Memoirs MCZ 4007

^Bcmoirs of tbe flDuscum of (Iomparattv>e Zoology AT HARVARD COLLEGE Vol XL No A NEW MYLODON BY GLOVER M ALLEN WITH FOUR PLATES CAMBRIDGE, printeo for tF)e U.S.A.: flDuseum September, 1913 NEW MYLODON A While collecting fossils in Nebraska, in 1880, for the tive Zoology, Museum Mr Samuel Garman obtained a nearly perfect of this fragmentary, Compara- skull, with a large part of the skeleton of a Ground-sloth, Mylodon mains of together Since the re- genus hitherto discovered in North America have been extremely it seems desirable to publish a brief description of the specimen and to make such comparisons as possible between this and other described It proves to be a true species genus Paramylodon, and like Mylodon, approaching in certain respects the the latter seems to have been a browsing rather than a grazing type such as M robustus and M harlani must have been it appears to represent an undescribed species, I have named it Since honor in of its discoverer Mylodon garmani, Type from — Well preserved skull and parts the Pleistocene of the fauna, General Characters it differs on either practically —A of the skeleton, the same in the Z., Samuel Garman, 1880 as that of the Hay Springs precise details of the situation are conformation of the in outline like a figure side; the fourth lower No 8429 M C large species of about the size of conspicuously upper molar being fifth is Pleistocene, though lacking from which nov Niobrara River, Nebraska Horizon — The locality probably Mid sp M harlani, last molars, the with a constriction in the middle molar much elongated and laterally compressed, with the greater axes of the internal lobes nearly longitudinal instead of transverse Skull high and much narrowed from side to side, with high sagittal crest; pterygoids deep and rounded in side view, palate long and narrow with a very deep and narrow interpterygoid much fossa Edentulous portion of the tip of the rami contracted Description of Skeleton In the following description of the type specimen, sible made comparison with Mylodon robustus, M I have as harlani, far as pos- and Paramylodon A 320 nebrascensis Of the NEW MYLODON Owen's first, memoir classic (1842) treats in detail, and the Museum possesses a mounted skeleton from the Pampas formation of Argentina No complete account of the North American M harlani has been published, and since the type consisted of but a portion of the lower doubt attaches to the identification referred to the same of other Cope species some teeth, fragments of the skeleton later described and figured what first (1895) jaw with the are doubtless the upper teeth of this animal, and Loidy and others have described and figured bones which are believed likewise to represent it No complete skull seems to have been found, but Cockerell in 1909 published an account of a cranium without teeth from Colorado which, after careful comparison of photographs, I believe is identical with referable the teeth on which names currently included sodalis, M To harlani the same species are probably Cope founded Mylodon in the synonymy of M renidens and harlani M garmani follows The skull (Plates practically perfect and 1, is 2) sulcidens, Cope's Mylodon The based on an ungual phalanx, remains unknown M description of except for the loss of a few chips here and there, clearly that of an adult animal resembles that of other species of Mylodon, but is In general outline extremely narrow The profile is a nearly straight line with a slight depression above the orbit specimen the actual depression is The skull) palatal profile is is accentuated through a slight crushing it dorsal (in tlie in of the nearly parallel with the general dorsal outline but produced backward, would pass nearly through the center of the The pterygoids extend downward occipital condyles, as in Paramylodon from the palatal plane to a distance about equal to one half the height of the its plane if braincase The rostrum in side view is abruptly truncate, nearly at right angles to the dorsal profile The upper half its is general outline convex, the lower half nearly vertical, or slightly concave, thus resembling Cockerell's specimen from Colorado, here considered M harlani, but differing from Paramylodon, which the lower half extends gently forward and downward and premaxillae extend some 80 terior profile of the skull is gently mm and in advance of this The maxillae boundary The pos- evenly convex, beginning at a point on the dorsal margin directly above the posterior base of the squamosal process curve if in Its continued passes through the posterior third