n^o,50 ^ FIELDIANA

GEOtOGYUBRARy Geology NEW SERIES, NO. 50

Notoungulata and of the Early Chucal Fauna, Northern Chile

Darin A. Croft

John J. Flynn Andre R. Wyss

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July 30, 2004 Publication 1528

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Geology NEW SERIES, NO. 50

Notoungulata and Litopterna of the Early Miocene Chucal Fauna, Northern Chile

Darin A. Croft John J. Flynn

Department of Anatomy Department of Geology Case Western Reserve University Field Museum of Natural History School of Medicine 1400 South Lake Shore Drive 10900 Euclid Avenue Chicago, Illinois 60605-2496 Cleveland, Ohio 44106 U.S.A. U.S.A. Andre R. Wyss Department of Geology Field Museum of Natural History Department of Geological Sciences 1400 South Lake Shore Drive University of California—Santa Barbara Chicago, Illinois 60605-2496 Santa Barbara, California 93106 U.S.A. U.S.A.

Published July 30, 2004 Publication 1528

PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY © 2004 Field Museum of Natural History

ISSN 0096-265 1 PRINTED IN THE UNITED STATES OF AMERICA Table of Contents 9. Upper dentition of holotype of Altity- potherium chucalensis, SGOPV 4100, a partial skull with portions of all pre- molars and complete molars 21 Abstract 1 10. Portions of lower dentition oi Altity- Introduction 1 potherium chucalensis, SGOPV 4100 .... 22 Geographic and Geologic Setting 2 1 1 . Holotype of Eotypotherium chico, Materials and Methods 2 SGOPV 5157, a partial right maxilla Abbreviations 4 and zygomatic arch with P3-M3 27 Systematic Paleontology 4 12. Upper dentitions referred to Eotypo- 4 Notoungulata therium chico 28 4 13. Partial left mandible with m2-3, imbricatus 5 SGOPV 5158, referred to Eotypothe- Adinotherium sp 8 rium chico 29 11 14. Comparison of the degree of fusion of Altitypotherium paucidens 12 the tibia and fibula among selected 20 Altitypotherium chucalensis typotheres 32 Eotypotheriuum chico 25 15. Isolated upper cheek teeth referred to 31 Hegetotherium cf. H. mirabile 34 Hegetotherium cf. H. mirabile 33 16. Lower dentitions referred to Hegeto- Litoptema 36 therium cf. H. mirabile 35 36 17. Selected postcranial specimens referred to indet 39 Theosodon sp. indet 38 Theosodon sp. Phylogeny of Mesotheriines 40 18. Strict consensus trees of mesotheriine Age and Faunae Comparisons 42 relationships 43 Discussion and Conclusions 47 Acknowledgments 49 Literature Cited 49 List of Tables

List of Illustrations 1. Measurements for Chucal specimens of Nesodon imbricatus 6 2. Measurements for specimens of Altity- potherium paucidens 12 1 . Geography and geology of the Chucal 3. Development of suborbital fossa and Formation 3 size of infraorbital foramen in selected 2. of Partial skull Nesodon imbricatus, mesotheriines 19 SGOPV 4053 7 4. Measurements for specimens of Altity- 3. Bivariate of lower molar dimen- plot potherium chucalensis 20 sions for Adinotherium and Nesodon 8 5. Measurements for specimens of Eoty- 4. Partial left ?i2 of Adinotherium, potherium chico 26 4064 9 SGOPV 6. Measurements for Chucal specimens of and 5. Relative sizes of mesotheriines Hegetotherium mirabile 37 toxodontids from Chucal, as illustrated 7. List of characters and character states 10 by the size of the ulna used in phylogenetic analysis of me- 6. Morphology of the proximal radius in sotheriine relationships 41 mesotheriines and Adinotherium 11 8. Character-taxon matrix for phylogenet- 7. Holotype of Altitypotherium paucidens, ic analysis of mesotheriine relation- SGOPV 4038, a partial rostrum with ships 42 left II, left P4-M3 and right P4-M1 .... 13 9. of middle-latitude early to 8. Lower dentitions referred to Altitypo- middle Miocene faunas of northern therium paucidens 14 Chile and Bolivia 45

m 10. Ungulates of selected low-, middle-, 12. Revised taxonomic list of the Chucal and high-latitude Miocene faunas of Fauna 47 46 13. Body mass estimates of mesotheri-

1 1 . faunal resemblance indices ines 48 (Simpson coefficients) among selected low-, intermediate-, and high-latitude Miocene faunas of South America 47

IV Notoungulata and Litopterna of the Early Miocene Chucal Fauna, Northern Chile

Darin A. Croft John J. Flynn Andre R. Wyss

Abstract

This study describes the notoungulates and Htopterns (endemic South American ungulates) from the Chucal Fauna of northern Chile. Eight are known to date, including seven notoungulates and one litoptern. The bulk of the toxodontid notoungulate material, including a well-preserved partial skull, is referred to Nesodon imbricatus. A few postcranial elements and a single partial tooth are referred to Adinotherium sp. indet. Poorly preserved dental ma- terial may represent a third (indeterminate) toxodontid. Fragmentary dental and postcranial remains are referred to Hegetotherium cf. H. mirabile (Hegetotheriidae). Theosodon sp. indet. (Litopterna: Macraucheniidae) is recorded on the basis of a variety of diagnostic limb bones, but dental remains of this taxon are not yet recorded at Chucal. Three new species of meso- theriid notoungulates are described: Altitypotherium paucidens, Altitypotherium chucalensis, and Eotypotherium chico. The largest, Altitypotherium paucidens, differs from all previously described mesotheriids in the loss of an upper premolar (P3). Altitypotherium chucalensis is represented by an associated skull and mandibles plus postcranial remains. Eotypotherium chi- co, based on gnathic remains, is the smallest mesotheriid known. Bracketing radioisotopic dates and biostratigraphic correlation argue for referral of the Chucal Fauna to the Santacrucian South American Land "Age" (late early Miocene). The forms from Chucal are the only mesotheriids known for this temporal interval and also mark the earliest known occurrence of mesotheriines. A phylogenetic analysis places the three taxa from Chucal as early diverging members of the Mesotheriinae, with Eotypotherium chico representing the outgroup to all re- maining members of the clade. In the presence and abundance of mesotheriines and in the absence of interatheriids, the Chucal Fauna more closely resembles geographically proximate (but younger) faunas in Bolivia and the Precordillera of northernmost Chile than temporally correlative faunas from southern South America. This pattern indicates significant faunal pro- vinciality in South America during the late early Miocene and suggests that the intermediate latitudes might have been a center of diversification for mesotheriines and potentially other groups of .

Introduction Flynn «fe Wyss, 1998; Flynn, 2002). These extra- Patagonian faunas demonstrate, for one, that lat- Study of South American fossil mammals has itudinal provinciality characterized South Amer- traditionally focused on faunas from the high lat- ican mammal faunas for much of the Cenozoic, itudes, especially Patagonian Argentina (Patter- necessitating sampling of a wide geographic son &. Pascual, 1972; Simpson, 1980). The dis- range for any given time slice to gain a fuller covery of faunas elsewhere in South America understanding of mammal evolution on the con- (e.g., Bolivia, Brazil, Chile, Colombia) has con- tinent (Pascual et al., 1985; Wyss et al., 1994; tributed to more complete understanding of the Madden et al., 1997). evolution of South American mammals but has Our research team has been working to un- also revealed unanticipated complexities (see cover and develop fossil mammal faunas of var-

FIELDIANA: GEOLOGY, N.S., NO. 50, JULY 30, 2004, PP. 1-52 ious ages throughout the length of Chile. The Charrier et al., 2000, 2002; Womer et al., 2000; Chucal Fauna represents the northeasternmost of Chavez, 2001; Bond & Garcia, 2002; Flynn, Croft, these fossiliferous localities. The first fossil ver- et al., 2002), including initial paleontological re- tebrate specimen from this fauna, discovered in ports, geochronologic analysis, and studies of the 1992 during the course of geologic mapping syntectonic deposition of the fluviolacustrine sedi- northeast of Salar de Surire (Fig. 1), pertains to ments of the Chucal Formation (Fig. 1). Fossilif- Nesodon, an early Miocene toxodontid notoun- erous strata of the Chucal Formation are well ex- gulate (Charrier, Mufioz, Wyss, et al., 1994). To posed on both limbs of a major N-S-oriented determine whether the Chucal Formation would growth anticline (the Chucal Anticline), which doc- produce other identifiable fossil mammal re- uments marked thickness and facies variation on mains, a return trip to the area was undertaken either flank and at least four progressive erosional in July 1998. This expedition yielded a variety unconformities (U1-U4 in Charrier et al., 2002; of well-preserved specimens, including a diver- Fig. 1; see also Riquelme & Herail, 1997, and Ri- detailed in et al. sity of endemic ungulates, as well as the oldest quelme, 1998). As Charrier chinchilline (Flynn, Croft, et al., 2002). A (2002), the Chucal Formation at Cerro Chucal is second expedition to the area in 2001 produced thickest (—600 m) on its west-dipping (35-40°) many additional specimens and at least five spe- western flank (informal Members W1-W4) and is cies not recorded previously (Charrier et al., thinner on its steeply east-dipping (generally >50°) 2002). The present study provides descriptions eastern flank (informal Members E1-E3), where and taxonomic analyses of the most diverse and the syntectonic erosional unconformities are most abundant component of the Chucal Fauna, of its pronounced. Mammal fossils are most common in notoungulates, as well as of its single litoptern. the floodplain facies (and some lacustrine-influ- Prior to discovery of the Chucal Fauna, only enced intervals) in the lower parts of Members W3 isolated Cenozoic mammal specimens had been and W4 and the fluviatile facies of Members El reported from northern Chile. The first, a meso- and E3 (Charrier et al., 2002). theriid mandible (MLP 86-VIII-lO-l), was col- Unconformities separate the Chucal Formation lected by D. Pacci in 1969 in the area of Caragua from the underlying Lupica Formation (early (approx. 18° 25 'S, 69°35'E) west of the town of Miocene, dated at 21.7 ± 0.8 Ma at Chucal and Belen. The second, a nearly complete mesotheriid at >18.5 Ma elsewhere in the region) and the skull and mandibles with associated postcrania overlying Quebrada Macusa Formation (the base (SGOPV 4004), was discovered in 1989 (Salinas of which is dated at 17.5 ± 0.4 Ma at Cerro Chu- et al., 1991), probably from the same locality as cal; Muiioz, 1991; Riquelme, 1998; Bond & Pacci's specimen. Both specimens were collected Garcia, 2002; Charrier et al., 2002). The Chucal from the Huaylas Formation, a unit demonstrably Formation, therefore, was deposited and deformed younger (middle late Miocene, definitely <16 Ma very rapidly (possibly over considerably less than ~ and most likely 10.8-1 1.7 Ma; Flynn et al., in 4-5 million years); it is no older than 22.5 Ma press) than the Santacrucian-aged horizons de- (possibly 18.5 Ma) and no younger than about 17 scribed here. The two mesotheriid specimens from Ma. Thus, based on both the biostratigraphic oc- Caragua (and a third discovered in the same area currences and radioisotopic constraints, we con- by our team in 2001) have been referred to a new sider the mammalian fossils from the Chucal For- mesotheriine taxon (Flynn et al., in press). mation in this region to represent a single short- duration assemblage, the Chucal Fauna (Charrier et al., 2002; Flynn et al., 2002).

Geographic and Geologic Setting

Material described herein is derived from the Materials and Methods <600-m-thick Chucal Formation near Cerro Chu- cal, located on the Chilean Altiplano northwest of Upper tooth loci are indicated by uppercase let- the Salar de Surire (18°43'S, 69°10'W). Several ters (e.g., II, P2, Ml) and lower tooth loci by

earlier studies have detailed the geology of this re- lowercase letters (e.g., il, p2, ml); deciduous gion (e.g., Mufioz, 1991; Charrier, Mufioz, & Pal- teeth are indicated by a "D/d" preceding the tooth ma-Heldt, 1994; Charrier, Mufioz, Wyss, et al., position. Terminology for toxodontid molar mor- 1994; Riquelme & Herail, 1997; Riquelme, 1998; phology follows Madden (1990). All measure-

FIELDIANA: GEOLOGY CROFT ET AL.: CHUCAL UNGULATES merits were taken to the nearest O.I mm using MA, South American Land Mammal "Age"; C\, digital calipers. consistency index; RI, retention index; RC, re- We recognize that many groups (e.g., Nesodon- scaled consistency index. Metacarpals and meta- tinae, Hegetotheriinae), as currently conceived, tarsals are abbreviated MC and MT, respectively. are likely paraphyletic. Because these names are familiar to South American paleomammalogists, we continue to employ them in their traditional sense until phylogenetic definitions and/or alter- Systematic Paleontology nate names are proposed. Taxonomic names that are potentially invalid Mammalia Linnaeus, 1758 because of synonymy (e.g., Mesotherium "angus- Notoungulata Roth, 1903 tirostmm") are indicated through the use of quo- Toxodontia Owen, 1853 tation marks. Toxodontidae Gervais 1847 To our knowledge, no comprehensive analysis Nesodontinae Murray, 1866 of the stratigraphic and geographic occurrences of the taxa considered in the present study has been Diagnosis—The Nesodontinae, as traditionally published previously. The distribution cited for conceived (e.g., Nesodon, Adinotherium, Proadi- each taxon therefore represents a preliminary ef- notherium, etc.), is likely a paraphyletic group of fort to detail the geologic formations in which that toxodontids lacking derived character states pre- taxon is known to occur based on firsthand ob- sent in other toxodontid subclades (Madden, servations and summary compilations of Bonde- 1990; Nasif et al., 2000). Specimens from Chucal sio et al. (1980), Marshall et al. (1983), Savage are referred to the Toxodontidae based on large and Russell (1983), Mones (1986), Madden size; presence of very hypsodont cheek teeth; (1990), and Marshall and Sempere (1991). cheek teeth with protocone and hypocone united The SALMA remains controversial early in wear; upper molars with distinct and per- (Flynn & Swisher, 1995; Madden et al., 1997; sistent first crista; lingual origin of the crochet in

et be- cross section of i 1 Flynn, Croft, ai., 2002). We distinguish upper molars; triangular ; hyp- tween Friasian in its traditional sense (Friasian selodont, procumbent, and tusklike 13; and re- sensu lato; subsuming the , , duced enamel along the lingual portions of the and Friasian sensu stricto SALMAs) and the lower molars (Madden, 1990; Cifelli, 1993; Nasif term's more restrictive definition (Friasian sensu et al., 2000). Nesodontines differ from other tox- stricto; including only the temporal interval char- odontids in absence of derived mandibular sym- acterized by the type assemblage in southern physis morphology (Madden, 1990); unreduced Chile, and correlative faunas), following Flynn, sagittal crest (Nasif et al., 2000); lack of hypse- Croft, et al. (2002). lodont molars (although M3 roots form only in old individuals; Madden, 1990); absence of sim-

plified, straight ectoloph (i.e., lacking distinct par- astyle, paracone, and metacone) on P2-4; pres- Abbreviations ence of lingual folds on upper molars that become completely isolated as fossettes; and presence of AMNH, American Museum of Natural History, two lingual folds plus an accessory fossettid in New York; FMNH, Field Museum of Natural His- the lower molars. tory, Chicago; GB, Servicio Geologico de Bolivia (housed at the Museo Nacional de Historia Nat- ural, La Paz); MACN, Museo Argentino de Cien- Nesodon Owen, 1846 cias Naturales, "Bernardino Rivadavia," Buenos Aires; MLP, Museo de La Plata, Argentina; Type Species—Nesodon imbricatus. MNHN, Museum National d'Histoire Naturelle, Included Species—The type, Nesodon con- Paris; PU, Princeton University Collection (now spurcatus, and Nesodon cornutus. housed at Yale University, New Haven, Connect- Diagnosis—A nesodontine differing from icut); SGOPV, vertebrate paleontology collec- Proadinotherium in larger size; greater degree of tions, Museo Nacional de Historia Natural, San- hypsodonty; presence of II with trapezoidal cross tiago; Ma, megannum; mm, millimeter; cm, cen- section (triangular in Proadinotherium); absence timeter; S.I., sensu lato; s.s., sensu stricto; SAL- of cingulae in II; presence of simple and rounded

