Abstract
We describe the most complete South American marsupial association of Huayquerian Age (late Miocene). Specimens were recovered from several new localities of central and northern La Pampa province (central Argentina), at levels assignable to Cerro Azul Fm.: Bajo Giuliani, Quehue, Telen, El Guanaco, and Laguna Chillhue. Loessoid sediments studied from this formation are indicative of lacustrine deposits overlaid by eolian levels bearing evidences of pedogenesis. A study of these levels at each one of the new localities led to their correlation in an integrated profile of Cerro Azul Fm. This formation corresponds to «Epecuen Fm.», at least in Salinas Grandes de Hidalgo, and probably also to the upper levels of Arroyo Chasica Fm. The studied marsupials are representative of almost all major lineages (orders) of South American Neogene marsupials. The marmosine didelphid Zygolestes tatei sp. nov. differs from the type species of the genus in its larger size, unreduced third lower premolar, and in the less reduction of the metaconid in the last lower molar. Another marmosine, Thylamys pinei sp. nov., differs from other Marmosini in the twinning of the para- and metaconid in the lower molars, and in the wider talonid of the m4. The Monodelphini marmosines Thylatheridium hudsoni y T. dolgopolae are abundant in several localities of this formation; their study confirms close affinities between this genus and Monodelphis . The didelphines Hyperdidelphys pattersoni and an indeterminate species of Lutreolina are also represented by a few specimens. A mandibular fragment including part of the last molar may represent the oldest record of a Sparassocynidae in central Argentina. The Borhyaenidae and Thylacosmilidae (Sparassodonta) are also recorded by a few, fragmentary specimens. Pliolestes venetus sp. nov. (Paucituberculata, Caenolestidae) differs from the type species of the genus in its smaller size and in the larger, less displaced metaconid in the first lower molar. Microtragulus rusconii (Argirolagida, Argirolagidae) is generalized with respect to the other species of this genus in having a less reduced talonid in the m4, and shows closer affinities with M. catamarcensis than with M. reigi . Hyperdidelphys, Lutreolina, Thylatheridium, Achlysictis , and, probably Microtragulus , are common taxa with those of the Valle de Santa Maria and Puerta de Corral Quemado, in Catamarca province (northwestern Argentina). On the contrary, Pliolestes and Zygolestes constitute exclusive taxa of Cerro Azul Fm. for central Argentina during the Huayquerian Age. The marsupial association recovered from levels of Cerro Azul Fm. is the most abundantly recorded from Upper Miocene levels in South America. Its taxonomic composition confirms previous hypotheses on the important faunal turnover that happened in this continent, as a consequence of the environmental changes occurred since the medial Miocene.
Highlights
Se describe la asociación de marsupiales sudamericanos fósiles de edad Huayqueriense (Mioceno tardío) más completa hasta ahora conocida
We describe the most complete South American marsupial asociation of Huayquerian Age
The Monodelphini marmosines Thylatheridium hudsoni y T. dolgopolae are abundant in severallocalities of this formation; their study confirms close affinities between this genus and Monodelphis
Summary
En este trabajo se describen marsupiales exhumados en afloramientos asignables a la Formación Cerro Azul (Linares el al., 1980) procedentes de las siguientes localidades de la provincia de La Pampa (se mencionan entre paréntesis los respectivos departamentos): Bajo Giuliani (Capital), El Guanaco (Capital), Telén (Loventué), Quehué (Utracán), Laguna Chillhué (Guatraché) y Salinas Grandes de Hidalgo (Atreucó) (ver fig. 1). En este trabajo se describen marsupiales exhumados en afloramientos asignables a la Formación Cerro Azul (Linares el al., 1980) procedentes de las siguientes localidades de la provincia de La Pampa (se mencionan entre paréntesis los respectivos departamentos): Bajo Giuliani (Capital), El Guanaco (Capital), Telén (Loventué), Quehué (Utracán), Laguna Chillhué (Guatraché) y Salinas Grandes de Hidalgo (Atreucó) Desde un punto de vista litológico, los niveles hasta ahora asignados a la «Formación Epecuén» fueron considerados como una extensión hacia el norte de aquellos que afloran en el curso inferior del arroyo Chasicó, correspondientes precisamente a la Formación Arroyo Chasicó (Pascual y Bocchino, 1963; Fidalgo el al., 1975). En la provincia de La Pampa se registra una situación similar entre las Formaciones Arroyo Chasicó y Cerro Azul.
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