Revista Chilena de Historia Natural 64: 119-125,1991 A new Adianthid Litoptern (Mammalia) from the Miocene of Chile

Un nuevo Litopterno de la Familia Adianthidae (Mammalia) del Mioceno de Chile

RICHARD L. CIFELLI Oklahoma Museum of Natural History and Department of Zoology University of Oklahoma Norman, OK 73019 USA

ABSTRACT

A new species of Adianthus is described from the Río Cisnes (type locality of the Friasian age), Miocene of Chile. The species is represented by unusually complete remains, including the first postcranial elements known for a member of the family Adianthidae. In its skeletal anatomy, Adianthus godoyi, new species generally resembles lightly-built Santa- crucian proterotheriids. The new species is unique among litopterns in having the proximal tibia and fibula solidly fused. Like Santacrucian proterotheres, Adianthus godoyi was probably cursorially adapted; the narrowness of the an- terior dental arcade suggest that it was a selective-feeding herbivore, and perhaps consumed mixed vegetation in an open habitat. Adianthus godoyi appears to be closely related and to an as yet unidentified species from the early Santacrucian (Notohippus fauna) of Argentina and to Adianthus bucatus, from the Santacrucian of that country, which otherwise represents the latest known occurrence of the family Adianthidae. The occurrence of Adianthus godoyi in the type fauna of the Friasian thus suggests either that the family was more long-lived than had been previously appreciated, or that the type Friasian local fauna is more similar to those of Santacrucian age than their placement in different land-mammal ages would suggest. Key words: Adianthus, Chile, Friasian, Gal era Formation, Mammalia.

RESUMEN

Se describe una nueva especie del genero Adianthus, de Rio Cisnes (localidad tipo de la edad Friasense), Mioceno de Chile. La especies está representada por restos excepcionalmente completos, incluyendo los primeros elementos post- craneanos del esqueleto que se conocen para un miembro de la familia Adianthidae. En cuanto a la morfologia del esqueleto, Adianthus godoyi, nueva especie, es similar a los Proterotheriidae pequefios del Santacrucense. La nueva especie es única entre los Litopterna en la fusion solida de la parte proximal de la tibia y la fibula. Adianthus godoyi, como los Proterotheriidae santacrucenses, estaba probablemente adaptado para locomoci6n cursorial. La estrechez de la arcada dental sugiere que la especie, probablemente fue un herbivoro selectivo, posiblemente consumiendo una vegetaci6n mixta en un ambiente abierto o llano. Adianthus godoyi parece estar muy relacionado a una especie todavfa no identificada del Santacrucense temprano (Notohippidense) de la Republica Argentina, y a Adianthus bucatus, del Santacrucense, que ademas de la nueva especie, representan la ultima aparici6n de la familia Adianthidae. La presencia de Adianthus godoyi en la fauna tipo del Friasense sugiere que la familia Adianthidae fue más longeva que anteriormen- te supuesto, o que la fauna tipo del Friasense es más similar ala fauna del Santacrucense de lo sugerido por su ubicaci6n en una edad mamifero diferente. Palabras claves: Adionthus, Chile, Formaci6n Galera, Friasense, Mammalia.

