Revista de la Asociación Geológica Argentina 63 (4): 613 - 624 (2008) 613 JURASSIC TETRAPODS AND FLORA OF CAÑADÓN ASFALTO FORMATION IN CERRO CÓNDOR AREA, CHUBUT PROVINCE Ignacio H. ESCAPA1, Juliana STERLI2, Diego POL1 and Laura NICOLI3 1 CONICET. Museo Paleontológico Egidio Feruglio. Trelew, Chubut. Email: [email protected], [email protected] 2 CONICET. Museo de Historia Natural de San Rafael, San Rafael, Mendoza. Email: [email protected] 3 CONICET. Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Buenos Aires. Email: [email protected] ABSTRACT The plant and tetrapod fossil record of the Cañadón Asfalto Formation (Middle to Late Jurassic) found in Cerro Cóndor area (Chubut Province) is summarized here. The flora is dominated by conifers (Araucariaceae, Cupressaceae sensu lato) but also includes ferns and equisetaleans. The tetrapod fauna is composed of dinosaur taxa described in the 70's as well as other remains recently described and other vertebrate groups such as amphibians, turtles, and mammals. The amphibian remains have been interpreted as representatives of a new species of Notobatrachus, considered one of the most basal members of the anuran lineage. Similarly, turtle remains have been recently recognized as a new species of basal turtle, bringing valuable infor- mation about the early evolution of this group. The dinosaur remains are largely dominated by saurischian taxa, represented by basal forms of Eusauropoda and Tetanurae. In addition, three different mammalian species have been identified and con- sidered as early representatives of an endemic Gondwanan mammalian fauna. The fossil record of this formation represents the most completely known biota from the continental Middle to Late Jurassic of the Southern Hemisphere and one of the most complete of the entire world. Keywords: Jurassic, Patagonia, Paleobiogeography, Flora, Fauna. RESUMEN: Flora y tetrápodos del Jurásico de la Formación Cañadón Asfalto en el área de Cerro Cóndor, provincia de Chubut. Se resume bre- vemente el registro de plantas y tetrápodos fósiles de la Formación Cañadón Asfalto (Jurásico Medio a Superior) en el área de Cerro Cóndor, provincia de Chubut. La flora está conformada por coníferas de las familias Araucariaceae y Cupressaceae sensu lato dominando la asociación, la cual se completa con helechos y equisetales en proporciones menores. La fauna de tetrápodos se compone por los clásicos dinosaurios descriptos en los 70`s, a los que se suman nuevos restos pertenecientes a este grupo, así como anfibios, tortugas y mamíferos coleccionados en la última década. Los restos de anfibios han sido inter- pretados como representantes de una nueva especie de Notobatrachus, considerado uno de los miembros más basales del lina- je de los anuros. De igual modo, los restos de tortugas han sido recientemente reconocidos como una nueva especie de tor- tuga basal la cual aporta valiosa información acerca de la evolución temprana de este grupo. Los restos de dinosaurios se encuentran mayormente dominados por saurisquios, representados por formas basales de Eusauropoda y Tetanurae. Asimismo, tres diferentes especies de mamíferos han sido identificadas y consideradas como representantes basales de una fauna de mamíferos endémica de Gondwana. El registro de las formas clásicas en conjunto con los grupos taxonómicos recientemente descriptos, representan la biota del Jurásico Medio a Superior continental más completa de Gondwana, y una de las más completas a nivel global. Palabras clave: Jurásico, Patagonia, Paleobiogeografía, Flora, Fauna. INTRODUCTION Silva Nieto et al. (2003) have identified vial system on the lacustrine previous de- two members in the Cañadón Asfalto posits (Cabaleri et al. 2005). Alternatively, The Jurassic Cañadón Asfalto Formation Formation: Las Chacritas in the lower some of the fluvial deposits traditionally crops out along the middle Chubut river section and Puesto Almada in the upper referred to the Cañadón Asfalto Forma- valley (Fig. 1). This unit transitionally portion of the unit. The lower member is tion have been considered a different overlies volcanic rocks of the Lonco Tra- mostly dominated by lacustrine sedi- unit: the Cañadón Calcáreo Formation pial Formation and is uncomformably ments with volcanic intercalations at the (Proserpio 1987, Figari and Courtade overimposed by the Cretaceous Chubut base, while the upper one is mainly silici- 1993). From a sequence stratigraphy Group (Page et al. 1999). clastic and it represents a prograding flu- viewpoint, Figari et al. (1996) interpreted 614 I.H. ESCAPA, J. STERLI, D. POL AND L. NICOLI Figure 1: Geological map of the Cerro Cóndor area, Chubut Province. Modified from Silva Nieto et al. (2002). the Cañadón Asfalto basin as a rift