MESOPLODON STEJNEGERI True.

Mesoplodon stejnegeri True, Proc. U. S. Nat. Mus., vol. 8, p. 584. Oct. 19, 1885.

This species was originally described from a single cranium of a young individual, which was collected by Dr. L. Stejneger on Bering Island, Commander Group, Bering Sea, in 1883. With but a single skull, the characters of the species could not be very satisfactorily defined, and some European cetologists have been inclined to doubt its validity.[30] In 1904, however, another skull was obtained by the National Museum, which made it certain that the species was entirely distinct from M. bidens or other known forms of the genus. Early in the year mentioned Dr. D. S. Jordan, president of Stanford University, called my attention to a small whale, which stranded on the coast of Oregon, 1½ miles south of the United States life-saving station on South Beach, Yaquina Bay, near Newport, in February, and proved later to represent the present species. Doctor Jordan’s information was obtained from Mr. J. G. Crawford, of Albany, Oregon, who wrote him in part as follows, under date of March 7, 1904:

Herewith I enclose a stereograph of a head of a member of the whale family, which I made at Yaquina Bay, Oregon. The animal was 17 feet long, with fluked tail, soft, smooth skin, blowhole on top of head, and two tusks in the mandible, but no [other] teeth in the mouth. The tusks are thin and apparently hollow. Length of head, 32 inches; width, 14 inches; height, 11 inches; blowhole, 5 inches. Eyes low on head. Width of mandible [jaw] at end: Upper, 1½ inches; lower, 1¾ inches. Width between tusks, 3 inches. The blubber was about 2 inches thick on the head. It went ashore about the 15th of February, 1½ miles south of the life-saving station on South Beach, 2½ miles south of Newport, Oregon. The head had been severed before I arrived.

A clipping from the Oregonian newspaper contains the following:

Albany, Oregon, March 2 [1904]. A peculiar specimen of the whale variety has been reported on the Oregon coast, near Newport. J. G. Crawford, of Albany, has just returned from a trip to Newport, where he made a picture of the head of the strange animal. The body was washed upon the beach during the recent storm which swept the coast. It is about 15 feet long. * * * Residents of the vicinity say they have never seen anything like it on the Oregon coast. * * * On either side of the mouth are two villainous-looking tusks several inches in length. They are at the back of the mouth, and extend up to a level with the top of the upper jaw. They are very wide and flat, squared on top. The mouth has no other teeth. * * *

The head is equipped with a blowhole, like that of a whale. The eyes are very low, almost underneath the lower jaws.

The body is in a good state of preservation, the flesh having been torn but little by the birds.

On receipt of the foregoing information, letters were immediately addressed to Mr. Crawford and also to the keeper of the life-saving station at South Beach, Capt. Otto Wellander, asking that, if possible, the entire skeleton be preserved. Captain Wellander replied that the whale had not been dead long when washed ashore; that he had tried to find the body, but that the high tides had either carried it away or buried it under driftwood.

The skull when cleaned passed into the possession of Mr. J. G. Crawford, who sent to the Museum some excellent photographs of it, and also of the head before the flesh had been removed. Later he sent the skull itself to the Museum for my examination, and finally very generously presented it to the Museum in exchange.

The skull is that of an adult individual, in nearly perfect condition, with the mandible and teeth. The parts missing are the left malar, the left tympanic bone, the distal ends of the pterygoids and the proximal ends of the premaxillæ. ([Pl. 3], fig. 2.)

SKULL.

The Oregon skull exhibits all the characters included in the original diagnosis of the species,[31] but two of these, namely, the lack of a groove in front of the premaxillary foramen, and the vertical position of the premaxillæ distally, I do not at present consider of any importance, as they are shared by M. bidens. The species, as represented by the Oregon skull, however, presents other characters which clearly differentiate it from any other species of the genius. As it is without a basirostral groove, it allies itself in that respect to M. bidens, europæus, and hectori. Unlike those species, it has the premaxillary foramen behind the maxillary foramen, and in this respect resembles densirostris and grayi. Perhaps the most salient characters in which stejnegeri differs from bidens and all other known species are the erect position and flat surface of the supraoccipital and the very prominent backward extension of the frontal plate of the maxilla. This backward extension is so great that when the beak is horizontal a vertical line through the posterior margin of the maxilla passes considerably behind the temporal fossa. The only species which approaches stejnegeri in this respect is hectori, but in the latter the supraoccipital instead of being flat above the condyles is very strongly convex.

