NOTES ON THE OSTEOLOGY AND DENTITION OF THEGENERA DESMOSTYLUS AND CORNWALLIUS.
By Oliver P. Hay,Associate of the Carnegie Institution, of Washington.From Dr. Edward M. Kindle, of the Canada Geological Survey,tlie writer has received for examination a large tooth of Desmostylus,which was presented to the Victoria Memorial Museum, at Ottawa,by Dr. C. W. Newcombe, of Victoria, British Columbia. It had beenpurchased from a dealer in curiosities and was reported to have beenbrought from Alaska. This report may be true, but it is hardly to bedepended upon. The tooth no doubt belongs to Desmostylus^ but in-asmuch as neither the locality nor the formation is known it wouldbe unsafe to identify it specifically. It appears to be a left uppermolar.Tlie tooth sent from Victoria (pi. 1, figs. 1, 2) had not yet come intoUbe, the unabraded sunmiits of its columns showing each the peculiardepression and central nipple-like elevation. Only the base of theroot is present, and there are indications that it consisted of twofangs. The greatest length of the tooth is 61 mm. ; the height 57mm., including the base of the root. From the edge of the enamelto the summit of the columns is 51 mm. The thickness, where great-est, is 38 mm. The tooth consists of eight columns. Of these, threeform a front transverse row; then come two rows, each of twocolumns; and at the rear is a single column. The transverse rowsare oblique to the axis of the tooth, being directed from the outsideinward and backward, as may be seen by figure 1 cited.As will be observed, the intervals between the columns are occu-pied by cement, and this is of a lighter color than the surfaceof the enamel. This cement rises from the root to the summit ofthe columns. Below the bases of the second and the third columnsthe cement continues to the center of the base of the root, lyingevidently in a valley which seems to mark the division of the rootinto two fangs. The front of the tooth presents two tracts ofcement, one on each side of the median column, and it spreads overthe front of these anterior columns nearly half way to their sum-mits. It is pro1)able that originally a large part of the crown wasNo. 2521
?
Proceedings U. S. National Museum, Vol. 65, Art. 8.
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2 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 65.covered with a thin coat of cement. On the inner face of the tooththere still adheres a part of the maxiliary bone. So far as thewriter sees, it is impossible to determine where in the molar seriesthis tooth belongs. No surface shows contact with a tooth in frontor behind.The determination of the dentition of Desmosfi/Iiis is a matterof great interest. An examination of Yoshiwara and Iwasakrsfigures' shows that there is, in front of their first molar, a smalltooth consisting of only four columns. In the skull from Oregon,which the writer described in lOla,^ there is in front of a molar(pi. 57, 23) apparently corresponding to that figured by the Japaneseauthors, and composed of the same number of columns, 8, the baseof a smaller tooth which was regarded 'as the first molar (pi.57, 22). This supposed first molar, instead of being made up ofeight columns, appears to have only five. The tooth in front ofthis (pi. 57, 21) is represented by the base of the crown and theroot, and it has a diameter of 17 mm. On plate 58 of the papercited, was presented the figure of a tooth which had four columnsand which was believed to be the fourth premolar. This appearsto correspond to the hinder premolar described by Yoshiwara andIwasaki. Now, according to these identifications, the Oregon skulldiffers from the one found in Japan in having between the sup-posed last premolar with four columns and the molar with eightcolumns another tooth possessing apparently only five columns. Itis improbable that the two species differed in such an importantrespect.An examination of my figure ^ shows that the molar indicated by23 was emerging behind and above the supposed first m.olar 22.This tooth 22 can hardly be a premolar, for this might be expectedto appear only after the molar behind it had come into action. Onemight insist also that it is not a milk tooth, because there appearsto be no premolar to replace it, as shown by Yoshiwara and Iwasaki'sfigure. Plate 2 of the Japanese authors shows that another molar(their M-) was moving downward and forward to take its placeagainst the molar then in action?that is, it appears that the uppermolars, on coming into place, move downward and forward as inthe mastodons and elephants.If, now, we grant that, as the supposed first molar (22) of theOregon specimen became worn down, the next molar (23) movedforward, pushed it out, and took its place, the condition seen inYoshiwara and Iwasaki's specimen would be produced. Accordingto this interpretation, the hinder premolar of the paper last cited
1 Journ. Coll. Sci., Japan, Imp. Univ., vol. 16, 1902, pi. 2 ; pi. 3, fig. 4.zProc. U. S. Nat. Mus., vol. 49, p. 381, pi. ol.? Idem. pi. \>7.
