Affinities and palaeobiogeographic significanceof the Mongolian Paleogene genus Phenacolophus

AFFINITIES AND PALAEOBIOGEOGRAPHIC SIGNIFICANCE OF THE MONGOLIAN PALEOGENE GENUS PHENA COLOPHUS by MALCOLM C. M c K E N N A * and EARL M A N N I N G * *

R£stn, ag

ABSTRACT

Du ma~4riel nouveau permet d'augmenter nos connaissances sur la morphologie du genre Phenacolophu~, ongul,4 peu connu du Pal4oc~ne et du d4but de l'Eoc~ne (?) de l'Est de l'Asie. On consid~re i'ci Phenacoiophus comme un Arsinoith~re primitif, en se fondant sur la pr4sence de carac~ t~res d4riv4s qu'il poss6de en commun avec Arsinoitherium, forme a&icaine de l"Oligoc~ne inf4rieur de la formation Jebel' el Qatrani, et avec Criuadiatherium de l'Eoc~ne sup4rieur ou de l'Oligoc~ne des Carpathes m4ridionales de Roumanie.

Ad,ditional material.' has increased our knowledge of the morphology of the poorly known ungulate genus Phenacolophus from the Paleocene and (?) earliest Eocene of eastern Asia. Herein we regard YPhenacolophus as a primitive ars,inoithere on the basis of derived characters shared with Arsinoitheri=m from the early Oligocene Jebel el Qatrani Formation of Africa and Crivadiatherium from the !ate Eocene or OIigocene of the southern Carpath~ians Mountains of Romania.

MOTS*CLI~S : MAMMALIA, PLACENTAIRES (EMBRITHOPODA, PHENACOLOPHLIS), PALI~OGIENE, ANATOMIE SQUELETTE, CLASSIFICATION, CHINE, MONGOLIE. KEY WORDS: MAMMALIA PLACENTAL (EMBRITHOPODA, PHENACOLOPHUS), PALAEOGENE, SKELETON, CLASSIFICA~ TION, CHINA, MONGOLIA.

* Frick Curator, Department of Vertebrate Paleontology, The American Museum of Natural History, New York, N.Y. 10024, U.S.A., and Professor of Geology, Columbia University, New York, N.Y. 10027, U.S.A. ** Scientific Assistant, Department of Vertebrate Paleontology, The American Museum of Natural History, New York, N.Y. 10024, U.S.A.

G4obios, M4m. sp4cial 1

p. 61-8,5, 1 fig., 5 pl.

Lyon, septembre 1977

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CONTENTS Introduction

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Systematics . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Genus Phenacalophus MATTHEW ~ GRAN~ GER, 1925 . . . . . . . . . . . . . . . . . . . . . . . . . . Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . .

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Rel,ationships and classification of Phenaco-

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References

Ph,enacolophus [allax MATTHEW ~ GRANGER, 1925 . . . . . . . . . . . . . . . . . . . . . . . . . .

Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . Material . . . . . . . . . . . . . . . . . . . . . . . . . . Measurements . . . . . . . . . . . . . . . . . . . . . Redescription . . . . . . . . . . . . . . . . . . . . . .

lophuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................

64 64 65 66

71 73

INTRODUCTION This paper redes,cribes an enigmatic fossil mammal from the early Tertiary o~f eastern Asia that has been more or less ignored for more than fifty years. Using the original specimen plus additional specimens we attempt to bring together what is now known about Phenacolophus MATTHEW 6 GRANGER, 1925, originally described from the Gashato fauna of Om6n6 Gobi, south-central Mongolian People's Republ,ic. W e interpret the known morphology of these specimens, most of which are incomplete, poorly preserved, and difficult to study in any case because they are housed in two widely separated collections. Following the redescription, which in itself involves considerable interpretation, we then speculate that Phenacolophus is a sister group of Arsinoitherium (early Oligocene, Jebel el Qatran, i Formation, Fayum, Africa) and Crivadia:th,erium from the late Eocene or early Ol,igocene of the Hateg depression, Romania (Radul,esco et al., 1976). W . D . Matthew ~ W . Granger dismi;ssed without discussion the possibility of arsinoithere relationship, but we hypothesize that certain characters are synapomorphic (shared-derived). During a brief trip to Moscow in 1964 M. McKenna observed that additional parts of the type specimen of Phenacolophus [aUax were probably present in the collections of the Soviet Academy of Sciences made in the course of a joint Soviet-Mongolian Expedition in 1948 and that add,itional specimens of Phenacolophus were presen't there as well. Thanks to both the Soviet Academy of Sciences and the American National Academy of Sciences, a one-month exchange visit

was arranged for M. McKenna in 1965. Casts ot the original specimens o'f Phenaco,lophu~s [allax housed in the American Museum of Natural History were taken to the Soviet Union in april 19,65, where it was demonstrated that a left lower jaw fragment of an immature .ind'ividua} represented by various bones and teeth in the Soviet collection fitted against the broken surface of the type specimen in the American colilection of 1923. Study of the combined materiat was begun at once and a purely descriptive manuscript drawing together all available morphology o'f Phenacolophus [allax was produced while M. McKenna was in Moscow, but th,is was later put aside because of the urgency of other work. F.S. Szalay 6 M. McKenna (19,71, p. 278) briefly mentioned the work in progress on Phenacdophus in their review of the Gashato fauna ant its correlatives in eastern Asia, but at that time they contin,ued to classify the genus as some sort of aberrant con.dylarth, distinctive at the family level:. This view was not appreciably diffe~ rent from the views of W . D . Matthew and W . Granger many years earlier. In 196,5 C. RaduIesco, Institutul de Speolog,ie ¢ Emil Racovita ~, Bucharest, wrote to M. McKenna, requesting an opinion concerning the affinities of a newly collected ~ late Eocene or early Oligocene fossil mammal from Romania. This specimen consisted of three highly distincrive teeth unl,ike those of any mammal previously reported from Europe. In his reply M. McKenna suggested that the new Romanian find had significant similarities to both Arsinoitherium and Phenaco,lophus, although these animal~s were

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known to occur only in the fossil record of Africa and eastern Asia, respectively. C. Radulesco accepted these surprising conclusions, but publication of a manuscript describing the new Romanian specimens was atso delayed until recently (Radulesco et al., 197'6). W e have drawn on it extensively in the preparation of the present paper. W e thank the Soviet and American Academies of Sciences for numerous courtesies including financial aid and, especially, K.K. Flerov, B.A. Trofimov, V. I. Zhega~lo, and the l'ate Y. A. Orlov for their help in 19,64 and 1966. Various other individuals too numerous to name have contributed comments and criticism, but we thank C. Radutesco,

in particuliar, for his help and for a draft of the published description of the Romanian arsinoithere. C. Tarka has prepared ~he illustrations with is usual skill, incorporating figures supplied by C. Radulesco in plates 4 and 5. The following abbreviations are used to designate institutional collections : A M N H - American Museum of Natural History, Department of Vertebrate Paleontology, N e w York. N. Y. A N P I N - Academy of Sciences of the LI.S.S.R., Paleontological Institute, Moscow.

