Estudios Geol., 56: 127-133 (2000)

COMMENT ON «EL REGISTRO MAS ANTIGUO DE HIPPIDION OWEN, 1869 (MAMMALIA, PERISSODACTYLA) EN AMERICA DEL SUR» BY J. PRADO, M. T. ALBERDI AND M. REGUERO E. P. Tonni * and A. L. Cione *

Introduction Prado et al. (1998: 90) stated that «...respecto a la "Edad-mamífero" Uquiense, consideramos que no The Pampean area of Argentina (mainly in the es aconsejable descartar su validez. La localidad de Bonaerian region) includes the most complete Esquina Blanca tiene varias ventajas sobre los aflo­ biostratigraphic representation of the continental ramientos de la costa Bonaerense, ya que es una latest Miocene to Recent times in South America secuencia con una singular potencia, donde los (Pascual et al., 1965; Marshall et al., 1983,1984; niveles portadores de mamíferos están asociados a Cione and Tonni, 1995a, b, c, 1996). lt has been tobas volcánicas y donde existen valiosos datos demonstrated that first occurrences of several paleomagnéticos. Si bien los registros nuevos con mammal taxa of Holarctic origin in the late Ceno­ precisión estratigráfica son aún escasos, los nuevos zoic beds of the Pampean area are relevant for trabajos de campo son prometedores». establishing the local biostratigraphic scheme and We have extensively discussed the history, con­ understanding those migration events that resulted ceptual development, correlation, and fauna} record in a remarkable modification of the indigenous of the «Piso Uquiense» and equivalent units elsew­ fauna. One of these taxa is the family Equidae. here (Cione and Tonni, 1995a, b). We suggested The first appearance of horses in South America that the Uquía Formation is not valid as a stratotype is recorded from sediments of a new local late of a chronostratigraphic (or even biochronologic) Pliocene stage, the Marplatan, which replaces the unit and proposed a new local chronostratigraphic former «Uquian Land-mammal age» of Pascual et (and geochronologic) unit, the Marplatan, with type al. (1965) according to Cione and Tonni (1995a; sections in the Bonaerian sea coast cliffs. We also fig. 1). took the «Uquian» case as a base for discussing the In a recent publication, Prado et al. (1998: 90) «Land-mammal age» concept and their use in South stated that the oldest record of the family Equidae America. Besides, the Código Argentino de Estrati­ (and «indudablemente» of the genus Hippidion) in grafía (1992) recommend not using the term «Edad South America comes from the stratotype of the mamífero» (<Ensenadan and younger than the to other regions, paleobiologic studies (paleobiogeo­ Chapadmalalan. graphy, community evolution, macroevolution) and environmental reconstruction. For this, we proposed a succesion of biostratigraphic units in the fossilife­ Discussion rous late Cenozoic strata of the Pampean area: Trigo­ don gaudryi, Neocavia depressidens, Paraglyptodon 1. «Uquian Land mammal age» vs Marplatan chapadmalensis, Platygonus scagliai, Akodon (Ako­ Stage/Age. don) lorenzinii, Paractenomys chapadmalensis, Toly-

* Departamento Científico Paleontología Vertebrados. Museo de La Plata. 1900 La Plata, Argentina. E-mail: [email protected]@museo.fcnym.edu.ar 128 E. P. TONNI AND A. L. ClONE

Concerning to the «Uquian», we found that the SOUTH EPOCHS AMERICAN LOCAL ZONES sections of the Quebrada de Humahuaca were not STAGES adequated as type sections of a stage-age younger HOlOCENE PLATAN li90510muS maximus ~U~~~J ~(~..!!!..~.!.h.íP..P..!:!..§ J neogeus than Chapadmalalan and older than Ensenadan BONAERIAN Megatherium -a;ericanum because: w Z w U 1) The Uquía Formation has no stratigraphic 2 ~ypeutes relationships with other significatively fossiliferous Vl ENSENADAN W ~paeus ..J units and is tectonically disturbed (see description in "- Prado el al., 1998). There is no recognized sequence - - - -f------:-l of fossiliferous units in the area representing the late