FIELDIANA: GEOLOGY F3 fossette on upper molars; reduction of lingual Bond and Garcia (2002) questionably referred enamel band on ml; presence of flattened and three poorly preserved and fragmentary - sharply angled posterior external face of ml tal- tid teeth from the upper part of the Chucal For- onid; and presence of deep, wide lingual groove mation to Palyeidodon, a taxon resembling Ne- on molars (groove is shallow in Proadinothe- sodon that occurs in slightly younger deposits hiim). Differs from Adinotherium in larger size (early middle Miocene Friasian s.s. and Collon- (approximately twice as large in linear dimen- curan SALMAs; Madden, 1990). They further sions), absence of angled posteroventral border of noted that these teeth (all pertaining to a single mandible, presence of II with trapezoidal cross individual) possess a mix of features normally section (kidney shaped in Adinotherium), pres- found in those two taxa as well as some distinct ence of P2-4 lingual precingulae, presence of rel- features (autapomorphies) that indicate it might atively larger lower premolar row (p2-p4 length represent a new taxon. The dental similarities of >50% ml-m3 length in Nesodon, <50% in Adi- Nesodon and Palyeidodon make them difficult to notherium), absence of anterior and entohypocon- distinguish without sufficiently complete and ulid folds on p3, relatively lower-crowned p4, re- well-preserved specimens. Moreover, some of the duction of lingual enamel band on ml, presence characters used by Bond and Garcia (2002) to dif- of flattened and sharply angled posterior external ferentiate the two are of ambiguous utility: the face of ml talonid, and distinct calcaneal mor- absence of a posteroexternal fossette in M 1 (char- phology (see Scott, 1912). Differs from nearly acteristic of Palyeidodon) also occurs in some contemporaneous Palyeidodon (likely a basal tox- specimens oi Nesodon (e.g., FMNH P10379), the odontine and not a nesodontine, fide Madden, Ml lingual fold becomes isolated with wear in 1990; Cifelli, 1993; Nasif et al., 2000) in unre- both Nesodon and Palyeidodon (although this is duced sagittal crest, presence of more developed not the case for M2 and M3; Madden, 1990), and upper premolar parastyles, presence of upper pre- it is unknown whether the isolated Ml they de- molar lingual precingulum, presence of parastyle scribed would eventually have formed roots (as in sulcus on Ml, presence of accessory fossette on Nesodon) or would have maintained open roots upper premolars, presence of F3 accessory fos- (as in Palyeidodon) later in life. Additionally, the sette in upper molars, isolation of primary lingual specimens described by Bond and Garcia (2002) fold as fossette in later wear stages in M2 and differ in several respects from both Nesodon and M3, presence of more persistent F3 fold/fossette Palyeidodon: the parastylar region is much more in upper molars, and presence of accessory fos- pronounced and is deflected lingually instead of settid in lower molars (Madden, 1990; Cifelli, labially (as noted by Bond and Garcia), the ec- 1993; Nasif et al., 2000). toloph is strongly convex instead of straight or Distribution—Santa Cruz Formation, Patagon- slightly concave (also noted by Bond and Garcia), ia, Argentina, late early Miocene age, Santacru- and the teeth (especially Ml) are significantly cian SALMA (Scott, 1912; Madden, 1990); Chu- larger than those of both Nesodon (Scott, 1912) cal Formation, northern Chile, late early Miocene and Palyeidodon (Madden, 1990). It may there- age, Santacrucian SALMA; Cura-Mallfn Forma- fore represent a new toxodontid, but one that cur- tion, south-central Chile, late early Miocene age, rently is too poorly represented to be named. Santacrucian SALMA (Croft, Radic, et al., 2003); Pending description of more diagnostic material, unnamed formation (possibly equivalent to Rio we consider these teeth to pertain to an indeter- Zeballos Formation), southern Chile, late early minate toxodontid. Miocene age, Santacrucian SALMA (Flynn, No- vacek, et al., 2002). Comments—Nesodon is best known from the Nesodon imbricatus Owen, 1846 rich late early Miocene Santa Cruz deposits along (Figures 2, 4, Table 1) the Atlantic coast of Patagonia (Scott, 1912). Re- cent studies suggest that Nesodon may serve as a Referred Specimens from the Chucal For- useful index taxon for the Santacrucian SALMA mation—SGOPV 5073, partial skull with broken (Croft, Radic, et al., 2003). Reports of Nesodon right ?I2, right P2-M3, isolated left M2; SGOPV from other time periods and from areas outside of 4043, fragmentary and poorly preserved skull and Chile and Patagonia are poorly substantiated and right mandible; SGOPV 4027, left postorbital pro- are therefore not included in the above list (Flynn, cess; SGOPV 4054, incisor/canine and other tooth Croft, et al., 2002; Croft, Radic, et al., 2003). fragments (unprepared); SGOPV 4066, left M3;

CROFT ET AL.: CHUCAL UNGULATES Table 1 . Measurements for Chucal specimens of Nesodon imbricatus.

P2 P3 P4 Ml M2 M3

Upper dentition L W W W W W W

SGOPV 5073 (R) 19.8 25.2 21.6 28.3 31.4 27.6 45.1 34.5 58.6 31.3 SGOPV 5073 (L) 44.0 34.4 SGOPV 4066 (L) 46.4 (26.6)

m2 ni3

Lower dentition W W

SGOPV 4105 (R) 39.8 17.2 SGOPV 4099 (L) (75) (22)

SGOPV 5036, right mandibular fragment with terior premolars. All three premolars show mod- portions of ?p3-4; SGOPV 4105, right m2; erate wear, and the only occlusal feature remain- SGOPV 4099, left mandibular fragment with m3; ing is the central fossa. The fossa is a very small SGOPV 5118, right ?dp; SGOPV 4018 partial left oval in P2 and is larger and more elongate an- glenoid; SGOPV 5225, left humerus (see Charrier, teroposteriorly in P3 and P4. Murioz, Wyss, et al., 1994); SGOPV 4044, prox- A noteworthy feature of the premolar series is imal left ulna fragment; SGOPV 4040, fragmen- the variation in the level of the occlusal surfaces tary large postcranial bones, right metacarpal II, of the teeth. The occlusal surface of P4 is at the and right magnum; SGOPV 4015, fragmentary same level as the molars, while that of P2 is more postcranial bones (associated with SGOPV 5036). dorsally situated, approximately 1.75 cm nearer Age and Distribution—Santa Cruz Formation, the base of the tooth. The third premolar bridges Patagonia, Argentina, late early Miocene age, this gap in occlusal surfaces; most of P3 is at the Santacrucian SALMA; Chucal Formation, north- same level as P2, but the posterior quarter has ern Chile, late early Miocene age, Santacrucian been worn such that it forms an extremely steep SALMA. dentine slope (ranging from 45° to 85° at the lin- Diagnosis—Differs from Nesodon conspurca- gual and labial margins, respectively) that blends tus in larger size. Differs from N. cornutus in low- into the anterior face of Ml. As in many other er occiput and absence of dermal horn. notoungulates, enamel is absent along the labial Description—The most complete specimen of portions of both the posterior face of P4 and the Nesodon imbricatus in the Chucal collections is anterior face of Ml in this area, resulting in the SGOPV 5073, a partial skull with much of the confluence of the two dentine surfaces. right toothrow preserved. Although the bone is The first and second upper molars are both trap- not especially well preserved, most of the teeth ezoidal. The ectolophs are straight with little ev- are in excellent condition. The skull is partially idence of a parastyle or parastyle sulcus. Only the prepared, and the occlusal surfaces of right P2- central fossa is present on the occlusal surface of M3 have been exposed, as has the entire length Ml. In M2, the bifurcate primary lingual enamel of an associated left M2 (almost certainly from fold has become isolated as a large, bifurcate, cen- the same individual but displaced from its alveo- tral fossa. The F3 fold is present as a small fos- lus). Other teeth are present as "float" in the sette located almost directly posterior to the point block containing the skull but remain unprepared. of bifurcation of the central fossa. The third upper Dental measurements for this and other specimens molar is nearly triangular in shape and displays referred to N. imbricatus are presented in Table 1 . less wear than the two anterior molars. Both the The premolars of SGOPV 5073 are all roughly primary lingual enamel fold and the F3 fold are quadrangular in outline. The anterior half of P2 is present; the former has not yet become isolated not preserved, portions of the anterior and lingual by wear, while the latter recently has. faces of P3 are missing, but P4 is essentially com- Specimen SGOPV 5118 is apparently an un- plete. The ectoloph of each tooth includes a par- erupted deciduous right lower premolar Its lack astyle and parastyle sulcus. These structures are of wear, small size, and lack of roots suggest it most pronounced in P2 and less so in more pos- was from a very young individual. The anterior

FIELDIANA: GEOLOGY Fig. 2. Partial skull of Nesodon imbricatus, SGOPV 4053, including right ?I2 and P2-M3. A. Right lateral view. B. Occlusal view. Scale bars equal 5 cm.

and posterior faces converge slightly toward the large long bones associated with a right MC II base (in lingual view), indicating that the tooth and right magnum. would not have increased in size with further de- Comments—The size difference between Ne- velopment. It is similar in overall form to the an- sodon imbricatus and N. conspurcatus is pro- terior tooth of MLP 12-245, a partial right man- nounced, implying that the validity of the two dible with ?dp4-ml from Santa Cruz referred to species is well founded (Croft, Radic, et al., Nesodon imbricatus (pers. observ.). 2003); in this regard, specimens from Chucal Relatively few postcranial bones from Chucal compare well with N. imbricatus (Fig. 3). The sta- are referable to Nesodon; these include the left tus of N. cornutus is less certain; the species is humerus found in 1992 (SGOPV 5225), a partial represented only by the holotype (a nearly com- left glenoid (SGOPV 4018), a proximal left ulnar plete skull with heavily damaged teeth) and is dis- fragment (SGOPV 4044), and some fragmentary tinguished from other species by skull proportions

CROFT ET AL.: CHUCAL UNGULATES 3.0- SGOPV 5035, phalanx, many small bone frag- ments; SGOPV 4065, partial femoral head, prox- imal ?MT II, many limb bone fragments; SGOPV 4084, proximal portions of left ulna and radius, ?elbow sesamoid (Figs. 5, 6). Description—Only a single dental specimen clearly attributable to Adinotherium has been col- lected from Chucal: SGOPV 4064, a partial tooth, probably left i2 (Fig. 4). The tooth preserves only the base of its crown and part of the root; none of the occlusal surface is present. The root mea- sures 5.6 X 6.5 mm. Enamel is restricted primar-

ily to the front of the tooth but extends slightly onto the mesial surface toward the crown. The

labial enamel is much thicker than the mesial. The

labial enamel forms an inverted triangle in ante- rior view, with a rounded apex and a base formed by the broken surface of the tooth. In size and morphology, the specimen closely resembles the Fig. 4. Partial left ?i2 of Adinotherium, SGOPV base of left i2 of FMNH PI 3097, a specimen of 4064, in labial view. Scale bar = 5 mm. Adinotherium from Santa Cruz, Argentina; it is much smaller than FMNH UC1330, a specimen of Nesodon from Santa Cruz. The tooth is asso- Comments—Although Scott (1912) noted dif- ciated with various mandibular fragments, includ- ferences in the vertebral column, scapula, and an- ing a partial right articular condyle that compares kle of Adinotherium and Nesodon, morphological well with Adinotherium. characters currently used to distinguish the two A second craniodental specimen, SGOPV

1 Nasif et It to taxa are all craniodental (Madden, 990; 401 1, may pertain to Adinotherium. appears al., 2000). The limb bones of toxodontids are fair- be a partial maxilla preserving the bases of two ly easy to distinguish from those of other endemic teeth, a fragment of a third, and part of the alve- South American ungulate clades (e.g., litopterns, olus of a fourth. Based on the portions of teeth astrapotheres, pyrotheres) and other contempora- that are present and the size of the alveolus, the neous notoungulates (e.g., mesotheriids, hegetoth- most notable aspect of SGOPV 4011 is the dra- eriids). Given the significant metric differences matic mesial-to-distal increase in tooth size; this between Adinotherium and Nesodon, postcranial resembles the condition seen in the premolar se- specimens of the two Santacrucian toxodontids ries of Adinotherium and does not closely resem- can be discriminated on the basis of size alone ble the condition present in any other specimens (Scott, 1912; Croft, Radic, et al., 2003). Since from Chucal. The fragmentary nature of the spec- only a single tooth of Adinotherium (a partial in- imen precludes a precise identification, however. cisor. Fig. 4) has been collected at Chucal, refer- Despite the paucity of dental remains, several ence of postcranial elements to this taxon is based well-preserved postcranial specimens (primarily on their similar morphology—but much smaller forelimb elements) increase confidence in the rec- size—compared to Nesodon (Fig. 5). ognition of Adinotherium at Chucal. Specimen SGOPV 4084 includes proximal fragments of the left ulna and radius (Figs. 5, 6). The radius is Adinotherium sp. indet. much more robust than that of the larger mesoth- (Figures 4-6) eriids at Chucal (e.g., A. chucalensis, SGOPV 4042) and differs most conspicuously in having a Referred Specimens from Chucal—SGOPV very pronounced interosseous crest (Fig. 6). Sim- 4064, partial ?left i2, partial right articular con- ilarly, the fragmentary ulna, while preserving only dyle, various ?mandibular fragments (Fig. 4); the distal portion of the sigmoid notch, differs SGOPV 4012, left unciform, proximal left MC IV, from the corresponding bone of mesotheriids in the cor- left MC V, dorsal half of right magnum, many lacking a well-demarcated fossa distal to small- other partial hand/foot bones and bone fragments; onoid process (Fig 5.). Except for its much

CROFT ET AL.: CHUCAL UNGULATES ^^v^^l Fig. 6. Morphology of the proximal radius in mesotheriines and Adinotherium. A. FMNH PI 4482, proximal left radius of "Typotheriopsis sp." from the late Miocene Araucano Fm. of Catamarca, Argentina. B. SGOPV 4042, proximal right radius (pictured as left) of A. chucalensis (Mesotheriinae, described in text). C. SGOPV 4084, proximal - left radius of Adinotherium. All specimens are in medial view. Scale bars 2 cm.

ements of Nesodon while differing in morphology ytherus) and the Mesotheriinae (including Friasian from those of mesotheriids (and other notoungu- s.l. and later forms) characterized by the loss of lates). — I2-P2/i3-p3 and the presence of persistently tri- Comments As discussed below (Litoptema) lobed upper molars, among other features (Fran- appendicular bones of the major South American cis, 1965; Villarroel, 1974a; Cerdeiio &. Montal- clades are ungulate easily distinguished (Cifelli, vo, 2001; Reguero & Castro, 2002; Croft, Flynn, 1983, 1985, Those from Chucal here re- 1993). & Wyss, 2003; Flynn et al., in press). Mesothe- ferred to the Toxodontidae Nesodon and Ad- (viz., riids are absent from faunas of age are similar in but differ inotherium) morphology and had not been recorded in faunas of Santacru- markedly in size. This difference is well illustrat- cian age prior to their discovery at Chucal (Flynn, ed by SGOPV 4044, a partial left proximal ulna Croft, et al., 2002). of Nesodon, versus SGOPV 4084, a partial left Mesotheriines are in great need of systematic proximal ulna oi Adinotherium (Fig. 5); the depth revision (Pascual & Bondesio, 1985; Cerdeiio & of the ulna just distal to the trochlear notch of the Montalvo, 2001; Flynn, Croft, et al., 2002; Croft, former is approximately 8 cm, while the corre- Flynn, & Wyss, 2003; Flynn et al., in press), mak- sponding measurement of the latter is less than 3 ing taxonomic assignments of newly discovered cm. The specimens attributed to Adinotherium forms challenging. Based on Francis's (1965) re- above are all fully ossified and therefore do not vision of Argentine taxa and the subsequent de- pertain to immature individuals of Nesodon. scription of additional forms from Bolivia (Vil- larroel, 1974a,b), Flynn et al. (in press) recog- nized seven valid mesotheriine Zittel, 1892 potentially "gen- era" and described a new taxon from the middle Mesotheriidae Alston, 1876 Mesotheriinae Simpson, 1945 Miocene Huaylas Formation of northern Chile. A character that has traditionally been impor- is the Mesotheriids are traditionally divided into two tant in mesotheriine imbrication: subgroups: the Trachytheriinae (comprising De- degree to which the anteroextemal comer of an seadan and earlier forms, most assigned to Trach- upper cheek tooth overlaps the posteroexternal

CROFT ET AL.: CHUCAL UNGULATES 11 Table 2. Measurements for specimens of Altitypotherium paucidens. Fig. 7. Holotype of Altitypotherium paucidens, SGOPV 4038, a partial rostrum with left II. left P4-M3 and right

P4-M 1 . A. Left lateral (above, pictured as right) and occlusal (below) views. B. Line drawings of occlusal morphology = (toothrows not in natural position). Scale bars I cm.