SYSTEMATICS

Order Embrithopoda Family Arsinoitheriidae Phenacolophus MATTHEW & GP.ANGER, 1925

Phenacolophus MATTHEW ~ GRANGER, 1925, p. 8. Procoryphodon FLEROV, I957a, p. 73 ~ TYPE SPECIES : Phenacdophus [a,llax MATTHEW GRANGER, 19'25, p. 8. DISTRIBUTION: 7 Paleocene, China; 1,atest Paieocene or earliest Eocene, Gashato, Om6n6 Gobi, Mongolian People's Republic. DIAGNOSIS : Lower incisors 2 stout, vertically placed, not procumbent. I, and Ia larger than Ie, which in the available specimen is crowded forward out o'f the dental' arcade. Ia somewhat blade-like, with long

1. Procoryphodon has been correctly relegated to synonymy with Phen,acolophus, but V.Y. Reshetov's (1975, p. 43) curious usage of the term ¢ Phenacolophus so{ivagus GABtrNIA>> suggest, unless it is mereIy a lapsus that the regards Paraphenacodus GaBtrNIA, 1971, p. 233, whose type species is Paraphenacodus soliva~gusfrom the lower or middle Eocene of the Zaisan Basin of Kazakhstan, to be a synonym of Phenacolophus. The lower molars of Paratohenacodus soLivagus are about hMf the size of those of Phenacolophus and resemble those of bunodont artiodactyls. They do not belong to Phenacotophus. 2. In this study we will treat all teeth anterior to the P4 locus as though they are not deciduous teeth. Ca,vea~ emptor!

stout root. Lower canine small. Diastema absent. Pl and P2 single~rooted ; Pa double-rooted. Anterior premolars increasingly complex rearward but not molarfform; dP4 fully molariform, P4 nearly molariform. M1-Ma with reduced paralophid and paraconid, but with high metaconid possessing posterior descending crest; low, curved cristid obliqua; high entoconid connected to hypoconid by notched incipient lophid : weak anterior cingulure; very strong shelf~l'ike posterior cingulum rising linguad to apex below and behind entoconid ; hypoconulid not present as a separate cusp;, p 2 p 3 small, single-rooted, dP 4 complex, semi-molariform. M1-M ~ with conules still distinct, but dental pattern incipiently lophodont: paracone, paraconule, and protocone joined into protoloph ; anterior wing of metacone and/or mesostyle, part of metaconule, and hypocone forming incipient metal~oph ; connection bet'ween metaconule and protocone almost compl.etely abandoned. Cingula al'most completely surrounding upper molars; posterior cingulum broad. Hypocones with posterobucally descending crest, Zygoma arising over M '2, not farther forward; occiput low, with tow sagittal crest. Astragalus <>, with astragalar foramen in young individuals but 'with astragalar cana} appearing to fill with cancellous bone in adults. Lateral wal,1, of as tragalar trochlea vertical ; main 'weight of fibula directed past astragalus to bear on calcaneum. Neck of astragalus narrowed to a trench, head laterally extended, more rounded than in Mon9olo~ therium ; sustentacular facet curving around convex sustentacular facet of calcaneum. Cal'caneum stout,

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with strong fibular facet; sustentacular facet with mediat extension. Tarsus and carpus probably functionally serial, but technically alternating in that in life there was probably a contact between the astragalus and cuboid of the hind foot, and between the l'unar and unciform of the front foot, though these .contacts were probably not very significant. Five more or less equal toes on the front foot. Both manus and pes plantigrade, but more flexible than in early Asiatic uintatheres.

Phenacolophus

fallax

MATTHEW ~ GRANGER, 1925

Phenacolophus [allax MATTHEW 6 GRANGER, 1925, p. 8.

Procorgphodon prim,aevus FLEROV, 1957a, p. 74. TYpE SPECIraEN: A M N H 20411/AN P I N 476-6, plus probably A N P I N 476-5, collected by the American Museum of Natural History in 1923 and by the Soviet-Mongolian Expedition of 1948, respectively (see text). DISTRIBUTION :? Paleocene, China ; latest Paleocene or earl~iest Eocene, Gashato, Om6n6 Gobi, southcentral Mongolian People's Republic. DIAGNOSIS : As for the genus. MATERIAL : In their first paper on the Gashato fauna, W . D. Matthew <~ W . Granger (1925, p. 1) stated that the early Cenozoic Gashato Formation ties unconformably upon the Cretaceous Djadochta Formation and comprises not tess than 200 feet (67 meters) of reddish and drab sediments which are very sparingly fossiliferous. The remains of t:)h,enacolophus were atl found within a small area, and the rest of the original Gashato collection, all diminutive forms, came from two small knolls not far distant. The preservation of the American Museum of Natural History collection of Ph,enacolophus is quite distinctive, the bones being crushed, incrusted, and greatly eroded by windblown sands. These factors have all but obliterated many important features of morphology and make the study of these specimens extremely dffficulit. Materials of Phenecolophus collected in 1948 by a SovietMongolian Expedition and now housed by the Paleontological Institute of the Soviet Academy of Sciences are from exactly the same locality as the American specimens because the preservation

is identical and because part of the left lower jaw of A M N H 20411 was left behind at the site for 25 years and was collected by the Soviet-Mongolian Expedition in 1948. Study of the combined collections indicates that perhaps half a dozen individual of the genus Phenacolophus are represented in the two col.lections by various jaws, teeth, and bones. Fortunatel'y, the type specimen itself seems to belong to a partial skeleton, although this appears to be an individual that was not yet fully adult. The type specimen is A M N H 20411, consisting of a right lower jaw with P.~dP4MI-.M3 (plate 1, fig. 1), left lawer jaw fragment with 1/2 M1-.M~ (to which a left anterior jaw fragment labeled A N P I N 476-6 attaches to provide P~PadP41/2M1) (pIate 1, fig. 2), and a battered and sandblasted right maxilla with M1-M ~ (plate 1, fig. 3). A N P I N 476-6 incl'udes a left maxillary fragment bearing what we consider to be P2P~dp4 of the same individual (plate 2, fig. 1)..If these conclusions are correct, P~-32~3dP%M1-31"3 are availabl,e in a single individual, housed in two distant museums. A second individual is represented by a crushed and poorly preserved right lower jaw, A N P I N ~t7&4 (plate 2, fig. 2), variously estimated by as us 8 % larger in P4-M~ length, 2 % larger in M3 length, and 27 % larger in depth of jaw beneath Ma than in the type specimen. Some, though not all, of this last measurement may be attributed to crushing, but there is also a difference in depth attributable to age, sex, or individual variation. A right lower jaw fragment with It-P1 label',ed A N P I N 4'76.5 (plate 2, fig. 3), may belong either to the type or to the same individual as A N P I N 476-4, but could, of course, also represent still another individual. It is preserved in the same manner as the type and is not crushed, but unfortunately it cannot be fitted either to A M N H 20411 or A N P I N 47&6. A third and fourth individual are represented by the type left .lower jaw fragment with M.~-M,~ of <>FLEROV, 1957a, labeled A N P~IN 476-1 (plate 2, fig. 4), and a right jaw fragment with an erupting ? M3, labeled A N P I N 476.2, believed by K.K. Flerov to represent the same individualL The synonymy of <>with Phenacolophus was pointed out by E.L. Simons (19:60, p. 10) on the basis of Mc 3. This is unlikely if AN PIN 476-1has M2-Ma and AN PIN 476-2 has M~ because the Ma of the former has erupted and is worn, in contrast to M.~ o.f AN PIN 476-2. We. believe K.K. Flerov's ~dentification of the teeth of AN PIN 476-I as M~-M.~ to be correct, tempting as it may be to claim that they are M1-M,~.

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Kenna's preliminary work on Phenaco4ophus+ Study of all of these specimens confirms that Procoryphodon and Phen~acolophus are one and the same genus, and we suggest that the type of Procoryphodon prim aevus is simply an uncrushed specimen of a large male of Phenacolophus [allax, not necessarily a distinct species. These same conclusions were independently reached by K.K. Flerov between 1960 and 1964, and the specimen tabels in Moscow changed accordingly. An edentulous maxil:la, A M N H 20437, may belong to an individual of Phenacotophus and other individuals could be represented by symphysia} parts of three paratype lower jaws, labeled AMN:H 2'043,0. These could not be fitted to A N P I N 476-I ou 47,6-2, though the preservation is similar. In addition to the jaws and maxillary fragments there are a number of skeletal parts, unfortunately admixed with bones of IDrodin:oceras+ Fortunately, the s:keleton o'[ a close relative of Prodinoceras, Mongo,lotherium, is now wel'l known thanks to K. K. Flerov (1957b) and E. I+ Dani.lova (1959) and it permits probable segregation of the Prodfnoceras bones on a morphological basis as well as on the basis of size. In the American col.lection the skeleton of Phenacolophus is represented by an occiput, two calcanea (the right calcaneum of a young individual, probably the type specimen, was figured by W . D . Matthew 6 W . Granger, 1925, p. 10, fig. 12), a right astragalus (plate 2, fig. 5), and rniscel'Ianeous bone fragments of the femur, vertebrae, etc. In the Russian collection is an astragalus (heavily encrusted), a proximal end of a tibia with epliphysis unfused and separated, an o!ecranon of an ulna with separated epiphysis, parts of two front feet, and various fragments of vertebrae, scapula, etc. These bones are of a young adul.t, and we tentatively attribute them to the type specimen because of its retention of dP4 although this is o'f course not certain. MEASUREMENTS : A N P I N 476-4 P4~Ma M1-Ma Pd, length M1, length M,> length Ma, length jaw depth lingually under Ma jaw depth lingually under P4 4. Approximate.