Another very marked character of stejnegeri is that the extension of the lateral free margin of the orbital plate of the frontal, anterior to the orbit, is equal to the length of the orbit itself. In bidens and all other known species this extension is only from one-third to one-half the length of the orbit. Numerous other distinguishing characters will be mentioned in the course of the following description of stejnegeri, which is drawn from the adult Oregon skull, but modified when necessary by reference to the type skull from Bering Island. Comparisons are made chiefly with M. bidens, which is on the whole the best known species.

In the Oregon skull of stejnegeri, the breadth between the post-orbital processes does not exceed the length from the occipital condyles to the maxillary notches. The skull is, therefore, narrower in proportion to its length than in any other species of the genus except hectori, as represented by the skull figured by Flower. This skull was, however, that of a young individual. It is probable that in adults of this species the skull is broader than in stejnegeri.

In the latter species, again, the length of the brain-case, between the occipital condyles and the maxillary notches, is just equal to the distance from the latter point to the distal end of the maxillæ, and the rostrum, including the premaxillæ, is much shorter than in other species of Mesoplodon, except hectori, as represented by the young skull above mentioned.

The foramen magnum is very small, being less in width than the condyle on either side of it. In this respect it differs widely from bidens and other species (as far as can be ascertained from the figures available), except europæus, in which the relative size is about the same.

The supraoccipital rises vertically above each condyle to the very top of the skull, being neither convex nor strongly bent forward as in other species, and especially bidens. In the median line, however, while the occipital bone is flat immediately above the foramen magnum, it is deeply concave higher up and without a median ridge. The outline of the occipital crest, viewed from behind, is semicircular. In all the foregoing characters the occipital region differs widely from that of bidens and other species. The only close resemblance is found in the old skull of europæus from Long Branch, New Jersey, and even here the sides of the occipital above are far less prominent, their outline is much more convex, the occipital crest is angular, and the median depression is less pronounced.

Dorsal aspect ([Pl. 3], figs. 1, 2).—The most noticeable feature of the upper surface of the skull is the large backward extension of the frontal plates of the maxillæ, the free margins of which converge strongly. The outline of the anteorbital region is rounded. The anteorbital notch is a shallow emargination. Anterior to this is a second still shallower emargination, the “pseudo-notch.” The margin between the two is much thickened, but does not form a distinct projection or tubercle, as in bidens and other species. The superior orifices of the nares are unsymmetrical as regards position, the left being somewhat in advance of the right. The maxillæ are concave around the maxillary foramen, and external to this foramen is an elongated ridge about as in europæus. The rostral portion of the maxillæ is broad at the base but tapers more rapidly than in bidens. The margin is thick. At the middle of the beak the outline of the maxillæ at a lower level is visible from above, which is not the case in bidens or europæus. The rostral portion of the premaxillæ is oblique proximally and vertical distally. Unlike bidens, these edges are sharp throughout. The mesethmoid ends opposite the maxillary foramina. Anterior to it is seen the concave upper surface of the vomer, which, however, becomes flat distally. At about the middle of the beak the anterior end is clasped by the posterior forked end of a “mesirostral” ossification, which has a convex surface. This ossification begins proximally below the edges of the premaxillæ, but its surface rises gradually anteriorly, and at the end of the beak it is much above the premaxillæ. The end of the beak consists of the consolidated mass of the premaxillæ and mesirostral ossification, the whole being convex above and below, but flat on the sides. The ossification has a deep median groove, which reaches to within 95 mm. of the tip of the beak.

