4.5 Article

The skull of Sanajeh indicus, a Cretaceous snake with an upper temporal bar, and the origin of ophidian wide-gaped feeding

Journal

ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY
Volume 197, Issue 3, Pages 656-697

Publisher

OXFORD UNIV PRESS
DOI: 10.1093/zoolinnean/zlac001

Keywords

macrostomy; Pan; Serpentes; total evidence phylogeny; Toxicofera

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Recent phylogenetic analyses provide different interpretations of the origin and interrelationships of snakes. A new Late Cretaceous snake specimen helps resolve the origin of wide-gaped feeding. Phylogenetic analyses suggest that wide-gape condition in mosasaurs and snakes may have evolved independently. Intermediate morphology preserved in the specimen indicates that ingestion of large prey items preceded wide-gaped, unilateral feeding.
Recent phylogenetic analyses differ in their interpretations of the origin and interrelationships of snakes, resulting in polarized views of snake ecology, habit and acquisition of features associated with wide-gaped feeding (macrostomy). Here, we report a new specimen of the Late Cretaceous nest predator Sanajeh indicus that helps to resolve the origin of macrostomy. The new specimen preserves an ossified upper temporal bar and a posteriorly expanded otooccipital region that lacks a free-ending supratemporal bone and retains a lizard-like palatomaxillary arch that allows limited movements during swallowing. Phylogenetic analyses of a large-scale total evidence dataset resolve Sanajeh near the base of Pan-Serpentes, as the sister group of Najash, Dinilysia and crown-group Serpentes. The Cretaceous Tetrapodophis and Coniophis represent the earliest-diverging members of Pan-Serpentes. The Cretaceous hindlimbed pachyophiids and Cenozoic Australian 'madtsoiids' are inside crown Alethinophidia, whereas mosasaurs are recovered invariably within anguimorphs. Our results suggest that the wide-gape condition in mosasaurs and snakes might have evolved independently, as functionally distinct mechanisms of prey ingestion. The intermediate morphology preserved in Sanajeh indicates that ingestion of large prey items (macrophagy) preceded wide-gaped, unilateral feeding (macrostomy), which appeared 35 Myr later, in the common ancestor of pachyophiids, Cenozoic Australian 'madtsoiids' and alethinophidians.

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