5'8 mm 4 45 4 12,3 ----14,1 ± 14,3 16,6 ± 33 4 29 * 5

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A N P I N 476-5 Ia, greatest diameter Ia, width normal to diameter at base of crown canine, present hight of apex above Ia canine, present hight of apex above P, canine, projected maximum diameter canine, present height of ename} crown above base Pt, maximum diameter Pl, maximum width normal to diameter jaw depth lingually under Pl

7,0 mm 4,7 3,3 * 5,4 4 5,7 4 6,4 4 7,0 4,3 24,0

A N P I N 476.-6 plus A M N H 20411 , type specimen, young individual p2, antero-posterior length pa, antero-posterior length pa, projected width, normal to antero-posterior diameter dP 4, maximum diameter ectoloph dP 4, maximum width along metaloph P:2-,dP4 P~Ma Pa-Ma dPd-'Ma M,-Ma M~-Ma jaw depth lingually under dP4 P2, greatest diameter P2, width, normal to diameter Pa, greatest diameter Pa, width across talonid dPd, length dPd, trigonid width dPd, talonid width M1, length M1, trigonid width M> talonid width M> length

5,5-6,0 mm 6,t 5,1 11 A -~9,6 q23,5 :+ 70,0 62,7 53,8 41,8 29,5 24 4 7,7

5,1 9,7 5,9 12,1 q6.A 4 7,0 4 12,4 4 8,2' ! 3,2

5. Jaw somewhat crushed and therefore this figure prohably several percent too great.

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M2, M2, M3, M3, Ma,

trigonid width talonid width length trigonid width talonid width

8,9 8,9 15,8 9,3 9,9

REDESCRIPTION :

Dentition : Dental formula 33 11 44 33. The lower incisors, canine and Pl are present in A N P I N 476~5 and alveoli and roots for these teeth are present in the miserably preserved paratypes, assuming their correct identification as specimens of Phenacolophus. The long-rooted incisors are stout, especially I1 and I3. I~ probably lies in an unnatural position in its alveolus, having slipped partly out before burial, but the alveolLus itself has been crowded forward out of the dental arcade in two specimens. Possibly I~ was in the process of being eliminated from the dentition. The robust symphysis is quite steep, at an angle of about 45 ° to the dental row, and does not extend posterior to Pl. The crown of I1 is missing and that of I~ is heavily damaged, but on I2 a suggestion of a rib is present on the lingual side of the tooth. This vertical rib is present toward the rear of the lingual face of Ia, and I3 evidently was more anteroposteriorly elongated than I2 and formed a blade~li'ke tooth, strengthened lingualb/ by the rib, which served as a buttress. The apex of the tooth was apparently toward the front of this blade-like tooth. W h a t is interpreted as the canine stands at present with its apex well above Ia and Pl, but it has surely slipped in its alveolus. As with the I2, the canine is smaller than either of its neighbors, and its alveolus is laterally displaced. The canine apparently possessed a smalll heel formed from the expanded bases of a rib and a posterior crest. The canine is thus somewhat premolariform. Pl (tooth behind canine of A N P I N 476.5) is a stout single-rooted tooth, hardly smaller than P~ (tooth in front of P3 of A N P I N 476-6), and is now set behind the lingual margin of the displaced canine root. Its apex is well forward and from the apex an anterior crest is directed slightly linguad. The lingual surface of Pl is convex in contrast to P2. A posterior crest is 9resent, which curves sl:ighfly labiad giving a sinuous curve to the crest edges as seen from above. A small hell was apparently present but prob~ably consisted of a sin~ gle sma]l swelling at the base of the posterior crest. Two of the paratype jaws indicate that there 'was no diastema at any point. P2, P3, and what is interpreted here as d P4 are

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demonstrated by the lower jaw fragment of A N P I N 476-6. W h a t are interpreted as dP4 and P4 are more poorly known in A M N H 20411 and A N P I N 476-4. P~ is a single rooted tooth, whose crown possesses a high protoconid with a convex labial and a flattened lingual side and a weak paralophid which curves linguad; there was apparently no heel cusp. The tooth is presently rotated in the jaw so that its front end is lingually placed and its posterior end labially placed, but heavy posterolabial wear indicates that this may have been the actual orientation in life, at least for this one individual. W e a r has removed the enamel from the whole posterior slope of the protoconid, labial to the posterior crest. Unfortunately, p2 is not well enough preserved to yield much information about occlusion, but there is some suggestion that unusual wear was occurring between p2 and P2. P'3 is much larger than Pc, but it is not m,olariform. It resembles Pe but possesses a distinct heel possibly consisting of a small cusp or crest, and possibly comprised of an entoconid rather than a hypoconid. W e a r and post-mortem erosion have obliterated several important features, but the apex of the prot,oconid is far forward, high, and is preceded by a sharp, steep, anterior crest that turns only slightly linguad. From the apex at least two and perhaps as many as three crests slope downward to the rear. Of these, a labial crest prol~ongs the labial wall of the pro toconid to form a shearing surface against which p3 worked. Another crest curves posterolinguad and then to the rear to continue as the heel crest. A small metaconid couId have been present when the crest was unworn. A third, minor ridge consists of the top of the lingual walt of the tooth, ctP4 is fully molarfform, has two roots af which the posterior is t,he larger, and has the usual therian cusps. In contrast to that of its permanent counterpart, P4, the trigonid of dP4 is atmost as low as the talonid and is more open, occupying a relatively greater part of the tooth than in P4. The paral0phid is reduced and may have two apices, one central and the other at its junction with the strong anterior cingulum. The latter curves around the anterolabial base of the protoconid. The metaconid lies postero-lingual to the protoconid and does not support a metastylid. The heel supported a high entoconid, a low hypoconid, and a posterior cin, gulum, but wear is heavy and details are obscure. The wear, especially relative to the molars, and the elongation of this tooth suggest convincingdy that it is dP4, a contention supported by the separated epiphyses of the limb bones (provided they are truly associated) and by the l'esser jaw depth compared to other individuals. No trace of

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a permanent tooth bel,ow dP4 may be seen in A N P I N ~i76.-6, however. LIn'f,ortunately, what is interpreted in this paper as the permanent P4 is preserved only in A N P I N 476-~t. Judged from the battered remains, P4 is not so elongate as dP4, possesses a high trigonid with a weaker paralophid bearing little if any development of a paraconid, has the metaconid approximately opposite the protoconid or only a little posterior to that position, and has some sort of crest 'from the metaconid to the entoconid region in addition to what appears to be a cristid obliqua. The latter extends from a strong hypoc,onid anterolinguad toward the middle of the rear wall of the trigonid. The talonid is much lower than the trigonid. A strong posterior cingulure rises to a 1,ingual apex behind the entoconid region. M1 is not very well preserved on either the type specimen (plus A N P I N ~t76-6.) or A N P I N "t76.-~t, and its structure is determined with the aid of the other molars - - a dangerous procedure. It is the smallest molar, and also the narrowest. A small paraconid was present at the lingual end of a paralophid, but this cusp was apparently rather tow (ex.cept on M~ of A N PII.N ~I76-'t, where it was apparently moderately high), simply a rise at the end of the crest as in ? Ma of A N PiIN zi76-2. By analogy with Ma of A N P I N zt76-1 and other, more poorly preserved teeth of that and other specimens, a very narrow anterior cingulum is probably present but obscured by damage or by the close proximity of dP4 in A M N H 20'{11. The entoconid of M1 'was considerably higher than the hypoconid. A crest runs from the protoconid posterolingual to the metaconid, which is the higher of these two cusps, and then a posteriorly directed crest plunges steeply to join a crest running forwards from the entoconid. On A N P I N 476~1 (M~-Ma) a very small metasty}id may be present as a saml; swelling in the base o'f this distinctive crest. This tiny feature is either absent or has been obliterated on other specimens. Except for part of the trigonid, M~ is best r)reserved in A N P I N ~t76-1 (type of Procorgphodon prima:evus FLEROV, 1957a) and will be described here mainly on the basis of that specimen although M2 is kno'wn from four examples, all of which are utilized. M..~ is intermediate in size between M~ and Me. The M2 trigonid ( A M N H 20"t1!) is of about the same height relative to the talonid as on M~ or Me, and of the three trigonid cusps the metaconid is the highest. The trigonid is not open, but quite constricted. A smal} paraconid is present as a rise at the end of the paralophid, just behind the entoconid of M,. From the protoconid, the notched

