CONICET | Buscador de Institutos y Recursos Humanos

The dinosaur record in Chile is mostly composed of trackways of theropods, sauropods and ornithopods, and few bone remains of sauropods and one of ornithopod; all of these occur north of latitude 39ºS. In this note we report the first dinosaur bones found in southern Chile, in the central Patagonian Cordillera, in Aysén (ca. 46ºS). The Upper Mesozoic stratigraphic record in this region is dominated by volcanic formations, mainly pyroclastic, of Late Jurassic and Aptian age (the Ibáñez and Divisadero formations, respectively), separated by a marine succession deposited in the Austral Basin during the Tithonian to Aptian (Coyhaique Group). During the summer of 2004 dinosaur fossils were found in the mountains south of lago General Carrera in the region of Aysén, in southern Chile, representing the first findings of dinosaur remains in southern Chile. The Upper Mesozoic stratigraphic record in the central Patagonian Cordillera of the Aysén region, in southern Chile, is dominated by volcanic formations, mainly pyroclastic, of Late Jurassic and Aptian age (the Ibáñez and Divisadero formations, respectively), separated by a marine succession deposited in the Austral Basin during the Tithonian to Early Aptian (Coyhaique Group). In the area west of río Maitenes, south of lago General Carrera, a succession of sandstones, calcareous laminites and tuffs, with vertebrate (including dinosaur remains) and wood fossils form a distinctive facies association. These fossils occur in green coarse-grained sandstones and pebbly sandstones, interbedded with red ignimbrites. Although these dinosaur-bearing beds are faulted and folded, they are inferred to overlie the Ibáñez Formation, and are thus assigned to the Toqui Formation. The vertebrate fossils consist of abundant fragmentary dinosaur bones, being the most relevant those of theropods (meat-eater dinosaurs). The pieces discovered (which represent probably more than 15 individuals, presumably belonging to one or two mid-sized species), include part of a left hindlimb and a left manus of a single individual. Some characters observed in the manus (such as proximal end of metacarpal I applied to metacarpal II; medial condyle of metacarpal I dorsal to lateral condyle; metacarpal III longer than metacarpal II, etc.), suggest a close phylogenetic relation with the Tetanurae (a clade of derived neotheropods); particularly, the bones show resemblance with some North American basal tetanurans, such as Allosaurus and Acrocanthosaurus. South American Lower Cretaceous tetanurans are scarce, and those from Chile are virtually unknown. It is well known that tetanurans proliferated in Gondwana by the Late Jurassic, and that some tetanuran lineages (for instance carcharodontosaurs) survived in the Late Cretaceous. The Chilean theropods found at Aysén would show that large tetanurans were abundant throughout all the Cretaceous, at least until theropods belonging to other groups (e.g. abelisaurus) acquired increasing importance. In this regard, we understand that these remains contribute to a more complete picture on the Gondwanan theropod evolution during the Cretaceous.

enviar mensaje