CROFT ET AL.: CHUCAL UNGULATES 13 Fig. 8. Lower dentitions referred to Altitypotherium paucidens. A. SGOPV 4024, partial left mandible with fragmentary il-2 and complete p4-m3 in occlusal view. B. SGOPV 4101, partial right mandible and symphysis with = full dentition plus left il-2 in lateral (above) and occlusal (below) views. Scale bars 1 cm.

northern Chile, late early Miocene age, Santacru- and dens, Latin for "tooth," in reference to the cian SALMA. lack of P3, a characteristic feature of this species. Etymology—Aid, in reference to the Altipla- Diagnosis—A mesotheriine that differs from no, the high plateau of northern Chile and neigh- all other mesotheriines in the absence of P3. boring Bolivia and Peru, where the referred spec- Differs from Microtypotherium in presence of imens were collected, and typotherium, in refer- deep, narrow postpalatal notch that extends to the ence to the familiar root commonly used in me- level of M3 (does not reach M3 in Microtypo- sotheriine taxon names; pauci, Latin for "few," therium); presence of subtriangular II that is

14 FIELDIANA: GEOLOGY pointed distally, with two lingual sulci (a single poorly defined lingual plication in Caragua New mesial sulcus is present in Microtypotherium); Taxon); presence of enlarged M3 middle lobe (not presence of enlarged M3 middle lobe (not sur- surrounded by other two lobes); relatively smaller rounded by other two lobes); presence of one la- il (il/i2 <1.50 in Altitypotherium, between 1.50 bial sulcus on premolar ectolophs (two sulci pre- and 2.00 in Caragua New Taxon); presence of sent in Microtypothehum); and absence of short- rounded il with little or no lingual sulcus (sub- ened m2 (length/width between 1.60 and 2.30 in triangular with smooth sulcus in Caragua New Altitypotherium, <1.6 in Microtypothehum). Taxon); presence of one labial sulcus on premolar Differs from Eutypotherium in the root of zy- ectolophs (two sulci present in Caragua New Tax- gomatic arch being directed perpendicular to Ml on); presence of Ml middle lobe with lingually (posteriorly directed from the level of M 1 or M2 convergent anterior and posterior sides (subpar- in Eutypotherium); presence of deep, narrow post- allel in Caragua New Taxon); absence of exten- palatal notch that extends to the level of M3 (wide sive lingual exposure of Ml middle lobe; and and shallow in Eutypotherium); presence of sub- smaller size (based on dental measurements, ap- triangular II that is pointed distally, with two lin- proximately 20% smaller than Caragua New Tax- gual sulci (wide and rounded with lingual sulcus on). in Eutypotherium); presence of rounded il with Differs from Typotheriopsis in presence of pos- little or no lingual sulcus (subtriangular with terolaterally divergent upper and lower diastemata smooth sulcus in Eutypotherium); presence of one (parallel in Typotheriopsis); absence of well-de- labial sulcus on premolar ectolophs (two sulci veloped suborbital fossa; presence of deep, nar- present in Eutypotherium); absence of extensive row postpalatal notch that extends to the level of lingual exposure of Ml middle lobe; and smaller M3 (does not reach M3 in Typotheriopsis); pres- size (based on dental measurements, approximate- ence of subtriangular II that is pointed distally, ly 20% smaller than Eutypotherium tehmannnit- with two lingual sulci (wide and rounded with lin- schei). gual sulcus in Typotheriopsis); presence of en- Differs from Plesiotypotherium in posteriorly larged M3 middle lobe (not surrounded by other diverging upper and lower diastemata (parallel in two lobes); relatively smaller il (il/i2 <1.50 in Plesiotypotherium); absence of well-developed Altitypotherium, between 1.50 and 3.00 in 7\'- suborbital fossa; presence of deep, narrow post- potheriopsis); presence of rounded il with little palatal notch that extends to the level of M3 (wide or no lingual sulcus (subtriangular with smooth and shallow in Plesiotypotherium); subtriangular sulcus in Typotheriopsis); presence of M 1 middle II that is pointed distally, with two lingual sulci lobe with lingually convergent anterior and pos- (wide and rounded with lingual sulcus in Plesi- terior sides (subparallel in Typotheriopsis); ab- otypotherium); presence of rounded i 1 with little sence of extensive lingual exposure of Ml middle or no lingual sulcus (subtriangular with smooth lobe; and smaller size (based on dental measure- sulcus in Plesiotypotherium); presence of one la- ments, approximately 30% smaller than Typo- bial sulcus on premolar ectolophs (two sulci pres- theriopsis chasicoensis). ent in Plesiotypotherium); presence of Ml middle Differs from Pseudotypotherium in presence of lobe with lingually convergent anterior and pos- posterolaterally divergent upper and lower diaste- terior sides (subparallel in Plesiotypotherium); ab- mata (parallel in Pseudotypotherium); absence of sence of extensive lingual exposure of M 1 middle well-developed suborbital fossa; presence of deep, lobe; and smaller size (based on dental measure- narrow postpalatal notch that extends to the level ments, approximately 30% smaller than Plesioty- of M3 (does not reach M3 in Pseudotypotherium); potherium achirense). lesser degree of molar imbrication (< 1 .25 in Al- Differs from Caragua New Taxon (Flynn et al., titypotherium, >1.50 in Pseudotypotherium); in press) in presence of posteriorly divergent up- presence of short, subtriangular P4 without central per and lower diastemata (parallel in Caragua fossette (P4 is bilobed in Pseudotypotherium); rel- New Taxon); lesser degree of molar imbrication atively smaller il (il/i2 <1.50 in Altitypotherium, (<1.25 m Altitypotherium, between 1.25 and 1.50 between 2.00 and 3.00 in Pseudotypotherium); in Caragua New Taxon); presence of subtriangular presence of rounded il with little or no lingual II that is pointed distally, with two lingual sulci sulcus (trapezoidal with well-demarcated lingual (wide and rounded with lingual sulcus in Caragua sulcus in Pseudotypotherium); presence of one la- New Taxon); presence of short, subtriangular P4 bial sulcus on premolar ectolophs (two sulci pre- without central fossette (P4 bilobed with short and sent in Pseudotypotherium); absence of elongate

CROFT ET AL.: CHUCAL UNGULATES 15 > P4 (length/width < 1 .50 in Altitypotherium, 1 .50 measurements, A. paucidens is approximately in Pseudotypotherium); absence of elongate Ml 10% larger than A. chucalensis). (length/width <1.75 m Altitypotherium, ^1.75 in Description—The holotype of A. paucidens Pseudotypotherium); presence of Ml middle lobe consists of a moderately well-preserved rostrum with lingually convergent anterior and posterior (Fig. 7). The nasals have been crushed, and much sides (subparallel in Pseudotypotherium); absence of the premaxilla is missing, but the left side pre- of extensive lingual exposure of Ml middle lobe; serves the zygomatic arch, palate, and all the up- absence of elongate m2 (length/width between per teeth. 1.60 and 2.30 in Altitypotherium, >2.30 in Pseu- The inferior surface of the zygomatic arch is dotypotherium); and smaller size (based on dental slightly damaged but preserves a well-developed measurements, approximately is 25% smaller than surface for the origin of the masseter. A shallow Pseudotypotherium exiguum). suborbital fossa is present on the dorsal surface Differs from Mesotherium in posterolaterally of the arch. This fossa is similar in its degree of divergent upper and lower diastemata (parallel to development to that of the holotype of Eutypo- strongly convergent in Mesotherium); presence of therium superans (MACN 11079), though it is poorly defined suborbital fossa (absent in Meso- oriented differently; in A. paucidens, the primary therium); lesser degree of molar imbrication axis of the fossa is anteroposterior, whereas in E. (<1.25 in Altitypotherium, >1.50 in Mesothe- superans it is transverse. In mesotheriines in rium); presence of subtriangular II that is pointed which the suborbital fossa is developed to an even distally, with two lingual sulci (wide and rounded greater degree, it is also oriented transversely with lingual sulcus or wide and compressed la- (e.g., Typotheriopsis silveyrai, MLP 36-XI-10-2). biolingually with two lingual sulci in Mesothe- The suborbital fossa is demarcated posteriorly by rium); presence of short, subtriangular P4 without a thick strut of bone oriented perpendicular to the central fossette (P4 is persistently bilobed in Me- toothrow. A large, elliptical infraorbital foramen sotherium); relatively smaller il (il/i2 <1.50 in is present, its major axis oriented dorsoventrally; Altitypotherium, >3.00 in Mesotherium); presence it measures 10.5 X 5.5 mm. of rounded il with little or no lingual sulcus (trap- Very little of right II is preserved in SGOPV ezoidal with well-demarcated lingual sulcus or el- 4038, but left II is well preserved except for its liptical with smooth sulcus in Mesotherium); pres- occlusal surface; in cross section, the major axis ence of one labial sulcus on premolar ectolophs of the tooth is set at an angle of approximately (two sulci present in Mesotherium); absence of 45° to the sagittal plane. Much of the premaxilla elongate P4 (length/width <1.50 in Altitypothe- is missing from the left side of the specimen, re- > rium, 1 .50 in Mesotherium); absence of elongate vealing nearly the entire dorsoventral extent of 1 1 . Ml (length/width <1.75 in Altitypotherium, It is a strongly curved tooth (approximating a 90° >1.75 in Mesotherium); presence of Ml middle arc) and lacks any evidence of a root. The entire lobe with lingually convergent anterior and pos- surface of the tooth is covered by enamel, with terior sides (lingually divergent in Mesotherium); the exception of the damaged occlusal surface. An absence of extensive lingual exposure of Ml mid- isolated 1 1 referred to this species (SGOPV 4024) dle lobe; absence of elongate m2 (length/width better demonstrates the occlusal morphology of between 1 .60 and 2.30 in Altitypotherium, >2.30 the upper incisor; it is roughly subtriangular in in Mesotherium); and smaller size (based on den- cross section and pointed distally, with two tal measurements, approximately 20% smaller smooth sulci present on the lingual face. The oc- than Mesotherium maendrum and half the size of clusal surface is worn such that it is strongly con- Mesotherium pachygnathum). cave. Differs from A. chucalensis (described below) A large incisive foramen is present on the an- in absence of P3; presence of elongate Ml terior surface of the palate just posterior to the (length/width >1.3 in A. paucidens, <1.3 in A. pair of incisors. It measures approximately 9.5 X chucalensis); middle lobe of M3 unreduced, not 7.3 mm and is divided longitudinally by a septum surrounded by anterior and posterior lobes; pres- that is recessed relative to the surface of the pal- ence of narrower lower molars (widths <6.7 mm ate. Large (nearly 25 mm long), posteriorly di- in A. paucidens, >:7.3 mm in A. chucalensis); vergent diastemata separate the pair of incisors

1 flat presence of elongate m3 ( 5-20% longer than m2 from the cheek teeth. The palate is relatively in A. paucidens, similar in length to m2 in A. chu- anterior to the cheek teeth but is highly arched calensis); and slightly larger size (based on dental between them.

16 FIELDIANA: GEOLOGY The lone upper premolar (P4) is subtriangular The second upper molar of A. paucidens differs in outline and has a single sulcus located near the from Ml in having a slightly more rectangular anterior edge of its labial surface. The occlusal middle lobe, although the anterior and posterior surface is featureless, and there is no evidence of faces still converge lingually. The last upper mo- a lingual groove or plication, as occurs in many lar has a smaller anterior lobe, similar to that seen mesotheriines. The shallower implantation angle in Ml, and a small, anterolingually directed pos- of this tooth is reflected in the anteroposteriorly terior lobe. The middle lobe therefore has sub- elongate wear on the occlusal surface. The three equal anterior and posterior faces. The enamel upper molars are of typical mesotheriine form. surface of this lobe does not reach the lingual face Each is rectangular with a pronounced parastyle of the tooth but rather has a thick covering of and three lobes extending lingually from the ec- cementum that fills the portion of the lingual face toloph (formed by two labially directed invagi- between the anterior and posterior lobes. The mid- nations of enamel from the lingual margins of the dle lobe of M3 is proportionately larger than that teeth). The first upper molar in A. paucidens is of A. chucalensis, and thus (unlike in A. chuca- proportionately more elongate than the corre- lensis) this lobe remains unenclosed by the ante- sponding tooth in A. chucalensis, and the three rior and posterior lobes. A small but distinct in- lobes increase in size posteriorly. The anterior vagination of enamel occurs on the lingual face lobe is directed posterolingually, while the pos- of the posterior lobe; greater wear would presum- terior lobe is roughly perpendicular to the ecto- ably obliterate this structure. The posterior face of loph; the middle lobe therefore approximates a M3 bears a slight indentation near its center, iso- right triangle, with the hypotenuse forming its an- lating a posteriorly directed extension of the ec- terior face. The presence of a strongly triangular toloph known as the "fourth lobe" (Francis, Ml middle lobe is unique among described me- 1965). sotheriines, with the exception of Microtypothe- The degree of cheek tooth imbrication in A. rium choquecotense (Villarroel, 1974b) and the paucidens is 1.16. The enamel is thinnest along other taxa from Chucal. However, one of the spec- the anterior and posterior faces of the cheek teeth, imens from Nazareno, Bolivia (GB Naz-014) fig- causing the occlusal surfaces of these teeth to join ured by Oiso (1991, p. 658, plate 2) and assigned with wear. Almost no enamel is visible on the ''' to Plesiotypotherium sp." also appears to pos- posterior face of M3. The cheek teeth are covered sess this feature. Other mesotheriine specimens by moderate amounts of cementum. This cemen- (e.g. GB Naz-001, GB Naz-013, GB Naz-047) tum fills the lingual invaginations of enamel on from that site figured by Oiso (1991) lack a tri- the molars (that demarcate the three lobes) and is angular Ml middle lobe. It is unknown whether especially thick along the lingual face of M3 this represents individual or interspecific variation (much thicker than the enamel of the middle among the specimens from Nazareno. Based on a lobe). The hypselodont nature of the cheek teeth phylogenetic analysis of mesotheriines (below), is visible in left M3 and right M 1 of the holotype. the presence of a triangular Ml middle lobe is The dimensions of M 1 of the holotype of A. judged ancestral for the group. paucidens are similar to those of Microtypothe- The posterior lobe of Ml bears a slight lingual rium choquecotense (see below), the smallest me- plication in the posterior end of its lingual face. sotheriine known until now (Villarroel, 1974b). This plication is increasingly prominent on M2 The second and third upper molars are signifi- and M3. A similar condition is present in the ho- cantly shorter \x\ A. paucidens than in Microty- lotype of Plesiotypotherium achirense (although potherium, resulting in a shorter molar row over- not noted in the original description; Villarroel all. In size, A. paucidens closely matches most "" 1974a, p. 267, fig. 9), in the holotype of Pseu- specimens assigned to Plesiotypotherium sp." dotypotherium carhuense (MLP 37-III-7-1), and by Oiso (1991). also in a juvenile specimen of Trachytherus spe- Several partial lower dentitions are referred to gazzinianus (MACN 3264) figured by Patterson A. paucidens based on their relatively longer and

(1934b, fig. 24). The increased prominence of this narrower cheek teeth (as compared to the holo- feature in more posterior cheek teeth, coupled type of y4. chucalensis, SGOPV 4100, an associ- with its absence in a more mature specimen of ated skull and mandibles). The best preserved of Trachytherus (e.g., FMNH PI 3281), suggests that these is SGOPV 4101, a partial mandible and this feature may be widespread among meso- symphysis with complete right dentition plus left theriids but is lost with wear. il-2 (Fig. 8B). The symphysis, as in other me-