INTRODUCTION Tertiary genera, Adiantoides (Casamayoran to Divisaderan) and Indalecia (Casamayo- Adianthid litopterns are among the poorest ran) are generally placed in the family known of indigenous South America (Simpson et al., 1962, Bond & Vucetich mammals, being represented by relatively 1983 ), but are here considered to re- scarce isolated teeth and dentulous jaw present another group, perhaps the Sparno- fragments. Adianthidae probably share a theriodontidae (Soria 1980) or Indaleciidae most recent common ancestry with Ma- (Bond and Vucetich 1983, Soria 1989), craucheniidae (Cifelli 1983a). The earliest that is hypothesized to have converged on adianthid appears to be Proectocion, from Adianthidae in some dental features (see the Casamayoran of Chubut Province, also Cifelli & Soria 1983, Cifelli 1985, Argentina (Cifelli 1983a). Two other early Soria 1989). The greatest diversityof Adianthidae is known from the Deseadan, where four species, representing three ge- (Received in 7 june 1990) nera (Proadiantus, Tricoelodus, and Thada- 120 CIFELLI nius) are present. One monotypic genus is Diagnosis. Species closely similar to, but known from each of the succeeding land- slightly larger than A. bucatus. Lower mammal ages, the Colhuehuapian (Pro- premolars broader and of more robust heptaconus) and Santacrucian (Adianthus), construction than in that species. the last-named genus representing the latest Description. Wear on the lower denti- hitherto known record of the family. tion of Duke-MNHN 89-109 (Fig. 1) is A new species of Adianthus, described more advanced than on the type of Adian- herein from the Rio Cisnes local fauna, thus bucatus, MACN A-1812, the only Chile, is of interest in that it is represented other lower dentition surely referable to a by a complete jaw and by postcranial species of Adianthus. The incisors and materials, neither of which have been canines, which are worn flat, project previously reported for any member of anteriorly and are arranged in a tight the family. The occurrence of Adianthus U-shaped arcade at the front of the jaw. l1 in the type local fauna for the Friasian is strongly compressed mesiodistally; 12 is Land-mammal Ae implies either a temporal less compressed, and 13 is oval in occlusal range extension for the family or a closer view. Faint grooves are present at the affinity of the Rio Cisnes local fauna with posterolabial borders of 13 and the canine, the Santacrucian than previously recognized. as described for Adianthus bucatus (Cifelli Abbreviations used in the text: Duke- & Soria 1983). P1, also worn flat, is broader MNHN, specimen collected by joint Duke than the corresponding tooth of A. bucatus MNHN expedition and deposited in the and, perhaps, was higher crowned as well, Museo National de Historia Natural, Santia- go, Chile; MACN, Museo Argentino de A Ciencias Naturales "Bernardino Rivadavia", Buenos Aires, Argentina; MLP, Museo de La Plata, La Plata, Argentina.

SYSTEMATIC PALEONTOLOGY Family Adianthidae Ameghino, 1891 Genus A dianthus Ameghino, 1891 Adianthus godoyi, new species

Type specimen-Duke-MNHN CH89-109, lower jaw and partial skeleton including mandibular symphysis and left ramus, with right 11 _3 , C, and P1, and left l1 -3, C, P 1 . 4 , and M1 . 3 ; distal part of humeral shaft, one lumbar vertebra, both in- nominates, proximal right femur, distal left femur, left tibia/fibula lacking the distal end of the fibula, and several fragments. Hypodigm. -The type only. Horizon and locality. -Duke-MNHN locality 15, Galera Formation, XI Region, Chile. Fig. 1: Adianthus godoyi, new species. Right Etymology. -For Alejandro Godoy, mandibular ramus (Duke-MNHN CH89-109, type) who coordinated Duke-MNHN field acti- in oclusal (A), lateral (B), and inferior (C) views. vities, in recognition of his contributions to Adianthus godoyi, nueva especie. Rama de la mandibula the research program and his companionship derecha (Duke-MNHN CH89-109, tipo), en vistas oclusal in the field. (A), labial (B) y ventral (C). MIOCENE LITOPTERN FROM CHILE 121 although this is difficult to determine owing to differences in relative wear. The succeeding premolars, P2 _ 4 , are similar to those of A. bucatus except for being c broader and having a more robust ap- A pearance. The lower molars are bicrescentic and lack secondary coronal complications such as fossettids or entolophids; the coronal pattern is nearly obliterated from M1 , while M3 is just coming into wear. The molars increase in length from first to third; M2 is the broadest tooth of the series. With wear, M3 would increase in length because its distal edge slopes posteriorly. Dental measurements are given in Table 1.