I
AKT. s. THE GENERA DESMOSTYLUS AND CORNWALLIUS HAY. 3would be the fourth premolar and the tooth immediately behind itthe second molar, while the molar shown at a distance behind wouldbe the third.In 1923 * the writer proposed the new name Gomwallius^ based onDesmostyluB sookensh Cornwall.^ Through Director Francis Ker-mode, of the Provincial Museum of Natural History, Victoria, Brit-ish Columbia, the writer received for examination both of the teethfigured by Cornwall. These teeth are illustrated on the plates (pi.1, figs. 4, 5, and pi. 2. figs. 1-5).It has occurred to the writer that these teeth may be milk teethof Desmostylus and that the larger one (pi. 1, figs. 1, 2, pi, 2, figs.4, 5) may correspond to that called in my paper of 1915 the firstmolar. The tooth is of appropriate size. The length is 48.5 mm.,tlie width 34 mm. The corresponding dimensions of what the writerregarded as the first molar ^ were estimated to be in length 40 mm.,and width 28 mm., but the measurements were taken at the somewhatnarrowed base of the tooth. The low crown of the tooth of C. soo-kensis accords with the idea that it is a milk tooth.it seems certain that the tooth which in my paper of 1915 (pi. 57)was designated by the numeral 21 is either a milk molar or the pre-molar which would follow it; also that it corresponds in position tothe tooth Pm of Yoshiwara and Iwasaki's plate 2, and to the smalltooth of their plate 3, figure 4. The Oregon skull belonged evi-dently to a younger animal than did the Japanese skull. In thelatter it seems that the premolar, if such it is, had not yet beenpushed out to the level of the molar behind it. In the Oregon speci-men it is possible that the milk tooth 21 had not yet been replaced.As already said, the tooth designated 23 was lying immediatelyabove the greater part of the tooth 22. The former might, there-fore, be taken as fourth premolar. Because of the great size of thetooth and the number of its columns, this appears wholly unlikely.The tooth 23 must be a molar.We may possibly get an explanation of the dentition of Desmo-stylus from that of the mastodons. In some of these the premolars areretarded in their development, in others even wholly suppressed.The suppression of premolars began with the hindermost one. Thesame modification of the dentition has been demonstrated in theiSirenia. In the earliest members of the group, as Protosvren fra.ssi,''the tooth formula was the typical one, i. 3, c. i, pm. 4, m. 3. Accord-ing to Andrews ^ the dental formula was the same in Eotheriumaegypticum. Abel tells us that since the middle Eocene there has
* Pan-Amei-. Geologist, vol. 39, p. 106, text-fig. 4.^Canad. Field-Naturalist, vol. 36, p. 122, 4 figs.? Proc. U. S. Nat. Mus.,. vol. 49, pi. 57, 23.
' Abel, Jahib. Min., Geol.. Pal., 1906, vol. 2, pp. 50. 51.^Cat. Tert. Vert. Fayum, 1906, p. 207.
PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 65.been a progressive reduction of the replacement teeth. In Halithe-rium the hindermost preniohir was not developed, and the corre-sponding milk tooth assumed the form of a molar.We may then regard it as possible that the tooth 22 of my plate67 is a milk tooth which was assuming the form of a molar, and whichwas not to be displaced by a premolar, but by the first molar. Thetooth in front of it is then the third premolar, or the correspondingmilk molar. A deep pit in front of it represents the second pre-molar or milk molar, and a minute pit in front of that represents thefirst juvenile tooth.As to the tooth on which I based the genus CornwalUus it is thenpossible that it is the liindermost milk tooth of Desmostylus; but thisis for the future to determine. I proceed to give a description of it
:
The tooth (pis. 1, 2, figs. 4, 5) has suffered some loss of enamel ontwo columns, as shown by the figures. All of the columns havesuffered some wear, but that they were of small height originally isevident. In two of them the wear hadnot reached the core of dentine. Thecolumns taper rapidly from the baseto the summit. Text figure 1 presentsa view of this tooth before a fragmentof the second inner colunm had beencemented in its place. It shows thatthe dentine core, broad at its base,tapers rapidly to its summit, as wasnecessary in a low-croAvned tooth. Asseen from the figures, there are in front two large columns, and be-hind these two somewhat smaller ones. At the rear is a column ofwhich a part is gone. It appears quite certain that the snag ofenamel at the right of the gap (pi. 1, fig. 4) formed part of a cuspwhich adhered to the hinder column. Whether it could be countedas the sixth column is doubtful. The tooth is taken to belong inthe right maxilla.The length, measured in the axis of the tooth, is 45 mm. ; the totallength 48.5 mm. ; the greatest thickness, 34 mm. ; the height of thecrown in front, 23 mm. On the front end there is a cingulum whichdoes not occupy the whole width of the tooth. At the inner end ofthis are two small cusps., llootward from the edge of this cingulumthere is a surface 10 mm. long and 4 mm. deep, which is worn fromcontact with a tooth in front. Between the cingulum and the grind-ing surface there is on each of the two anterior columns an extensiveworn surface. No such surface is seen on the hinder end of thetooth. The cingidum is not developed on the sides and rear of thetootli; but at the outer end of the first transverse valley there is alarge tubercle, worn at the summit and showing a pit of dentine. At
Fig. 1.-
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Tooth of CohnwalliussooKENSis. View from innerSIDE. Type.
ART. 8. THE GENEKA DESMOSTYLUS AND CORNWALLIUS HAY. 5the inner end of the same valley is a much smaller tubercle. A singletubercle appears at the outer end of the second valley and is closelyapi^lied against the hindermost column. The rear of this column ismissing.There belonged to this tooth quite certainl}^ two roots, but theseare broken off (pi. 2, fig. 5). A considerable pulp cavity remains,27 mm. long and 15 mm. wide. It is slightly constricted near themiddle of the length, indicating thus the parting of the roots.From Director Kermode was received also the tooth which wasdescribed and figured in 1917 ^, as Desmostylus hcsperus^ and whichCornwall, in his paper cited, figured as Desmostylus sookensis. Itwas found in the sandstone cliffs near the mouth of Coal Creek,British Columbia, by Miss M. Egerton. If was sent to L. M. Laiiibe,paleontologist in the Geological Survey, Ottawa, whose remarks onit are published on the page above cited. Mr. Lambe identified itprovisionally as tlie upper right first molar. He did this possiblyrelying on my identification of the first molar in my paper of 1915.The length of the tooth (pi. 2, figs. 1-3) is 33 mm. ; the width 24mm.; the height of the crown, 16 mm. It is somewhat more w^ornthan the tooth described in the previous paragraph, but it is evi-dent that the columns were originally low. It had two well -devel-oped roots (pi. 2, fig. 3) of equal size. These are now broken offsquarely just below the crown. The transverse diameters of theseroots are close to 18 mm. At the plane of fracture they are not en-tirely separated from each other. The tooth is supposed to belongto the left side of the lower jaw, because the cingulum is better de-veloped on the left side of the tooth. It consists of six' columnsarranged in three transverse pairs. Of the anterior pair the innercolumn is the largest of all. The inner column of the third pair isvery small and the wear had not exposed the dentine. Cornwall,perhaps correctly, did not count it as one of the columns. On thefront of the tooth, in the midline, is a broad tubercle which may beregarded as a talon or a part of a cingulum. On the outer facethere is a slight cingulum-like ridge at the bases of the two frontcolumns. Between the second and third columns is a tubercle or cusp.On the inner face there is little or no trace of the cingulum. Onthe front end of this tooth there is an extensive surface polished bycontact with a tooth in front. This begins at the level of the grind-ing surface and descends not only to the talon, but in a narrowingstrip nearly to the base of the crown. Above the talon the polishedsurface is 15 mm. wide from side to side. A small polished surfaceis found on the hinder end of the tooth.