of the occipital condyle, thus more as in Paramylodon than in the Colorado skull whose condyles mostly outside the posterior outline of the lie cranium In dorsal view, the most striking character is the braincase, whose greatest breadth, measured the extreme narrowness of at the junction with the NEW MYLODON A is orbital processes The heavy on the braincase in a slightly smooth surface tl>e meet the strong sagittal crest overhanging ridge, which passes anteriorly into occipital crests of the frontal region, The the blunt supraorbital angle their surface much roughened is than the width between the rounded supra- slightly less squamosal process, elongation than in Paramylodon The The outhne The latter The width nasals so that the sides (i slightly viewed from of the palate, of the base in front, is is which parallel to the top, nearly double that of the top, is posterior view of the skull is There is no indica- almost horseshoe-shaped in outline, with The extreme narrowness fact that the extreme height of of the braincase this occipital face much wider than high, so that its outline skull, as in is is here emphaconsiderably Paramylodon, nearly a semicircle is each side between the condyle and the lambdoid ridge sion, dam- a trapezoid, of whose surface digastric muscle is this A strong median ridge extends from the upper lip of the foramen magnum dorsally lambdoid ridge which forms tlie boundary of the posterior face of the On less bony nasal septum by the is much and smooth greater than the width, whereas in the Colorado face temporal muscles though the maxillaries) converge dorsally e the convexity dorsal sized tips of the nasals, slightly inflated is of the nasal opening, formed by the The of the broader and nearly square, with is which the base, formed by the bones tion of a attachment and have been convexly rounded, and did not project beyond the sides to of the muzzle is with a poorly defined prolongation to sides of the braincase are nearly vertical for the Anterior to the orbit the rostrum aged, seem 321 to the skull a triangular depres- marked by several small ridges, for the attachment of the The foramen magnum, as in Paramylodon, looks downward is as well as backward, and about one half the surface In ventral view, (Plate 2, fig of the condyles is ventral 3) the palate is seen to be long, contracted and expanded anteriorly with its greatest width just in front of the In contrast to the form of palate shown by Mylodon robustus, tooth posteriorly first that of the present species the front edges of the first is produced some 50 teeth, and is mm long, narrow, anterior to a line joining and very slightly expanded and with widely divergent sides The Its walls are parallel, and interpterygoid fossa is extremely deep and narrow The pterygoids are likewise parallel anteriorly converge to form a pointed arch anteriorly, instead of being broad, blunt, to the long axis of the skull of the apart and diverge but little ventrally in contrast to those Colorado skull and Paramylodon, in which the pterygoids flare widely NEW MYLODON A 322 The mandible, in comparison with that of the latter genua, The coronoid interest is and the ramus, instead of especial of tapering process is smaller, strongly towards the symphysis is of nearly the same depth at tliat point as at the level of the last molar, which is in correlation with the elongated rostrum less Certain of the cranial bones and the teeth require further mention The nasals are broad anteriorly, with a combined width of 70 mm at the nasal orifice but taper rapidly back to about the level of the orbit, where, on account of the nearly complete disappearance of the median boundary through and by reason fusion of a slight crushing of the frontals, their outlines Apparently, however, there be traced expansion such as Brown figures The malar s (Plate 3, fig in is little if any indication of a posterior Paramylodon bones are complete and separate 7) or jugal bly they were but loosely articulated with the maxillaries portion Proba- Tlie upper anterior The ascend- concavely rounded to form the lower border of the orbit is cannot ing wing of the bone has a deep notch for the reception of the squamosal process In the South American Mylodon robustus the portion of bone dorsal to the notch is is produced backward so that the distance from its tip to the point of the notch nearly twice that from the tip of the bone forming the ventral side of the notch to the same point This bone is can species nor for Paramylodon, but difference that the length, the dorsal is in our specimen it presents the noteworthy