The mandibular symphysis is solidly D E fused. The symphyseal region is laterally compressed, and the incisors and canines project anteriorly in spoutlike fashion. A shallow labial fossa is present beneath P11 _ 2 , and a small foramen is located beneath

M1 , about midway from the dental to the inferior margin of the mandible. The horizontal ramus deepens markedly beneath

M1 The ascending ramus rises normally with respect to the horizontal ramus. The coronoid process is not preserved, but the mandibular condyle is located well above Fig. 2: Adianthus godoyi, new species (Duke- the tooth row. The borders of the mas- MNHN CH89-109, type). A, proximal right seteric fossa are not clearly delimited, nor femur in anterior view; B, distal left femur in are other muscle scars well marked. The anterior view; C, right innominate in lateral view; angle projects well posterior to the ascend- D-F, left tibia and fibula in anterior (D), lateral ing ramus, but appears to have had a gently (E), and posterior (F) views. rounded profile rather than a sharp hook. Adianthus godoyi, nueva especie (Duke-MNHN CH89- The angle is slightly deflected medially. 109, tipo). A, porci6n proximal del fémur derecho, vista anterior; B, porci6n distal del fémur izquierdo, vista The humerus deserves no more than anterior; C, pelvis derecha en vista lateral; D-F, tibia y passing comment because so little of it is fibula izquierdas en vistas anterior (D), lateral (E) y preserved. What remains of the distal end posterior (F). TABLE 1

Dental Measurements (mm) of Adianthus godoyi, new species (Duke-MNHN CH89-109). Medidas (mm) de los dientes de Adianthus godoyi, nueva especie (Duke-MNHN CH89-109). pl L 4.2 M1 L 8.6 P1 w 3.1 M1 w 5.2 p2 L 6.3 M2 L 11.1 P2 w 3.6 M2 w 5.4 p3 L 6.3 M3 L 12.9 p3 w 4.1 M3 w 5.2 p4 L 7.8 p4 w 4.5 122 CIFELLI indicates that the olecranon fossa was timated length of the femur ( 151 mm). It fenestrate, as is common among cursorial is proportionately longer and less robust mammals such as Santacrucian pro- than the corresponding element in terotheres. Both innominates are nearly Theosodon, being more comparable to complete, although neither preserves the Santacrucian proterotheres in these respects. tip of the ilium or the medial part of the No groove for the patellar tendon is present ischium. The pelvis (Fig. 2) generally on the cnemial crest. A prominent crest, resembles that of Santacrucian pro- indicating the insertion of the semi- terotheres, figured by Scott (1910). The membranosus muscle, is present at the base of the ilium is more slender than in posteromedian border of the proximal Theosodon. The ilium flares ventrolaterally tibia. Laterally, the proximal part of the to a slender tip, much as in Thoatherium; fibula is solidly fused to the tibia, a condi- the dorsomedial (sacral) part of the ilium tion unknown in any other litoptern. A is not so strongly projecting dorsally nor strong protuberance, for attachment of the so extensively developed as in Theosodon. peroneus longus muscle, is present at the A well-marked protuberance and a keel, anterior margin of the proximal fibula. The indicating the origin of the rectus femoris distal fibula is lacking, but it was not fused muscle, is present near the anterior border to the tibia. The distal tibia is deeply of the acetabulum. A well-marked knob, grooved for the trochlea of the astragalar perhaps marking the attachment of the body, as in all litopterns (Cifelli 1983b ). A anterior gemellus muscle, is present on the prominent beak is present posteriorly and dorsolateral margin of the ischium, just the medial malleolus is lacking, features posterior to the acetabulum; this pro- also shared by all other litopterns. tuberance is not present, or at least achieves lesser development, in Theosodon. Neither femur is complete, but the morphology of the entire element is re- DISCUSSION presented (Fig. 2). The head is more or less spherical. The greater trochanter is The genus Adianthus was founded by robust and is generally similar to that of Ameghino (1891) for the species A. bucatus "Proterotherium" or Theosodon (although (the spelling of which was later emended, the rugosity for insertion of the deep gluteal variably and in all cases invalidly, by muscle is less extensive than in the latter Ameghino and others), based on an upper genus), lacking the tall, dominating ap- cheek tooth. He later ( 1894) referred to pearance of Thoatherium or Prothoatherium the species a partial mandible, MACN (Cifelli & Guerrero 1989). The lesser A-1812. The original specimen of the trochanter is unremarkable in size or form. species, evidently lost during Ameghino's The third trochanter, where the gluteus lifetime (there is no evidence of any maximus inserted, is located about one-half researcher having studied it since 1891), the distance from femur head to condyles. apparently belonged to a caviomorph It is knoblike but, compared to Theosodon, rodent. Following a suggestion by Simpson is modest in development. A slight ridge on et al. (1962), Soria (1981) suggested that the lateral surface of the distal femur shaft MACN A-1812 might be taken as a neotype marks the origin of the vastus lateralis of the species. This was adopted by Cifelli muscle, and a small eminence at the base of & Soria (1983), and a proposal for designa- the medial condyle indicates the origin for tion of neotype under the plenary powers the medial head of the gastrocnemius, but (Cifelli & Soria 1984, 1985) was approved the element is otherwise devoid of muscle by the International Commission on scars or rugosities. The distal femur is not Zoological Nomenclature. Ameghino as anteroposteriorly expanded as in either ( 1903-4) added a Colhuehuapian species, 3 Theosodon or Santacrucian proterotheres. based on a left M , to the genus. This The left tibia (Fig. 2), which is complete, species was removed to Proheptaconus, as is slightly shorter ( 128 mm) than the es- P. patagonicus by Soria (1981), who de- MIOCENE LITOPTERN FROM CHILE 123

