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See also:CETACEA (from the Gr. ,See also:Eros, a See also:whale)
, the name of the mammalian See also:order represented by whales, dolphins, porpoises, &c
.
From their See also:fish-like See also:form, which is manifestly merely an See also:adaptation to their purely aquatic See also:life, these creatures are often regarded
as fishes, although they are true mammals, with warm See also:blood, and suckle their See also:young
.
by a single crescentic See also:aperture, near the vertex of the See also:head
.
The bones generally are spongy in texture, the cavities being filled with oil
.
In the vertebral See also:column, the cervical region is See also:short and immobile, and the vertebrae, always seven in number, are in many See also:species more or less fused together into a solid See also:mass
.
The odontoid See also:process of the second cervical vertebra, when that See also:bone is See also:free, is usually very obtuse, or even obsolete
.
In a See also:paper on the form and See also:function of the cervical vertebrae published in the Jenaische Zeitschrift for 1905, Dr O
.
Reche points out that the shortening and soldering is most pronounced in species which, like the right-whales, live entirely on See also:minute organisms, to See also:capture which there is no See also:necessity to turn the head at all
.
Accordingly we find that in these whales the whole seven cervical vertebrae are fused into an immovable solid mass, of which the See also:compound elements, with the exception of the first and second, are but little thicker than plates
.
On the other See also:hand, in the finner-whales, several of which live exclusively on fish, and thus require a certain amount of mobility in the head and See also:neck, we find all the cervical vertebrae much thicker and entirely See also:separate from one another
.
Among the See also:dolphin See also:group the See also:narwhal and the See also: The beluga, too, which is believed to feed on large and active fishes, would likewise seem to require mobility in the same region in order to effect their capture . On the other hand, the See also:porpoise preys on See also:herrings, pilchards and See also:mackerel, which in their densely packed shoals must apparently fall an easy See also:prey with but little exertion on the See also:part of their captor, and we accordingly find all the neck-vertebrae very short, and at least six out of the seven coalesced into a solid Immovable mass . None of the vertebrae are See also:united to form a sacrum . number in mammals, sometimes considerably; they See also:present the exceptional See also:character of having epiphyses at both ends . The See also:pelvis is represented by a pair of small See also: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 See also:outer See also:surface of these are fixed other small bones or cartilages, the rudiments of the See also:hind-See also:limb . See also:Teeth are generally present, but exceedingly variable in number . In existing species, they are of See also:simple, See also:uniform character, with conical or compressed crowns and single roots, and are never pre-ceded by See also:milk-teeth . In the See also:whalebone whales teeth are absent (except in the foetal See also:condition), and the See also:palate is provided with numerous transversely placed horny plates, forming the whale-bone." Salivary glands are rudimentary or absent . The See also:stomach is complex, and the See also:intestine simple, and only in some species provided with a small caecum . The See also:liver is little fissured, and there is no See also:gall-See also:bladder . The blood-vascular See also:system is complicated by See also:net-like expansions of both See also:arteries and See also:veins, or retia mirabilia . The larynx is of See also:peculiar shape, the See also:arytenoid cartilages and the epiglottis being elongated, and forming a tubular prolongation, The See also:general form is essentially fish-like, the spindle-shaped See also: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 See also:tissue, called " flukes," forming a See also:horizontal triangular propelling See also:organ, notched behind in the See also:middle See also: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 See also:external sign of See also: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 See also: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 See also:state . Immediately beneath the skin is a thick layer of See also:fat, held together by a mesh of tissue, constituting the "blubber," which retains the See also:heat of the body . In nearly all species a compressed dorsal fin is present . The See also:eye is small, and not provided with a true lacrymal apparatus . The external See also:ear is a minute aperture in the skin situated at a short distance behind the eye . The nostrils open separately or id a d PMx, Premaxilla . AS, Alisphenoid . Mx, Maxilla . PS, Presphenoid . ME, Ossified rtion of the See also:mes- Pt, Pterygoid . ethmoid. pn, Posterior pares . an, Nostrils . Pl, See also:Palatine . Na, Nasal . Vo, Vomer . IP, Inter-parietal . Symphysis of See also:lower See also:jaw . Fr, Frontal. id, Inferior dental See also:canal . Pa, Parietal. cp, Coronoid process of lower jaw . SO, Supra-occipital. cd, Condyle . ExO, Ex-occipital . See also:Angle . BO, Basi-occipital. sh, Stylo-hyal . Sq, Squamosal. bh, Basi-hyal . Per, Periotic. th, Thyro-hyal . The lumbar and caudal vertebrae are numerous and large, and, as their See also:arches are not connected by articular processes (zygapophyses), they are capable of free See also:motion in all directions . The caps, or epiphyses, at the end of the vertebral bodies are flattened disks, not uniting until after the See also:animal has attained its full dimensions . There are largely See also:developed See also:chevron-bones on the under See also:side of the tail, the presence of which indicates the distinction between caudal and lumbar vertebrae . In the See also:skull, the See also:brain-case is short, broad and high, almost spherical, in fact (fig . I) . 