A transitional snake from the Late Cretaceous period of North America

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Snakes are the most diverse group of lizards1, but their origins and early evolution remain poorly understood owing to a lack of transitional forms. Several major issues remain outstanding, such as whether snakes originated in a marine2, 3, 4 or terrestrial5, 6 environment and how their unique feeding mechanism evolved1, 7, 8. The Cretaceous Coniophis precedens was among the first Mesozoic snakes discovered9, but until now only an isolated vertebra has been described9, 10 and it has therefore been overlooked in discussions of snake evolution. Here we report on previously undescribed material11 from this ancient snake, including the maxilla, dentary and additional vertebrae. Coniophis is not an anilioid as previously thought11; a revised phylogenetic analysis of Ophidia shows that it instead represents the most primitive known snake. Accordingly, its morphology and ecology are critical to understanding snake evolution. Coniophis occurs in a continental floodplain environment, consistent with a terrestrial rather than a marine origin; furthermore, its small size and reduced neural spines indicate fossorial habits, suggesting that snakes evolved from burrowing lizards. The skull is intermediate between that of lizards and snakes. Hooked teeth and an intramandibular joint indicate that Coniophis fed on relatively large, soft-bodied prey. However, the maxilla is firmly united with the skull, indicating an akinetic rostrum. Coniophis therefore represents a transitional snake, combining a snake-like body and a lizard-like head. Subsequent to the evolution of a serpentine body and carnivory, snakes evolved a highly specialized, kinetic skull, which was followed by a major adaptive radiation in the Early Cretaceous period. This pattern suggests that the kinetic skull was a key innovation that permitted the diversification of snakes.

At a glance


  1. Dentary of Coniophis precedens.
    Figure 1: Dentary of Coniophis precedens.

    UCMP (University of California Museum of Paleontology) 50000 in lateral (a), medial (b), ventral (c) and dorsal (d) view. mec, Meckelian canal; mf, mental foramen; sp, splenial facet; sr, subdental ridge; sur, surangular notch; th, thecae.

  2. Maxilla of Coniophis precedens.
    Figure 2: Maxilla of Coniophis precedens.

    ae, UCMP 53935, anterior part of maxilla in medial (a), lateral (b), ventral (c), dorsal (d) and anterior (e) view. fi, UCMP 49999, posterior maxilla in medial (f), lateral (g), ventral (h) and dorsal (i) view. j, k, AMNH (American Museum of Natural History) 22413, posterior maxilla in lateral (j) and medial (k) view. fos, fossa for nasal capsule; fp, facial process; idr, interdental ridge; ju, jugal articulation; lf, labial foramina; nar, narial margin; nas, nasal contact; pp, palatine process; pmp, premaxillary process; prf, prefrontal facet; saf, superior alveolar foramen; ss, supradental shelf; vom, vomerine process.

  3. Vertebrae of Coniophis precedens.
    Figure 3: Vertebrae of Coniophis precedens.

    a, AMNH 26999,vertebra from cervical region. b USNM (United States National Museum) 2143, holotype anterior trunk vertebra. c, AMNH 26833, middle trunk vertebra, d, YPM-PU (Yale Peabody Museum, Princeton collection) 16845, posterior trunk vertebra. Shown (from top to bottom) in anterior, posterior, dorsal, ventral and lateral views.

  4. Skull in lizards, Coniophis and modern snakes.
    Figure 4: Skull in lizards, Coniophis and modern snakes.

    a, Heloderma (Varanoidea). b, Reconstruction of Coniophis, with missing elements after Anguidae and basal snakes Najash and Dinilysia. c, Epicrates (Macrostomata).

  5. Phylogeny of Ophidia, showing relationships of Coniophis and evolution of cranial kinesis.
    Figure 5: Phylogeny of Ophidia, showing relationships of Coniophis and evolution of cranial kinesis.

    Adaptations permitting cranial kinesis (shown at left in the boa Epicrates) cluster near the base of the snake tree, but following the divergence of Coniophis. Coniophis exhibits an intramandibular joint (1). Serpentes exhibits a maxilla–premaxilla joint (2), loss of maxilla–vomer contact (3), a nasofrontal joint (4), a maxilla–prefrontal joint (5), a mobile dentary symphysis (6) and an articular saddle joint (7). Alethinophidia is characterized by a reduced postorbital bar (8) and a palatine–pterygoid hinge (9). Macrostomata is characterized by a hinged supratemporal (10). Characters 4* and 7* are unknown for either Coniophis or Najash. Stratigraphic data from ref. 18.


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  1. Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520-8109, USA

    • Nicholas R. Longrich &
    • Jacques A. Gauthier
  2. Department of Organismic and Evolutionary Biology, Biological Laboratories, 16 Divinity Avenue, Harvard University, Cambridge, Massachusetts 02138 USA

    • Bhart-Anjan S. Bhullar


N.R.L. designed the research, identified specimens, collected data, performed the phylogenetic analysis and wrote the paper. B.-A.S.B. designed the research, collected data and wrote the paper. J.A.G. collected data, contributed data and wrote the paper.

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