SANANDRESI- Paractenomys chap<'Idma1ensls Cenozoic such as can be found in different sections ~ AN ------in the Pampean area. For the moment, in the late ~ - --- ..J Cenozoic units of the Quebrada de Humahuaca, only a:a. VOROHUEAN ---Akodon (A.}- [oren:¡:inii---- Montehermosan, several geologic and magnetostratigraphic studies lower Chapadmalalan, upper Chapadmalalan, lower have been carried out. Presently, Ar40-Ar39 laser Marplatan, middle Marplatan, upper Marplatan, fusion dating in the underlying uppermost beds of Ensenadan, Bonaerian, Lujanian, and Platan stages in the Chapadmalalan was also done (Schultz el al., the Pampean area. Besides, those biozones are being 1998a, b; Zárate el al., 1998). These dates support tested with additional fossil evidence and calibrated magnetostratigraphic studies in the Bonaerian coast with isotopic and magnetostratigraphic methods (e.g. Orgeira, 1991) and contradict the interpreta­ (Tonni el al., 1999a, b). tion by Prado and Alberdi (1994) and Ortiz Jaure- COMMENT ON «EL REGISTRO MAS ANTIGUO DE HIPPIDION OWEN, 1869 (MAMMALIA, PERISSODATYLA) 129 guizar el al. (1995; see our fig. 2). However, the most important reason for using the coastal out­ PALEOMAG NE- crops is the remarkable fossil content (with abun­ STAGE Me TiC SEQUENCE SALMA dant micromammals) in very accessible sections. Finally, while it is true that the Uquía Formation is thick and amenable to magnetostratigraphic studies and radiometric dating, it possibly spans a smaller part of the time that represents the post-Chapadmala­ w Lujanian lan and pre-Ensenadan sequence in the Pampean z area. According to biostratigraphic evidence w (Paraclenomys chapadmalensis, Glyplodon), radio­ u metric dates, and magnetostratigraphic analyses, o Walther el al. (1996, 1998; see also Prado el al., .... Enseno ­ 1998) suggested that the middle and upper levels of don the Uquía Formation at Esquina Blanca, should be CIl correlated with the Sanandresian (Zone of Paracle­ W nomys chapadmalensis) and the 10wermost levels (paleomagnetic site 4; from where no equid fossil ...J - was reported) could be perhaps older than Sanan­ Q. ---- dresian. Additionally, Walther el al. (1996, 1998) correlated the section with the early Matuyama Uquian Chron (Chrons C2 An to C2r; younger than 2.6 Ma; late Pliocene). These conclusions agree with the .-­ magnetostratigraphic studies (e.g. Orgeira, 1991 -- w - and papers cited therein) and radiometric dating in z GAUSS Buenos Aires area (Schultz el al., 1996, 1998) (see Chapad ­ alsoTonnielal.,1999b). w u malalan Prado el al. (1998) reinterpreted the profile at o Esquina Blanca of Marshall el al. (1982). However, ...J they wrongly 10cated the dates in the section becau­ Q. se they inverted them. The sample LGM 202 with a date of 3.54 0.04 million years, was actually Fig. 2.-Pliocene to Holocene chronology of southern South ± America by Prado and Alberdi (1994). Note the treatment of obtained from the lowest dacite tuff (about 25 m), «Land mammal ages», with diachronic boundaries. The «stage» and the sample LGM 201, with dates of 3.7 ± 0.5 label actually correspond to epoch. The lower boundary of and 3.8 ± 0.2, from the upper reworked vitric tuff «Uquian» (= MarR1atan) is remarkably young in comparison with the new Ar4 -Ar,9 laser fusion dating of the uppermost (150 m; see Marshall el al., 1982). The cause of the beds of Chapadmalalan (3.3 Ma according Schultz et al.. mistake probably lies on that the older dates come 1998a, b). This new dating is close to the age determinations from samples stratigraphically higher than the using magnetostratigraphy in the area and the Quebrada de Humahuaca (see Orgeira, 1991; Walther et al., 1996, 1998). In younger ones. Besides, Marshall el al. (1982) consi­ the Pampean area, the upper beds of the Yorohuean and Sanan­ dered as valid younger dates for the same levels, not dresian present reversed polarity, which suggests that they considered by Prado el al. (1998) but discussed by range to the Chron C2r (younger than 2.6 Ma; see Cione and Tonni, 1999). Boundaries between chrons correspond to papers Cione and Tonni (1995a, 1999). previous to that of Cande and Kent (1992). 2. Supposed first South American record of Equidae in the Uquía Formation. sian substage). The record consist in a skull for­ Equid remains come from middle and upper merly referred to Onohippidium by Reig (1957) levels of the Uquía Formation (Prado el al., 1998) which comes from Vorohuean beds at the locality which seem to be correlated with the Sanandresian Baliza Chica, near Miramar, partido de General (Zone of Paraclenomys chapadmalensis; Walther el Alvarado and is housed in the Museo Municipal de al., 1996, 1998; see a1so Prado el al., 1998, p. 89). Ciencias Naturales de Mar del Plata (collection In the Pampean area, equids are first recorded in the number: MMP 381). Remarkably, this stratigraphic Zone of Akodon (Akodon) lorenzinii (biostratigraphic provenance was accepted by Alberdi and Prado basis of the Vorohuean substage; see Alberdi and (1992: 270; 1993: 13) and the material was for­ Prado, 1993: 14; see also Reig, 1957; Cione and merly identified as Hippidion principale (Lund, Tonni, 1995: 147, 149) which underlies the typical 1845) (which is a species found in the Bonaerian­ Zone of Paraclenomys chapadmalensis (Sanandre- Lujanian) by them. Later, Alberdi and Prado (1995: 130 E. P. TONNI ANO A. L. ClONE

