The second suborder is formed by the seals, walruses and eared seals,
which differ from the rest of the Carnivora mainly in the limbs being
modified for aquatic progression; the two upper segments being very
short and partially enveloped in the general integument of the body,
while the third, especially in the hind extremities, is elongated,
expanded and webbed. There are always five well-developed digits on each
limb. In the hind-limb the two marginal digits (first and fifth) are
stouter and generally larger than the others. The teeth also differ from
those of the more typical Carnivora. The incisors are always fewer than
3/3. The chsek series consists generally of four premolars and one molar
of uniform characters, with never more than two roots, and with conical,
more or less compressed, pointed crowns, which may have accessory cusps,
placed before or behind the principal one, but are never broad and
tuberculated. The milk-teeth are small, simple and shed or absorbed at
an early age, usually either before or within a few days after birth.
The brain is relatively large, the cerebral hemispheres broad in
proportion to their length, and with numerous and complex convolutions.
There is a very short caecum; the kidneys are divided into numerous
distinct lobules. There are no Cowper's glands. Teats two or four,
abdominal. No clavicles. Tail always short. Eyes large and exposed, with
flat cornea. The nostrils close by the elasticity of their walls, and
are opened at will by muscular action.
The members of this group are aquatic, spending the greater part of
their time in the water, swimming and diving with great facility,
feeding mainly on fish, crustaceans and other marine animals, and
progressing on land with difficulty, but always coming on shore for the
purpose of bringing forth their young. They are generally marine, but
occasionally ascend large rivers, and some inhabit inland seas and
lakes, as the Caspian and Baikal. Though not numerous in species, they
are widely distributed over the world, but occur most abundantly on the
coasts of lands situated in cold and temperate zones.
As mentioned in the article CREODONTA, the true seals (_Phocidae_),
together with the walruses, may be directly descended from the primitive
Creodont Carnivora. The eared seals, on the other hand, show signs of
affinity with the bears; but as they are of earlier geological age than
the latter, they cannot be derived from that group.
Seals.
The true seals (family _Phocidae_) are the most completely adapted for
aquatic life of all the Pinnipedia. When on land the hind-limbs are
extended backwards and take no part in progression, which is effected
by a series of jumping movements produced by the muscles of the trunk,
in some species aided by the fore-limbs. The soles of the feet are
hairy. There is no pinna to the ear, and no scrotum, the testes being
abdominal. The upper incisors have simple, pointed crowns, and vary in
number in the different groups. All have well developed canines and
5/5 teeth of the cheek series. In those species of which the
milk-dentition is known, there are three milk molars, which precede
the second, third, and fourth permanent molars; the dentition is
therefore p. 4/4, m. 1/1, the first premolar having as usual no milk
predecessor. The skull has no post-orbital process and no alisphenoid
canal. The fur is stiff and adpressed, without woolly under-fur.
In the typical group, or subfamily _Phocinae_, the incisors are 3/2.
All the feet have five well-developed claws with the toes on the
hind-feet subequal, the first and fifth not greatly exceeding the
others in length, the interdigital membrane not extending beyond them.
In the genus _Halichoerus_ the dentition is i. 3/2, c. 1/1, p. 4/4, m.
1/1; total 34. Molars with large, simple, conical, recurved, slightly
compressed crowns, having sharp anterior and posterior edges, but
without accessory cusps, except sometimes the two hinder ones of the
lower jaw. With the exception of the last one or two in the upper jaw
and the last in the lower jaw, all are single-rooted. Vertebrae: C. 7,
D. 15, L. 5, S. 4, Ca. 14. Includes only one species _H. grypus_, the
grey seal of the coasts or Scandinavia and the British Isles.
In _Phoca_ the dental formula is as in the last, but the teeth are
smaller and more pointed. Molars with two roots (except the first in
each jaw). Crowns with accessory cusps. Vertebrae: C. 7, D. 14-15, L.
5, S. 4, Ca. 11-14. Head round and short. Fore-feet short with five
strong, subcompressed, slightly curved, subequal, rather sharp claws.
