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domingo, 15 de março de 2015

The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution

Nature Communications 6,Article number:5996 doi:10.1038/ncomms6996
Received
Accepted
Published

Abstract

The previous oldest known fossil snakes date from ~100 million year old sediments (Upper Cretaceous) and are both morphologically and phylogenetically diverse, indicating that snakes underwent a much earlier origin and adaptive radiation. We report here on snake fossils that extend the record backwards in time by an additional ~70 million years (Middle Jurassic-Lower Cretaceous). These ancient snakes share features with fossil and modern snakes (for example, recurved teeth with labial and lingual carinae, long toothed suborbital ramus of maxillae) and with lizards (for example, pronounced subdental shelf/gutter). The paleobiogeography of these early snakes is diverse and complex, suggesting that snakes had undergone habitat differentiation and geographic radiation by the mid-Jurassic. Phylogenetic analysis of squamates recovers these early snakes in a basal polytomy with other fossil and modern snakes, where Najash rionegrina is sister to this clade. Ingroup analysis finds them in a basal position to all other snakes including Najash.

At a glance

Figures

left
  1. Skull elements assigned to new genera and species of Middle Jurassic to Lower Cretaceous snakes.
    Figure 1
  2. Jaw elements of earliest snakes.
    Figure 2
  3. Vertebral comparisons of earliest snakes (yellow background) to Najash and Coniophis (green background) vertebrae.
    Figure 3
  4. Phylogeny of earliest known snakes and other fossil and living snakes.

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