CROFT ET AL.: CHUCAL UNGULATES 17 sotheriines, is solid and completely fused; there is of the tooth but rather slopes to a low point at the no evidence of a suture. Its labial surface is posterior end of the labial side. The first and sec- smoothly rounded, joining the external surfaces of ond lower molars are roughly the shape of a figure the mandibles. The lingual (dorsal) surface is eight; the trigonid and the talonid are both round- strongly excavated, forming a long, concave spout ed and are separated by a deep labial sulcus ori- flanked by the second lower incisors. This spout ented slightly posterolingually. The second molar appears to be proportionately narrower and deeper is slightly larger than the first. In both molars a than that of E. lehmannnitschei. The right dentary very slight sulcus is present on the posterior end is approximately 27 mm high at the level of p4 of the lingual face. The trigonid of m3 is similar and 35 mm high at the posterior end of m3. A in size and shape to that of m2, but the talonid is wide, shallow, slightly roughened groove runs elongate with a pointed posterior end, typical of along the lingual surface of the right dentary. At mesotheriines. A moderately pronounced sulcus is the posterior margin of m3, this groove is posi- present on the lingual face of the talonid at ap- tioned about midway between the superior and in- proximately the midpoint, and a little-pronounced ferior surfaces of the ramus; its anterior end lies sulcus is present about halfway between the mid- near the base of the horizontal ramus at the level point and the posterior edge of the tooth. The pos- of p4. No mandibular foramen is observed, likely terior end of m3 is visible in its entirety; the tooth because of incomplete preservation of the speci- is 31 mm high, and its "root" is completely open. men. A mental foramen occurs on the external Occlusal relief is highest on the molars where the surface of the right dentary, just anterior to p4, at deep labial sulcus divides the trigonid from the a level slightly higher than the dorsoventral mid- talonid (being formed of more resistant enamel) point of the horizontal ramus. It lies almost di- and the dentine surface of the talonid is the low- rectly lateral to the base of 12. est. All cheek teeth are covered by a moderate The first lower incisor has a gently convex la- amount of cementum. bial face and more strongly convex lingual face. Comments—The most unusual characteristic of Enamel covers the external surface of the tooth A. paucidens is its single upper premolar (all other but is completely absent from the occlusal sur- mesotheriines having two). Although large cracks face. The occlusal surface is gently concave, with are present in the rostrum immediately anterior of the points of highest relief being the two labial this tooth in the holotype, evidence for the lack corners of the tooth. In mesial view, the tooth is of an alveolus for an additional premolar is per- gently curved and procumbent, nearly aligned suasive; the specimen was recovered as three sep- with the anterior surface of the mandibular sym- arate pieces (subsequently glued together), per- physis. The second lower incisor is significantly mitting a thorough examination of the region im- smaller than the first, though not as proportion- mediately anterior of the preserved cheek teeth. ately reduced as in later-diverging mesotheriines. The absence of a second premolar is clearly not It is peglike in overall form. While the long axis a preservational artifact. The single premolar in of il runs nearly perpendicular to the sagittal A. paucidens is assumed to be P4, but the possi- plane, that of i2 is parasagittal. The most pro- bility of another homology cannot be excluded. In nounced wear occurs on a surface approximately lateral view, the premolar is not implanted parallel perpendicular to the tooth's vertical axis. Addi- to the anterior face of Ml, as P4 is in other me- tional wear occurs on the posterior face of the sotheriines, but rather approaches it at an angle of tooth. The left 12 is visible in its entirety; it is ~15°; a small portion of the maxilla (lacking an approximately 25 mm long and has an open base. alveolus) is present between the bases of these A small amount of cementum covers portions of teeth. This space suggests that the single large all the incisors. The diastema separating 12 from premolar may represent an enlarged P3 that pres- p4 on the right side is incompletely preserved but ently fills all or most of the space formerly oc- was likely approximately 15 mm long. cupied by both P3 and P4 (no concomitant reduc- The lower cheek teeth resemble those of other tion in the number of lower cheek teeth seems to mesotheriines. The sole lower premolar has a have occurred). While the loss of a cheek tooth small trigonid and a larger talonid. The dentine of in this position would be an unusual occurrence the occlusal surface is fully confluent between the among mammals, mesotheriines are already pe- trigonid and talonid; no fossettes or sulci are pre- culiar in having three deciduous premolars that sent. The occlusal surface of the talonid is not are replaced by only two permanent premolars. worn completely perpendicular to the vertical axis These permanent premolars are conventionally re-

18 FIELDIANA: GEOLOGY Table 3. Development of suborbital fossa and size of infraorbital foramen in selected mesotheriines. Relative = size cross-sectional area of infraorbital foramen (estimated as an ellipse )/M 1 occlusal area (estimated as a rectangle). Holotype specimens are denoted with an asterisk (*) next to the specimen number Table 4. Measurements for specimens of Altitypotherium chucalensis.

II P3 P4 Ml M2 M3

Upper dentition W W W W W W SGOPV4100(R) Fig. 9. Upper dentition of holotype oi Altitypotherium chucalensis, SGOPV 4100, a partial skull with portions of all premolars and complete molars. A. Line drawing of occlusal morphology of right P3-M3. B. Skull in right = lateral (above) and occlusal (below) views. Scale bars 1 cm.

innominate including acetabulum, proximal and SGOPV 5110, left il; SGOPV 5178, right i2; distal portions of left femur, distal half of left tib- SGOPV 5084. partial right mandible with base of ia, partial ?left fibula, left ulna and radius (lacking p4, ml -2; SGOPV 4103, partial right mandible distal portion of each), proximal portion of right with partial p4, ml-2; SGOPV 5048, partial right radius, atlas and axis (articulated) plus various ml; SGOPV 5170, left ml; SGOPV 5089, right other vertebrae; SGOPV 4110, partial left man- m2; SGOPV 5090, right m2; SGOPV 5085, par- dible and symphysis with il-2 on both sides, left tial left mandible with base of m2; SGOPV 5126, p4-ml, partial left m2, and partial left Ml; partial right m2; SGOPV 5128, partial right m2; SGOPV 5179, right il; SGOPV 5109 right il; SGOPV 5101, left m2; SGOPV 5052, left m2;

CROFT ET AL.: CHUCAL UNGULATES 21 Fig. 10. Portions of lower dentition of Altitypotherium chucalensis, SGOPV 4100. A. Posterior left mandible and ascending ramus in lateral view (pictured as right). B. Partial right mandible with p4-m3 in occlusal view (pictured = as left). Scale bars 1 cm.

SGOPV 5127, partial left m2; SGOPV 4032, right imens were collected and typotherium, in refer- m3; SGOPV 5083, partial right mandible with ence to the familiar root commonly used in me- base of m3; SGOPV 51 19, left m3; SGOPV 4107, sotheriine taxon names; chucalensis, in reference partial right m3. to Chucal, the area in which the holotype and all Questionably Referred Specimens—SGOPV referred specimens were discovered. 5138, partial right p4; SGOPV 5173, partial right Diagnosis—A mesotheriine differing from all p4. other described mesotheriines in having an un- Type Locality—Loc. C-ALT-01-19; Chucal elongate Ml (length/width <1.30 in A. chucalen- Formation (Member W4 of Charrier et al., 2002); sis, >1.30 in all other mesotheriines). west flank of Chucal Anticline. Differs from Microtypotherium in presence of Age and Distribution—Chucal Formation, deep, narrow postpalatal notch that extends to the northern Chile, late early Miocene age, Santacru- level of M3 (does not reach M3 in Microtypo- cian SALMA. therium); presence of subtriangular II that is Etymology—Alti, in reference to the Altipla- pointed distally, with two lingual sulci (a single no, the high plateau of northern Chile and neigh- mesial sulcus is present in Microtypotherium); boring Bolivia and Peru, where the referred spec- presence of one labial sulcus on premolar ecto-

22 FIELDIANA: GEOLOGY lophs (two sulci present in Microtypotherium); New Taxon); presence of rounded il with little or and absence of shortened m2 (length/width be- no lingual sulcus (subtriangular with smooth sul- tween 1.60 and 2.30 in Altitypotherium, <1.6 in cus in Caragua New Taxon); presence of one la- Microtypotherium). bial sulcus on premolar ectolophs (two sulci pre- Differs from Eutypotherium in the root of zy- sent in Caragua New Taxon); presence of Ml gomatic arch being directed perpendicular to Ml middle lobe with lingually convergent anterior (posteriorly directed from the level of M 1 or M2 and posterior sides (subparallel in Caragua New in Eutypotherium); presence of deep, narrow post- Taxon); absence of extensive lingual exposure of palatal notch that extends to the level of M3 (wide M 1 middle lobe; and smaller size (based on dental and shallow in Eutypotherium); presence of sub- measurements, approximately 20% smaller than triangular 1 1 that is pointed distally, with two lin- Caragua New Taxon). gual sulci (wide and rounded with lingual sulcus Differs from Typotheriopsis in posterolateral ly in Eutypotherium); presence of rounded il with divergent upper and lower diastemata (parallel in little or no lingual sulcus (subtriangular with Typotheriopsis); absence of well-developed sub- smooth sulcus in Eutypotherium); presence of one orbital fossa; presence of deep, narrow postpalatal labial sulcus on premolar ectolophs (two sulci notch that extends to the level of M3 (does not present in Eutypotherium); absence of extensive reach M3 in Typotheriopsis); presence of sub- lingual exposure of Ml middle lobe; and smaller triangular II that is pointed distally, with two lin- size (based on dental measurements, approximate- gual sulci (wide and rounded with lingual sulcus ly 20% smaller than Eutypotherium lehmannnit- in Typotheriopsis); relatively smaller il (il/i2 schei). <1.50 in Altitypotherium, between 1.50 and 3.00 Differs from Plesiotypotherium in posteriorly in Typotheriopsis); presence of rounded il with diverging upper and lower diastemata (parallel in little or no lingual sulcus (subtriangular with Plesiotypotherium); absence of well-developed smooth sulcus in Typotheriopsis); presence of M 1 suborbital fossa; presence of deep, narrow post- middle lobe with lingually convergent anterior palatal notch that extends to the level of M3 (wide and posterior sides (subparallel in Typotheriop- and shallow in Plesiotypotherium); subtriangular sis); absence of extensive lingual exposure of Ml II that is pointed distally, with two lingual sulci middle lobe; and smaller size (based on dental (wide and rounded with lingual sulcus in Plesi- measurements, approximately 30% smaller than otypotherium); absence of enlarged middle lobe of Typotheriopsis chasicoensis). M3 (surrounded by other lobes in A. chucalensis); Differs from Pseudotypotherium in presence of presence of rounded il with little or no lingual posterolaterally divergent upper and lower diaste- sulcus (subtriangular with smooth sulcus in Ple- mata (parallel in Pseudotypotherium); absence of siotypotherium); presence of one labial sulcus on well-developed suborbital fossa; presence of deep, premolar ectolophs (two sulci present in Plesioty- narrow postpalatal notch that extends to the level potherium); presence of M 1 middle lobe with lin- of M3 (does not reach M3 in Pseudotypotherium); gually convergent anterior and posterior sides lesser degree of molar imbrication (<1.25 in Al- (subparallel in Plesiotypotherium); absence of ex- titypotherium, >1.50 in Pseudotypotherium); tensive lingual exposure of Ml middle lobe; and presence of short, subtriangular P4 without central smaller size (based on dental measurements, 30% fossette (P4 is bilobed in Pseudotypotherium); rel- smaller than Plesiotypotherium achirense). atively smaller il (il/i2 <1.50 in Altitypotherium, Differs from Caragua New Taxon (Flynn et al., between 2.00 and 3.00 in Pseudotypotherium); in press) in presence of posteriorly divergent up- presence of rounded il with little or no lingual per and lower diastemata (parallel in Caragua sulcus (trapezoidal with well demarcated lingual New Taxon); lesser degree of molar imbrication sulcus in Pseudotypotherium); presence of one la- (<1.25 m Altitypotherium, between 1.25 and 1.50 bial sulcus on premolar ectolophs (two sulci pre- in Caragua New Taxon); presence of subtriangular sent in Pseudotypotherium); absence of elongate II that is pointed distally, with two lingual sulci P4 (length/width <1.50 \n Altitypotherium, >1.50 (wide and rounded with lingual sulcus in Caragua in Pseudotypotherium); absence of elongate Ml New Taxon); presence of short, subtriangular P4 (length/width <1.75 in Altitypotherium, >1.75 in without central fossette (P4 bilobed with short and Pseudotypotherium); presence of M 1 middle lobe poorly defined lingual plication in Caragua New with lingually convergent anterior and posterior Taxon); relatively smaller il (il/i2 <1.50 in Alti- sides (subparallel in Pseudotypotherium); absence typotherium, between 1.50 and 2.00 in Caragua of extensive lingual exposure of Ml middle lobe;

CROFT ET AL.: CHUCAL UNGULATES 23 absence of elongate m2 (length/width between much of the palatal and basicranial anatomy of is is 1 .60 and 2.30 in Altitypotherium, >2.30 in Pseu- this taxon preserved. The palate arched, but dotypotherium); and smaller size (based on dental not to the degree exhibited by A. paucidens. The measurements, approximately 25% smaller than postpalatal notches are narrow and deep, extend- Pseudotypotherium exiguum). ing to the posterior edge of M3. The notch is fully Differs from Mesotherium in posterolaterally prepared on the right side, demonstrating a round- divergent upper and lower diastemata (parallel to ed morphology more resembling a foramen than strongly convergent in Mesotherium); presence of a notch. The general structure of the ear region of poorly defined suborbital fossa (absent in Meso- mesotheriines has been described elsewhere (Pat- therium); lesser degree of molar imbrication terson, 1934a, 1936) and will not be repeated (<1.25 in Altitypotherium, >1.50 in Mesotheri- here, although this specimen should prove useful um); presence of subtriangular II that is pointed for future comparative studies within the Meso- distally, with two lingual sulci (wide and rounded theriidae and other typotheres. with lingual sulcus or wide and compressed la- The most obvious difference in the dentition biolingually with two lingual sulci in Mesotheri- between this taxon and A. paucidens is the pres- um); presence of short, subtriangular P4 without ence of two premolars in A. chucalensis (inter- central fossette (P4 is persistently bilobed in Me- preted as P3 and P4, but see discussion above). sotherium); absence of enlarged middle lobe of This is a primitive character state that A. chuca- M3 (surrounded by other lobes in A. chucalensis); lensis shares with all previously described me- relatively smaller il (il/i2 <1.50 in Altitypothe- sotheriines. The possibility that these teeth rep- rium, >3.00 in Mesotherium); presence of round- resent deciduous premolars instead of permanent ed il with little or no lingual sulcus (trapezoidal ones can be ruled out; the labial faces of the two with well-demarcated lingual sulcus or elliptical teeth on the holotype are exposed to their bases with smooth sulcus in Mesotherium); presence of (approximately 25 mm in P4), confirming their one labial sulcus on premolar ectolophs (two sulci hypselodont condition and the lack of overlying present in Mesotherium); absence of elongate P4 replacement teeth above. They also do not dem- (length/width <1.50 in Altitypotherium, >1.50 in onstrate the occlusal morphology typical of me- Mesotherium); absence of elongate Ml (length/ sotheriine deciduous premolars teeth (see Francis, width <1.75 in Altitypotherium, >1.75 in Meso- 1965), instead exhibiting the typically adult mor- therium); presence of Ml middle lobe with lin- phology of featureless occlusal surfaces that are gual ly convergent anterior and posterior sides subtriangular in shape. (lingually divergent in Mesotherium); absence of In the holotype and one of the referred speci- extensive lingual exposure of M 1 middle lobe; ab- mens (SGOPV 4033, a fragmentary palate), P3 sence of elongate m2 (length/width between 1 .60 and P4 are closely appressed to each other and to and 2.30 in Altitypotherium, >2.30 in Mesotheri- Ml. In another specimen (SGOPV 5056, a partial um); and smaller size (based on dental measure- right maxilla with P3-4), there is a small (~2 ments, approximately 20% smaller than Mesothe- mm) diastema between them, although both are rium maendrum and about half the size of Meso- implanted at approximately the same angle. A sin- therium pachygnathum). gle sulcus is present near the posterior end of the Differs from A. paucidens in presence of P3, labial face of P3, whereas P4 exhibits a sulcus absence of elongate Ml (length/width <1.3 in A. situated near the anterior end of the labial face as chucalensis, > 1 .3 in A. paucidens), presence of in A. paucidens (and Typotheriopsis). The P3 is M3 with middle lobe surrounded by other two smaller than P4, and neither exhibits any sign of lobes, presence of wider lower molars (widths a fossette or lingual plication. In SGOPV 5056, ^7.3 mm in A. chucalensis; ^6.7 mm in A. pau- the entire posterior face of P4 is visible, demon- cidens), absence of elongate m3 (similar in length strating the near total lack of enamel on this sur- to m2 in A. chucalensis, 15-20% longer than m2 face. On the anterior face of this tooth, enamel is in A. paucidens), and slightly smaller size (based absent only from a small strip along the labial on dental measurements, A. chucalensis is ap- edge. The same is true for P3. proximately 10% smaller than A. paucidens). A. chucalensis is further distinguished from A. Description—A. chucalensis is the only me- paucidens by the absence of an elongate Ml, an sotheriine species from Chucal for which the ho- ancestral character state shared only with Trach- lotype includes associated upper and lower den- ytherus among mesotheriids. Unlike Trachyther- titions (SGOPV 4100, Figs. 9, 10). Additionally, us, however, the middle lobe of Ml in A. chuca-