monstrated it to be synonymous with P. semblages and systematics of the mammals trelewensis Bordas, 1936, which was based themselves remain to be properly evaluated. on a badly preserved skull with part of the As summarized by Simpson (19.40, p. 666), upper dentition. An undetermined genus "Virtually no stratigraphic data have been and species of Adianthidae, represented by published, or apparently preserved with the a mandible with M1 _ 2 , is known from an collections, and the little that is known early Santacrucian (Notohippus) faunule in includes the statement... that the fossils Santa Cruz Province, Argentina (Cifelli & from the most important locality, Rio Frias, Soria 1983). This specimen (MLP 68-1-17- were found at several different levels and 192) may represent the lower dentition of are not all of the same age". In his initial P. patagonicus, but it cannot be compared notice on fossil vertebrates from the Rio directly with that species because of non- Cisnes area, Roth ( 1908) described three comparable representation. The generic different faunal levels, corresponding to status of Proheptaconus is thus, by implica- localities identified by their relative eleva- tion, uncertain. Of the known species of tion above sea level. It is probable, although Adianthidae, Adianthus godoyi appears not demonstrated, that the type of Adian- most closely related to A. bucatus and the thus godoyi is from approximately the same undetermined genus and species (possibly level as Roth's intermediate faunal zone. representing the lower dentition of However, Roth later (1920, 1925) revised Proheptaconus patagonicus). Deseadan taxa the identifications upon which he had (species of Thadanius, Proadiantus, and based these zones, so that their status and Tricoelodus) share presumably derived circumscription is in question. morphology (such as the anterior place- Remains of Adianthus godoyi are sug- ment and labial attachment of the lower gestive (although not indicative) of pa- molar entoconid resulting, in advanced leobiology of the species and, by implica- species, in the development of an en- tion, the paleobiology of other pygmy tolophid) not seen in Colhuehuapian and litopterns, for which little is known other later species. Adianthus bucatus, A. godoyi, than the cheek teeth. The muzzle appears and the species represented by MLP to have been extremely narrow relative to 68-1-17-192 are derived with respect to jaw breadth at the cheek tooth battery. the Deseadan taxa in having much higher Relative oral dimensions have been shown crowned cheek teeth and completely to be important factors in resource parti- bicrescentic lower molars lacking distinct tioning among living ungulates (Owen- talonid cusps (entoconid, hypoconulid, Smith 1985, 1989). Based on a com- hypoconid). prehensive survey of living ungulates, The latest hitherto known record of Janis & Ehrhardt (1988) found relative Adianthidae is that of Adianthus bucatus, muzzle width to vary predictably with from Corriguen Aike (see Marshall 1976), dietary preference, selective feeders having Santa Cruz Formation, of Santacrucian narrower muzzles. Among the selective age. Adianthus godoyi derives from the feeders, narrowest muzzle width was found Rio Cisnes at the type locality for the among mixed feeders in open habitat, Friasian Land-mammal Age (Marshall et which select grass and low level di- al., 1983), thus implying a range extension cotyledenous material, and among high for the family, greater temporal equivalence level browsers, which eat leaves from between the Rio Cisnes local fauna and branches. Quantitative comparison of fossil "typical" Santacrucian faunas than pre- with recent data is not possible in the viously recognized, or both. Unfortunately, present case. However, the small body size the status and biochronologic relationships of Adianthus godoyi, coupled with its of the Friasian Land-mammal Age itself are extremely narrow muzzle, suggests that it rather uncertain. Assemblages supposed to was a selective feeder, possibly feeding on represent local faunas of this age are mixed vegetation in an open habitat. represented by relatively small collections; The postcranial skeleton of Adianthus stratigraphic relationships of these as- godoyi, although incompletely known, is 124 CIFELLI

