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.
Highlights
The previous oldest known fossil snakes date from B100 million year old sediments (Upper Cretaceous) and are both morphologically and phylogenetically diverse, indicating that snakes underwent a much earlier origin and adaptive radiation
The previous understanding of the fossil record of early snake evolution (Late Mesozoic) relies on isolated vertebrae from Africa[1] (100 Myr ago), isolated jaws and vertebrae from North America[2,3] (98–65 Myr ago), a number of nearly complete snakes, some with rear limbs[4,5,6,7], from the circum-Mediterranean region (98–95 Myr ago), and two taxa of relatively complete snakes, one with rear limbs, from Argentina (94–92 Myr ago[8,9] and 86–80 Myr ago[10,11]). This morphologically, ecologically and phylogenetically diverse assemblage of snakes appears in the fossil record around the world almost simultaneously (B100–94 Myr ago)
We report on four new species of significantly older fossil snakes (167–143 Myr ago) recognized from cranial and postcranial remains found in the United Kingdom, Portugal and the United States
Summary
The previous oldest known fossil snakes date from B100 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 B70 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). We report on four new species of significantly older fossil snakes (167–143 Myr ago) recognized from cranial and postcranial remains found in the United Kingdom, Portugal and the United States These new data extend the known geological range of snakes by nearly 70 million years into the mid-Mesozoic, indicating that their origin was coincident with the known radiation of most other major groups of squamates in the mid-Jurassic[12,13] during the final stages of the break-up of Pangaea into Laurasia and Gondwana. The youngest snake taxon and materials recognized here are found in rocks dated as Tithonian (B150 Myr ago; Upper Jurassic) to Berriasian (B140 Myr ago; Lower Cretaceous) outcropping near Swanage, Dorset, Southern England[15]
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