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 See also: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 See also:beak, formed of the maxillae, premaxillae, vomer, and mesethmoid See also: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 See also:shoulder-See also: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 See also: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 V . 25which projects into the posterior See also:nares, and when embraced by the soft palate forms a continuous passage between the nostrils and the trachea, or See also:wind-See also:pipe, in a more perfect manner . The brain is relatively large, See also: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 See also: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 See also:action of a muscle into the mouth of the young animal, so that sucking under See also:water is greatly facilitated . Whales and porpoises are found in all seas, and some dolphins and porpoises are inhabitants of the larger See also:rivers of See also:South See also:America and See also:Asia . Their organization necessitates their passing their life entirely in the water, as on See also: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 See also:movement in the water thus necessitated, the See also:principal See also: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 II of which above the surface is absolutely necessary . Of numerous erroneous ideas connected with natural See also:history, few are so widespread as that whales spout through their See also:blow-holes water taken in at the mouth . But the " spouting," or " blowing," of whales is nothing more than the See also:ordinary See also:act of expiration, which, taking See also: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 See also:air taken in at the last See also:inspiration, which is charged with vapour in See also:con-sequence of the See also:respiratory changes . This rapidly condensing in the See also:cold See also:atmosphere in which the phenomenon is often observed, forms a column of See also: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 See also:top of the water, some of which may thus be driven upwards with the blast, tending to See also:complete the illusion . From photographs of spouting rorquals, it appears that the height and See also: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 " See also:sulphur-bottom " (Balaenoptera sibbaldi) averaging only about 14 ft. in height, although it may occasionally reach 20 ft . As regards their See also:powers of See also:hearing, the capacity of cetaceans for receiving (and acting upon) See also:sound-waves is demonstrated by the practice of shouting on the part of the fishermen when engaged in See also:driving a shoal of porpoises or See also:black-fish into shallow water, for the purpose of frightening their intended victims . As regards the See also:possession of a See also:voice by cetaceans, it is stated that one species, the " buckelwal " of the Germans, utters during the breeding-See also:season a prolonged scream, comparable to the scream of a steam-See also:siren, and embracing the whole musical See also:scale, from See also:base to See also:treble . In respect of anatomical considerations, it is true that the external ear is much reduced, the " pinna " being absent, and the See also:tube or " meatus " of very small calibre . On the other hand, the See also:internal auditory See also:organs are developed on the See also:plan of those of ordinary mammals, but display certain peculiar modifications (notably the remarkable See also: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 See also:smell, judging from the rudimentary condition of the olfactory organs, must be in See also: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 See also: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 See also:calm, and, in the case of piscivorous species, to recognize by the See also: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 See also:rock-See also:bound coasts . In the See also:Christiania Nyt Magazin for Naturvidenskaberne, vol. xxxviii., Dr G . Guldberg has published some observations on the body-temperature of the See also:Cetacea, in which he shows how extremely imperfect is our knowledge of this subject . As he remarks, it is a See also: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 See also:pond in the United States . With the larger whales such a mode of See also:procedure is, however, obviously quite impracticable, and we have, accordingly, to rely on See also: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 See also:Sibbald's :orqual three days after See also:death still stood at 3 ° C . The various observations that have been taken have afforded the following results in individualcases: Sperm-whale, 40° C.; See also:Greenland right-whale, 38.8° C.; porpoise, 35.6° C.; liver of a second individual, 37.8° C.; See also:common See also:rorqual, 35.4° C.; dolphin, 35.6° C . The See also:average blood-temperature of See also:man is 37° C., and that of other mammals 39° C.; while that of birds is 42 C . The See also:record of 4o° 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 See also:West See also:African dolphin, all the Cetacea are predaceous, subsisting on living animal See also:food of some See also:kind . One kind alone (Orca) eats other warm-blooded animals, as See also: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 See also:staple of the food of many is constituted by cuttle-fishes and squids . In See also:size cetaceans vary much, some of the smaller dolphins scarcely exceeding 4 ft. in length, while whales are the most See also: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 See also:extinct dinosaurian See also:reptiles . With some exceptions, cetaceans are generally timid, inoffensive animals, active in their movements and affectionate in their disposition towards one