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rear wal'l of the trigonid continues to the metaconid and then turns sharply to the rear as a short, steep crest followed by a minute swelling (metastyiid). The cristid obliqua turns forward but does not quite join the mid'dI'e of the base o'[ the posterior trigonid wall. Moreover, a subsidiary projection runs linguad from its anterior end to meet the anterior end of a forward-directed crest from the entoconid. This subsidiary branch of the cristid obliqua, together with the hypoconid, entoconid, and their associated crests, encloses tee principal talonid basin. The anteroiabiaI surface of the hyp,oconi.d (wal'l of cristid obl'iqua) is concave for the reception of the paracone and paraconuie of M a. Occlusion with the strong prototoph of M 2 is made possible by the great tingual extensi.on of the valley between the protoconid and hypoconid. The posterior slope of the hypoconid is nearly flat. The entoconid is higher than the hypoconfd, as in Mz and Me, and both cusps are connected as an incipient notched lophid. At the rear o:f the talonid is a very broad posterior cingulum that rises linguad and is broader at the middle, although it supports a small swel~Iing behind the entoconid. There is no lingual cingulum and only a faint trace of a labial cinguium between the bases of the protoconid and hypoconid. These 'features are not all compl'etelv shown in K.K. Flerov's illustration. Ma is known from five examples {incl:uding the erupting tooth of A N P I N "t76-2). It is the largest lower moIar. Of the three trigonid cusps, the metaconid is the highest. K.K. Flerov's (1957a) illustration of Ma of A N P I N 476-1 does not indicate that the apex and front half of the metaconid are broken away on that specimen and thus the il.Iustration gives a false impression of t~he trigonid morphology. Certain features of the structure of the trigonid may be seen better on A N P I N 476-2 and on the right lower jaw of A M N H 20all1. The enamel on the posterior slope of the paralophid was apparently thin, for, in A N P I N 47~6-1, it has been worn away in early wear of the tooth, producing a sharp knife-edge along the crest of the paralophid. This sharpness was maintained by differential wear of the underlying dentine and the thick anterior enamel wall o:f the p'aralophid - - more or less as in roden.t incisors. The hypocone of M 2 presumably occluded with the ]:ron~ siop.e of the paraIophid and with the posterior cingul,um of M2. The posterior cingulum of M ,2 <, with the posterior slope of the Ma paraIophid though contact was not p.ossible and the wear was caused by food. In front of the paralophid, at its base and below the level of the posterior cingulum of M2, 'was a very weak anterior cingulum on A N

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P I N 476-1. This cingulum is only about one quarter as wide as indicated in K.K. Ferov's drawing {1957a, fig. 1). It is not possible to see this cingulum on any of the other specimens, but presumably each of the lower mol;ars of Phenaco[ophus possessed such a weak anterior cingul,um hidden by the massive posterior cingulum of the tooth anterior to it. Also, such a feature would easily be obscured by interdental wear in mature individual's, A faint indication of this cingulum is seen on the right M8 of A M N H 20411. A high, notched shearing wall curves between the protoconid and metaconid; this worked against the anterior wall of the protol:oph of M ~. From the metaconid a short posteriorly directed crest descends steeply, sweklin9 slightly at the base to produce a rudimentary metastylid, and then connects to a low anteriorly directed crest from the lingual edge of the entoconid, thus closing the talonid basin lingually. Part of this may be seen in 'previous illustrations, especial;ly in K. K. Flerov's labial view of Ma (but not in the occlusal view). The same features are present in the erupting tooth of A N P I N 476-2 and are faintly indicated in the American Museum specimens. There is but one talonid basin, lying between the cristid obtiqua, metastytid crest, anterior entoconid crest, entoconid, and a high notched incipient lophid connecting the entoconid with the slightly lower hypoconid. The cristid obliqua does not possess an anterior lingual spur, but simply curves forward to join the base of the posterior wall of the trigonid a little more than half way toward the lingual side. There is a faint indication of an anterolabial rib on the entoconi,d on A N P I N 476-1, but no trace of this occurs on A M N H 20411. On the anterolabial corner of the hypoconid a crest appears to descend forward to join (or become) the labial cingulum. This feature is damaged in all specimens. A very broad posterior cingulum rises to a lingual apex below the posterior end of the entoconid. This feature was inaccurately illustrated by K.K. Flerov (1957a, fig. 1). A N P,IN '~7G6 includes a fragment of the left maxil'lary bearing the battered remains of three teeth, identified here as 1~2 p:2, pi3, and dP 4. These could, of course, be more anterior teeth, but the break in morphology between t~he most posterior tooth and its predecessor suggests that the former is dP 4 and that the specimen is from the type individual. Of the tooth identified as P~ almost nothing can be said except that it appears to have been single-rooted and somewhat smaller than P2 - - only a part of the tooth remains in the alveolus. P'~ was approximately the size o{ p2

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and is well enough preserved to permit a guess about its pattern, thoug~h little can be said. If breakage and differential sandblasting by the winds are not the cause, p3 appears to have an external cingulum, a single main cusp (paracone), and both anterior and posterior dorsol'abiatly curving wings from the paracone apex. Possibly a swelling on the posterior crest may represent a metacone. There is no protocone, unless we have misidentified it as the paracone. It is significant that pa is so simple, contrasting strongly with contemporary uintatheres, pantodonts, etc., and with late Eocene Moeritherium. Indeed, in the late Paleocene and early Eocene most ungulates had at least a protocone on P~. dP 4, though heavily worn and abraded, nevertheless presents some interesting features. A paracone, metacone, lingual shelf, and broad posterior cingulum are present. The tooth has at least two roots and is trian9ular in outline, the lingual shelf becoming broader to the rear. From the paracone a <> is a valley, the anterior one shallow and l:he posterior one transverse and deep. The posterior valley is limited at the rear by a posterior cingul'um, which appears to terminate 1,abially in a small metastyle immediately behind the metacone. Anterior to the paracone there is possibly a parastyle. A crest from the parastyle area evidently swept around the anterior base of the paracone, though all but a trace of it is now missing. W e can see no sig,nificant similarity o:f the d P 4 to pantodont dPds (Simons, 19.60, p. 43-4~i, fig. 4) or to dP 4 of Arsino,itherium, which is completely molariform and lophodon't (Andrews, 1906, p. 21, fi 9. 7). Unfortunately, upper mil:k teeth are not yet known in uintatheres {Wheeler, 1961, p. 57, 58), thus preventing that potentially interestin9 comparison. The right maxil'lary of the type specimen bears the remain of M1-M a and from these clues the following resurrection of the molar morphology has been attempted. About all than can be said of M t on the basis of its preserved features is that it is the smallest molar and has four main cusps, a parastyle, prominent lingual and posterior cingula, and possibly conules incorporated in transverse lophs. There are either four roots or three roots with the tingual root dividing. A transverse valley for the reception of the M1 hypoconid separated the protoloph