On the hind-feet the claws much narrower and less curved. The species
of this genus are widely distributed throughout the northern
hemisphere, and include _P. barbata_, the bearded seal; _P.
groenlandica_, the Greenland seal; _P. vitulina_, the common seal; _P.
hispida_, the ringed seal of the north Atlantic; _P. caspica_, from
the Caspian and Aral Seas; and _P. sibirica_, from Lake Baikal. (See
SEAL).
The members of the second subfamily, _Monachinae_, have incisors 2/2;
and the molars two-rooted, except the first. On the hind-feet the
first and fifth toes greatly exceeding the others in length, with
nails rudimentary or absent. In the genus _Monachus_, the dentition is
i. 2/2, c. 1/1, p. 4/4, m. 1/1; total 32. Crowns of molars strong,
conical, compressed, hollowed on the inner side, with a
strongly-marked lobed cingulum, especially on the inner side, and
slightly developed accessory cusps before and behind. The first and
last upper and the first lower molar smaller than the others.
Vertebrae: C. 7, D. 15, L. 5, S. 2, Ca. 11. All the nails of both fore
and hind feet very small and rudimentary. Represented by _M.
albiventer_, the monk-seal of the Mediterranean and adjacent parts of
the Atlantic, and the West Indian _M. tropicalis._
The other genera of this section have the same dental formula, but are
distinguished by the characters, of the cheek-teeth and the feet. They
are all inhabitants of the shores of the southern hemisphere.
In _Ogmorhinus_ all the teeth of the cheek-series have three distinct
pointed cusps, deeply separated from each other, of which the middle
or principal cusp is largest and slightly recurved; the other two are
nearly equal in size, and have their tips directed towards the middle
one. Skull much elongated. One species, _O. leptonyx_, the
sea-leopard, widely distributed in the Antarctic and southern
temperate seas. In _Lobodon_ the molars have compressed elongated
crowns, with a principal recurved cusp, rounded and somewhat bulbous
at the apex, and one anterior, and one, two or three posterior
distinct accessory cusps. One species, _L. carcinophagus_, the
crab-eating seal. In the third genus, _Leptonychotes_, represented by
_L. weddelli_, the molars are small, with simple, subcompressed,
conical crowns, and a broad cingulum, but no distinct accessory cusps.
Finally in the white seal (_Ommatophoca rossi_) all the teeth are very
small, those of the cheek-series with pointed, recurved crowns, and
small posterior and still less developed anterior accessory cusps.
Orbits very large. Nails rudimentary on front and absent on hind-feet.
The skull bears a considerable resemblance to that of the next
subfamily.
The presence of two pairs of upper and one pair of lower incisors is
characteristic of the members of the subfamily _Cystophorinae_, in
which the teeth of the cheek-series are generally one-rooted. The nose
of the males has an appendage capable of being inflated. First and
fifth toes of hind-feet greatly exceeding the others in length, with
prolonged cutaneous lobes, and rudimentary or no nails. In the typical
genus _Cystophora_ the dentition is i. 2/1, c. 1/1, p. 4/4, m. 1/1;
total 30; the last molar having generally two distinct roots. Beneath
the skin over the face of the male, and connected with the nostrils,
is a sac capable of inflation, when it forms a kind of hood covering
the upper part of the head. Nails present, though small on the
hind-feet. Represented by _C. cristata_, the hooded or bladder-nosed
seal of the Polar Seas. In _Macrorhinus_ the dentition is numerically
the same as in the last, but the molars are of simpler character and
all one-rooted. All the teeth, except the canines, very small
relatively to the size of the animal. Hind-feet without nails.
Vertebrae: C. 7, D. 15, L. 5, S. 4, Ca. 11. Nose of adult male
produced into a short tubular proboscis, ordinarily flaccid, but
capable of dilatation and elongation under excitement. One species,
_M. leoninus_, the elephant-seal, or "sea elephant" of the whalers,
the largest of the whole family, attaining the length of nearly 20 ft.
Formerly abundant in the Antarctic Seas, and also found on the coast
of California.