad at the base, and gradually contracting towards the apex, where it is somewhat curved downwards. Vertebrae: C 7, D 11, L 9, Ca 23; total 50. Cervical vertebrae free. Flippers broad, short and rounded, all the digits being tolerably well developed, except the first. Anterior part of head rounded; no distinct snout. No dorsal fin, but a low ridge in its place. See Beluga.
In all the remaining genera of Delphinidae the cervical region of the vertebral column is very short, and the first two, and usually more, of the vertebrae are firmly united. The common porpoise (Phocaena communis, or P. phocaena) is the typical representative of the first genus, in which the teeth vary from 18 to 25, are small, and occupy nearly the whole length of the rostrum, with compressed, spade-shaped crowns, separated from the root by a constricted neck. Rostrum rather shorter than the cranium proper, broad at the base and tapering towards the apex. Premaxillae raised into tuberosities in front of the nostrils. The frontal bones form a somewhat square elevated protuberance in the middle line of the skull behind the nostrils, rising above the flattened nasals. Symphysis of lower jaw very short. Vertebrae: C 7, D 13, L 14, Ca 30; total 64. First to sixth cervical vertebrae and sometimes the seventh also, coalesced. Flippers of moderate size, oval, slightly sickle-shaped, with the second and third digits nearly equal in length, and the fourth and fifth well developed, but shorter. Head short, moderately rounded in front of the blow-hole. Dorsal fin near the middle of the back, triangular; its height considerably less than the length of the base; its anterior edge frequently furnished with one or more rows of conical horny tubercles.
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 Porpoise.)
Fig. 9.—Beluga or White-Whale (Delphinapterus leucas). From a specimen
Next comes the Indo-Malay genus Orcella, in which the 12 to 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 Grampus.
|Fig. 10.—The Grampus or Killer (Orca gladiator).|
The lesser killer or black killer, Pseudorca crassidens, has its 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 Ca’ing Whale.
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 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 Dolphin.
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 Eurhinodelphidae, typified by the European Miocene Eurhinodelphis, but also including the contemporary Patagonian Argyrocetus and the nearly allied European Cyrtodelphis. All these were very long-beaked dolphins; and in Argyrocetus, at all events, the occipital condyles, instead of being closely pressed to the skull, are as prominent as in ordinary mammals, while the nasal bones, instead of forming mere rudimentary nodules, were squared and roofed over the hind part of the nasal chamber.
In the Miocene Squalodon, representing the family Squalodontidae, the dentition is differentiated into incisors, canines and cheek-teeth, the hinder ones of the latter series having double roots and compressed crowns carrying serrations on the hinder edge; generally the dental formula has been given as i. 3, c. 1, p. 4, m. 7, the single-rooted cheek-teeth being regarded as premolars and those with double roots as molars. Dr Abel is, however, of opinion that the formula is better represented as i. 3, c. 1, p. 8 or 9, m. 3; the teeth reckoned as molars corresponding to those of the creodont Carnivora. The single-rooted cheek-teeth are regarded as due, not to the division of double-rooted ones, but to the fusion of the two roots of teeth of the latter type. In Squalodon the nasal bones were of the modern nodular type, but in the Miocene Patagonian Prosqualodon they partially covered the nasal chamber.
At present there is a gap between the most primitive squalodonts and the Eocene zeuglodonts (Zeuglodontidae), which are regarded by Messrs Max Weber, O. Abel and C. W. Andrews as the direct forerunners of the modern-toothed whales, forming the suborder Archaeoceti. It is, however, right to mention that some authorities refuse to admit the relation of the Archaeoceti to the whales.
In the typical zeuglodonts the long and flat skull has large temporal fossae, a strong sagittal crest, a long beak formed mainly by the premaxillae (in place of the maxillae, as in modern whales), and long nasal bones covering over the nasal chamber, so that the nostrils opened about half-way down the beak. All the cervical vertebrae were free. Normally the dentition in the typical genus Zeuglodon (which is common to the Eocene of North America and Egypt) is i. 3, c. 1, p. 4, m. 3; the cheek-teeth being two-rooted, with compressed pointed crowns, of which the fore-and-aft edges are coarsely serrated. In the Egyptian Zeuglodon osiris the number of the molars is, however, reduced to 2, while some of the earlier cheek-teeth have become single-rooted, as in the squalodonts. The probable transitional form between the latter and the zeuglodonts is the small Microzeuglodon caucasicus described by the present writer, from the Caucasus. As regards the origin of the zeuglodonts themselves, remains discovered in the Eocene formations of Egypt indicate a practically complete transition, so far at least as dental characters are concerned, from these whale-like creatures to the creodont Carnivora. In the earliest type, Protocetus, the skull is practically that of a zeuglodont, the snout being in fact more elongated than in some of the earliest representatives of the latter, although the nostrils are placed nearer the tip. The incisors are unknown, but the cheek-teeth are essentially those of a creodont, none of them having acquired the serrated edges distinctive of the typical zeuglodonts; and the hinder premolars and molars retaining the three roots of the creodonts. In the somewhat later Prozeuglodon the skull is likewise essentially of the zeuglodont type, although the nostrils have shifted a little more backwards; as regards the cheek-teeth, which have acquired serrated crowns, the premolars at any rate retain the inner buttress supported by a distinct third root, so that they are precisely intermediate between Protocetus and Zeuglodon. Yet another connecting form is Eocetus, a very large animal from nearly the same horizon as Prozeuglodon; its skull approaching that of Zeuglodon as regards the backward position of the nostrils, although the cheek-teeth are of the creodont type, having inner, or third, roots. It is noteworthy that Zeuglodon apparently occurs in the same beds as these intermediate types.
It follows from the foregoing that if zeuglodonts are the ancestors of the true Cetacea—and the probability that they are so is very great—the latter are derived from primitive Carnivora, and not, as has been suggested, from herbivorous Ungulata. The idea that the zeuglodonts were provided with a bony armour does not appear to be supported by recent discoveries.
Authorities.—The above article is based on that by Sir W. H. Flower in the 9th edition of this work. See also W. H. Flower, “On the Characters and Divisions of the Family Delphinidae,” Proc. Zool. Soc. (London, 1883); F. W. True, “Review of the Family Delphinidae,” Proc. U.S. Museum, No. 36 (1889); R. Lydekker, “Cetacean Skulls from Patagonia,” Palaeontol. Argentina, vol. ii: An. Mus. La Plata (1893); W. Dames, “Über Zeuglodonten aus Ägypten,” Paläontol. Abhandlungen, vol. i. (1894); F. E. Beddard, A Book of Whales (London, 1900); O. Abel, “Untersuchungen über die fossilen Platanistiden des Wiener Beckens,” Denks. k. Akad. Wiss. Wien., vol. lxviii. (1899); “Les Dauphins longirostres du Bolérien,” Mém. musée d’hist. nat. belgique (1901 and 1902); “Die phylogenetische Entwickelung des Cetaceengebisses und die systematische Stellung der Physeteriden,” Verhandl. deutsch. zool. Gesellschaft (1905); E. Fraas, “Neue Zeuglodonten aus dem unteren Mittelocean vom Mokattam bei Cairo,” Geol. und paläontol. Abhandl. ser. 2, vol. vi. (1904); C. W. Andrews, “Descriptive Catalogue of the Tertiary Vertebrata of the Fayum” (British Museum, 1906). (R. L.*)