similar to that of other small-bodied Adianthidae (Mammalia, Litopterna). Revista de Ia Asociacion Geologica Argentina 38: 107-117. Miocene Litopterna. The presence of a CIFELLI RL (1983a) The origin and affinities of the fenestrate olecranon fossa on the humerus, South American Condylarthra and early Tertiary of hind limb proportions similar to those of Litopterna (Mammalia). American Museum No- vitates 2772: 1-49. Santacrucian proterotheres, and of a CIFELLI RL (1983b) Eutherian tarsals from the late specialized articulation of the distal tibia Paleocene of Brazil. American Museum Novitates with the astragalus, are suggestive of some 2761: 1-31. CIFELLI RL (1985) South American ungulate evolution degree of cursorial adaptation for the and extinction. In: Stehli FG & SD Webb (eds) species. The significance of the proximally The great American biotic interchange: 249-266. fused tibia and fibula is unclear, but this Plenum Press, New York. feature is often associated with cursorial or CIFELLI RL & J GUERRERO (1989) New remains of Prothoatherium colombianus (Litopterna, Mam- saltatorial locomotion in recent mammals malia) from the Miocene of Colombia. Journal of (Howell 1965). In the postcranial skeleton, Vertebrate Paleontology 9: 222-231. Adianthus godoyi is generally more com- CIFELLI RL & MF SORIA (1983) Systematics of the Adianthidae (Litopterna, Mammalia). American parable to three-toed Santacrucian pro- Museum Novitates 2771: 1-25. terotheres, such as Diadiaphorus, than to CIFELLI RL & MF SORIA (1984) Adianthus bucatus the presumably more closely related Ameghino, 1891 (Mammalia): proposed designa- tion of a neotype under the plenary powers. (and contemporaneous) macraucheniid Bulletin of Zoological Nomenclature 41: 56-57. Theosodon. However, these similarities, CIFELLI RL & MF SORIA (1985) Designation of a neotype for Adianthus bucatus Ameghino, 1891 such as the relative robusticity of the (Mammalia) under the plenary powers: a response. femur and the relative development of Z.N. (S.) 2430. Bulletin of Zoological Nomenclature sacroiliac contact, are presumably size- 42: 103-109. HOWELL AB (1965) Speed in animals: their specializa- related rather than indicative of relationship: tions for running and leaping. Reprint of 1944 Theosodon is much larger than either edition. Hafner Publishing Co., New York. Adianthus godoyi or Santacrucian Pro- JANIS CM & D EHRHARDT (1988) Correlation of relative muzzle width and relative incisor width terotheriidae. with dietary preference in ungulates. Zoological Journal of the Linnean Society 92: 267-284. MARSHALL LG (1976) Fossil localities for Santacrucian (early Miocene) mammals, Santa Cruz Province, Argentina. Journal of Paleontology 50: 1129-1142. 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