15

NEBRASKA GEOLOGICAL SURVEY

EDWIN HINCKLEY BARBOUR, State Geologist

VOLUME 3 PART 6

A NEW GENUS OF RHINOCEROS FROM SIOUX COUNTY,

NEBRASKA

BY

HAROLD). COOK

A NEW GENUS OF RHINOCEROS FROM SIOUX COUNTY,

NEBRASKA I

By Harold J. Cook

The present genus is based on a specimen (No. H. C. 105, CoIl. of the writer) found in an exposure of the Lower Harrison beds, on the ranch of M1'. James H. Cook, nt Agate, Sioux County, Nebraslm, at a point about four miles west of the Agate Spring Fossil Quarry. The boue­bearing horizon at this spot is nearly if not identical1~- the same as that in the Agate Spring Quarry, and these beds -the Lower Harrison- are now quite well established as a phase of the Lower Miocene.

The type consists of a good skull, part of the left mandible, and the atlas and axis. All are splendidly preseITed, save that the skull has been slightly twisted laterally in the region of the nasals. These remains were closely associated with those of the little four-horned an­telope-like Syndyoceras, the three- toed horse Parahippus, a small camel, and other animals.

In an earlier paper, this specimen was provisionally referred to the genus Aceratherinl1l (Coenopus),2 but sub­sequent study seems to warrant its being generically separa ted from that genus. ,]lherefore, the name Meta­coenopus is proposed.

In Metacoenopus there is but one upper incisor, in contrast with two in Coenopus. The brain case is pro­portionally larger, the skull is more robust, particularly in the anterior portion, and is relatively deeper than' in the latter genus. The nasals are longer and heavier, as are the premaxillae. The teeth are sonwwhat more hypsodont, and the mandible is deeper and heavier than in Coenopus. The conton1" of the skuH is quite different, being more smoothly turned than in any known speiees of Coenopus, and it does not narrow so l'apidly anteriorly.

In the type of :M. egregins, the nasals, nre very long, extending well beyond the premaxillae. There is a slight

~46 NEBRASKA GEOLOGICAL SURVEY

dOWllW<1l'd thickening of the nasals at the point where H

horn mmally occurs in th e Rhinof'erotidap, which may indicate a rudimentary horn, but it is (luitc different from the type of development found in the nasa h of' the Direr­atberes. The skull is relatively longer, proportionately narrower, and deeper than that of the contemporanr Diceratheres. 1'he atlas, axis, and mandible are heavier, and the rnandihlelacks the outward turn or flange <'on1­monly found in the Diceratheres. 3 The shape and propor­tions of the naeals differ l'udieally in these two genera, being much longer llnd situated higher ubo'-e the premax­illae in Metacoenopus, and not showing the !louble-horn tendency found in Diceratherium.

M. egregius appears to agree best among the known species with Coenopus (Aceratheril1m) occidentalis, Leidy, found in the middle Oligocene i)f ~outh Dakota and Ne­braska, but is a much more advall<'ec1 type in many re­spects, notably in the development of the brain, the loss of an incisor, and the increa~cd size. The anterior portion of the skull of Metacoenopus egregius is rplatively and actually longer and hea\"ier than that of Coenopns occi­dentalis, and the sknll of tlJe latter is mucJJ ll10re sharpl~' pointed. Both the na.sa ls and premaxillae are longer and heavier, and the nm:al aperture is much larger in the fonner type. M. egregius was a much heavier animal than C. occidentalis.

In M. egregius, the temporal ridges unite in forming a sagittal crest, which rises quite aJ)luptly near the occiput, adding materially to the general saddle-shaped appearance of the skull.

The grinding teeth show a comparatively simple pat­tern, and the first premolar is essentially a functional gri nding tooth. On the premolars, the cingulum extends ::n oun, the front and inner sides. The premolars are s imple, ha "ing no anticrochet and only a suggestion of a cr ochet. The meta.loph in the fourth upper premolar is not r ec 1 ced in relation to the protoloph as in Coenopus, but is st rongly developed. In the upper molars, the anti­

MEAS UREMENTS 247

crochet is somewhat developed in th e firs t and ::;econd, a modera te crochet is present, and a small crista appears in M ~ . 'The cingulum on the molars is interl'uvted on tIle o iuternaJ face opposite both the protocone a nd llypOCOlW .

Den tal l:i'ol'mula : I 2- C;! , ' p~

? , M2 s·: , .

MEASURE MENTS Mm.

Greatest length . .. .. ... . ... . .. ... .. . 473 Extreme width aeross zygomatic a rc lie" . . .... . . 245 Distance between orbits acr oss fron ta],.; . . .. . . .. .. . . 140 Width of bra in case . . .. .. .... . .. . .. . . . .. . . 90 Length of uppel" molar-premolar :" E' ri (:'s-left ~ id e .. . 202 Length of upper molars, left s ide .. 102 L ength of lower molar s, left s id l' ... 100 Length of diastema P. ] to iril·i :-, ()1' . . . .. . . . . .. .. . . .. . f)l

II <11'0 IIi .J H IlU'" Coo k

Americau Ml.I seulU of ;\"utun d Hi::; tory. New York, Deeember 9,1908.

(Prin ted a nd dis tribu ted ~I a rc il . 1 ~09.)

1. See Am. Nat. Vo l. X LII. Au g . 1 9 0 8.

See L e idy Proc. Ac Nat. Sci. 1 850, 11 9, 276; 1853, 392 ; 1857 , 8 9; 1 865, 1, 6; O wen 's R e p . Geo l. SUI'V . , vVisconsin , e tc. 1852 . 55 2 . L e idy . Proc . AL. Nat. Sc i. , 18 5 ] 331: 1 85 4 , 1 5 7 ; Le idy . Jo. Ac. Nat. Sc i .. Vo l. VI! , p. 220 . ] 869. Osbo rn ; Me m. Am. "i u . Nat. Rist . . pp . 1 50-158 .

3. See Barbour. NebI'. Geo l. Survey. Vo l. 2. Part 4 . See P e te rson. Science, XXIV . No. 6 0 9, pp. 28 1-28 2, 1 9 06. See Ann a ls of th e Carneg ie M use um , Vo l. l V. No.1 . 1906.

248 :"EBRASI\:A GEOLOGI CAL SURVEY

E:\FL.-\:\ATlO =' 0 [" PL .-\TE I

Thre e vi e ws. A. toP. U. pala line. e.....ide ,- jew of ~ 1\ 1I1l Of ;\I et acoenOlillS E:,!reg-i tls. J<1,

natural siz.e.

NEBRA SKA G 80L0 :7( CAL SU RVEY '·OL UME 3. p.un 6. PLATE l

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SKULL OF M~:TAC08NOPUS E(JK8GlU~. COOK. ~