THE RELATIONSHIPS OF THE ARCTOSTYLOPIDAE (MAMMALIA) NEW DATA AND INTERPRETATION RICHARD L. CIFELLI,' CHARLES R. SCHAFF,- AND MALCOLM C. McKENNA CONTENTS Abstract. The dental morpholog steini, hitherto known onl) from pari Abstract cheek- tooth series is desi rilx-d on the ba Introduction collected specimen including .i near!) Acknowledgments per and lower dentition \U arctoMylopid • Abbreviations from North America principally from th Paleontology 5 Systematic Basin, Wyoming, are apparentl) referable l Order new 5 Arctostylopida, gle species, which therefore ranges from the lati 5 Family Arctostylopidae luiiian through the ( larklorkian Other an I 6 Matthew, 1915 to the \si.m Arctostylops genera are restricted I'.ileogi A. steini Matthew, 1915 6 A previously described 5pe< ies "l Matthew and Granger, Palaeostijlops sty/ops is placed in a new genus Gashal 1 1 1925 Arctostylopidae and its constituent subordii P. iturus Matthew and Granger, are diagnosed, and a h\ pothesis "I relationshi| 1925 1 5 in the family is presented B) comparison witl 15 new l>\ / Gashatostylops genus ungulate morphohpe as represented et .. 15 G. macrodon (Matthew al., 1929) latum, Asiostylops spumes is hypothesized 20 and 1976 ... Sinostylops Tang Yan, most primitive member ol the family; Both 1976 ... 20 S. promissus Tang and Yan, notios and B. progressus retain man) primitivi Bothriostylops Zheng and Huang, tures but clearK hear some ol the spec lalizatkx 22 other 1986 in Palaeostijlops, Arctostylops, and and 1986 ... North \mt B. notios Zheng Huang, genera. Of these derived taxa, and 1976) sister taxou to the n B. progressus (Tang Yan, tostylops may be the 1978 22 are in distributioi Anatolostylops Zhai, genera, all of which Vsiatfc 23 A. dubius Zhai, 1978 ato/osfy/opi and an as \et unnamed sp< 1979 23 taxa that be most dote!) n Asiostylops Zheng, specialized sister ma) A. spanios Zheng, 1979 to Gashatostylops th. Kazachostylops Nesov, 1987 Comparison of morphotypes tor K. occidentalis Nesov, 1987 daeand for southern Notoungulata sug Irorn within th.- oUm Arctostylopidae?, incertae sedis ivation of one group is unlikeb This Allostylops Zheng, 1979 rentlv known, compai 1979 most similai A. periconatus Zheng, indicates that notoungulate indet. acquin Arctostylopidae, genus and species tostylopids were independent!) the Arcto- Comparative Dental Morphology of basis for an exclusive relationship taxa is a d. to Notoungulata as sister single stylopidae and The Notoungulata of South America acter. The ankles ol arctostylopids and shan Discussion are divergently specialized eutherian morpnotype Possible Relationships not present in a ^ is. herefon Remaining Resemblances family Arctostvlopulae for th, Distinctness of Arctostylopida Notoungulata Relatives unknowi Holarctic faunas remain members of the group r. i 1 and De- although Oklahoma Museum of Natural History .uammaUtrom.h. I Nor- er enigmatic of Zoology, University of Oklahoma, mo. partment Because it is a well-defined man, Oklahoma 73019. relationship I Uni- out obvious elose 2 of Zoology, Harvard Museum Comparative the M,t opidaei 02138. groups, versity, Cambridge, Massachusetts IV. iati Arctostylopida 3 of Natural History, Central American Museum removes the i York 10024. Notoungulata Park West at 79th Street, New York, New Zool 152 Bull. Mus. Comp Bulletin Museum of Comparative Zoology, Vol. 152, No. 1 to Neo- leocene or early Eocene link of Holarctic the Arctostylopidae have been integral to mammal faunas and in accordance tropical suggests, the development of correlations of early with other evidence now available, that whatever strata (Dashzeveg, 1982; Ginger- inter American connections of mammal faunas oc- Tertiary curred must have been earlier in time. The geometry ich and Rose, 1977; Matthew and Granger, ol li\ pothesized relationships among the Arctostylop- 1925; Szalay and McKenna, 1971). was most abundant id. te and the fact that the group Arctostylops, represented by the type .Hid diverse in Asia suggest an Asian, rather than (and only) species, A. steini, was described \.