Research ArticleEVOLUTIONARY BIOLOGY

The burrowing origin of modern snakes

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Science Advances  27 Nov 2015:
Vol. 1, no. 10, e1500743
DOI: 10.1126/sciadv.1500743
  • Fig. 1 Modern snakes originated as burrowers, based on their inner ear morphology.

    (A) Snake skulls in right lateral view, showing that the inner ear (orange) locates inside the braincase and opens to the stapes (blue) in the middle ear. Ear and skull models are not to scale. (B) Inner ear of Laticauda colubrina, an aquatic species. (C) Ptyas mucosa, terrestrial generalist. (D) Xenopeltis unicolor, a burrowing species. (E) Hypothetical ancestor of crown snakes, predicted as burrowing with 70.1% probability. (F) D. patagonica, predicted as burrowing with 93.4% probability. (G) Phylogeny of all snakes and lizards in this study, adapted from Gauthier et al. (8), Pyron et al. (19), and Yi and Norell (20).

  • Fig. 2 The braincase and inner ear of D. patagonica (MACN-RN 1014).

    (A) Braincase of D. patagonica, showing the right otic region in lateral view. (B) X-ray CT model of MACN-RN 1014, with the inner ear highlighted in blue. (C) Bony inner ear of D. patagonica. FO, foramen ovale; LR, lagenar recess; SC, semicircular canal; V, vestibule. Scale bars, 5 mm.

  • Fig. 3 Principal components analyses of the vestibular shape.

    (A and B) The inner ear of X. unicolor (A) represents the shape on the negative side of principal component 1 (PC1), whereas the inner ear of L. colubrina (B) represents the positive side. (C) D. patagonica clusters with modern active burrowers. (D) The hypothetical ancestor of crown snakes clusters with modern burrowers and limbless generalists. We listed the species of each data point in fig. S4. Ear models are not to scale.

  • Fig. 4 Total body size of D. patagonica compared with extant snakes.

    Loxocemus bicolor is the largest extant burrowing snake, growing up to 160 cm (16); Leptotyphlops carlae is the smallest extant snake (21).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/10/e1500743/DC1

    Materials and Methods

    Fig. S1. Vestibular shape of all samples.

    Fig. S2. Placement of shape variables.

    Fig. S3. Regression of centroid size to scores of principal component 1.

    Fig. S4. Distribution of shape variables reconstructed for the hypothetical ancestor of crown snakes.

    Fig. S5. Principal components analyses of vestibular shape.

    Fig. S6. Missing data in shape variables.

    Fig. S7. An alternative phylogeny for all samples.

    Table S1. Taxon sampling in the three habitat groups.

    Table S2. MANOVA test of Procrustes coordinates among the three habitat groups.

    Table S3. Scores of the first two principal components.

    Table S4. Accuracy of the linear discriminant function analysis.

    Table S5. Habit predictions for D. patagonica and the hypothetical ancestor of modern snakes.

    Table S6. Habit predictions for D. patagonica and the hypothetical ancestor of modern snakes.

    Table S7. Habit predictions for D. patagonica and the hypothetical ancestor of modern snakes.

    Table S8. CT scanning parameters*.

    Reference (32)

  • Supplementary Materials

    This PDF file includes:

    • Materials and Methods
    • Fig. S1. Vestibular shape of all samples.
    • Fig. S2. Placement of shape variables.
    • Fig. S3. Regression of centroid size to scores of principal component 1.
    • Fig. S4. Distribution of shape variables reconstructed for the hypothetical ancestor of crown snakes.
    • Fig. S5. Principal components analyses of vestibular shape.
    • Fig. S6. Missing data in shape variables.
    • Fig. S7. An alternative phylogeny for all samples.
    • Table S1. Taxon sampling in the three habitat groups.
    • Table S2. MANOVA test of Procrustes coordinates among the three habitat groups.
    • Table S3. Scores of the first two principal components.
    • Table S4. Accuracy of the linear discriminant function analysis.
    • Table S5. Habit predictions for D. patagonica and the hypothetical ancestor of modern snakes.
    • Table S6. Habit predictions for D. patagonica and the hypothetical ancestor of modern snakes.
    • Table S7. Habit predictions for D. patagonica and the hypothetical ancestor of modern snakes.
    • Table S8. CT scanning parameters*.
    • Reference (32)

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