297) assigned the Baliza Chica material to Hippi­ Castellanos, A. (1950). El Uquiense. Sedimentos neóge• dion devillei. Accordingly, Alberdi and Prado nos de Uquía (Senador Pérez) de la Provincia de Jujuy (1996: 664), in a range chart, do not include the (Argentina). Rev. Univ. Nac. Litoral, Fac. Cienc. Mat., Fís., Quím. y Nat., 36: 1-55. species Hippidion principale in the «Uquian». Pre­ Cione, A. L. and Tonni, E. P. (1 995a). Chronostrati­ sently, there is debate conceming equid systematics graphy and «Land mammal-ages» in the Cenozoic of in South America. If the view of MacFadden (1997) southem South America: principies, practices and the is accepted, Onohippidium would be the oldest Uquian problem. 1. Paleontol., 69: 135-159. equid genus in South America but if the view of Cione, A. L. and Tonni, E. P. (l995b). Una nueva escala Alberdi and Prado (1998) is accepted, Hippidion bioestratigráfica y cronológica para el Cenozoico tar­ dío de la parte austral de América del Sur. In: Evolu­ would be the oldest equid genus in the continent. ción biológica y climática de la región pampeana In sum, there is no published evidence sustaining durante los últimos cinco millones de años. (Alberdi, that equid remains from the Quebrada de Humahua­ M. T., Leone, G. and Tonni, E. P. eds.), Monografías ca are older than those from the Vorohuean beds at CS/C, 12: 47-74. Baliza Chica in the Atlantic coast (this latter a Cione, A. L. and Tonni, E. P. (1 995c). El estratotipo de record not considered by Prado et al., 1998). On the los pisos Montehermosense y Chapadmalalense (Plio­ ceno) de esquema cronológico sudamericano. Ameghi­ contrary, there is biostratigraphic evidence (for the niana, 32: 369-374. moment restricted to two taxa) that supports that Cione, A. L. and Tonni, E. P. (1996). Inchasi, a Chapad­ Uquía remains are younger. malalan (Pliocene) locality in Bolivia. Comments on the Pliocene-Pleistocene continental scale of southem South America. 1. South Amer. Earth Sci., 9: 22 I -236. ACKNOWLEDGEMENTS Cione, A. L. and Tonni, E. P. (1999). Biostratigraphy and chronological scale of the uppermost Cenozoic of We would like to thank to the following people and institu­ the Pampean area. In: Quatemary vertebrates of South tions: Mariano Bond, Diego Verzi, and María Guiomar Vucetich, America. (Tonni, E. P. and Cione, A. L. eds.), Q. South for reviewing the manuscript. Agencia Nacional de Promoción Amer. Ant. Pen., 12: 23-51. Científica y Tecnológica, Consejo Nacional de Investigaciones Cione, A. L., Tonni, E. P., Bond, M., Carlini, A, Pardiñas, Científicas y Técnicas, Comisión de Investigaciones Científicas U. F. J., ScilIato Yané, G., Vucetich, M. G. and Verzi, de la Provincia de Buenos Aires and Universidad Nacional de La D. (1999). Occurrence charts of Pleistocene mammals in Plata for financial support. the Pampean area, eastem Argentina. In: Quatemary vertebrates of South America. (Tonni, E. P. and Cione, AL. eds.), Q. South Amer. Ant. 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