24 FIELDIANA: GEOLOGY lensis appears to persist throughout the tooth's mately 7X4 mm. The posterior part of the in- wear and does not become isolated as a fossette ferior edge of the angle is inflected medially. (based on examinations of Hngual faces and bases Slightly anterior to this, a pronounced shelf is pre- of isolated teeth). Like Microtypotherium and the sent on the lateral surface. The mandible's lateral other Chucal mesotheriines, the anterior and pos- surface is fairly smooth, but the medial surface of terior sides of the middle lobe of M 1 in A. chu- the angle and ascending ramus exhibits a series calensis are lingually convergent, making the lobe of well-pronounced ridges, suggesting that a well- triangular. This middle lobe is relatively smaller developed medial pterygoid muscle inserted in than in any of these other taxa, completely sur- this area. rounded by the subequal anterior and posterior The lower cheek teeth are similar to those of

1 for their lobes. The second upper molar resembles M , ex- A. paucidens, except relatively smaller cept that the parastyle is more pronounced and the size. Additionally, the talonid of m3 is propor- middle lobe slightly larger. Imbrication of the up- tionately shorter and narrower per molars is slight, as in all the other mesother- A partial skeleton and other postcranial speci- iines from Chucal and a few additional taxa (see mens are referred to A. chucalensis (SGOPV Table 7). The third upper molar most closely re- 4042). These will be described in detail and com- sembles that of Microtypotherium, with a small pared to other mesotheriid postcrania elsewhere. middle lobe surrounded by the other two. No lin- Comments—Although roughly similar in size gual sulcus is evident on the posterior lobe. A to A. paucidens, A. chucalensis is clearly distin- fourth lobe is present in M3 but is slightly shorter guished from the former species by the suite of and broader than that of A. paucidens. Enamel is character states presented in the diagnosis. absent from the posterior face. All upper cheek teeth are covered by a moderate amount of ce- mentum, which is thickest lingually as in A. pau- Eotypotherium chico, species novum cidens. The degree of cheek tooth imbrication in (Figures 11-13, Table 5) A. chucalensis is 1.22.

The anterior lower dentition of A. chucalensis Holotype—SGOPV 5157, partial right maxilla is best exhibited by SGOPV 4110, a partial left and zygomatic arch with P3-M3 (Fig. 11). mandible with left and right il-2, left p4-ml, par- Hypodigm—SGOPV 5108, partial right II; tial left m2, and partial left Ml. These teeth are SGOPV 5074, partial left maxilla with P3-M1 very similar to the corresponding teeth of A. pau- and partial M2 (Fig. 12A); SGOPV 5156, partial cidens. The symphyseal region is unknown. palate with right P3-M3 (M2 damaged labially; The cheek teeth and the posterior portion of the Fig. 12B); SGOPV 5124, little-worn left maxil- mandible are preserved in the holotype (Fig. 10). lary fragment with Ml and partial P4, M2; The horizontal ramus is less robust than that of SGOPV 5132, left Ml/2; SGOPV 5175 right Ml/ A. paucidens; it measures approximately 18.5 mm 2; SGOPV 5095, partial left Ml/2; SGOPV 5134, deep between p4 and ml and 30 mm deep at the partial left Ml/2; SGOPV 5133, left M3; SGOPV posterior face of m3. On the left side, it appears 4071, symphysis with portions of left and right that a mental foramen is present but incompletely il-2; SGOPV 5050, right ml; SGOPV 5129, right preserved; its position is similar to that of A. pau- mandibular fragment with partial ml; SGOPV cidens. The anterior edge of the ascending ramus 5159, partial right ml/2; SGOPV 5160, partial creates an angle of slightly less than 90° with the right ml/2; SGOPV 5158, partial left mandible horizontal ramus and ends in a broad coronoid with m2-3 (Fig. 13); SGOPV 5086, partial right process. At its vertical midpoint, the ascending mandible with bases of m2-3; SGOPV 5093, right ramus measures approximately 35 mm from its m3. anterior to its posterior edge. The coronoid pro- Type Locality—Loc. C-ALT-01-12; Chucal cess rises approximately 13.5 mm above the level Formation (Member E3 of Charrier et al., 2002); of the articular condyle and is nearly 20 mm long. east flank of Chucal Anticline. The articular condyle is broad, smooth, and —14 Age and Distribution—Chucal Formation, mm wide. The angle of the mandible is large, but northern Chile, late eariy Miocene age, Santacru- the bone comprising much of it is quite thin. A cian SALMA. mandibular foramen is present along the lingual Etymology—Eo, Greek for "dawn," in refer- side of the dentary, where the horizontal ramus ence to the relative antiquity of this species with joins the ascending ramus. It measures approxi- respect to previously known mesotheriines, and

CROFT ET AL.: CHUCAL UNGULATES 25 Table 5. Measurements for specimens of Eotypotherium chico.

II P3 P4 Ml M2 M3 Ml/2

Upper dentition Fig. 11. Holotype of Eotypotherium chico, SGOPV 5157, a partial right maxilla and zygomatic arch with P3-M3. - A. Labial (above) and occlusal (below) views. B. Line drawing of occlusal morphology. Scale bars 1 cm.

sette absent in Eutypotherium, lingual plication ments, approximately 40% smaller than Eutypo- sometimes present); presence of il that is rounded therium lehmannnitschei). in cross section with little or no lingual sulcus Differs from Plesiotypotherium in absence of (subtriangular with smooth sulcus in Eutypothe- well-developed suborbital fossa and large infra- rium); presence of subquadrangular P3 (subtrian- orbital foramen; absence of well-developed zy- gular in Eutypotherium); absence of elongate Ml gomatic plate; presence of subtriangular II that is (length/width <1.30 in Eotypotherium, between pointed distally, with mesial sulcus (wide, round- 1.30 and 1.75 in Eutypotherium); absence of ex- ed, with lingual sulcus in Plesiotypotherium); tensive lingual exposure of Ml middle lobe; and presence of short, subtriangular P4 with central much smaller size (based on dental measure- fossette (fossette absent in Plesiotypotherium, lin-

CROFT ET AL.: CHUCAL UNGULATES 27 Fig. 12. Upper dentitions referred to Eotypotherium chico. A. SGOPV 5074, partial left maxilla (pictured as right) with P3-M1 and partial M2 in occlusal view. B. SGOPV 5156. a partial palate with right P3-M3 in labial (above) = and occlusal (below) views. C. Line drawing of occlusal morphology. Scale bars 1 cm.

28 FIELDIANA: GEOLOGY Fig. 13. Partial left mandible with m2-3 in occlusal view, SGOPV 5158. referred to Eotypotherium chico. Scale bar = 1 cm.

gual plication sometimes present); presence of il (based on dental measurements, approximately that is rounded in cross section with little or no half the size of Typotheriopsis chasicoensis). lingual sulcus (subtriangular with smooth sulcus Differs from Caragua New Taxon in presence in Plesiotypotherium); presence of subquadran- of wide postpalatal notch not reaching the level gular P3 (subtriangular in Plesiotypotherium); ab- of M3 (narrow and reaching the level of M3 in sence of elongate Ml (length/width ^1.30 in Caragua New Taxon); lesser degree of molar im- Eotypotherium, between 1.30 and 1.75 in Plesi- brication (<1.25 in Eotypotherium, between 1.25 otypotherium); presence of Ml middle lobe with and 1.50 in Caragua New Taxon); presence of lingually convergent anterior and posterior sides subtriangular II that is pointed distally, with me- (subparallel in Plesiotypotherium); absence of ex- sial sulcus (wide, rounded, with lingual sulcus in tensive lingual exposure of Ml middle lobe; and Caragua New Taxon); presence of short, subtrian- much smaller size (based on dental measure- gular P4 with central fossette (fossette absent in ments, approximately half the size of Plesioty- Caragua New Taxon, lingual plication present); potherium achirense). relatively smaller il (il/i2 <1.50 in Eotypothe- Differs from Typotheriopsis in absence of well- rium, between 1 .50 and 2.00 in Caragua New Tax- developed suborbital fossa and large infraorbital on); presence of i 1 that is rounded in cross section foramen; absence of well-developed zygomatic with little or no lingual sulcus (subtriangular with plate; presence of wide postpalatal notch not smooth sulcus in Caragua New Taxon); presence reaching the level of M3 (narrow in Typotheriop- of subquadrangular P3 (subtriangular in Caragua sis); presence of subtriangular 11 that is pointed New Taxon); absence of elongate Ml (length/ < distally, with mesial sulcus (wide, rounded, with width 1 .30 in Eotypotherium, between 1 .30 and lingual sulcus in Typotheriopsis); presence of 1.75 in Caragua New Taxon); presence of Ml short, subtriangular P4 with central fossette (fos- middle lobe with lingually convergent anterior sette absent in Typotheriopsis); relatively smaller and posterior sides (subparallel in Caragua New il (il/i2 <1.50 in Eotypotherium, between 1.50 Taxon); absence of extensive lingual exposure of and 3.00 in Typotheriopsis); presence of i 1 that is Ml middle lobe; absence of two lingual sulci on rounded in cross section with little or no lingual m3 talonid; and much smaller size (based on den- sulcus (subtriangular with smooth sulcus in 7\'- tal measurements, approximately 40% smaller potheriopsis); presence of subquadrangular P3 than Caragua New Taxon). (subtriangular in Typotheriopsis); absence of sin- Differs from Pseudotypotherium in absence of gle labial sulcus on premolar ectolophs; absence well-developed suborbital fossa and large infra- of elongate M 1 (length/width ^ 1 .30 in Eotypoth- orbital foramen; absence of well-developed zy- erium, between 1.30 and 1.75 in Typotheriopsis); gomatic plate; lesser degree of molar imbrication presence of Ml middle lobe with lingually con- (<1.25 in Eotypotherium, >1.50 in Pseudotypo- vergent anterior and posterior sides (subparallel in therium); presence of short, subtriangular P4 with Typotheriopsis); absence of extensive lingual ex- central fossette (fossette absent and tooth bilobed posure of Ml middle lobe; and much smaller size in Pseudotypotherium); presence of M3 with mid-

CROFT ET AL.: CHUCAL UNGULATES 29 die lobe surrounded by the other two (not sur- proximately 40% smaller than Mesotherium rounded in Pseudotypotherium); relatively smaller maendrum, 60% smaller than Mesotherium pach- il (il/i2 <1.50 in Eotypotherium, between 2.00 ygnathum). and 3.00 in Pseudotypotherium); presence of il Description—This mesotheriine is much that is rounded in cross section with little or no smaller than the other two known from Chucal; lingual sulcus (trapezoidal with well-demarcated indeed, it represents the smallest mesotheriid lingual sulcus in Pseudotypotherium); presence of known. In addition to its small size, it is distin- subquadrangular P3 (subtriangular in Pseudoty- guished from all other mesotheriines by the reten- potherium); absence of elongate P4 (length/width tion of several primitive character states lost in <1.50 in Eotypotherium, ^1.50 in Pseudotypo- other taxa (see phylogenetic analysis below). therium); absence of elongate Ml (length/width The holotype (SGOPV 5157; Fig. 11) consists ^1.30 in Eotypotherium, ^1.75 in Pseudotypo- of a partial right maxilla and zygomatic arch bear- therium); presence of Ml middle lobe with lin- ing P3-M3. The superior surface of the zygomatic gually convergent anterior and posterior sides arch is well preserved, and the suborbital fossa is (subparallel in Pseudotypotherium); absence of present but poorly developed, much less so than extensive lingual exposure of Ml middle lobe; ab- in Eotypotherium. A second specimen referred to sence of elongate m2 (length/width between 1 .60 Eotypotherium (SGOPV 5074; Fig. 12A) also pre- and 2.30 in Eotypotherium, >2.30 in Pseudoty- serves this region and confirms the lack of a well- potherium); and much smaller size (based on den- developed fossa. The zygomatic plate is also tal measurements, approximately 40% smaller poorly developed, more resembling the condition than Pseudotypotherium exiguum). seen in Trachytherus than other mesotheriines. Differs from Mesotherium in presence of poor- The infraorbital foramen, although small in ab- ly defined suborbital fossa (absent in Mesothe- solute size (4.0 X 3.5 mm), is similar to that of rium); absence of well-developed zygomatic most other mesotheriines when scaled to body plate; presence of wide postpalatal notch not size (Table 3). reaching the level of M3 (narrow in Mesotherium, No upper incisors are preserved in the holotype sometimes extending to the level of M3); lesser (only II would be predicted to be present), but degree of molar imbrication (<1.25 in Eotypo- their morphology can be discerned from an iso- therium, >1.50 in Mesotherium); presence of sub- lated partial II referred to this taxon based on its triangular II that is pointed distally, with mesial small size (SGOPV 5108). Like II of Altitypo- sulcus (wide, rounded, with lingual sulcus or wide therium, that of Eotypotherium is subtriangular and compressed labiolingually with two lingual and pointed distally in cross section. However, un- sulci in Mesotherium); presence of short, subtrian- like Altitypotherium, a single mesial sulcus is pre- gular P4 with central fossette (fossette absent and sent on II instead of two lingual ones. In this tooth bilobed in Mesotherium); presence of M3 respect, the tooth resembles that of Trachytherus with middle lobe surrounded by the other two (not and Microtypotherium. Unlike that of Trachyth- surrounded in Mesotherium); relatively smaller il erus (and like those in all other mesotheriines), II (il/i2 <1.50 in Eotypotherium, >3.00 in Meso- is completely surrounded by enamel, save for its therium); presence of il that is rounded in cross occlusal surface. section with little or no lingual sulcus (trapezoidal As in A. chucalensis, Eotypotherium possesses with well-demarcated lingual sulcus or elliptical two premolars, presumably P3 and P4. These are with smooth sulcus in Mesotherium); presence of both subquadrangular (as opposed to subtriangu- subquadrangular P3 (subtriangular in Mesothe- lar, as in most other mesotheriines), and each pos- rium); absence of elongate P4 (length/width sesses a single labial sulcus. Although the occlu- <1.50 in Eotypotherium, ^1.50 in Mesotherium); sal surfaces of the premolars in the holotype are absence of elongate Ml (length/width <1.30 in featureless, another specimen referred to Eoty- Eotypotherium, ^1.75 in Mesotherium); presence potherium (SGOPV 5074, a partial left maxilla of Ml middle lobe with lingually convergent an- with P3-M1 and partial M2) demonstrates that terior and posterior sides (lingually divergent in these likely vary in occlusal morphology with Mesotherium); absence of extensive lingual ex- wear in this species. In SGOPV 5074, a small posure of Ml middle lobe; absence of elongate enamel lake is present in the center of P3. Pre- m2 (length/width between 1.60 and 2.30 in Eoty- sumably, this is the remnant of a lingual sulcus potherium, >2.30 in Mesotherium); and much that has been isolated with wear and that would smaller size (based on dental measurements, ap- probably have disappeared altogether with addi-

30 FIELDIANA: GEOLOGY tional wear. The presence of such an internal sul- The lower incisors are procumbent and implanted cus (or an enamel lake) in P3 is unknown among at an angle, as in other mesotheriines. Little of the mesotheriines, although it has been reported in occlusal morphology is preserved, save for the an-