? Rep. Provijicial Mus. Nat. Hist., Victoria, B C, for 1916, p. 42, pi. 9, figs. 2, 3.
6 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 65.This tooth does not agree in structure with any yet described. Itmost resembles the teeth described by Yoshiwara and Iwasaki^? aslower second premolars. In those teeth, however, there are threecolumns in the hinder transverse row.There are some reasons why the larger of the two teeth referred toCornwaUius sookensis can not be regarded as identical with thetooth 23 of the Oregon specimen. These are as follows
:
(1) The outer border of the Oregon tooth is straight; in the Vic-toria tooth this border is strongly curved. (2) The transverse rowsof columns in the Oregon tooth appear to be arranged more obliquelyto the long axis of the tooth than in that from Victoria. (3) Thehinder end of the Victoria tooth is considerably broader than in theone from Oregon.Until some lucky discovery shall decide the matter one way orthe other, the writer proposes to maintain the genus Cormvalh'vsand to regard the larger of the two teeth (pis. 1, '2. tigs. 4, 5) as anupper molar, and the smaller one (pi. 2, figs. 1-3) as a lower molar,not the hindermost. The larger tooth is taken as the special type ofCor-nvmUius sookensis.The cliffs in the vicinity of Sooke. Vancouver Island, ought to becarefully and frequently searched for additional materials of thissirenian.In their description of the skull of Desmostylus Yoshiwara andIwasaki attribute to Desmostylvs two pairs of lower tusks and onepair of upper ones. The lower tusks projected some distance fromthe jaw. The upper tusks were said not to have yet come intofull growth, only the left tooth being slightl}^ visible beneath theruptured surface of the maxilla. Their figure ^^ shows what wasseen of this tusk.In my description of Desmostylus from Oregon I referred to whatseemed to be an upper tusk. Although this was said ^' to showonly on the right side, there is on each side a projection at thefront of the specimen which represents the same structure. Asshown by my figures, a fragment of the snout about 30 mm. long hadbeen broken off in exhuming the skull and had later been cementedin its place. Recently, wishing to come to a decision regarding thissupposed tusk, the writer removed the fragment and cleaned offboth surfaces of the break. The view presented Avas not satisfac-tory. The circumference of the supposed tusk could not be tracedon the side next the mid-line. Next, the matrix was ground downand polished to see whether any structure was hidden. What wasrevealed is shown in figure 3 of plate 1. On each side there ap-
'" PL 3, figs. 2 and 3.
".Tourn. Coll. Sci., .Tapan. Imp. Univ., vol. 16, 1002, pi. 1, Vp I.
'- Proc. U. S. Nat. Mus., vol. 44, p. 391.