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from the metacone, metaconule, and hypocone, and if an ectoloph was present it was low. M 2 is somewhat better preserved than M 1 and permits a few additional comments. The paracone, paraconule, and protocone are united to form a shearing protoloph whose anterior edge worked against the rear wall of the high trigonid of M.2. The paraconid occluded with the anterior ta.lonid basin of M2. There may be a low parastyle interme~ diate in size be¢ween those of ,M~ and M "~,but this is not clear. There is a strong hypocone, whose enareel is now abraded away, and a broad 'posterior cin~ gu'tum behind the hypocone. The cingulum appears to have borne a cusp posterobuccal to the hypo~ cone. The metacone forms a strong V-shaped cusp, whose apex is set almost as far linguad as the paraconule. The anterior limb of the V~shaped cusp is continuous via the metaconule with a notched crest, which runs to the protocone and which, in occlusion, crosses the notched lophid between the entoconid and hypoconid of the lower molar. A strong true metaloph, which sheared against ,the posterior slopes of the M2 hypoconid and entoco~ nid, is almost complete. Complete lophodonty would result from a further weakening of the metaconule-protocone crest and further filling of the hypoconid-entoconid notch. The prominence of the nearly completed metaloph is related to the size of the posterior cingulum of M2 and to para~ conid reduction in M3, so that one may conclude that a similar topography existed on ML judged from similarities o,f the lower cheek teeth to each other. W,hat W . D . Matthew ~ W . Granger (1925) identified as the prominent mesostyle in the upper molars is the anterolabial end of the anterior wing of the metacone <>. The presence of a metaconule on this tooth as well as on M ~ is suggested by the metaconule of M ~, Whether present as a distinct cusp or not, the metaconule region is part of the nearly completed metaIoph shearing mechanism. Judged from M 1 and M a, strong cingul~a surround most of the tooth. The posterior cingulum is especially broad posterobuccaI to the hypocone and could have supported a cusp there. The anterior end of the orbit was above M 2 (presumed to be the primitive ungulate orbit position) and the zygoma begins at that point, about as in Arsino,itherium and Mon9o,lo~ therium but in contrast with known early Pro~ boescidea, Sirenia an;d Desmostylia. M a is the largest and also the most fully preserved molar. Functional bilophodonty is essentially complete, but traces remain o'f former connections between the lophs. A cingulum surrounds the tooth but does not support a distinct parastyle. Pos-

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tero-bucc.al to the hypocone, the cingulum is expanded and may have supported a crest or cusp. The paracone is well-shown and high. From its apex a short cres~t descends to the rear to partly close off the valley between the main lophs. Also from the paracone apex the protoloph runs to the small paraconule, which is a svcet!ing incorporated in the protoloph. Evidently there was no longer any occlusion with an M ~ anterior talonid basin. From the paraconule a sinai.I, ridge branches off to the rear and then the protoloph continues posterolingually to jo.in th'e protocone. A faint crest runs posterolabiad from the protocone apex toward the base of the metaconule but, like the posterior ridge of the paraconule, rapidly diminishes in size. The incipient metaloph is more complex, consisting of the anterior wing of a V~shaped metacone term/hating in a strong mesostyle, part of a crescentshaped metaconule, and the hypocone, The posterior wing of the metacone and the apex of the metaconule both project to the rear in a distinctive manner, the latter quite close to the hypocone.

Limbs : The foot structure of Phenacolophus is potentially of great interest in that it has a bearing on the relationship of various <groups, but unfortunately we are able to add only a little to what is already known. Various foot bones attribuable to Phenaco,loph~s are at hand, but all are so mangled tha't our attempts to identify and interpret them have been largely frustrated. The rear foot bones are quite large relative to the teeth and jaws, especially the astragalus and calcaneum, but this is a common <> feature. The astragalus is represen'ted by a poorly preserved bone labeled A N PIN ~t75~17 and by A M N H 21757, a previously unprepared right astragatus. It is definitely of the <>rnor~ phological (not taxonomic) type 6 and is not referable to Proclinoceras because there is already a large fragmentary right astragaius 7 of that genus 6. There is, of course, a chance that these astragali belong instead to a primitive pantodont, but as yet there is no evidence to suggest the presence of true pantodonts at Gashato. E.L. Simons (1960, p. 61) states that in known barylambdfd pantodonts there is no astragaiar foramen. In AMNH 21757, attributed here to Phenacolophus, the astragalar canal is in the process of being filled by cancellous bone, but its course is still visible. The state of preservation of. the astragalus is in keeping with that expected in a young individual and we assign it to Phenaeolophas with a minimum of doubt. 7. There are also two battered Prodinoceras naviculars, with highly characterictic fused <>, a feature known also in periptychids.

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in the Russian collection (AN P I N zt7'6-16), which is closely similar in structure and size ot the astra~Iali of Mongolotherium ,e[removi and Bathyop~ soides. In size the Phenacolophus astragali measure 28,0 and 29,5 mm across the trochlea and 3,0,0 mm from the proximal end of the medial side of the trochlea to the distal end of the head. Distally, the astragali are quite deep. The width of the head is about 26 or 27 ram, but this measurement is difficult to interpret in view of the reduced neck and general continuity of the head with the trochlea. This latter feature is, of course, the main point of interest and, in accord with the rather flat trochlea and the plesiomorphous (primitive) retention of traces of an astragalar foramen, resembles the astragalus of Ectoconus, Pantolambda, and the earliest uintatheres. A departure from the taligrade condition (equally a similarity to mesonychids, Palaeomastodon, Arsinoitherium) is seen in the lack of a strongly projecting fibular facet. If the fibula contacted the astragalus significantly, it did so against the vertical wall of the trochlea and thus did not trans'fer weight to the astragal~us. The calcaneum possesses a fibular facet, so it is known that the fibula still extended past the astragalus to bear mainly or wholly on the calcaneum. In barylambdid pantodonts (Simons, 1960, p. 6,0) there was a fibular articulation with the astragalus, but not with the calcaneum. Articulation c~f the fibula with both the astragalus and calcaneum is primitive for mammals and occurs in Loxolo,phus 8, Ecto~ co,nus, Periptychus, Pantolambda (Matthew, 1937, p. 165), Arctocyon, Eoconodon, and early mesonychids. W e cannot determine whether there was an astragalar articulation with the cuboid, but from the structure of the ca'lcaneum it seems probable that there was, although perhaps contact was not extensive. On this poin~t would hinge the question of serial versus alternating tarsus, but that distinc~ tion is often, although not always, without much substance. Mongolotherium, for instance, has the astragalus and cuboid in con:tact, but only barely so, and we would regard that form as functionally serial, not functionally alternating as in American Eocene uintatheres and the hind foot of Arsinoitherium. See G . G . Simpson (1937, p. 21&224) for a penetrating analysis of the serial versus alter~ hating tarsus problem. If there is a distinct facet for the cuboid on the lateral side of the head of the Phenacolophus astragalus, it is obscured by 8. W.D. Matthew (1937, p. 317) stated that there is no articulation between the fibula and calcaneum of Loxolophus, but his description on p. 50 states that the fibular facet of the calcaneum is large.

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damage and poor preservation. The astragalar foramen appears to have been in the process of becoming filled with cancellous bone. Posterior to the plantar opening of the astragalar canal is a deep trench for the interosseus ligament on the plantar surface of the bone, between the astragalocalcaneal and sustentacular facets. The latter are not quite on the same plane, as in Mongolotherium, etc., but are close enough to it to match their counterparts on a referred calcaneum. The sustentacular facet appears to have curved downward at its medial edge, partly around the medial side of the convex susten:tacular facet of the calcaneum. This feature is quite different from the condition in Mongolotherium and Arsinoitherium, but similar to the sustentacular articulation in Palaeomastodon (Andrews, 1906). W e cannot say whether there was an ex;tensive medial projection of the head of the astragalus past the trochlea. In g enerafl, we conclude that the astragalus of Phenacotophus is divergent from that of some early ungulate near the origin of the uintatheres and may be significantly similar to the astragalus of perissodac.tyls, hyracoids, Moeritherium, Palaeomastodon, and

Arslnoitherlum. The massive calcaneum was described briefly by W . D . Matthew # W . Granger. The main points of interest are the fibular facet, upon which the fibula mainly rested, the rather internally directed dorsoventrally convex cuboid facet, and the convex sustentacular facet, whose medial edge was overlapped by a plantar projection of the sustentacu~ar facet of the astragalus. Evidently the hind foot was somewhat more mobile than that of its uintathere contemporaries. Parts of two front feet (unnumbered) are preserved in Moscow. The incomplete right manus includes the lunar, the magnum, the unciform, the nearly complete metacarpal V, and a part of metacarpal II:I. The lunar, magnum, and metacarpal I,I,I are in a straight ltine, an'd we can find no evidence of a centrale, though it may be present and fused to one of the other carpals. The proximal articulation of the lunar is co~avex in all ,directions, but most strongly convex proximodistally for articulation with the radius. The dorsal extent of this articular surface indicates a sharp bend in the foot at this point, but with the possibility of considerable mobility. Presumably the front foot was pl~antigrade, and the foot functionally serial, though there is contact between the lunar and unciform. The magnum is small, approximately 13 mm in proximodistal length on the dorsal surface of the foot. The unciform, in contrast, is easily the largest bone of the carpus. Its distal surface is dorsoventrally