bony wings forming the sides of the notch are of nearly only some 10 mm longer than the ventral portion descending portion of the malar but not described for any of the North Ameri- is similar to that of M Its anterior The margin is also much bowed it and the ascending out premaxillarics were evidently united, but were only loosely articulated with the maxillaries by a short stem which them at less The robustus in general form narrower and longer, with a wider concavity between portion cciual their anterior end The fitted into a deep median between cleft wings of the premaxillaries bevel over lateral the dorsal surface of the tips of the maxillaries, but are wholly separate from them The cleft for the reception of this articulating stem of extends posteriorly as a broad tance from deeper in tlie tip V for premaxillaries about 31 mm., or nearly one half the of the maxillary to the first tooth It is dis- apparently mucli the Colorado skull and in Paramylodon, extending nearly to the level of the large oval tooth (the second in length of the premaxillaries is Mylodon) The greatest median The tips are 54 mm., their combined width 96 thickened and shghtly concave below as the hps tlie if for aiding the prehensile power of A The passing is palate down NEW MYLODON much roughened and pitted, with a seems to be indicated The with the second tooth level of the penultimate molar, foramen is The narrow rounded ridge the center from the level of the front of the A opposite the back of the penultimate molar of less extent, 323 in the first tooth to a point similar ridge, but apparently Colorado skull, beginning on a level maxillopalatal suture extends forward to the and the palatal bone itself is smooth A large present at each side behind the last molar pterygoids in side view are very large the general outline of the palate and extend some 75 mm below In this respect they resemble those of Paramy- lodon and differ conspicuously from those of Mylodoji robustus and the Colorado which the pterygoids extend but shghtly below the general ventral outTheir interior surface, except for a narrow roughened rim, is smooth, skull in line but the exterior bears is small bony ridges for muscle attachments many a broad shallow concavity What appears to be the tympanic bone is a narrow horseshoe-shaped fused solidly with the os petrosum on each side depression 15 to 20 mm in for the eleventh to this depression and slightly posterior to 15 mm Posterior to this is element a roughened diameter for the reception of the articulating process The foramina of the stylohyal There in the posterointernal part of each it and twelfth nerves are internal The latter is the larger, about in diameter The occipital condyles have the characteristic bordering Their ventral surfaces are set obliquely to the frontal absent in Paramylodon plane and constitute more than half the articulating area transverse diameter spectively is be ridge, said to much In ventral view the greater than the longitudinal, 59 and 42 mm re- In the Colorado skull the length of the condyles seems to be greater in proportion to the width Teeth — There are The upper side upper and four five teeth in the series measures 160 mm in the lower jaw on each in alveolar length, the lower 156; the too throws in both jaws converge towards the posterior end of the palate The last upper tooth is but 21 mm from a distance equal to about two thirds of the last tooth is the level of the posterior narial opening, its own length In the Colorado skull nuich farther from this opening (58 mm.) nearly twice its own length The recurved first upper molar Its the smallest, slightly oval in outline, and a crown therefore further enhanced crown is by a is slight bevel of the first lower molar trifle directed posteriorly, and this appearance due to contact with the anterior part is of the Its diameters at the alveolus are — longitudinal, : NEW MYLODON A 324 19 mm., transverse The beveled much surface of the crown M the same as in The tooth 20 long is harlani (see Cojie, 1895) projects ahout 19 nun separated from the second by an interval of only nun second upper toolh Ukewise has its anterior portion recurved so that the from the socket and The crown thus 15, directed is is backward at a small angle to the palate sUghtly beveled by contact with the posterior facet of the The the crown opposes the second lower tooth The first front face is lower tooth, but general outline in section is with a longitudinal diameter of 36 nun., transverse 17, at the alveolus The tooth figured by Cope (1895) as the second upper molar of M harlani is an