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| Najash rionegrina Apesteguía & Zaher, 2006
in Garberoglio, Apesteguía, Simões, et al., 2019.
Illustration: Raúl O. Gómez.
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Abstract
Snakes represent one of the most dramatic examples of the evolutionary versatility of the vertebrate body plan, including body elongation, limb loss, and skull kinesis. However, understanding the earliest steps toward the acquisition of these remarkable adaptations is hampered by the very limited fossil record of early snakes. Here, we shed light on the acquisition of the snake body plan using micro–computed tomography scans of the first three-dimensionally preserved skulls of the legged snake Najash and a new phylogenetic hypothesis. These findings elucidate the initial sequence of bone loss that gave origin to the modern snake skull. Morphological and molecular analyses including the new cranial data provide robust support for an extensive basal radiation of early snakes with hindlimbs and pelves, demonstrating that this intermediate morphology was not merely a transient phase between limbed and limbless body plans.
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| Fig. 1 Najash specimens from LBPA. (A) MPCA 500, skull with atlas-axis in right lateral view. (B) MPCA 591, partial skull with articulated vertebrae in right lateral view. (C) MPCA 581, partial skull with atlas in left lateral view. (D) MPCA 564, articulated specimen with partial skull and postcranium in ventral view. (E) MPCA 419, dentary and associated vertebrae and ribs. (F) MPCA 480, partial skull with atlas in dorsal view. (G) MPCA 536, partial skull in ventral view. (H) MPCA 386, partial skull in ventral view. bo, basioccipital; ti, tibia. |
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| Fig. 2 CT scan reconstructions of the articulated skull of Najash (MPCA 500). (A) Right lateral view. (B) Left lateral view. (C) Dorsal view. (D) Ventral view.
II, optic foramen; V, trigeminal foramen; aiaf, anterior inferior alveolar foramen; amf, anterior mylohyoid foramen; at, atlas-axis; ang, angular; bo, basioccipital; cb, compound bone; co, coronoid; cri, crista interfenestralis; crt, crista tuberalis; d, dentary; ept, ectopterygoid; fr, frontal; iof, infraorbital foramen; j, jugal; mf, mental foramina; mx, maxilla; n, nasal; ot, otoccipital; pa, parietal; pbs, parabasisphenoid; pal, palatine; pmx, premaxilla; pof, postfrontal; prf, prefrontal; pro, prootic; pt, pterygoid; q, quadrate; smx, septomaxilla; so, supraoccipital; sp, splenial; st, supratemporal; stf, stapedial footplate; vo, vomer.
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| the legged snake Najash.
Illustration: Raúl O. Gómez,
Universidad de Buenos Aires, Buenos Aires, Argentina
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Fernando F. Garberoglio, Sebastián Apesteguía, Tiago R. Simões, Alessandro Palci, Raúl O. Gómez, Randall L. Nydam, Hans C. E. Larsson, Michael S. Y. Lee and Michael W. Caldwell. 2019. New Skulls and Skeletons of the Cretaceous Legged Snake Najash, and the Evolution of the Modern Snake Body Plan. Science Advances. 5(11); eaax5833. DOI: 10.1126/sciadv.aax5833
New fossils shed light on how snakes got their bite and lost their legs
phys.org/news/2019-11-fossils-snakes-lost-legs.html via @physorg_com
phys.org/news/2019-11-fossils-snakes-lost-legs.html via @physorg_com