ART. 8. THE GENERA DESMOSTYLUS AND CORNWALLIUS HAY.peared a number of cell-like spaces separated by thin walls of bone.It is evident that we have here a section across the right and leftmaxilloturbinal bones. There is no trace whatever of any uppertusk.The writer is led, therefore, to question the existence of an uppertusk in tlie Japanese specimen. Wliat the describers very naturallytook to be a tusk may be only the sandstone cast of one side of thenasal cavity. Over the surface of the cast naturally adhered someflakes of bone. Had a section been made across this region, themaxilloturbinal would probably have been discovered. The for-merl}^ supposed tusk of the Oregon specimen where it projects infront has the appearance of the end of a turbinal bone. In thisspecimen the bone seems to end a little behind the middle of thelength of the nasal opening. Although in the Japanese specimenthe supposed tusk is shown as continuing nearly to the front of the
Fig. 2.?Side view of skum. of Dksmostylus HE.sp^iF.rs. I'r, fkomal : Ju,JUGAL ; La, LACHRYMAL ; Po, PARIETAL ; Mx, MAXILLA ; .A'(/, NASAL ; I'lOJ-, VV.V.-MAXILLA ; Sq, SQUAMOSAL.nasal opening, it is possible that only the rounded surface of thematrix was seen.Recentl}^^^ in the discussion of the position and connections ofthe jugal bone in Desmost^/his^ the writer published a figure illus-trating the right side of the skull of the Oregon specimen. Throughinadvertence the lower branch of the hinder end of the frontal bonewas represented as cut off by a suture and was lettered os. Thisfigure is here reproduced (text fig. 2) with the necessary correction.It will be seen that the jugal terminates at about the middle ofthe lower border of the zygomatic process of the squamosal.In his paper of 1923 just cited the writer proposed to divide theSirenia into two suborders, Desmostyliformes and Trichechiformes.Some of the characters of the Demostyliformes may be expressed asfollows
:
Postorbital part of the skull broad and depressed. Preorbitalpart narrowed and moderately decurved. Temporal ridges feeblyTan-Amer. Geologist, vol. 39, p. 108, text fig. 5.45554?25?Proe.N.M.vol.65 11
8 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 65.developed. External nares far in front of the orbits. Nasal boneswell developed, embraced by the premaxillae. Periotic bones tightly-wedged among the adjacent bones. Grinding teeth composed ofclosely adhering columns, usually hypsodont. Enamel very thick.Two pairs of tusksi in lower jaw; none in upper jaw. GeneraDesmostylus and Cormcallius.EXPLANATION OF PLATES.Plate 1.Figs. 1-3. Desmostylus. Teeth aud part of skull. XI.1. Upper left molar of undetermined species of Desmostylus. Showingunworn grinding surface. On the left is a patch of the maxilla, mx.Between the columns of the teeth is seen the cement. Front endupward.2. View of same tooth showing the outer face. Front end toward theleft. Between the columns are seen the tracts of cement. At thehottom of the figure the layer of cement passes between the basesof two fangs of tlie root.3. Section across the snout of Desmostylus hesperus. Showing sectionsacross maxilloturbinal bones.4. Supposed upper molar of CormcalHus sookensi^. Showing grindingsurface. Type. Front end upward.5. Same molar showing the outer face. Front of tooth toward the left.Plate 2.Figs. 1-5. Teeth of Corn/walUus sookensis (Cornwall). XI.1. Supposed left lower molar. Showing grinding surface. Front endupwards.2. View of .same tooth. Showing outer face. Front end toward left.3. View of same tooth, showing a section of fracture across the base ofthe root. Surrounding all is the enamel (e) of the crown. Inside ofthis is seen the bhickened dentine id). In the center of each fang isseen the matrix filling the pulp cavity (j). c). Front end upward.4. View of supposed upper molar. Showing the inner face. Front endtoward right.5. View of same molar. Showing, around all, the base of the enamel e.Within this is the blackened layer of dentine, d. Within this isseen the yet large pulp cavity, pc. The front part of this is in adeep shadow. Front end upward.
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 65, ART. 8 PL. I
DESMOSTYLUS AND CORNWALLIUSFor explanation of plate see page 8
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 65, ART. 8 PL. 2
TEETH OF CORNWALLIUSFor explanation of plate see page