Sunday 30 June 2013

A fossil Snake from the Cretaceous of Brazil.

Snakes are generally accepted to have appeared and diversified during the Mesozoic, though their fossil record is not extensive. This is due to their lightly mineralized, easily disarticulated skeletons, which tends to result in Snake fossils, where they are found at all, tend to be poorly preserved and fragmentary. Nevertheless, by the late Cretaceous, a reasonable diversity of Snakes is known from sites across the world. How these early forms are related to modern Snakes is unclear, some retained limbs, and clearly could not be placed in any modern group, others are placed in extinct family Madtsoiidae, which died out in the Pleistocene, but most are too fragmentary for any taxonomic assignment. Fossils which can be placed with reasonable confidence in modern groups appear in the Palaeocene-Eocene.

In a preliminary paper published in the journal Acta Palaeontologica Polonica on 21 January 2013, Anne Hsiou of the Departamento de Biologia at the Universidade de São Paulo, Adriana Albino of the Departamento de Biología at the Universidad Nacional de Mar del Plata and Manuel Medeiros and  Ronny Santos of the Departamento de Biologia at the  Centro de Ciências Biológicas e da Saúde at the Universidade Federal do Maranhão describe a new Snake fossil from the Cenomanian (early Late Cretaceous, 99.6 to 93.5 million years ago) of northeastern Brazil.

The new Snake is named Seismophis septentrionalis, where 'Seismophis' means 'Earthquake-snake' and  'septentrionalis' means 'from the north'. The fossil was discovered at a site called Falésia do Sismito (Cliff of the Earthquake) on Cajual Island in the north of Maranhão State, which itself is in the north of Brazil.

The species is described from a pair of disarticulated mid-trunk vertebrae, not assumed to come from the same animal, though they are distinctive enough to say that they are Snake bones, and probably come from the same species. This is not unusual with Snakes fossils; the animals gain their extreme flexibility from having bones only lightly mineralized and loosely held together with tendons and muscles.

Seismophis septentrionalis, first specimen. Photographs (A1–E1) and schematic drawings (A2–E2), in anterior (A), posterior (B), lateral (C), dorsal (D), and ventral (E) views. Scale bar is 10 mm. Hsiou et al. (2013).

Seismophis septentrionalis, second specimen. Photographs (A1–E1) and schematic drawings (A2–E2), in anterior (A), posterior (B), lateral (C), dorsal (D), and ventral (E) views. Scale bar is 10 mm. Hsiou et al. (2013).

Due to the fragmentary nature of this material, it is not possible to say how this species is related to other Cretaceous or modern Snakes, but it is considered to be the oldest known Snake yet discovered in Brazil.

Map showing the locality where the specimen was found. Hsiou et al. (2013).

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