deve- tion has been referred to the Middle to ceous age (Silva Nieto et al. 2007). loped from the Triassic through the late Upper Jurassic (Callovian-Oxfordian) ba- The aim of this work is to summarize re- Cretaceous. These authors recognized a sed on its paleontological content (Fren- cent advances in the knowledge of the series of four major megasequences, the guelli 1949a, Tasch and Volkheimer Cañadón Asfalto Formation paleobiota second one corresponding with the Ca- 1970, Volkheimer 1971, Silva Nieto et al. in the Cerro Cóndor area, Chubut pro- ñadón Asfalto Formation. More recently, 2007). However, its age interpretation, vince. During the last ten years an inten- Silva Nieto et al. (2007) suggested that the which is mostly based on the fossils reco- sive fieldwork has been conducted and Cañadón Asfalto basin could be formed vered around the type locality (Cerro numerous new fossil localities have been by several pull-apart depocenters which Cóndor area), could not be entirely accu- discovered. There, several new plant, are not strictly contemporary. According rate for the remaining localities. For ins- reptile, mammal and amphibian taxa we- to these authors, each one of the depo- tance, recent palynological records from re unearthed from lacustrine sediments. centers would constitute an isolated ba- the upper section of the Cañadón As- In this contribution we are mainly focu- sin with its own evolutionary history. falto Formation in the northern area of sing on fossil tetrapods and plants, In general, the Cañadón Asfalto Forma- Cerro Cóndor suggest an early Creta- although the record of fresh water inver- Jurassic tetrapods and flora of Cañadón Asfalto Formation ... 615 tebrates is also remarkable (Tasch and water invertebrates have been found as sheath. Volkheimer 1970, Silva Nieto et al. 2007). well. Ferns: The ferns are a minor component The new specimens from Cañadón As- at Frenguelli site, but they are represen- Flora falto Formation are mostly dominated by ted by at least two morphospecies (see conifer branches, seed and pollen cones also Frenguelli 1949a). The low represen- Jurassic floras in southern Argentina are and isolated seeds with minor amounts tation of Pteridophyta in this locality is mostly known from Neuquén and Santa of equisetaleans, ferns and possible seed probably related with taphonomic bias Cruz provinces, but not much has been ferns. The conifers represent about 90 more than with a real representation of accomplished from the Chubut province. percent of the specimens recovered whi- the original flora. Considering that this However plant bearing sequences in le all the remaining groups represent the plant assemblage is dominated by plant Chubut province are widely distributed, 10 percent remnant. The high number of parts with higher preservational potential including Early trough Late Jurassic de- specimens collected has allowed a de-tai- (e.g. conifers branches, cones, seeds), a posits. Jurassic lithoestratigraphic units led description of some taxa, specialy high degree of selection and allochtho- from Chubut province bearing plant as- conifers referred to Araucariaceae and nous conditions ruled plant burying de- semblages are: 1) Taquetrén Formation Cupressaceae sensu lato families. One of position. (Bonetti 1964, Herbst and Anzótegui the most relevant characteristics of the Most of fern remains are assignable to 1968, Escapa et al. 2008a), 2) Pampa de flora is the complete absence of Cyca- the genus Sphenopteris (Fig. 2f), a morpho- Agnia Group (Herbst 1966), 3) Lonco dophyta (Cycadales and Bennetittales) taxon used to characterize only vegetati- Trapial Formation (Cortés and Baldoni and Ginkgophyta, which are usually do- ve parts. It is interesting to note that so- 1984) and 4) Cañadón Asfalto Formation minant in Early Jurassic floras. The ano- me additional fern-like remains are pro- (Frenguelli 1949a and b, Cortés and Bal- malous absence of these plant groups bably related to pteridosperms (seed doni 1984). In this regard, there have during the Middle and Late Jurassic in ferns), a group that shows vegetative sys- been constant discussions about the pro- Cerro Cóndor, which is reverted from tems similar to true ferns. per denomination of all of these geolo- the Early Cretaceous, could probably be Araucariaceae: Conifers of this family are gical units (see Silva Nieto et al. 2003 and a response to certain broad environmen- represented in the Frenguelli site by citations therein) but no consensus has tal/paleoclimatic changes associated with numerous well preserved leafy twigs, been achieved yet. For this reason, in this the dynamics of paleoclimatic belts du- female cones (Fig. 2d), and isolated ovu- paper we follow the formational names ring the