It will be seen that the conformation of the upper surface of the beak is quite different from that of bidens or any other species.

The maxillary foramina are large and directed forward, and have a distinct broad channel in front of them. In the Oregon skull the right foramen is single, but the left divided into two. The premaxillary foramina are a little behind the maxillary foramina. The distance between the maxillary foramina is less than that from the median line to the anteorbital notch. In bidens it is much greater.

Lateral aspect ([Pl. 9], figs. 1, 2).—A most noteworthy feature of the skull when viewed from the side is the great length between the orbit and the maxillary notch, which far exceeds that found in bidens and other species, being equal to the length of the orbit itself. The latter is about as long as the temporal fossa, which is somewhat flattened above, as in europæus. The outline of the supraoccipital is straight and nearly vertical. The zygomatic is more massive even than europæus and is especially thick below. The inferior outline of the beak is convex proximally as in europæus and layardi. There is no basirostral groove, the edges of the maxillæ being very thick in front of the maxillary notch. Over the orbit the maxillæ are thick and beveled, but not raised as in bowdoini.

Ventral aspect ([Pl. 6], figs. 1, 2).—The beak is convex in the proximal half, much as in europæus, but farther forward is concave, except in the median line, where there is a narrow ridge formed proximally by the vomer, which in the type skull appears as a narrow lozenge 60 mm. long. In the adult Oregon skull it is anchylosed with the premaxillæ. The maxillæ extend to within 107 mm. of the end of the beak. The under surface of the beak is much more like that of europæus than of bidens.

A narrow strip of the palatines extends around the base of the pterygoids in front, but the two strips do not meet in the median line. In the type-skull they do not extend inside the pterygoids. The expanded anterior end of the malar is very long and also forms the bottom of the maxillary notch, which is the case in europæus but not in bidens. The inferior borders of the pterygoids are convex anteriorly, as in europæus, and are continued laterally, so that the sinus is deep as in that species. The lachrymal is very long, the free margin having a length of 55 mm. The posterior margin of the zygomatic process is concave, rather than convex as in bidens.

The tympanic bulla does not differ materially from that of bidens in size or shape, as far as can be judged from the figures given in Van Beneden and Gervais’ Osteography (plate 26, figs. 4, 4a). The periotic is similar in size to the same bone in bidens, but the posterior end is more narrowly pointed and the anterior end is much lower, relatively. In europæus, as far as can be determined from the material at hand, the form and size of the earbone is similar to that of stejnegeri, but in the latter the anterior margin of the tympanic bulla is more nearly transverse and the posterior inferior groove is curved. ([Pl. 35], fig. 2.)

In the Annisquam skull, supposed to represent densirostris, although from a young individual, the earbone is very much larger, especially the periotic, which is also quite differently shaped.

MANDIBLE.

The mandible of stejnegeri is much broken in the region of the angle on both sides, but otherwise complete. As compared with a mandible of an adult bidens, the most conspicuous differences are the shortness of the symphysis, the sharp upward bend of the inferior margin anteriorly, and the large size of the alveolus. The symphysis in the adult Oregon specimen of stejnegeri is 140 mm. long, or scarcely more than in the young specimen of europæus from New Jersey, and exactly the same as in the adult type-specimen of the latter species, as figured by Van Beneden and Gervais. The alveolus lies entirely behind the symphysis, its anterior end being 160 mm. from the anterior end of the jaw. It is 113 mm. long and 18 mm. wide. The mandible is 62 mm. high at its middle point. The coronoid process is more anteriorly situated than in bidens and the portion of the posterior margin of the ramus which remains indicates that the angle was strongly directed backward. ([Pl. 11], fig. 4; [pl. 12], fig. 1.)

TEETH.