DP3 (Francis, 1965). In P4 the sulcus has simi- terior portion of left i 1 . No p4 referable to Eoty- larly been isolated by wear but differs from that potherium is known. The lower molars referred to of P3 in being "Y" shaped; the base of the "Y" this taxon closely resemble those of the other me- is directed lingually and the two arms anterola- sotheriines from Chucal, except for their smaller bially and posterolabially, isolating a very small size. Specimen SGOPV 5158 preserves a small middle lobe adjacent to the ectoloph. The mor- portion of the dentary, which is approximately 28 phology of P3-4 in SGOPV 5156 (a third maxilla mm deep at the posterior face of m3 (Fig. 13). referred to Eotypotherium; Fig. 12B) is similar to The corresponding measure from SGOPV 5086, that exhibited by SGOPV 5074, except that the likely from a young individual, is approximately 20 mm. fossettes are less pronounced, likely because of — greater wear. A lingual P4 sulcus (or plication) is Comments The most distinctive aspect of absent in Typotheriopsis and Microtypotherium Eotypotherium is its small size; it is approximate- two-thirds the size of A. choquecotense, variably present in Eutypotherium ly paucidens and Micro- it the small- (potentially interspecific variation) and Plesioty- typotherium choquecotense, making identified mesotheriine known. Vil- potherium (potentially intraspecific variation), and est, securely larroel described a consistently present in Caragua New Taxon, Pseu- (1978) specimen (GB 223) from near that he to dotypotherium, and Mesotherium (Francis, 1965; Quehua assigned Microty- cf. M. this as- Cerdeilo and Montalvo, 2001; Flynn et al., in potherium choquecotense; despite he noted that it was smaller than M. press). In none of these taxa, however, is the sul- signment, to the holo- cus isolated with wear or shaped like a "Y" The choquecotense (presumably referring and therefore was the smallest mesotheriine presence of isolated fossettes in the premolars in type) known. The dental measurements Eotypotherium most closely resembles the condi- provided by Villarroel indicate that this is tion seen in Trachytherus, suggesting that it is a (1978) specimen similar in size or a bit retained primitive feature (see phylogenetic anal- roughly to, perhaps larger than, the for il and ml ysis below). The fourth upper premolar is im- Eotypotherium; lengths are close to those measured for planted at —10° relative to Ml in the holotype, Eotypotherium, but the widths for these and other teeth are while P3 is at an even greater angle, closer to 25°. great- er. m2 is and m3 The first upper molar in the holotype has a tri- Similarly, slightly longer signif- than that of angular middle lobe, more reminiscent of that in icantly (50%) longer Eotypotherium. It is therefore unlikely that GB 223 represents a A. paucidens than A. chucalensis. A triangular taxon smaller than Eotypotherium. The only pub- lobe is also present in Ml of SGOPV 5156, while lished representing a mesotheriine pos- SGOPV 5074 exhibits a more rectangular middle specimen sibly smaller than Eotypotherium was collected by lobe, more typical of later mesotheriines. The Oiso (1991) in Nazareno, Bolivia, and included morphology of the middle lobe of Ml therefore without comment under '' seems somewhat variable in this taxon. This tooth Plesiotypotherium sp." (Oiso, 1991, table 2, GB Naz-060). If this isolated is also relatively elongate, unlike the condition Nazareno specimen (about half the size of Eoty- seen in A. chucalensis. The remaining molars re- potherium) represents an adult individual (the de- semble those of A. paucidens, save for their much ciduous premolars of mesotheriines resemble smaller size; the degree of imbrication (1.12) is adult permanent molars and have historically similar to that exhibited by other mesotheriines caused confusion; Francis, 1965), it from Chucal. undoubtedly represents a species distinct from the remaining The lower anterior dentition is represented by Nazareno specimens and would represent the SGOPV 4071, a symphysis bearing portions of smallest mesotheriine known. left and right il-2. As in other mesotheriines, the symphysis is completely fused and relatively even in this diminutive the thick; taxon, symphy- Simpson, 1945 sis is 8.5 mm thick at the midline. approximately Hegetotheriidae Ameghino, 1894 The dorsal surface of the is symphysis strongly Hegetotheriinae Ameghino, 1894 concave and spoutlike, as in A. paucidens. The spout is approximately 5 mm wide. Both il and Diagnosis—Hegetotheriids are distinguished i2 are small and rounded; i 1 lacks a lingual sulcus. from other notoungulates by the unique combi-

CROFT ET AL.: CHUCAL UNGULATES 31 B

Fig. 14. Comparison of the degree of fusion of the tibia and fibula among selected Santacrucian typotheres. A. Pachyrukhos moyani (Hegetotheriidae: Pachyrukhinae), AMNH 9242, left tibiofibula, pictured as right. B. Hegeto- therium mirabile (Hegetotheriidae: Hegetotheriinae), PU 15298, right tibiofibula. C. Protypotherium attenuatum (In- = teratheriidae: Interatheriinae), PU 15341, right tibia and fibula. All specimens in anterior view. Scale bars 1 cm. Individual illustrations are modified from Sinclair (1909).

nation of the following derived character states: a bilobed or weakly trilobed m3, whereas in all presence of hypselodont first incisors and cheek known pachyrukhines this tooth is sharply tri- teeth; presence of flat wall on lingual faces of up- lobed. Moreover, the Chucal taxon is larger than per and lower molars; presence of deep, labial sul- any described pachyrukhine, and occlusal outlines cus on ml and m2; presence of cementum; ab- of the upper molars are dissimilar. sence of fossettes in upper and lower cheek teeth; In addition to dental morphology, recovered and proximal and distal fusion of tibia and fibula postcranial elements support referral of this ma- (Cifelli, 1993; Croft, 2000). Among hegetothe- terial to the Hegetotheriinae. In most hegetothe- riids, hegetotheriines share a uniquely configured riids for which postcrania are known, the tibia and distal fusion of the tibia and fibula (see below) fibula are fused at both the proximal and the distal and lack many derived character states typical of ends. In typical pachyrukhines (e.g., Pachyrukhos, pachyrukhines. Derived character states of the Paedotherium, Tremacyllus), the distal fusion is dentition diagnostic of the Pachyrukhinae (and long, comprising approximately 40% the length of lacking in the Hegetotheriinae) include the pres- the two elements. The fibula bows medially at the ence of a sharply defined third lobe on m3 (Cer- proximal point of fusion but then bows laterally deno and Bond, 1998), significant reduction or ab- again at the distal articulation with the ankle (Fig. sence of I3-C/i3-c, and presence of i 1 much larger 14A). In overall structure, the condition resembles than i2. that seen in modern leporids (Sinclair, 1909). In Comments—The hegetotheriid material from hegetotheriines (and, potentially, the pachyru- the Chucal Formation includes isolated and/or po- khine Propachyrucos), the distal fusion is quite tentially associated dental and postcranial speci- short, approximately 15% the length of the tibia mens that fall within the size range typical of he- and fibula. Additionally, the fibula parallels the getotheriids. Currently, there are no size or mor- tibia throughout its length, resulting in a much phological differences suggesting that more than broader articulation distally—approximately equal one hegetotheriid taxon occurs in the Chucal Fau- in breadth to the fused proximal ends of the two na. Assignment to the Pachyrukhinae is precluded bones (Fig. 14B). A similar configuration occurs by the morphology of m3: the Chucal taxon has in interatheriids, but it differs from that of hege-

32 FIELDIANA: GEOLOGY totheriines in lacking complete distal fusion of the clarified the morphology of the Chucal taxon (es- tibia and fibula (Fig. 14C). Two partial hegeto- pecially characters of the upper dentition), sug- theriid tibiofibula specimens have been recovered gesting it more likely pertains to Hegetotherium. from the Chucal Formation, both with the hege- Bond and Lopez (1997) concluded that al- totheriine configuration of a short, broad distal fu- though P. torresi (the only species of Pseudohe- sion. getotherium) is a valid taxon, it should perhaps be included within Hemihegetotherium. In the above diagnosis and discussion below, Hemihegetothe- Hegetotherium Ameghino, 1887 rium subsumes '^Pseudohegetotherium'" torresi. The earlier members of the Hegetotheriinae Type Species—Hegetotherium mirabile. (i.e., Ethegotherium, Prohegetotherium, and He- Included Species—The type, H. convexum, H. getotherium) have upper molars that are roughly minum, H. anceps, and H. novum. rectangular in outline; the lingual and labial faces Diagnosis—A hegetotheriine differing from are approximately straight and parallel (Croft, Ethegotherium in absence of median labial sulcus/ 2000). In contrast, the upper molars of later forms groove between paracone and metacone on upper {Hemihegetotherium) have more convex lingual molars, presence of imbrication in lower molars, faces and posterior faces that are narrower than presence of lower canine root labial to toothrow, the rest of the occlusal surface. Additionally, the and presence of labial groove on m3 talonid. Dif- cementum is thicker in these later hegetotheriines, fers from Prohegetotherium in absence of median and molar paracones and metacones are less pro- labial sulcus between paracone and metacone on nounced than in earlier members of the group upper molars, presence of P2/p2 notably smaller (Bond and Lopez, 1997). Although hegetotheriid than P3/p3, presence of small diastemata between upper molars from the Chucal Formation exhibit i2 and p3, and reduction or absence of lingual relatively thick cementum, this feature is not de- groove on m3 talonid. Differs from Hemihege- veloped to the degree seen in later hegetotheri- totherium (including Pseudohegetotherium; see ines. Moreover, the cheek teeth are roughly rect- below) in absence of thick cementum on lingual angular in outline, with a posterior face that is faces of upper and lower molars, absence of mo- about as wide as the rest of the occlusal surface. lars with convex lingual faces and posterior faces The paracones and metacones are variably pro- that are narrow in comparison to the rest of the nounced on specimens from Chucal, but most ex- occlusal surface, variable presence of small but hibit a small yet well-demarcated parastyle and well-demarcated parastyle and parastyle sulcus on parastyle sulcus. The latter features are absent in Ml-2, and presence of notch on posterior face of later hegetotheriines. The single hegetotheriine M3. M3 known from Chucal also exhibits a prominent Distribution—Sarmiento Formation, Patagon- notch on the distal face. ia, Argentina, early Miocene age, Colhuehuapian A report of Hegetotherium from the middle SALMA (Bordas, 1939); Santa Cruz Formation, Miocene Quebrada Honda Fauna of Bolivia (Mar- Patagonia, Argentina, late early Miocene age, shall & Sempere, 1991) appears to be in error, Santacrucian SALMA (Sinclair, 1909); Chucal based on the taxon's large size and sharply tri- Formation, northern Chile, late early Miocene lobed m3 (pers. observ.); this fauna is thus ex- age, Santacrucian SALMA (present study); un- cluded from the cited distribution of Hegetothe- named formation (possibly equivalent to Rio Ze- ballos Formation), southern Chile, late early Mio- cene age, Santacrucian SALMA (Flynn, Novacek, et al., 2002); CoUon-Cura Formation, Patagonia, Hegetotherium sp. cf. H. mirabile middle Miocene age, Colloncuran SALMA (Bon- (Figures 15, 16, Table 6) desio et al., 1980); Nazareno Formation, southern Bolivia, ?middle Miocene age, ?Colloncuran Referred Specimens—SGOPV 5047, left II; SALMA (Oiso, 1991). SGOPV 5039, left maxillary fragment with bases Comments—The hegetotheriid material collect- of Pl-2; SGOPV 5120, right P3; SGOPV 5040, ed from Chucal in 1998 was tentatively referred right P4 (Fig. 15 A); SGOPV 5058, left ?M1 (Fig. to cf. Pseudohegetotherium torresi (Flynn et al., 15B); SGOPV 5121, left ?M1 (Fig. 15C); SGOPV 1999; Flynn, Croft, et al., 2002). Additional he- 5122, partial left ?M2 (lacking occlusal surface); getotheriine specimens collected in 2001 have SGOPV 5123, left M3 (Fig. 15D); SGOPV 4055,

CROFT ET AL.: CHUCAL UNGULATES 33 partial left mandible with root of c, pl-2 (Fig. 16A); SGOPV 5096, partial right mandible with root of c, pl-2; SGOPV 4104, partial left man- dible with p4-m3 (Fig. 16B); SGOPV 5042, left ml with labial fragment of mandible; SGOPV 5049, partial right mandible with ml-2; SGOPV 5082, partial left mandible with bases of ml-2; SGOPV 5222, partial right mandible with m2; SGOPV 4023, partial right mandible with talonid of ml, complete m2-3 (Fig. 16C); SGOPV 5038, partial right mandible with base of m3; SGOPV 5059, left distal tibiofibula fragment lacking epiphysis; SGOPV 5070, partial right leg and pes including distal tibiofibula (lacking epiphyses), calcaneus (epiphysis reattached), cuboid, ?meso- cuneiform, metatarsal IV, partial metatarsal ?III, proximal phalanx, distal phalanx; SGOPV 5224, left calcaneus. Diagnosis—Differs from Hegetotherium con- vexum in presence of M3 ^ M2 in length, absence of highly convex lingual face of M3, and presence of pronounced posteroexternal angle of M3. Dif- fers from H. minum in deeper mandibular ramus. Differs from H. anceps in presence of M3 ^ M2 in length. Differs from H. novum in presence of convex internal face on P2, presence of relatively wider cheek teeth, and presence of M3 ^ M2 in length. Age and Distribution—Santa Cruz Formation, Patagonia, Argentina, late early Miocene age, Santacrucian SALMA; Chucal Formation, north- ern Chile, late early Miocene age, Santacrucian SALMA. Description—The hegetotheriine specimens from Chucal are fragmentary, the most complete specimen being SGOPV 4104, a partial right man- dible with p4-m3 (Fig. 16B). A variety of other mandibular fragments with partial lower denti- tions are known, but the upper dentition is known exclusively from isolated teeth. Specimen SGOPV 5047 is a left upper first in- cisor with an occlusal surface measuring approx- imately 7.8 X 2.8 mm. It is rootless and was im- planted obliquely, as in other hegetotheriids. At least as judged from the length of the occlusal this is small for Fig. 15. Isolated upper cheek teeth referred to He- surface, specimen Hegetotherium getotherium cf. H. mirabile, in occlusal view. A. mirabile; the corresponding tooth in PU 15542 SGOPV 5040, P4. B. SGOPV 5058, left ?M1 right (pic- (Sinclair, 1909, Plate I) measures approximately tured as right). C. SGOPV 5121, left ?M1 (pictured as 11.5 X 3.0 mm, and in FMNH P13194 it mea- right). D. SGOPV 5123g, left M3 (pictured as right). X the Scale bars = 5 mm. sures approximately 10.0 2.9 mm. Since occlusal surface of the Chucal specimen is set at approximately the same angle to the rest of the tooth as in other specimens of H. mirabile ex- amined, this difference in surface dimensions may

34 FIELDIANA: GEOLOGY Fig. 16. Lower dentitions referred to Hegetotherium cf. H. mirabile. in occlusal view. A. SGOPV 4055, partial left mandible with root of c, pl-2. B. SGOPV 4104, partial left mandible with p4-m3. C. SGOPV 4023, partial right mandible with talonid of ml and complete m2-3 (viewed as left). Scale bars equal 5 rmn.

result from differences in wear. Alternatively, the Chucal compare favorably with specimens of H. Chucal specimen might be from a smaller than mirabile from Patagonia both in size and in mor- average individual (as in SGOPV 5123; Fig. phology (Fig. 15). Although somewhat small, the 15D). upper third molar (SGOPV 5123) has a pro- Most examples of the upper dentition from nounced notch in the posterior face of the tooth,