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concave medially for articulation with metacarpal IV but apparently not concave laterally. The proximal end of the uncfform is crescent,shaped and extends proximad to touch the distal lateral corner of the lunar. The proximal articular surface of metacarpal IIl is planoconvex and that of metacarpal V, planoconcave. Metacarpal V lacks the distal epiphysis because the animal was imm,ature, but it was obviously little if any reduced and suggests a five-toed plantigrade front foot. More

71

o'f the left manus is present than of the right, but the bones are mashed together and we have not been able to interpret them satisfactoriIy. Metacarpals I, II, IV, and V are present, and a space is present for metacarpal III, which may be represented by an isolated metapodial fragment, The head of metacarpal I is convex, whereas that of metacarpal V is planoconcave, AI,1 the metacarpals are approximately of the same size.

RELATIONSHIPS A N D CLASSIFICATION OF PHENACOLOPHUS In their preliminary description of the Gashato fauna, W . D . Matthew ~5 W . Granger (1925) devoted three pages of text, including illustrations, to the description of what was then known o.f Phen~acoIophus [allax but, in keeping with the preliminary nature of their paper, only the briefest discussion was presented. During the course of their writing, cursory comparisons were evidently made with hyracoids, arsinoitheres, perissodac:tyls, barytheres, proboscideans, and South American ungulates, and with the Condylarthra as that group was then understood, i.e., primitive ungulates horizontally classified, but no theory of relationship was developed; rather, close affinity of Phenacolophus ~allax with any group was denied and its provisional assignment to the Condylarthra was suggested [aute de mieux. W . D. Matthew ~) W . Granger simply recognized no significant similarities and therefore they turned their attention to other matters. F.S. Szalay ,@ M. McKenna {1971, p. 278) went only a little farther, in that they suggested that Phenacdophus might serve as the type of a new family of Condylarthra, but this view merely reflected a concept of morphological distance from the Phenacodontidae, Arctocyonidae, etc., rather than a construction based u,pon synapomorphous (shared-derived) characters. W e have now attempted such a theory of relationships ~by means of a cladogram given here (fig. 1). Although a Phenracolophus-like animal in the Paleocene of southern China has recently been mentioned by Y. Tong et al. (1976.), we have not been able to translate their paper and we do not known if the material is well enough preserved to permit additiona'l speculation about relationships. C. Radulesco et aL (1976) have described an arsinoithere from the early Tertiary of Romania, naming it Cri~adiatherium mackennai new genus

and species. The Romanian specimen consists of only three lower cheek teeth identified by C. Radulesco et el. as P4 M1 (not M2 as here) and part of M3, but these are unlike those of any previously described European Tertiary mammal known to us. At the same time they resemble cheek teeth of Arsinoitherium in features we judge to be significant. Furthermore, Criwadiatherium, whose morphology is adequately described by Radutesco et at., is intermediate in the morphocline Phenacolophu~ ~ Crivadiatherium Arsinoitherium. although closer to the last than to the first of these. Cri~,adiatherium mackennai was found in a sequence of continental sediments exposed in the Hateg depression of the southern Carpathian Mountains, between the Sebes and Poiana Rusca massifs on the north and the Retezat massif on the south. Although not yet completely studied, this sequence begins perhaps in the Paleocene and terminates in the ,}ate Oligocene. Oligocene entelodont remains have been found in this sequence and nearby correlatives (Kretzoi, 194i; Brunet, 1974), but the stratigraphic position of these with respect to the position of Crivadfatheriam is still unclear. C. Ra'dulesco et at. (I976) suggest that the age of the new genus could be any time from late Eocene to early Oligocene. W e suggest that the age may b'e Eocene rather than Ol'igocene. but we base this suggestion wholly on the known morphology of the animal rather than on detailed stratigraphic studies yet to be undertaken. The morpho.. logy of Crieadiatherium is intermediate in many respects between the morphology of Phenacolophus and Arsinoitherium. On the basis of information from all available specimens of Phenacolop,has fallax, composite drawings of the kno~wn upper and lower dentition were prepared (plate 3) These

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Fig. 1 - A theory o f relationships o f the arsinoitheres. Numbers at nodes refer to apomorphous characters shared by both branches but not by sister groups that branched off earlier. 1 - Unnamed taxon, essentially Paenungulata Simpson, 1945, p. 131, minus Pantodonta but withPerissodactyla added. South American mammals not considered here. Shared-derived characters : M~A3~becomelarger than M astragalar head develops somewhat flattened articulation with navicular bone. 2 - Metastylid accentuated ; paralophid lost. 3 - Hypolophid forms between entoconid and hypoconid of lower molars. Metaconule moves posteriorly and loses connection with protocone. 4 - Proboscidea, Sirenia, Desmostylia (together forming Tethytheria of McKenna, 1975), Hyracoidea, and Peris-sodaetyla. Entoconid and hypoconid become opposite each other, approximately at right angle to axis of horizontal ramus (forming a more efficient bflophodont molar). 5 - Arsinoitheriidae. M 3 hypoconulid small and merged with lingually steeply ascending, wide, posterior cingulum. 6 Unnamed taxon. Cheek-teeth become high-crowned. Cristid obliqua connects higher in metaconid area, subsuming metastylid. Talonid basin reduced to small lingual flexid ; ectoflexid deep. Paralophid reduced. Animal increases in size. Metaloph and protoloph fully formed (hypothetical in (Crivadiatherium maekennai but assumed on the basis of wear facets on the lower teeth). 7 - Arsinoitherium. Very large size. Extreme lophodonty, with paralophid reduced still more and cristid obliqua shifted lingually. Upper molars bilophodont but with anteroposterior lingual connection retained. External cingulum of upper molars absent. Premolars high-crowned and molariform. Some of these features may prove to characterize nodes 5 or 6 rather than 7 when more material is known. Orbit moved posteriorly (over anterior end of M3). Two sets of supraorbital horns present. Distal process of deltoid crest on humerus greatly enlarged. Subspinous part of scapula enlarged. Lambdoid crest inclined anteriorly. Nasals fused to premaxillae. Sch6ma th6orique des liens de parent6 des Arsinoith6res. Les chiffres des dichotomies se r6f~rent A des caract6res apomorphes communs aux deux branches mais non $ des groupes-fr6res qui se sont d6tach6s auparavant. 1- Taxon non d6fmi, correspondant essentiellement aux Paenungulata Simpson, 1945, p. 131, non compris les Pantodonta mais en y ajoutant les Perissodactyla. Les4nammif6res d'Am6rique du ~ud ne sont pas pris en consid6ration ici. Caract6res d6riv6s communs dans ce groupe : M ~ devient plus grande que M ~ ; la terminaison de l'astragale d6veloppe une articulation 16g6rement aplatie avec l'os naviculaire. 2 - Metastylide marqu6 ; perte du paralophide. 3 - L'hypolophide se forme entre l'entoconide et l'hypoconide sur les molaires inf6rieures. Le m6taconule se d6place vers l'arri6re et il perd sa liaison avec le protoc0ne. 4 - Proboscidea, Desmostylia (l'ensemble constituant les Tethytheria McKenna, 1975, Hyracoiitea et Perissodactyla. Entoconide et hypoconide sont en opposition, approximativement g angle droit avec l'axe du ramus horizontal (formant une molaire bilophodonte plus efficace). 5 - Arsinoitheriidae. M3 avec un hypoconulide petit et fusionn6 avec an large cingulum post6rieur remontant lingualement en pointe. 6 - Taxon non nomm& Les dents jugales acqui6rent une couronne ~lev6e. La cristida obliqua se retie plus haut dans l'aire du m6taconide. Le bassin du talonide se r6duit ~ un faible flexide lingual ; ectoflexide profond. Paralophide r6duff. L'animal augmente de taille. M6talophe et protolophe compl~tement form6s (hypoth6tiques chez Crivad~herium mackennai mais attest6s par la pr6sence de facettes d'usure aux dents inf6rieures). 7 - Arsinoitherium, tr6s grande taille. Lophodontie extr6me, avec un paralophide r6duit encore plus et une cristida obliqua d6plac6e lingualement. Molaires sup6rieures bilophodontes avec une liaison ant~ropost6rieure linguale vestigiale. Cingulum externe sup6rieure absent. Pr6molaires ~ couronne 6levee et molariformes. Quelques uns de ces traits pourront caract6riser les dichotomies 5 ou 6 plutft qu%7 lorsqu'un mat6riel plus complet sera connu. L'orbite se d6place en arri~re (au-dessus de la terminaison ant6rieure de M~). Pr6sence de deux ensembles de comes supra orbitaires. Processus distal de la cr~te deltoRie de l'hum6rus fortement accru. Partie sous @ineuse de la scapula agrandie. Cr6te lambdoide inclin6e vers l'avant. Nasaux fusionn6s avec les pr6maxillaires.