The teeth are remarkable for their size and form. They are somewhat more than twice as broad as teeth of adult males of bidens, as shown by the figures of Lankester[32] and Grieg,[33] and also a little longer. They are, in fact, probably broader than, or at least as broad as, the teeth of any other species of Mesoplodon, not excepting layardi. Sir William Turner remarks regarding a specimen of layardi examined by him that “the breadth of the tooth, where it emerged from the alveolus, was 3½ inches.”[34] He does not state, however, whether the measurement was taken along the top of the alveolus, at an angle with the transverse axis of the tooth, or along the transverse axis itself. At all events, the teeth figured by Owen and others are much less than 3½ inches broad. The teeth of adult europæus are only 2 inches broad, and of bidens, as already stated, 1½ inches broad.

In stejnegeri ([Pl. 12], figs. 1-3) the portion of the tooth above the alveolus is inclined slightly inward and backward, but the pointed tip curves outward so as to be vertical. When extracted from the alveolus, the whole tooth is found to be concave internally and convex externally. The posterior margin is convex and the anterior sinuous, a slight convexity occurring on the portion which projects above the alveolus. In this place the outer coating of cement is broken through, showing the underlying dentine or osteo-dentine, which is somewhat corroded or absorbed. This is particularly noticeable on the left tooth.

The upper margin of the tooth is transverse, or nearly at right angles with the anterior and posterior margins. The posterior angle is rounded and the anterior raised into an acute point by the projection of the dentine as a distinct, sharp cusp. The inferior end of the tooth is cut off obliquely and the margin is broken by numerous prominent rugosities. The surface of all that part of the tooth which is contained in the alveolus and covered by the gum above it is rugose, while the part above the gum is quite smooth and highly polished.

The right tooth has the following dimensions (in straight lines): Length of anterior border, 150 mm.; length of posterior border, 107; length of superior border, 54; length of inferior border, 86; average length of exposed dentine tip, 10; greatest breadth of tooth, antero-posteriorly, 81; greatest breadth of tooth, transversely, 15; distance from center of base of exposed portion, when in position in the alveolus, to tip of dentine projection, 82; distance from center of base of portion above the gum to tip of dentine projection, 70; distance from center of base of portion above the gum to center of inferior margin, 76.

The dimensions of the skulls are as follows, those of the type-specimen having been revised and corrected:

Dimensions of two skulls of M. stejnegeri.

Column headings: A: 143132 U.S.N.M. Yaquina Bay, Oregon, adult. B: 21112 U.S.N.M. Bering Id. Type (1715), young.

Measurements.AB
Total length715a633
Length of rostrum413a325
Distance from occipital condyles to distal end of maxillæ612567
Breadth between centers of orbits309279
Breadth between zygomatic processes310278
Breadth between temporal fossæ228212
Breadth between postorbital processes of frontals323...
Breadth of rostrum at base (between maxillary notches)172b158
Breadth of rostrum at middle4044
Depth of rostrum at middle5242+
Greatest breadth of anterior nares5654
Greatest breadth of premaxillæ proximally130118
Greatest breadth of premaxillæ in front of nares108109
Length of temporal fossa9286
Depth of temporal fossa6346
Antero-posterior length of orbit9682
Breadth of foramen magnum3839
Length of tympanic bulla48...
Breadth of tympanic bulla32...
Length of mandible610...
Length of symphysis138...
Distance from anterior end of mandible to alveolus166...

a Tip of rostrum lacking. b The skull is much worn around the left notch and the measurement is only approximate.

EXTERNAL FORM.

The photograph of the head ([Pl. 40], fig. 4) shows that the end of the beak was quite blunt, and the lower jaw quite a little longer than the upper. The superior margin of the lower jaw, which is concave in front of the tooth, is strongly convex and elevated at the side of it and behind it. The inferior margin of the upper jaw is straight anteriorly, but farther back appears to be pressed upward by the tooth. An examination of the skull shows that the mandible can be lowered so that the teeth are below the upper jaw, but when so lowered the space between the teeth and the upper jaw on each side is barely a quarter of an inch (6 mm.). With the integuments in place, it is doubtful whether the mouth could be opened any wider than is shown in the photograph. The convexity of the head, shape of the blowhole, position of the eye, etc., do not appear to differ materially from the same characters in adults of M. bidens.