CROFT ET AL.: CHUCAL UNGULATES 35 characteristic of Hegetotherium (Fig. 15D). Of the is not described as differing from H. mirabile in two posterior projections created by this notch, M3 shape (Ameghino, 1891). H. anceps may rep- the labial one is slightly longer. This feature is resent a species distinct from both H. mirabile and variable within Hegetotherium from Patagonia; H. convexum, or may be synonymous with the the labial projection ranges from slightly longer latter. H. novum was named by Bordas (1939) to significantly longer than the lingual (Sinclair, based on a partial skull recovered from Colhue- 1909). Several Chucal specimens from the same huapian strata in the Valle del Rio Chubut and locality (SGOPV 5121, left ?M1; SGOPV 5122, shares with both H. convexum and H. anceps the partial left ?M2; SGOPV 5123, left M3) may rep- shortened M3 in relation to M2. The other distin- resent the left upper molar series from a single guishing characters of H. novum described by individual. However, since this locality has pro- Bordas (1939) suggest this taxon may be distinct duced an abundance of isolated teeth from a va- from H. mirabile and other recognized species of riety of taxa, the basis for such an association is Hegetotherium. not compelling. Owing to the incompleteness of Hegetotherium The lower dentition of the Chucal hegetotheriid specimens from Chucal and the lack of a compre- is much better represented than the upper denti- hensive revision of Hegetotherium taxonomy, a tion; seven well-preserved partial mandibles have definitive identification of the material cannot been collected, although none preserves the inci- now be made. Nevertheless, no compelling evi- sors or p3. The specimens resemble H. mirabile dence argues against reference of these specimens in morphology and are comparable in size. As in to H. mirabile. Upper cheek teeth from Chucal M3, the morphology of m3 is variable among H. (Table 6) are wider than those of H. novum, and mirabile specimens both from Patagonia and from SGOPV 5039 confirms that P2 of the Chucal form Chucal. In some specimens, the labial talonid lacks the concave lingual face (characteristic of groove on m3 is very shallow; in others, it is pro- H. novum). Two mandibular fragments from Chu- nounced, lending the tooth a nearly trilobed ap- cal (SGOPV 5104 and SGOPV 5049) illustrate pearance. This feature is also variably expressed that the horizontal ramus below ml is deeper in in the three specimens from Chucal; in SGOPV the Chucal taxon than in H. minum (15.5 mm and 4023 (Fig. 16C) and SGOPV 5038, the groove is 15.4 mm in the Chucal specimens versus 14.0 mm very weakly present, whereas in SGOPV 4104 in H. minum). The single hegetotheriine M3 col- (Fig. 16B), the talonid groove is deep, and a third lected from Chucal (SGOPV 5123) is a small lobe is present (though it is not developed to the tooth, shorter than any of the other hegetotheriine extent seen in pachyrukhines). molars known from the area (Table 6). Although Comments—In his description of the typotheres this may imply that the Chucal Hegetotherium has of the Santa Cruz Beds, Sinclair (1909) referred an M3 shorter than M2 (as in H. convexum and all hegetotheriines in the Princeton collections to H. anceps), the lack of an associated M2 clouds Hegetotherium mirabile. He considered five other this interpretation; the possibility that this M3 taxa to be junior synonyms of H. mirabile (H. merely pertains to a smaller individual (whose M2 strigatum, H. cuneatum, H. costatum, ''Selathe- is not preserved) cannot be excluded. Moreover, rium'' pachymorphum, and ''Selatherium'" remis- even though the Chucal M3 is smaller than the sum) and listed three others as of questionable sta- other upper molars from Chucal, it is larger than tus (//. convexum, H. minum, and H. anceps). All M3 in the holotypes of both H. convexum and H. three questionable taxa were named by Ameghino anceps. The presence of a pronounced postero- based on Santacrucian specimens. The holotype external angle and the lack of a greatly concave of H. convexum is a partial left maxilla with M2- lingual face in this M3 differs from the holotype

3 figured by Ameghino (1891, fig. 30). If the fig- of H. convexum and more closely resembles H. ure and the description provided are accurate, the mirabile. specimen would not appear to pertain to H. mi- rabile (see diagnosis above) and may be distinct. H. minum is said to be distinguished from H. mi- Litopterna Ameghino, 1889 rabile primarily by its shallower mandibular ra- Macraucheniidae Gervais, 1855 mus (Ameghino, 1894), but the variability of this Cramaucheniinae Ameghino, 1902 character (especially with wear) is uncertain. H. anceps differs from H. mirabile in having an M3 Diagnosis—The postcrania (especially the tar- that is shorter than M2 (as in H. convexum) but sals) of litopterns are highly diagnostic and read-

36 FIELDIANA: GEOLOGY Table 6. Measurements for Chucal specimens of Hegetotherium mirabile.

Upper dentition Position W

SGOPV 5120 (R) Differs from Coniopternium (including Cali- found in articulation with a partial proximal ulna. phrium and Notodiaphorus sensu Cifelli & Soria, It measures approximately 4.5 cm across the con- 1983) in larger size (approximately 20-25% larg- dyles, the lateral being broader than the medial. er in linear dimensions) and in having broader cal- The lateral epicondyle is much larger than the me- caneus with larger peroneal facet, more robust dial, though a distinct process projects from the calcaneal tuber, and tendon grooves (Cifelli & So- posterior surface of the medial condyle. The olec- ria, 1983). Differs from Pternoconius in larger ranon fossa is very deep and the supratrochlear size (approximately 20-25% larger in linear di- fossa shallow; these two structures are not joined mensions); postcranial elements of Pternoconius by a foramen. are unknown. Differs from Polymorphis in much Little of the ulna is preserved in SGOPV 4037, larger size (approximately twice as large as Po- except for the articular surface and surrounding lymorphis in linear dimensions); we are unaware area. A pronounced intercondylar ridge bisects the of any postcrania referable to Polymorphis. sigmoid notch, separating the larger medial sur- Distribution—Early Miocene of Chubut, Ar- face from the smaller lateral one. It lateral view, gentina, Colhuehuapian SALMA (Simpson, 1935; the notch approximates a semicircle. A large ru- Soria, 1981); late early Miocene of Patagonia, Ar- gose area for attachment of the elbow flexors is gentina, Santacrucian SALMA; ?early middle present distal to the articular surface, and two Miocene of Rio Frias/Cisnes, Chile, Friasian s.s. small facets mark the proximal articulation of the SALMA (Kraglievich, 1930); middle Miocene of radius. The olecranon process is incompletely pre- , Colombia, SALMA (Cifelli served in SGOPV 4037 but measures more than & Guerrero, 1997); ?early late Miocene of Buenos 6.5 cm in length in SGOPV 4013. The latter spec- Aires Province, Argentina, SALMA imen preserves most of the ulna except its distal (Cabrera & Kraglievich, 1931). end and measures approximately 33 cm in length; Discussion—Cifelli and Guerrero (1997) sug- the corresponding bone in T. garretorum mea- gested that Chasicoan "Ci/Z/m/a" laevis (Cabrera sures 37.5 cm (Scott, 1910). A similar portion of & Kraglievich, 1931) and Mayoan "Phoenixau- the radius is preserved in SGOPV 4013. The chenia'" tehuelche (Kraglievich, 1930) may also proximal facet is oblong and gently concave and pertain to Theosodon. is reflected for a short distance onto the medial surface. A prominent tuberosity is present just dis- tal to the extension of the articular surface. The Theosodon sp. indet. ulnar and radial shafts are subequal in length and

(Figure 17) ; diameter. Of the manus, only the proximal portions of Referred Specimens—SGOPV 4013, articulat- MC II and III are preserved. These bones are sub- ed proximal left ulna and radius (Fig. 17 A); equal in size; the shaft of MC II is approximately SGOPV 4019, partial distal radius; SGOPV 4037, 1 8 mm in its greatest diameter. The second meta- associated limb bones including left and right tib- carpal has a roughly triangular proximal articular iae (lacking epiphyses except for the right distal surface for the trapezoid, the latter of which is epiphysis), articulated right distal humerus and incompletely preserved in SGOPV 4037. A prom- proximal ulna, right proximal humerus fragment, inent facet is present on the lateral surface for ?radius fragment, proximal left MT IV, proximal contact with the magnum; it is oriented at an angle right MC II and III, partial shafts of two other of approximately 45° to the long axis of the bone. large limb bones (Fig. 17B); SGOPV 4014, partial The medial surface of MC II overlaps the proxi- right calcaneus (Fig. 17C); SGOPV 5054, partial mal articular surface of MC III, creating one facet left calcaneus. that is positioned distally and another that is po- Description—The litoptern postcrania from sitioned laterally. Very little of MC III is pre- Chucal are among the best preserved limb bones served, but part of the surface articulating with of the fauna, but no elements of the pectoral or the distally oriented MC II facet is present. pelvic girdle are preserved. Most of the Chucal Of the hind limb, the tibia and portions of the litoptern postcranial elements pertain to a single pes have been recovered. Specimen SGOPV partial skeleton, SGOPV 4037. The proximal hu- 4037 includes both tibiae, mostly lacking epiph- merus from this specimen preserves little mor- yses. The right tibia, which preserves the distal phology, save for most of the articular surface of epiphyses, is approximately 24 cm long. Scott the head. The distal humerus is complete and was (1910) listed the length of the corresponding

38 FIELDIANA: GEOLOGY bone in T. garretorum as 27 cm. The astragalar number of specimens from the Chucal Formation surface of the tibia has two deep grooves for ar- and the lack of well-differentiated species within ticulation with the astragalar trochlea and a small Theosodon, the taxonomic reliability of these fea- lateral facet for articulation with the fibula. The tures currently cannot be assessed. Accordingly, a posterior portion of the intercondylar ridge ex- more tightly circumscribed identification of the tends much farther distally than the anterior por- Chucal taxon cannot be made at this time. tion.

Two partial calcanea are represented, SGOPV 4014 and SGOPV 5054; the former includes the poster two-thirds of the element, while the latter Phylogeny of Mesotheriines preserves the anterior half (Fig. 17C, D). The tu- ber is long, narrow, and dorsoventrally broad. A To assess the taxonomic affinities of the me- narrow, strongly convex facet is present for artic- sotheriids from Chucal, we performed a phylo- ulation with the fibula. Medial to this, a large, genetic analysis of mesotheriines based primarily triangular facet is present for articulation with a on an emended version of the data matrix of portion of the ectal facet of the astragalus. This Flynn et al. (in press; see also Cerdeiio & Mon- triangular facet is continuous distally with a talvo, 2001). A single character was added to this smaller, oval facet that articulates with the re- matrix (#29: Ml proportions), and an additional mainder of the ectal facet. The astragalar facet on character state was added to character #16 (state the sustentaculum is also oval, and a large non- #4: II subtriangular, pointed distally, with two tal- articular surface is interposed between this and onid sulci) and to character #26 (state #2: P3 ab- the other astragalar facets of the calcaneus. The sent). The list of characters used in this analysis distal surface of the calcaneus is almost saddle is presented in Table 7, and the complete data ma- shaped and evidently articulated only with the cu- trix is given in Table 8. Two analyses were per- boid; no distal articulation with the astragalus is formed, both using Archaeohyracidae as the out- indicated. group (following Cerdefio & Montalvo, 2001). In The fourth metatarsal (SGOPV 4037) is similar the first analysis, all characters were considered in size to MC II described above. Its proximal unordered. In the second, selected characters were articular surface, for articulation with the middle ordered (indicated in Table 7) on the basis of de- cuneiform, is gently convex and has a prominent velopmental and metric criteria (e.g., it was as- plantar hook. A prominent, oblong facet is present sumed that a taxon could not proceed from on the dorsal side of the medial surface for artic- "small" to "large" without passing through "me- ulation with MT III. A second facet for articula- dium"). For both analyses, trees were generated tion with MT III is only partly present along the using the heuristic search option in PAUP 3.11 medial surface of the plantar hook. Two small fac- for the Macintosh computer. OTUs with multiple ets are present on the lateral surface for articula- character states were considered polymorphic. tion with MT V. The first analysis (using unordered characters) re- Comments—As discussed by Cifelli and Guer- sulted in nine equally most parsimonious trees, rero (1997, p. 298), taxonomy within the Ma- each with a length of 93 steps. The second anal- craucheniidae is in a state of "general disrepair." ysis (using the ordered characters) resulted in 81 Theosodon has been reported from the Colhue- equally most parsimonious trees, each with a huapian (Simpson, 1935; Soria, 1981) through the length of 96 steps. The strict consensus trees for Chasicoan SALMA (Pascual, 1966)—a temporal the two analyses have identical topologies at the range of some 10 million years (Flynn & Swisher, base and near the crown of the tree, but the first 1995)—but many of these reports are based on analysis (with unordered character states) exhibits fragmentary remains of questionable taxonomic greater resolution in the middle (Fig. 18). We fa- utility. The Santacrucian members of Theosodon vor the first analysis, as it makes fewer assump- likely form a clade, but the differences among tions regarding character evolution and is better some of the species are unclear (Cifelli & Guer- resolved. rero, 1997). The relationships in the resulting consensus In size and morphology, the Chucal litoptern trees are nearly identical to those of Flynn et al. resembles the various species of Theosodon from (in press). Aside from the greater resolution in the the Santa Cruz Formation of Patagonia described unordered analysis, the only other difference is by Scott (1910). Owing to the relatively small that both analyses here suggest that E. lehmann-

40 FIELDIANA: GEOLOGY Table 7. List of characters and character states used Tabi.f. 7. Continued. in phylogenetic analysis of mesotheriine relationships. Characters with multiple derived character states were 22. Ratio of il/i2: <1.50 (0); between 1.50 and 2.00 ordered in analysis #2 unless denoted by an asterisk (*). (1); between 2.00 and 3.00 (2), >3.00 (3) 23.^ Section of il: subcylindrical (0); rounded with 1.* Rostrum: elongated and low (0); long and tall little or no lingual sulcus (1); subtriangular with (1); short, rodent like (2) smooth sulcus (2); trapezoidal with well-demar- 2. Lengthening of premaxillae: absent (0); poorly cated lingual sulcus (3); elliptical with smooth defined (1); very pronounced (2) sulcus (4) 3.* Anterior rostral notch (premaxillae): very 24. p3: present (0); absent (1) smoothly concave (0); forming obtuse angle (1); 25. Lower molars: with fossettes (0); without fos- forming acute angle (2); tall, wide, "U" shaped settes (1) (3) 26.* P3: subquadrangular (0); subtriangular (1); ab- 4. Diastemata (upper and lower): absent or little de- sent (2) veloped (0); posterolaterally divergent (1); par- 27. Premolar ectolophs: with two labial sulci (0); allel or gently convergent (2); very convergent, with one labial sulcus ( 1 ) convex (3) 28. P4 proportions (length/width): <1.50 (0); >1.50 5.* Postorbital process: short (0); long and transverse (1) (1); directed (2) 29. Ml (length/width): <1.30 (0); be- long, posteriorly proportions > 6. Suborbital fossa: absent (0); poorly defined (1); tween 1.30 and 1.75 (1); 1.75 (2) well developed (2) 30. Anterior and posterior sides of M 1 middle lobe: 1* Root of zygomatic arch: posteriorly directed lingually convergent (0); subparallel (1); lingual- from the level of Ml or M2 (0); perpendicular ly divergent (2) to Ml (1); perpendicular to Ml with biconcave 31. Lingual exposure of Ml middle lobe: little or edge (2) none (0); extensive (1) 8. Zygomatic plate: absent or hardly developed (0); 32.* m2 proportions (length/width); between 1 .60 and little developed (1); very developed (2) 2.30(0); >2.30(1); > 1.60 (2) 9.* Postpalatal notch: narrow, deep, and removed 33. Two pronounced lingual sulci on m3 talonid: ab- from M3 (0); wide and removed from M3 (1); sent (0); present (1) deep to the level of M3 (2) 10. Occipital notch: absent (0); present (1) 11. Paraoccipital process: short (0), long (1) nitschei and E. superans share a common ancestor 12. Dentition: mesodont (0); protohyposodont (1); exclusive of other mesotheriines; in et al. euhypsodont (2) Flynn = 13. Upper molar imbrication (imbrication width (in press), these two taxa form a polytomy with a from to 1 of 1 M2 parastyle M hypocone/width M later diverging clade of mesotheriines (node 5 of posterior face): <1.25 (0); between 1.25 and 1.50 Fig. 18). In the present analyses, this paring of (1);>1.50(2) Eutypotherium species is weakly supported by the 14. II : with continuous enamel (0); with labial enam- loss of a character the root of el only (1) single state, having 15. II: obliquely implanted and not procumbent (0); the zygomatic arch perpendicular to Ml (charac- and (1); more obliquely implanted procumbent ter #7, state 1 >0; variable in T. chasicoensis, lost transverse implantaton and procumbent (2) independently in M. hystatum). 16.* II: oval (0); subtriangular, pointed distally, with The names Mesotheriinae and Mesotheriidae mesial sulcus (1); wide, rounded, with lingual sulcus (2); wide and compressed labiolingually have never before been defined phylogenetically with two lingual sulci (3); subtriangular, pointed (sensu de Quieroz & Gauthier, 1990). The phy- with two sulci (4) distally, lingual togeny established here facilitates this undertaking 17. I2-I3-C-Pl/i3-c-pl: developed (0); reduced, at whereby names are explicitly tied to given clades. times absent in the adult (1); always absent (2) Consistent with we define Me- 18. P2: developed (0), reduced (1); absent (2) previous usage, 19.* P4: subtriangular, short, with central fossette (0); sotheriidae as all notoungulates more closely re- subtriangular, short, without central fossette (1); lated to Mesotherium than to Hegetotherium, Ar- bilobed, with short and poorly defined lingual chaeohyrax, or Oldfieldthomasia (essentially plication (2); bilobed, with well-developed and to node 1 of Fig. 1 8 its stem), and patent lingual plication (3) equivalent plus 20. M1-M2: subtriangular with fossette (0); with an- we define Mesotheriinae as all mesotheriids more terior and lobes posterior convergent, enclosing closely related to Mesotherium than to Trachy- a middle lobe that disappears with wear (I); with therus (node 2 of Fig. 1 8 plus its stem). persistent middle lobe (2) Following this definition of the name Meso- 21.* M3: subtriangular, with fossette (0); trilobed with the the little differentiated middle lobe (1); with short theriinae, phylogenetic analyses place middle lobe, surrounded by the other two lobes three Chucal mesotheriids at the base of the but still (2); with the middle lobe less enclosed Mesotheriinae, with Eotypotherium as its earliest shorter than the others (3) diverging member. Eotypotherium is a member of