another, especially the See also:mother towards the young, of which there is usually but one, or at most two at a See also:time . They are generally gregarious, See also:swimming in herds or " See also: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 See also:account of the oil yielded by the blubber of all of them; while whalebone, See also:spermaceti and See also: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 See also:quarter tons at See also:Aberdeen, although there teems to be some degree of doubt attaching to the statement . Soon after the middle of the last See also:century, the See also:price of this commodity was as See also:low as £15o per ton, but, according to Mr See also:Frank See also:Buckland, it suddenly leapt up to £620 with the introduction of " See also:crinoline " into ladies' See also:costume, and it has apparently been on the rise ever since . Ambergris, which is very largely used in See also: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 cuttlefishes and squids upon which these whales chiefly feed . Its See also:market-price is subject to considerable variation, but from £3 to £4 per oz. is the usual average for samples of See also:good quality . In 1898 a See also:merchant in Mincing See also:Lane was the owner of a lump of ambergris weighing 27o lb, which was sold in See also:Paris for about 85s. 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 See also: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 fugal . 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 See also: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, See also: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 See also:birth . The whalebone does not make its See also:appearance until after birth; and consists of a See also:series of flattened horny plates, between three and four See also:hundred in number, on each side of the palate, with a See also:bare See also:interval along the middle line . The plates are placed transversely to the long See also:axis of the palate, with short intervals between them . Each See also:plate or blade is somewhat triangular in form, with the base attached to the palate and the See also:apex See also:hanging downwards . The outer edge of the blade is hard and smooth, but the inner edge and apex fray out into long bristly See also:fibres, so that the roof of the whale's mouth ,looks as if covered with hair, as described by See also:Aristotle . At the inner edge of each principal blade are two or three much smaller or subsidiary See also: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 See also: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 See also: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 See also: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 " See also: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 See also: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 " See also:gum " of the whalers . Whalebone varies much in See also:colour in different species; in some it is almost See also:jet black, in others See also:slate colour, See also: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 See also: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 See also: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 See also: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 See also:throat and See also: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 See also:Arctic seas, the whalebone and oil of which are so much valued in See also: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 See also:northern and See also:southern hemispheres, and have been divided into species in accordance with their See also:geographical See also:distribution, such as B. biscayensis of the See also:North See also: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 See also: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 " See also:bonnet." This is a large horny excrescence, worn into hollows like a much-denuded piece of See also:limestone rock, growing probably in the neighbourhood of the blow-hole . More than one theory has been suggested to account for its presence . One See also:suggestion is that it indicates the descent of whales from See also:rhinoceros-like mammals; another that this species of whale is in the See also:habit of rubbing against rocks in order to free itself from barnacles, and thus produces a kind of See also:corn—although why on the See also: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 See also:shed on this particular spot . The pigmy whale (1eobalaena marginata) represents a genus agreeing with the right-whales in the See also: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 See also:American, Australian and New See also: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 See also:grey whale (Rachianectes See also: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 otherspecies . In the See also:skeleton the cervical vertebrae are free, and the first two ribs on each side expanded and united to form a large bony See also: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-See also:fourth the See also: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 See also:search of the shoals of small floating invertebrates which form their food, and are consequently broad in See also:beam, with a See also:float-shaped body and immovable neck . The humpback is of somewhat similar build, but with a smaller head, and probably attains considerable See also: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 See also: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 See also:sea . Among them are the most gigantic of all animals, B. sibbaldi, which attains the length of 8o 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 See also:British seas, but the question whether almost identical forms found in the See also: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 See also:report on the See also:zoology of the " See also:Discovery " expedition, published in 1907 by the British Museum, E . A .