ellipse, similar but with a The greater bevel on the anterior face an outer with nearly square outhne, third upi)rr tooth has three lobes, and two sides much inner, of wliich the posterior and rounded ends lingual side of the tooth A is much longer with nearly parallel tlie shallow sulcus separates these two lobes at the The posterior lobe forms a long heel which is bent at 45 degrees from the axis of the tooth row toward the median The outline is not essentially different from what Cope (1895, pi 10) an angle side of nearly figures for M harlani and photograph, the tooth anterior inner lobe is is renidens; about opposite the single outer the posterior lobe that The extreme breadth and as nearly as may be judged from a The practically the same in the Colorado specimen M its tip is in anteriorly is lobe, but so deflected the same straight line as that of the about 24 mm ; \\\v l(>ngtli in is first the axis of the tooth row from tip of the anterior iimer lobe to the back of posterior lobe is 29.6 mm., while the diagonal from the point of the latter to the tip of the outer lobe is mm 33 The fourth upper toolh toothrow, but is is narrow and compressed in the long axis of the set at an angle of nearly 45 degrees to the latter lobes, as does the preceding tooth, two inner and one outer, It but the has three last is con- and the posterior inner lobe is so than in M harlani and M renidens, siderably in advance of the anterior inner lobe; not much elongated, apparently much less by Cope In this respect the Colorado skull seems to resemble these two species and to differ from our specimen There is thus a greater dissunilarity as figured in the shape of the third and fourth upper teeth the three others slightly So compressed is it, that inner lobe 35.5 mm The fifth upper ; mm ; our animal than appears in outline is roughly a parallelogram, The dimensions concave on the posterior outhne inner lobe to tip of outer lobe 30 its of from the are: — tip of anterior latter point to tip of posterior front of anterior inner to end of posterior inner lobe 19 mm from that of M harlani and M reni- toolh differs decidedly A dens in that outline its i.s NEW MYLODON more that 325 of a figure eight, with a marlced constriction or waist which divides the tooth into a sUghtly larger anterior lobe with the outer corner in advance of the inner, and a smaller posterior lobe only slightly The asymmetrical long axis of the tooth coincides with that of the tooth- mm.; the breadth of the anterior lobe is 20 and of the In M harlani and in M renidens the tooth has a slightly row, and measures 30.5 posterior 15 mm concave external outline with a more marked internal concavity, but the posterior lobe thus defined does not ently the case in the Colorado expand again terminally, and the same The mandible in lateral outline resembles that of owing to the extreme narrowness The truncate of the skull, the much appar- M robustus, except that symphysis is less broadly num- anterior external openings of the dental canal are three in The anteriormost ber, arranged in longitudinal series others is skull The smaller and subequal of the smaller ones about mm is very large, the two vertical diameter of the first is 14 In Paramylodon the middle foramen The predental part of the jaw is much narrowed marked contrast to the broad square termination of M mm., is the from above, largest as seen in robustus This fact points to a narrow extensile tongue, for a browsing, rather than a grazing habit, which makes use slightly ramus tapers but little the coronoid process forward, in marked contrast is process slopes tip is tip of the jaw is from base of damaged As already the jaw The broad symphysis for cropping of a noticed, the in side view, to Paramylodon in which but one half as deep at the symphysis as at the base of the coronoid Directly above the posterior end of the symphysis, the tip of the jaw upward above the toothrow so that the depth at the extreme level of the quite equal to that at the base of the coronoid process, nearly 105 The condyle is slightly above the mm level of the toothrow, with its long axis nearly transverse The toothrows The extreme of the lower, as alveolar length of the row together and though of the general of other species The of is the upper jaw, converge posteriorly 156 Mylodon mm type, differ in details from those some 24 mm above the and about half that distance above the crowns is this tooth projects much The crown alveolus, of the succeeding teeth farther above the alveolus elliptical in section, scarcely reniform, since of concave four teeth are set close