CROFT ET AL.: CHUCAL UNGULATES 41 Table 8. Character-taxon matrix for phylogenetic analysis of mesotheriine relationships. Archaeohyracidae

Trachytheriinae Eotypothehum chico

Altitypotherium chucalensis Altitypothehum paucidens Microtypotherium choquecotense Eutypotherium lehmannnitschei Eutypotherium superans Caragua New Taxon Plesiotypotherium achirense

Typotheriopsis chasicoensis

Typothehopsis silveyrai Pseudotypotherium subinsigne Pseudotypothehum exiguum Mesotherium hystatum Mesotherium cristatum Mesotherium maendrum Mesotherium pachygnathum

Archaeohyracidae

Trachytheriinae Eotypothehum chico Altitypothehum chucalensis Altitypothehum paucidens Microtypothehum choquecotense Eutypothehum lehmannnitschei Eutypothenum superans Typothehopsis chasicoensis

Typothehopsis silveyrai Caragua New Taxon Plesiotypotherium achirense Pseudotypothehum subinsigne Pseudotypothehum exiguum Mesothenum hystatum Mesothehum chstatum Mesothenum maendrum Mesothehum pachygnathum

Fig. 18. Strict consensus trees of mesotheriine relationships based on the phylogenetic analyses in the present = = study. A. Strict consensus of nine trees resulting from the analysis with all characters unordered; length 82, CI = = 0.79, RI 0.83, RC 0.66. B. Strict consensus of 81 trees resulting from the analysis with some characters ordered = = = = (see Table 7); length 88, CI 0.74. RI 0.81, RC 0.60. In both trees, node 1 is Mesotheriidae, node 2 is Mesotheriinae, and nodes 3-5 are unnamed clades discussed in the text.

CROFT ET AL.: CHUCAL UNGULATES 43 Chasicoan (late Miocene) (Flynn, Croft, et al., differences between the ungulate fauna of Chucal 2002), new dates from a subsequent report (Bond and those from typical Santacrucian localities in & Garcia, 2002) have restricted the age the fauna Argentina and southern Chile (Table 10). Simpson to within a 4- to S-miUion-year-long interval (Ta- coefficients, comparing Chucal to these faunas, ble 9; see also Charrier et al., 2002). The over- range only from 43-57 (Table 11). These differ- lying Quebrada Macusa Formation has been dated ences arise primarily because mesotheriids—con- at 17.4 ± 0.4 Ma (Bond & Garcia, 2002), and the stituting one-third of the ungulate "genera" at underlying Lupica Formation has been dated at Chucal—have never before been recorded in San- 21.7 ± 0.8 Ma at Chucal (Riquelme, 1998) and tacrucian-aged strata. This lack of Santacrucian at 1 8.79 ± 0. 1 1 Ma in the surrounding area (Wor- mesotheriids elsewhere represents but a small por- ner et al., 2000). Based on the radioisotopic dates tion of an even larger middle Cenozoic gap in the from the Chucal region and the most recent re- fossil record of mesotheriids in higher latitudes: vision of SALMAs (Flynn & Swisher, 1995), this none has been recorded there between the Desea- interval overlaps with or slightly pre-dates the dan and Mayoan SALMAs (early to middle Mio- Santacrucian SALMA (-16.3-17.5 Ma). There is cene), a span of some 13 million years (Flynn & a remote possibility, however, that it coincides Swisher, 1995; Croft, Flynn, & Wyss, 2003). In with the Colhuehuapian SALMA (estimated to be contrast, mesotheriines are characteristic compo- 719-21? Ma since the Colhuehuapian is uncon- nents of Bolivian Miocene faunas (Table 10) and strained within the 24.5-1 7. 5-Ma gap between the a very large fraction of isolated Miocene verte- dated and Santacrucian SALMAs), as brate specimens collected in northern Chile and no such faunas have been dated. Paleomagnetic Bolivia are referable to mesotheriines (Marshall correlations for Chucal are not yet available, but & Sempere, 1991; Flynn et al., in press). samples for a preliminary analysis are currently Another conspicuous difference between the being analyzed. Chucal Fauna and typical Santacrucian faunas is These uncertainties notwithstanding, based on the complete absence of interatheriid notoungu- biochronologic evidence, the Chucal Fauna al- lates in northern Chile. In this respect, Chucal re- most certainly pertains to the Santacrucian SAL- sembles other middle-latitude Miocene faunas of MA; Nesodon likely is an indicator taxon of the Bolivia (i.e., Nazareno, Quebrada Honda, and

Santacrucian SALMA (Croft, Radic, et al., 2003), Achiri), in which interatheriids also are rare and/ as is Neoreomys (A. Kramarz, pers. comm.; Table or absent (Table 10). Although it is certainly pos- 12), and Hegetotherium mirabile is recorded only sible that interatheriids were present at Chucal but in Santacrucian deposits (see above). Taking into remain unsampled, the lack of specimens refer- account the geochronologic constraints on the able to this clade from among more than 300 Chucal Fauna, the Santacrucian SALMA may ex- identified specimens at least speaks to the rarity tend slightly older than previously believed, at of this group, if they existed in this region at that least in intermediate latitudes. This is not entirely time; it is difficult to envision a taphonomic bias unexpected, as most high-latitude strata bearing that would preserve other closely related and sim- Santacrucian assemblages are underlain by either ilarly sized typothere notoungulates (i.e., hege- an unconformity and/or marine strata, thus pre- totheriines and mesotheriines) to the exclusion of cluding determination of the complete duration of interatheriids. The absence of interatheriids is par- this SALMA; the youngest dated assemblages that ticularly striking given their abundance not only definitively pre-date the Santacrucian are —25.5- in the Santa Cruz Formation of Argentina (Sin- Ma Deseadan sites near Salla, Bolivia (Kay et al., clair, 1909) and the Santacrucian-aged Pampa 1998) and the -20.1 -Ma? Colhuehuapian Rio Las Castillo Fauna of southern Chile (Flynn, Novacek, Leilas assemblage from central Chile (Flynn et al., et al., 2002) but also in nearly all 1995). The greater resemblance of the Chucal through early Miocene faunas of South America. Fauna to lower Santacrucian levels compared to The close geographic proximity of the faunas in upper ones (Tables 10 and 11) lends additional which interatheriids are rare or absent (Bolivian support to the relative antiquity of the Chucal and Chilean Altiplano) suggests that some bio- Fauna. Paleomagnetic analyses curtently under geographic and/or ecological factor served to lim- way may further constrain the age of the Chucal it or exclude interatheriids from at least the west- Fauna and clarify the onset of the Santacrucian ern portion of these intermediate latitudes (east- SALMA. ern, noncordilleran faunas of this age are un- Despite several shared taxa, there are profound known) during much of the Miocene. In

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CO Table 11. Ungulate faunal resemblance indices Table 12. Revised taxonomic list of the Chucal fau- (Simpson coefficients) among selected low-, intermedi- na. ate-, and high-latitude Miocene faunas of South Amer- ica. Simpson coefficients were calculated as (# of shared genera/# of genera in the smaller fauna)* 100. Table 13. Body masses of mesotheriines estimated by regression of Ml length on body mass for extant ungulates = (based on the equation: ln[mass in g] 3.09*ln[Ml length in mm] +1.21 [Damuth, 1990]) and caviomorph = (based on the equation ln[mass in g] 3.09*ln[Ml length in mm] + 3.08 [Croft, 2000]). Holotypes are indicated by an asterisk (*) following the specimen number. terms of abundance, Chucal is similar to other cussed in this paper were skillfully prepared by early to middle Miocene faunas of Bolivia, where Lorie Barber, Matt Brown, Akiko Shinya, Wendy mesotheriines constitute a significant proportion Taylor, and Connie Van Beek. We thank Ralph of identified specimens (e.g., Cerdas; MacFadden Hitz, Rick Madden, Emesto Rodrigo Paz, Mar- et al., 1995). This is in stark contrast to both high celo Reguero, and Bmce Shockey for helpful dis- latitudes (Argentina) and the lower latitudes (e.g.. cussions on notoungulates and South American La Venta, Colombia; Kay et al., 1997) of South paleofaunas; Marcelo Reguero and Bruce Shock- America, where early to middle Miocene ey also helped improve this work by providing mesotheriines are uncommon or absent. In terms critical reviews. Most of the photographs were ex- of mesotheriine diversity, the Chucal Fauna is ecuted by Mark Widhalm, and line drawings were unique, even compared to Bolivian faunas also created by Marlene Donnelly. Our collaborators containing mesotheriines; no other South Ameri- on this project, Reynaldo Charrier and Gerard can locality records three contemporaneous spe- Herail, have been unstinting in their continuing cies of this clade. Bracketing dates indicate the support, and we gratefully acknowledge help in age of the Chucal mesotheriines is at least 17.5 the field from Gabriel Carrasco, Andres Charrier, ~ Ma (or 17-18 Ma taking into account the un- the Flynn family (Alison, Peter, Rachel), Claude certainty of the date from levels overlying the fau- Herail, and Sergio Villagran. A crew from the na), pre-dating the earliest Patagonian mesotheri- Quiborax Mine at Salar de Surire deserves special ines (Eutypotherium of the Mayoan SALMA) by thanks for pulling both of our mired field vehicles more than 5 million years. Although slightly out of a small streambed some distance from our younger than the Chucal specimens, other Boli- camp. Funding for this study was provided by the vian taxa also significantly pre-date Eutypother- National Geographic Society (Grant 5371-94), ium; both Microtypotherium cf. M. choquecotense with additional support from our home institu- and Plesiotypotherium minor have been collected tions, U.S. NSF grant DEB 9317943, and FON- from the Quehua Formation near Cerdas, Bolivia, DECYT Chile. Our paleontological investigations (16.5-15.5 Ma; MacFadden et al., 1995). Consis- in Chile have been undertaken in collaboration tent with the conclusion reached by Reguero and with the Museo Nacional de Historia Natural Castro (2001) based on trachytheriine relation- (Dra. Maria Eliana Ramirez, Directora; Daniel ships, the presence of the earliest members of the Frasinetti, Jefe, Paleontologia) and the Consejo de Mesotheriinae in northern Chile and Bolivia, in- Monumentos Nacionales (Sr. Angel Cabezas, Se- cluding early diverging species, suggests that the cretaria Ejecutivo), Santiago. intermediate latitudes of South America served as a center of diversification for this clade of no- toungulates (Croft, Flynn, & Wyss, 2003). Only later did this clade disperse to higher latitudes, not Literature Cited becoming common there until some 10 million Ameghino, p. 1891. Observaciones cn'ticas sobre los years after the group's origin. Although the ear- mamfferos eocenos de la Patagonia austral. Revista de Historia Natural, 1: 328-380. liest taxa occur in the modem high-altitude Alti- Argentina

. 1894. Enumeration synoptique des espfeces plano or Puna, the potential role of elevation in mammiferes fossiles des formations eocenes de Pata- this diversification is uncertain; paleoelevations at gonie. Boletin de la Academia Nacional de Ciencias, latitudes lower than these certainly were modem Cordoba, 13: 259-452. faunas elevations, and definitively low-elevation Bond, M., and M. Garci'a. 2002. Nuevos restos de tox- of this age are unknown from the midlatitudes. odonte (Mamalia, Notoungulata) en estratos de la For- macion Chucal, Mioceno, Altiplano de Arica, norte de Chile. Revista Geologica de Chile, 29(1): 81-91. Bond, M., and G. Lopez. 1997. Los Hegetotheriinae (Notoungulata, Hegetotheriidae) de la Formacion Ar- Acknowledgments royo Chasic6 (Mioceno superior), Provincia de Buen- os Aires, Argentina. Ameghiniana, 34(4): 533. This study was greatly facilitated by access to BoNDESio, R, J. Rabassa, R. Pascual, M. G. Vucetich, AND G. J. SciLLATO Yane. 1980. La Formacion Colldn specimens at the Museo de La Plata (courtesy of Cura de sus alrededores (Rio Ne- Rosendo Pascual and Marcelo Reguero) and the Pilcaniyeu Viejo y Republica Argentina). Su antigUedad y las con- Museo de Ciencias Naturales "Bernar- gro, Argentino diciones ambientales segiin su distribucion, su lito- dino Rivadavia" of Jose and (courtesy Bonaparte genesis y sus vertebrados. Actas del Segundo Congre- Alejandro Kramarz). The Chucal specimens dis- so Argentino de Paleontologi'a y Bioestratigrafia y

CROFT ET AL.: CHUCAL UNGULATES 49 Primer Congreso Latinoamerica de Paleontologia, CiFELLi, R. L., and J. Guerrero. 1997. Litopterns, pp. Tomo 3: 85-99. 289-302. In Kay, R. F, R. H. Madden, R. L. Cifelli, and J. J. Vertebrate in the BoRDAS, A. F. 1939. Diagnosis sobre algunos mamiferos Flynn, eds.. Paleontology The Miocene Fauna of La Colom- de las capas con Colpodon del Valle del Ri'o Chubut Neotropics: Venta, bia. Smithsonian Institution Press, D.C. (Repiiblica Argentina). Physis, 14: 413-433. Washington, Cabrera, A., and L. Kraglievich. 1931. Diagnosis Cifelli, R. L., and J. Guerrero Diaz. 1989. New re- of Prothoatherium previas de los ungulados fosiles del Arroyo Chasico. mains colombianus (Litopterna, Notas Preliminares del Museo de La Plata, Tomo 1: Mammalia) from the Miocene of Colombia. Journal 107-113. of Vertebrate Paleontology, 9(2): 222-231.

Cerdeno, E., and M. Bond. 1998. Taxonomic revision Cifelli, R. L., and M. F Soria. 1983. Notes on Desea- and phylogeny of Paedothehum and Tremacyllus (Pa- dan Macraucheniidae. Ameghiniana, 20: 141-153. from the chyrukhinae, Hegetotheriidae, Notoungulata) Croft, D. A. 2000. Archaeohyracidae (Mammalia, No- late Miocene to Pleistocene of Argentina. Journal of toungulata) from the Tinguiririca Fauna, central Chile, Vertebrate 18(4): 799-811. Paleontology, and the evolution and paleoecology of South Ameri- Cerdeno, E., and C. I. Montalvo. 2001. Los Meso- can mammalian herbivores. PhD diss.. University of theriinae (Mesotheriidae, Notoungulata) del Mioceno Chicago, Chicago, Illinois, 311 pp. Superior de La Pampa, Argentina. Revista Espailola Croft, D. A., J. J. Flynn, and A. R. Wyss. 2003. Di- de Paleontologia, 16(1): 63-75. versification of mesotheriids (Mammalia: Notoungu- a. S. G. J. J. Charrier, R., Chavez, Elgueta, Herail, lata: Typotheria) in the middle latitudes of South D. a. Croft. 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