>rth or South American, origin for the family. by Matthew (1915), based on a partial low- er jaw from the "lower Gray Bull beds, Clark Fork This local- INTRODUCTION Basin, Wyoming." ity is probably, but not certainly, Clark- Since the studies of Gaudry (1902, 1904, forkian in age (Rose, 1981). Matthew re- 1906, 1908) and Scott (1904), it has been ferred the genus without question to the widely accepted that South America's fau- Notoungulata, hitherto known only from na is largely autochthonous, a result of that South America, placing it in the "Entelo- continent having been isolated by sea nychia," a mixed assemblage that then barriers from the rest of the world for most contained the most primitive of known no- of the Tertiary. Endemism at high taxo- toungulates. Matthew believed Arctosty- nomic levels is particularly conspicuous lops to be early Eocene in age, which may among the land mammals, which under- well be the case, but is a matter of defi- \\ ent their great diversification and radia- nition. Further materials of the species tions largely within the span of the Ter- were not forthcoming for another 50 years, tiary. It thus came as a great surprise when, when a specimen was reported nearby from in the first part of this century, apparent the Silver Coulee beds of the Polecat Bench members of South America's largest and Formation near Princeton Quarry. This lo- most characteristic group of hoofed mam- cality is late Paleocene (late Tiffanian) in mals, the Notoungulata, were described age (Jepsen and Woodburne, 1969). Inten- from specimens recovered in Wyoming sive collecting by Gingerich, Rose, and as- Matthew, 1915) and Asia (Matthew and sociates in Clarkforkian beds of the Clarks Granger, 1925; Matthew, Granger, and Fork Basin has produced four additional Other Simpson, 1929). possible close rel- specimens, consisting of dentulous lower atives Holarctic among and Nearctic jaw fragments and isolated teeth (Ginger- mammal faunas had been and have con- ich and Rose, 1977; Rose, 1981). The single tinued to be suggested (Ameghino, 1906; report of Arctostylops steini from outside Gingerich, 1985; McKenna, 1981). None- the Clarks Fork Basin is that of McKenna theless, none of the proposed relationships (1980), who recorded the species from beds seemed so based on characteristic certain, of Clarkforkian age at Togwotee Pass, synapomorphies, as in the case of these northwestern Wyoming. for ungulates, the Holarctic Arctostylopi- However, related mammals had in the 'l.ir a possess strongly specialized dentition meantime been recovered from Asia. Pa- that resembles alone notoungulates among leontological work at Gashato in Mongolia mammals. For this reason, the Arctosty- by the American Museum of Natural His- have lopidae figured prominently in dis- tory's Central Asiatic Expeditions led to cussions of the origin and early dispersal the description of two species, Palaeosty- of South America's native land mammal lops iturus Matthew and Granger, 1925 fauna McKenna, 1981; Simpson, 1951, and "P." macrodon Matthew, Granger, L978 L980) and of in zoogeography gen- and Simpson, 1929. These species are (Colbert, 1973; 1957; Darlington, probably latest Paleocene in age (Szalay Simpson. 1965). In because of addition, and McKenna, 1971). More recent addi- their presence in North America and Asia, tions to the group have come from slightly • at deposits Naran Bulak, Mon- • younger Hua i (Gradzinski et al., 1969), the Paleo- golia Sinostylops pi cene and Eocene (or possibly The most Oligocene) recenl addition to the famil of China and (Tang Yan, 1976; Zhai, 1978; Kazachostylo) Zheng, 1979; Zheng and 1986), Neso\ Huang, L981 From the late l and the Paleocene of the USSR tashkent (Nesov, Svita of Kazakhstan i S5 1987), where seven additional described Since the initial descriptii species, placed in six genera, bear witness and stylops Palaeostylops Matthew I to a modest radiation of Matthew Arctostylopidae and Granger 1 identsl in the of Asia. 4 and early Tertiary Tang realized that these Holan ti< form Yan described includ- (1976) Sinostylops, some respects, more primitive than two from the late Paleocene ing species, known South American Notoungul of Anhui Province, China. S. while in other promissus respects the) are uniquel) the Dou-mu the (from Formation), type specialized. Their primitiveness is refl< is based on a mandibular ramus ed ol species, by placement the famil) \n t< with eight teeth; S. progressus (collected lopidae in Simpson's archaic notoungulate in the Shuang-ta-si Group and later trans- suborder Notioprogonia Simpson 1 ferred to a new genus, Bothriostylops) from 1945). However, the relationships ol Hoi- six jaw fragments. Anatolostylops dubius arctic to South American forms have n< was described by Zhai (1978) from the pu- been considered in detail Foi this reason tative early Eocene (but see below) Shi- a variety of opinions exist as to the place san-jian-fang Formation of the Turpan Ba- of origin of notoungulates and theii sub- sin, Xin-jiang Province, China. The species sequent dispersal patterns, with authors is known from a maxillary fragment with variously favoring northern Patterson 2 3 \-i.ui well-preserved M . Two additional gen- 1958) or. speeitiealb Matthew era and species were published by Zheng 1928; Zheng. L979 Smith American Marshall (1979). Asiostylops spanios, from the late (Hoffstetter, 1970: de Muizon and ( Paleocene Lan-ni-kong Member of the Chi- and Sige, 1983; Simpson 1951 en- l and I