known anteriormost lower toolh projects Paramylodon The the inner side is nearly In Its outline flat instead presents an anterior and a posterior beveled surface, NEW MYLODON A 326 the former facets much more The two nearly in a trans\'erse plane than the latter meet at a point shghtly posterior to the The vertical axis of the tooth long diameter of the tooth, which coincides with the axis of the toothrow, 25 mm., the breadth 16 The mm second lower tooth has a broad squarish external lobe, and two narrower internal lobes, of upper molar by a is fairly as figured which the posterior Compared with M is the longer and beveled by contact with harlani the anterior lobe seems better defined deep sulcus, which in the latter species by Leidy It by Cope (1895) (1855) merely a shallow concavity, is corresponds fairly well with the tooth figured as the second inferior molar of M renidens, but is The smaller discrepancies in outlines, however, seem trivial The third lower tooth has roughly the outline of a boot, of and heel form respectively the anterior and the posterior external boot leg the longer internal lobe with nearly parallel better M marked than in off renidens and M M harlani or the sulcidens, in with rounded angles lobes, This lobe sides species described which the outline it is difficult Indeed, two which the toe is is nmch by Cope as roughly a parallelogram how to see and the these last two can be distinguished from M was named on the basis of a separate third lower molar, closely resembling that of M harlani M small discrepancies are discounted if renidens but with the dimensions of the corresponding tooth of According to its describer "the internal extremity of the crown is sulcidens M harlani beveled on the posterior border, so that an obtuse ridge characterizes the posterior side of the crown, which The same the upper is condition separated from the posterior border of the external face." found is length of The third molar from M harlani, must, in our specimen and is the result of wear against differences claimed as separating I think, the third lower molar be considered merely individual is the breadth across the two external lobes known, fourth lower molar in its is sulcidens The greatest at an angle of nearly 45 degrees to the tooth row, and in our specimen measures 35 mm., practically as in The M is 23 mm M harlani (33 mm.) ; as against 20 in the latter very different from that of any species hitherto extreme elongation and lateral compression As in M harlani and Paramylodon it consists of an anterior and a jiostei'ior lobe connected by an isthmus Each lobe has an internal heel The long diameter of these lobes is nearly transverse to the axis of the toothrow in M harlani and in Paramylodon, but in the specimen here described external side there is is is at only a slight angle to this axis a slight concavity opposite the much more marked in M harlani and in first Paramylodon On the internal lobe, but this is a sharp depression PLATE PLATE Mylodon garmani Fig Fig — Side view of — Side view of jaws skull (ti|) of left ramus slightly broken) % "^ c o o / -V « ^'^ f >i^-'" '^ ^:^r ^^^^: * ^f " o N E r% \ PLATE PLATE Mylodon qabmani Fig Fig — Ventral view of — Lower jaws from above skull o N o PLATE PLATE MyLODON Fig Fig Fig Fig 10 Fig 11 Fig 12 G ARMANI — Complete hyoid apparatus view — Anterior view of the body of the hyoid — Jugal side view — Third ungual phalanx of fore — Second ungual phalanx fore — First ungual fore phalanx — Terininalphalanxoffoiu-th forefoot — Ungual phalanx hind — Ungual phalanx hind — Terminal phalanx hind — Terminal phalanx digit of hind Fig Fig Fig 13 in lateral in foot of foot of foot digit of of digit of foot of digit of foot Fig 14 of digit Fig 15 of of foot foot Mem Mtis Mvlodon, Phitf Conip Zool ^ 12 V, 7.V 1-t * ^ 7.5 I > PLATE PLATE Mylodon garmani Fig 16 Fig 17 Fig IS Fig 19 Fig 20 Fig 21 — Tip of loft —-Portion — — — — ramus of a Mylodon from Oregon, considcrpci as representing M harlani showing three artieulating facet.s anteriorly On its posterior side there are but the usual two facets, since it is the last of the three-faceted vertebrae Spine of one of the vertebrae anterior to the last, showing three facets on its posterior aspect Dorsal view of the atlas Lateral view of the axis Ental aspect of the fibula, showing (at the right-hand end) the facet for articulation with the upper end of the tibia, and (at the left-hand end) the astragalar and the tibial facets at nearly The surface of the former is slightly crushed right angles but in contact of a dorsal vertebra -igs* -s**^"*^' !0 o S3 U