m

were based upon Phenacolophus [allax alone and 'were not in'fluenced by the morphology of other taxa. Probably all of the morphology depicted pertains to the type specimen, a young individual retaining dP44 (a poorly preserved P4 is illustrated on plate 2, fig. 2). After receipt of illustrations of the Romanian arsinoithere, illus* trations were prepared comparing the lower dentitions of Phenecolophus, Arsinoith,erium, and the Crivadiatherium {pl'ates 4 and 5). In these we make no attemp to reconcile the highly apomorph upper molar pattern of Arsinoitherium with the poorly known upper molar pattern of Phenacolophus. Although the upper cheek teeth of Arsinoitherium are so apomorph as to almost defy interpretation, the lower cheek teeth are more conservative, even though they have become very high crowned in this African genus. Plates 4 and 5 attempt to

73

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demonstrate the similarities of the !ower dentitions by depicting the dentitions of all three genera at the same size, rather than at the same scale. W e regard Crivadiatherium as aImost certainly a somewhat more primitive arsinoithere than Arsinoitherium, and we present the cladis:tic hypothesis (fig. 1) that Phenecotophus is the sister group of these two genera. Th'e theory of relationships presented in figure 1 is the most parsimonious explanation of the facts that we have been able to devise. Its claims are all scientifically testable, W e suggest, based on presently available evidence, that Phenecolophus is best regarded as the most primitive known arsinoithere. Arsinoitheres in their ear!ier history, therefore, were more widespread than previous evidence has indicated.

REFERENCES ANDREWS C. xeV. ( 1 9 0 ' 6 ) . - Catalogue of the Tertiary gertebrata of the Fayum. Egypt. Brit. Mus., London, X X X V I I ÷ 3'24 p., 98 fig., 26 pl. BRUNET M. ( 1 9 7 4 ) . - Les Ent~lodontes des Phosphorites du Quercy. Paleeovertebrata, Montpellier, 1973, vol. 6, p. 87-108. DaNILOVA E. I. (t98'9). - - <> (in Russian). Zool. Zhur,, Moscow, vol. 38, n ° 7, p. 10691080, 3 fig. FLEROV K. K. (1957a). - - A new coryphodont from Mongolia, and on evolution and distribution of Pantodonta. Vertebrate PalAsietice, P4king, vol. 1, n ° 2, p. 73-8'1, 3 fig., 1 table. FLEROV K. K. (1957b). - - <> (in Russian). Trudy Peleont. Inst., Acad. Sci, U.S.S.R., Moscou, vol. 67, 82 p., 40 fig., 6 pl. GABUNIA L. K. ( 1 9 7 ' 1 ) . - <> (in Russian). Bull. Acad. Sei. Georgian ,S.S.R., Tbilissi, vol. 61, n ° 1, p. 233235. KRF,TZOI M. (1941). - - Siebenbiirgische Elotheriiden. Fdldt. Kdzl., Budapest, vol. 71, heft 7-12, p. 3~t5,-348, 2 fig.

MATTHEW-W. D. ( 1 9 3 7 ) . - Paleocene faunas of the San Juan Basin, New Mexico. Trans. Amer. Phil. Soc., Philadelphia, new set., voL 30, VII q-510 p., 85 fig., 65 pl. MATTHEW W . D. O GUaNaER W . (1925). - - Fauna and correlation of the Gashato Formation of Mongolia. Amer. Mus. Novitetes, New York, n ° 189, I2 p., 14 fig. MCKENNA M . C . (1975). - - Toward a phylogenetic classification of the Mammalia,, Chapter 2 in Luckett W . P. O Szalay F . S . (eds.), Phyto~ geny of the Primates : A mukidisciplinary approach. Plenum Press 4dit., New York, p. 21-46. RaDULESCO C., ILmSCO G. & ItmSCO M. (1976). - D4couverte d'un Embrithopode nouveau (Mamma:lie) dans le Pal~og~ne de la dfipression de Hateg (Roumanie) et consid4rations g~n4rales sur ,In g4ologie de Ia r~gion Monatshefte. N,eues [herb. Palfiont., Stuttgart, 11, p. 690-698, 2 fig. RESHETOV V . Y . (!975). - - <> (in R,us sian). In K,ramarenko N.N. (ed.), Luvsanvandan B., Voronin Y. I., Barsbold B., Rozhdestvenskii A. K., Trofirnov B. A. b Reshetov V, Y., <> (in Russian). Science Press, Moscow, p. 19-53, 18 fig.

74

SIMON'S E.L. (1960). - - The Paleocene Panto~ donta. Trens. Amer. Phil. Soc., Philadelphia, new ser., vol. 50, pt. 6, 99 p., 18 fig. SXMPSON G. G. (1937). - - The Fort Union of the Crazy Mountain Field, Montana, and its mamma}ian faunas. Bull. U.S. Nat. Mus., Washington, vol. 169, X -k 287 p., 80 fig., 10 pl. SIMPSON G. G. (19~45). - - The principles of classification and a classification of mammals. Bull. Amer. l~us. Nat. Hist. New York, vol. 85, X V I + 3~5,0 p.

--

SZALAY F. S. ~ MCKENNA M, C. (1971 ). - - Beginning of the age of mammals in Asia: the late Paleocene Gashato fauna, Mongolia. Bull. Amer. Mus. Nat. Hist., New York, vol. 1't4, art. 4, p. 271-317, 35 fig. TONG Y., ZHANG Y., Wm'~G B. ~ DINGS. (1976). - - <> (in Chinese). Vertebrata Pat~ Asiatica, P4king, vol. 14, n ° 1, p. 16-25, 7 fig. WHEELER W . (1961). - - Revision of the uintatheres. Bull. Peabod 9 Mus. Nat. Hist., n ° 14, 93 p., 9 fig., 14 pl.

PLATES

-

76

-

PLATE 1

Phenacolophusfallax MATTHEW & GRANGER, 1925. Latest Paleocene or earliest Eocene, Mongolian People's Republic. Scale. (x 1). Fig. 1

Incomplete right lower jaw of type specimen, AMNH 20411, with P3 dP4 M1 M2 M3 ; occlusal view (above) and labial view (below).

Fig. 2

Left lower jaw fragment of type specimen, AMNH 20 411, with attached cast of AN PIN 476-6 showing P2 P3 dP4 M1 M2 M3 ; occlusal view (above) and labial view (below).

Fig. 3

Fragmentary right maxilla of type specimen, AMNH 20411, with battered remains of M 1 M2 M3 ; occlusal view (left) and labial view (right).

Phenacolophus fallax MATTHEW & GRANGER, 1925. Pal6oc6ne terminal ou base de l'Eoc6ne, R6publique populaire de Mongolie. Echelle. (x 1). Fig. 1 - M$choire inf6rieure incompldte droite du spdcimen type, AMNH 2041 ! , avec P3 dP4 M1 M2 M3 ; vue occlusale (en haut) et rue labiale (au dessous). Fig. 2 - Fragment de la mfichoire inf6rieure gauche du sp6cimen type, AMNH 2041 !, accol6 au moulage du sp6chnen AN PIN 476-6 montrant P2 P3 dP4 M1 M2 M3 rue occlusale (en haut) et rue labiale (au dessous). Fig. 3 - Fragment de maxfllaire droit du specimen type, AMNH 20411, avec les restes 6cras6s de M1 M2 M3. Vue occlusale (~ gauche) et vue labiale (~ droite).