See also: 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 See also:crest behind the nostrils . Pterygoid bones thick, produced backwards, meeting in the middle line, and not involuted to form the outer See also: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 See also: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 772 until they are worn, without enamel . Upper surface of the skull See also: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 taw exceedingly long and narrow, the symphysis being more than See also:half the length . Vertebrae: C 7, D 11, L 8, Ca 24; total 50 . See also:Atlas, or first vertebra, free; all the other cervical vertebrae united by their bodies and spines into a single mass . See also: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 See also: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 . 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 coat-in 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 See also: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-See also: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 See also: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 . A second subfamily is represented by the See also:bottle-noses and beaked whales, and known as the Ziphiinae . In this group the lower teeth are rudimentary and concealed in the gum, except one, or rarely two, pairs which may be largely developed, especially in the male . There is a distinct lacrymal bone . Externally the mouth is produced into a slender rostrum or beak, from above which the rounded See also:eminence formed by a See also:cushion of fat resting on the cranium in front of the blow-hole rises somewhat abruptly . The blow-hole is single, crescentic and median, as in the Delphinidae . Flippers small, ovate, with five digits moderately well developed . A small obtuse dorsal fin situated considerably behind the middle of the back . Longitudinal grooves on each side of the skin of the throat, diverging posteriorly, and nearly meeting in front . In external characters and habits the whales of this group closely resemble each other . They appear to be almost exclusively feeders on cuttle-fishes, and occur either singly, in pairs, or in small herds . By their dental and osteological characters they are easily separated into four genera . In the first of these, Hyperoodon, or bottle-nose, there is a small conical pointed tooth at the apex of each half of the lower jaw, concealed by the gum during life . Skull with the upper ends of the premaxillae rising suddenly behind the nostrils to the vertex and expanded laterally, their outer edges curving backwards and their anterior surfaces arching forwards and overhanging the nostrils; the right larger than the left . Nasal bones lying in the hollow between the upper extremities of the premaxillae, strongly concavein the middle line and in front; their outer edges, especially that of the right, expanded over the front of the inner border of the maxilla . Very high longitudinal crests on the maxillae at the base of the beak., extending backwards almost to the nostrils, approaching each other in the middle line above; sometimes compressed and sometimes so massive that their inner edges come almost in contact . Preorbital notch distinct, and mesethmoid cartilage slightly ossified . Vertebrae: C 7, D 9, L 10, Ca 19; total 45 . All the cervical vertebrae united . Upper surface of the head in front of the blowhole very prominent and rounded, rising abruptly from above the small, distinct snout . Two species are known . See BOTTLE-NOSE WHALE . The typical representative of the beaked whales is Ziphius cuvieri, in which there is a single conical tooth of moderate size on each side See also: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 See also:age, and coalescing with the surrounding bones of the rostrum . Vertebrae: C 7, D 1o, L to, Ca 22; total 49 . The three anterior cervical vertebrae united, the rest free . 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, occasion-ally developed to a great size . In the skull the region round the nostrils is as in Hyperoodon, except that the nasals are narrow and more sunk between the upper ends of the premaxillae ; like those of Hyperoodon, 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 to, L lo or II, Ca 19 or 20; total 46 to 48 . Two or three anterior cervicals united, the rest usually free . 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, com- posed of dentine, which, instead of surmounting a See also: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 See also: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. europaeus, M. densirostris, M. layardi, M. grayi and M. hectori; but there is still much to be learned with regard to their characters a specimen taken off and distribution . This group was abundant in the See also:Pliocene age, as attested by the frequency with which the imperishable long, cylindrical rostrum of the skull, of more than See also:ivory denseness, Is found among the rolled and waterworn animal remains which compose the " bone-See also:bed " at the base of the Red See also:Crag of See also:Suffolk . Finally, in Arnoux's beaked whale (Berardius arnauxi), 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 ro, L 12, Ca 19; total 48 . The three anterior cervicals welded, the rest free and well developed . Apparently this whale has the See also:power of thrusting its teeth up and down, exposing them to view when attacked . In a family by themselves—the Platinistidae—are placed three cetaceans which differ from the members of the preceding and the following See also:groups in the mode of See also: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 . See also:Pectoral limbs broad and truncated . Dorsal fin small or obsolete . In habits these dolphins are fluviatile or estuarine . In the Indian susu, or See also:Ganges dolphin (Platanista gangetica), the teeth number about !lu on each side, are set near together, are rather large, cylindrical, and See also: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 See also:lens . Blow-hole longitudinal, linear . Vertebrae : C 7, D II, L 8, Ca 25 ; total 51 . A small caecum . No pelvic bones . Dorsal fin represented by a low See also:ridge . The second genus is represented by Thia geoffroyi, of the See also: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 See also:mere ridge
.
The long cylindrical rostrum externally furnished with scattered, stout and crisp hairs
.
