Research ArticleEVOLUTIONARY BIOLOGY

New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake body plan

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Science Advances  20 Nov 2019:
Vol. 5, no. 11, eaax5833
DOI: 10.1126/sciadv.aax5833
  • 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.

  • 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.

  • Fig. 3 Snake phylogeny and cranial evolution.

    (A) Majority-rule consensus of Bayesian inference analyses of dataset 1 (morphology-only). pol, postorbital loss; crcf, presence of full crista circumfenestralis (continuous system of bony crests surrounding the fenestra ovalis and the lateral aperture of the recessus scalae tympani, formed by prootic and otoccipital). Colored branch indicates Gondwanan radiation of basal snakes of Mesozoic origin as shown in the map (B) Gondwana during the Mesozoic, with the distribution of the fossil taxa in the analysis [1: Najash and Dinilysia (Patagonia, Argentina); 2: Menarana (Madagascar); 3: Sanajeh (India); 4: simoliophiids (Middle East); 5: Cenozoic madtsoiids of Cretaceous origin (Australia)]; (C) otic region of Najash, showing the absence of crista circumfenestralis in basal snakes; and (D) otic region of Anilius, showing the presence of full crista circumfenestralis in Serpentes (crown or modern snakes) consisting of crista interfenestralis (cri), crista prootica (crp), and crista tuberalis (crt). bt, basal tubera; rst, lateral aperture of the recessus scalae tympani.

  • Fig. 4 Snake phylogeny and divergence times.

    Relaxed-clock Bayesian inference analysis of dataset 2 (combined evidence). Majority-rule consensus tree of the major diapsid and squamate lineages, with region of interest (blue square, see complete tree in fig. S4) zoomed in, showing snakes and closer clades against a geological time scale. Colored branch indicates Gondwanan radiation of basal snakes. Numbers at nodes indicate the median value for the divergence time estimates for each clade.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaax5833/DC1

    Supplementary Text

    Fig. S1. CT scan reconstructions disarticulating individual cranial elements of Najash (MPCA 500).

    Fig. S2. Morphological data–only Bayesian inference analysis of dataset 2.

    Fig. S3. Morphological data–only maximum parsimony analysis of dataset 2.

    Fig. S4. Combined evidence relaxed-clock Bayesian inference analysis of dataset 2.

    Fig. S5. Maximum parsimony analysis of dataset 1.

    Fig. S6. Bayesian analysis of dataset 1.

    Table S1. Measurements (length in millimeters) of the preserved portion of the selected elements of the described specimens.

    Table S2. Stratigraphy and age for the newly included fossil taxa used for tip-dating calibrations.

    Table S3. Accession numbers for the sampled molecular data for the additional extant taxa included here relative to the molecular data available in Simões et al. (25).

    Movie S1. Micro-CT scan video of Najash skull MPCA 500, pitch mode.

    Movie S2. Micro-CT scan video of Najash skull MPCA 500, roll mode.

    Movie S3. Micro-CT scan video of Najash skull MPCA 500, yaw mode.

    Data file S1. Nexus file for morphological phylogenetic ingroup dataset, with MrBayes command used for uncalibrated Bayesian analysis.

    Data file S2. (Nexus_File_Dataset2_Combined_MrBayes) Nexus file for combined phylogenetic diapsid-squamate dataset with MrBayes command used for uncalibrated Bayesian analysis.

    Data file S3. (Nexus_File_Dataset2_Combined_MrBayes_Clock) Nexus file for combined phylogenetic diapsid-squamate dataset with MrBayes command used for relaxed-clock Bayesian analysis.

    Data file S4. (Nexus_File_Dataset2_MorphologyOnly) Nexus file for morphological phylogenetic diapsid-squamate dataset.

    References (4171)

  • Supplementary Materials

    The PDFset includes:

    • Supplementary Text
    • Fig. S1. CT scan reconstructions disarticulating individual cranial elements of Najash (MPCA 500).
    • Fig. S2. Morphological data–only Bayesian inference analysis of dataset 2.
    • Fig. S3. Morphological data–only maximum parsimony analysis of dataset 2.
    • Fig. S4. Combined evidence relaxed-clock Bayesian inference analysis of dataset 2.
    • Fig. S5. Maximum parsimony analysis of dataset 1.
    • Fig. S6. Bayesian analysis of dataset 1.
    • Table S1. Measurements (length in millimeters) of the preserved portion of the selected elements of the described specimens.
    • Table S2. Stratigraphy and age for the newly included fossil taxa used for tip-dating calibrations.
    • Table S3. Accession numbers for the sampled molecular data for the additional extant taxa included here relative to the molecular data available in Simões et al. (25).
    • Legends for movies S1 to S3
    • Legends for data files S1 to S4
    • References (4171)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Micro-CT scan video of Najash skull MPCA 500, pitch mode.
    • Movie S2 (.mp4 format). Micro-CT scan video of Najash skull MPCA 500, roll mode.
    • Movie S3 (.mp4 format). Micro-CT scan video of Najash skull MPCA 500, yaw mode.
    • Data file S1. Nexus file for morphological phylogenetic ingroup dataset, with MrBayes command used for uncalibrated Bayesian analysis.
    • Data file S2. (Nexus_File_Dataset2_Combined_MrBayes) Nexus file for combined phylogenetic diapsid-squamate dataset with MrBayes command used for uncalibrated Bayesian analysis.
    • Data file S3. (Nexus_File_Dataset2_Combined_MrBayes_Clock) Nexus file for combined phylogenetic diapsid-squamate dataset with MrBayes command used for relaxed-clock Bayesian analysis.
    • Data file S4. (Nexus_File_Dataset2_MorphologyOnly) Nexus file for morphological phylogenetic diapsid-squamate dataset.

    Files in this Data Supplement:

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