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PLATE 2

Phenacolophus fallax MATTHEW & GRANGER, 1925. Latest Paleocene or earliest Eocene, Mongolian People's Republic. Scale. (x 1). Fig. 1

-

Cast of p2 p3 dp4 in maxillary fragment included in AN PIN 476-6, probably part of type specimen ; occlusal view (left) and labial view (right).

Fig. 2 - Cast of fight lower jaw of a different individual, AN PIN 476-4, with battered and sand-blasted remains of P3 P4 M1 M2 M3 ; occlusal view (above) and labial view (below). Fig. 3 - Cast of AN PIN 476-5, left lower jaw fragment with I 1 12 13 CP 1 ; occlusal view (above) and labial view (below). Fig. 4 - Cast of AN PIN 476-1, left lower jaw fragment with damaged M2 M3, type ofProcoryphodon primaevus FLEROV, 1957a ; occlusal view (above) and labial ,dew (below). Fig. 5 - Right astragalus, AMNH 21757 ; trochlea, seen from the front in approximately the orientation the bone would have had in life (left) ; same, with navicular facet rotated away from view and astragalar foramen area rotated into view (center) ; and view of flattened navicular facet (fight).

Phenacolophus failax MATTHEW & GRANGER, 1925. Pal6oc~ne terminal ou base de l'Eoc~ne, R6publique populaire de Mongolie. Echelle. (x 1).

Fig. 1 - Moulage de p2 p3 dp4 darts un fragment de maxillaire indus dans le specimen AN PIN 476-6 probablement partie du sprcimen type ; vue occlusale (/: gauche) et vue labiale (/: droite). Fig. 2 - Moulage de mfichoire infrrieure droite d'un autre individu, AN PIN 476-4, avec des restes ~cras~s et errodrs par le sable de P3 P4 M1 M2 M3 ; vue occlusale (an-dessus) et vue labiale (an-dessous). Fig. 3 - Moulage de AN PIN 476-5, fragment de m~choire infrrieure gauche avec I 1 12 13 (~1 ; vue occlusale (andessus), rue labiale (au-dessous). Fig. 4 - Moulage de AN PIN 476-1, fragment de m~choire infrfieure gauche avec M2 M3 endommag~, type deProeoryphodon pKmaevus FLEROV, 1957a ; vue occlusale (au-dessus) et vue labiale (au-dessous). Fig. 5 - Astragale droit, AMNH 21757 ; trochlre, vue de face suivant l'orientation approximativement que l'os aurait eu ehez le vivant (/t gauche) ; le meme, avec la facette naviculaire cachre et le foramen de l'astragale mis en 6vidence (an centre) ;vue de la facette naviculaire 6crasre (h droite).

G6obios M6m. sp6cial 1

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PLATE 3

Phenaeolophus fallax MATTHEW & GRANGER, 1925. Latest Paleocene or earliest Eocene, Mongolian People's Republic. Scale (x 1.75). Fig. 1 - Composite reconstruction of fight p2 p3 dp4 M 1 M2 M3, based upon AMNH 20411 (type) and AN PIN 476-6. M3 fairly well preserved, but quality of preservation deteriorates steadily toward anterior premolars ; labial view (above) and occlusal view (below). Fig. 2 - Composite reconstruction of fight I 1 12 13 CP 1 P2 P3 dP4 M1 M2 M3, based upon all available specimens ; occlusal view (above) and labial view (below).

Phenaeolophusfallax MATTHEW & GRANGER, 1925. Pal~oc~ne terminal ou base de l'Eoc~ne, R6publique populaire de Mongolie. Echelle. (x 1,75).

Fig. 1 - Reconstitution composite de p2 p3 dp4 M1 M2 M3 droite, fond6e sur AMNH 20411 (type) et AN PIN 476-6. M3 assez bien conserv~e, mais la qualit~ de pr6servation se d6t6riore notablement vers t'avant jusqu'aux pr~molaires ant~rieures ; rue labiale (au-dessus) et rue occlusale (au-dessous). Fig. 2 - Reconstitution composite de I 1 12 12 CP 1 P2 P3 dP4 M1 M2 M3, fond6e sur tousles specimens disponibtes ; rue occlusale (au-dessus) et vue labiale (au-dessous).

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PLATE 4

Comparison of lower dentitions, depicted at uniform size for ease of comparison. Occlusal views. Scales as shown by centhneter bars.

Fig. 1 - Composite reconstruction of right P2 P3 dP4 M1 M2 M3 ofPhenacolophusfallax (reversed), latest Paleocene or earliest Eocene, Mongolian People's Republic. Fig. 2 - Left P4 M2 1/2 M3 of new late Eocene or Oligocene Romartian arsinoithere Crivadiatherium mackennaL unnumbered specimen, collections of the Institutul de Geologie si Geofizica, Bucharest, adapted from Radulesco et aL,(1976). Fig. 3 - Left P2 P3 P4 M1 M2 M3 of African early Oligocene Arsinoitherium zitteli, AMNH 13549.

Comparaison des dentitions inf6rieures, ramen6es h une m6me grandeur pour rendre facile la comparaison. Vues occlusales. Echelles donn6es par les centim~tres figur6s.

Fig. 1 - Reconstitution composite de P2 P3 dP4 M1 M2 M3 de Phenacolophus fallax (invers6), Pal6oc6ne terminal ou d6but de l'Eoc4ne, R6publique populaire de Mongolie. Fig. 2 - P4 M2 et moiti6 de M3 gauche, du nouvel Arsinoithere de Roumanie Crivadiatherium mackennai (Eoc6ne sup6rieur ou Oligoc6ne), sp6cimen non catalogu4, collections de Institutul de Geologie si Geofizica, Bucarest, adapt6 de Radulesco et aL,(1976). Fig. 3 - P2 P3 P4 M1 M2 M3 gauche d'Arsinoitherium zitteli de l'Oligoc4ne inf6rieur d'Afrique, AMNH 13549.

PL 4 M.C. McKenna and E. Manning

G6obios M6m. sp6cial 1

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PLATE 5

Comparison of lower dentitions, depicted at uniform size for ease of comparison. Labial views. Scales as shown by centimeter bars.

Fig. 1 - Composite reconstruction of right P2 P3 dP4 M1 M2 M3 ofPhenacolophus failax (reversed), latest Paleocene or earliest Eocene, Mongolian People's Republic. Fig. 2 - Left P4 M2 1/2 M3 of new late Eocene of Oligocene Romanian arsinoithere, Oqvadiatherium mackennai unnumbered specimen, collections of the Institutul de Geologie si Geofizica, Bucharest, adapted from Radulesco et al., 1976. Fig. 3 - Left P2 P3 P4 M1 M2 M3 of African early Oligocene Arsinoitherium zitteli, AMNH 13549.

Comparaisons de dentitions inf6rieures, ramen6s ~ une m6me grandeur, pour rendre facile ia comparaison. Vues labiales. Echelles donn6es par les centim6tres figures.

Fig. 1 - Reconstitution composite de P2 P3 dP4 M1 M2 M3 de Phenacolophus fallax (myers6), Pal6oc6ne terrninN ou d6but de l'Eoc6ne, R@ublique populaire de Mongolie. Fig. 2

P4 M2 et moitid de M3 gauche du nouvel Arsinoith~re de Roumaaie, Crivad~ad*erium mackennai (Eocene supdrieur ou Oligoc~ne). Sp@imen non catalogud, collections de l'Institutul de Geologie si Geofizica, Bucarest, adapt6 de Radulesco et alii (1976).

Fig. 3 - P2 P3 P4 M1 M2 M3 gauches d'Arsinoitheriura zitteli de l'Oligoc6ne inf6rieur d'Afrique,

AMNH 13549.

Pi. 5 M.C. McKenna and E. Manning

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