The third type is Stenodelphis blainvillei, the See also:River Plate dolphin, a small See also: Blow-hole transverse . In several respects this species connects the two preceding ones with the Delphinidae (see DOLPHIN) . The last family of existing cetaceans is the above-mentioned Delphinidae, which includes the true dolphins, porpoises, grampuses and their relatives . As a See also: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 See also:attachment lost in the posterior ribs . Sternal ribs ossified . The blow-hole is trans-verse, crescentic, with the horns of the See also:crescent pointing forwards . First on the long See also: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 See also:lie horizontally in the maxilla, and in the See also:female remain permanently concealed within the socket, so that this See also: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 See also:spiral grooves and ridges, See also:running in a sinistral direction . Vertebrae: C 7, D II, 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 (Delphinaplerus 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 See also:diameter of the tooth, and implanted obliquely, the crowns inclining forwards especially in the upper jaw . Skull rather narrow and elongated, depressed . Pre-maxillae See also: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 down-wards . Vertebrae: C 7, D II, 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 Ji to it, are small, and occupy Fm . 8: Upper surnearly the whole length of the rostrum, with See also:face of the Skull of compressed, See also:spade-shaped crowns, separated male Narwhal (Mono-from the root by a constricted neck. See also:don monoceros), with Rostrum rather shorter than the cranium the whole of both proper, broad at the base and tapering to- teeth exposed by re-wards the apex . Premaxillae raised into moval of the upper tuberosities in front of the nostrils . The wall of their alveolar f rontal bones f See also:orm a somewhat square elevated cavities . 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 3o; total 64 . First to sixth cervical vertebrae and sometimes the seventh also, coalesced . Flippers of moderate size, See also: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 See also: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 . See also:Abel, is entitled to See also:rank as a distinct species, with the name of Phocaena relicta . This Black Sea porpoise is readily distinguished from the Atlantic species by the See also:contour of the See also:profile of the head, which, in place of forming a continuous See also: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 See also:idea being that these cetaceans are near akin to fresh-water members of the group, and therefore unsuited to withstand an excessively saline See also:medium . From the Taman See also:Peninsula, on the north See also: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 See also: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.) Next comes the Indo-See also:Malay genus Orcella, in which the to It, 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 See also: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 See also:Bay of See also:Bengal, and O. fluminalis, from the See also:Irrawaddy river, from 300 to 900 M. from the sea . In the See also:grampus, or killer, Orca gladiator (or 0. 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 to, Ca 23; total 51 or 52; bodies of the first and second and sometimes the third cervical vertebrae united; the rest free . The lesser killer or black killer, Pseudorca crassidens, has its 8-12 8- I 2 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 See also: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 . Pre-maxillae 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 It, 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 See also: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 See also:vertical height . Next comes the ca'See also: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 io, L 9, Ca 24; total 5o; 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 (See also:Delphinus delphis) is the typical repre- sentative 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, See also: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 See also: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 See also: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 -- 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 See also: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 . 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 See also: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 See also:geological series as the upper Cretaceous . Many of these present much more generalized characters than their See also:modern representatives, while others indicate apparently a transition towards the still more See also:primitive zeuglodonts, which, as will be shown later, are themselves derived from the creodont See also:Carnivora . In the Pliocene deposits of See also:Belgium and See also: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 See also:Tertiary deposits of See also: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 See also: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 Fio . DD.—The Grampus or Killer (Orca gladiator) . 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 . taken in the river St See also:Lawrence and exhibited in See also:London, 1877 . Eurhinodelphidae, typified by the See also: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 See also:double roots and compressed crowns carrying serrations on the hinder edge; generally the dental See also:formula has been given as i . 3, c . 1, p . , m. i, the single-rooted cheek-teeth being regarded as premolars and those with double roots as molars . Dr Abel is, however, of See also:opinion that the formula is better represented as i . 3, c. p . 8 o9r 9, m . I; 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 See also: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 See also:gap between the most primitive squalodonts and the See also:Eocene zeuglodonts (Zeuglodontidae), which are regarded by Messrs Max See also:Weber, O . Abel and C . W . See also:Andrews as the See also:direct forerunners of the modern-toothed whales, forming the sub-order 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 See also:Egypt) is i . R, c. f, p . , m. s ; the cheek-teeth being two-rooted, with compressed pointed crowns, of which the fore-and-aft edges are coarsely serrated . In the See also:Egyptian Zeuglodon See also:osiris the number of the molars is, however, reduced to 1, 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 See also: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 See also:rate retain the inner See also: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 See also: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 See also:probability that they are so is very great—the latter are derived from primitive Carnivora, and not, as has been suggested, from herbivorous See also:Ungulata . The idea that the zeuglodonts were provided with a bony See also:armour does not appear to be supported by See also:recent discoveries . |
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