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. 2010 Mar 2;8(3):e1000322.
doi: 10.1371/journal.pbio.1000322.

Predation upon hatchling dinosaurs by a new snake from the late Cretaceous of India

Jeffrey A Wilson  1 , Dhananjay M Mohabey, Shanan E Peters, Jason J Head
Affiliations

Predation upon hatchling dinosaurs by a new snake from the late Cretaceous of India

Jeffrey A Wilson et al. PLoS Biol. .

Abstract

Derived large-mouthed snakes (macrostomatans) possess numerous specializations in their skull and lower jaws that allow them to consume large vertebrate prey. In contrast, basal snakes lack these adaptations and feed primarily on small prey items. The sequence of osteological and behavioral modifications involved in the evolution of the macrostomatan condition has remained an open question because of disagreement about the origin and interrelationships of snakes, the paucity of well-preserved early snake fossils on many continental landmasses, and the lack of information about the feeding ecology of early snakes. We report on a partial skeleton of a new 3.5-m-long snake, Sanajeh indicus gen. et sp. nov., recovered from Upper Cretaceous rocks of western India. S. indicus was fossilized in association with a sauropod dinosaur egg clutch, coiled around an egg and adjacent to the remains of a ca. 0.5-m-long hatchling. Multiple snake-egg associations at the site strongly suggest that S. indicus frequented nesting grounds and preyed on hatchling sauropods. We interpret this pattern as "ethofossil" preservation of feeding behavior. S. indicus lacks specializations of modern egg-eaters and of macrostomatans, and skull and vertebral synapomorphies place it in an intermediate position in snake phylogeny. Sanajeh and its large-bodied madtsoiid sister taxa Yurlunggur camfieldensis and Wonambi naracoortensis from the Neogene of Australia show specializations for intraoral prey transport but lack the adaptations for wide gape that characterize living macrostomatan snakes. The Dholi Dungri fossils are the second definitive association between sauropod eggs and embryonic or hatchling remains. New fossils from western India provide direct evidence of feeding ecology in a Mesozoic snake and demonstrate predation risks for hatchling sauropod dinosaurs. Our results suggest that large body size and jaw mobility afforded some non-macrostomatan snakes a greater diversity of prey items than previously suspected on the basis of extant basal snakes.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Fossil snake preserved within a sauropod dinosaur nesting ground.
Photograph of blocks collected at Dholi Dungri, India preserving the snake Sanajeh indicus, n. gen. n. sp., in association with a partial clutch of three titanosaur eggs (oogenus Megaloolithus) and a titanosaur hatchling (GSI/GC/2901–2906). Beginning from the center of the lower portion of the photograph, the articulated skeleton of Sanajeh is coiled in a clockwise fashion around a crushed Megaloolithus egg (egg 3, at the junction of three blocks), with its skull resting on the topmost loop of the coil. The uncrushed Megaloolithus egg (egg 1) at right pertains to the same clutch, which would have contained six to 12 eggs. A second uncrushed Megaloolithus egg (egg 2) from the same clutch is still at the site. At lower right are the front quarters of a titanosaur hatchling, including elements of the thorax, shoulder girdle, and forelimb preserved in anatomical articulation. The titanosaur hatchling was approximately 0.5 m long, or one-seventh the length of Sanajeh (3.5 m long). No other sauropod bones were found at the site. Please see Figure 2 for interpretive map of specimen. Scale bar equals 5 cm.
Figure 2
Figure 2. Fossil snake preserved within a sauropod dinosaur nesting ground.
Interpretive map of blocks shown in Figure 1.
Figure 3
Figure 3. Skull of S. indicus, n. gen. n. sp.
(A) Photograph of block GSI/GC/2903 showing the position of preserved cranial elements, which rest in near anatomical articulation upon a chain of vertebrae (anterior towards top). The braincase was removed from the block prior to final preparation, but its original position (gray tone) can be seen in Figure 1. (B–E) Half-tone drawings of the braincase in (B) dorsal; (C) ventral; (D) left lateral; and (E) right lateral views. aac, Atlas-axis complex; ap, accessory process of the crista interfenestralis; ci, crista interfenestralis; ct, crista tuberalis; f, frontal; fo, fenestra ovalis; jr, juxtastapedial recess; l, left; mn, mandible; mx, maxilla; oc, occipital condyle; oto, otooccipital; pa, parietal; pal, palatine; pbp, parabasisphenoid processes; pbs, parabasisphenoid; pr, prootic; pvc, posterior vidian canal; r, right; rst, recessus scalae tympani; sc, sagittal crest; so, supraoccipital; st, supratemporal; v–vii, openings for cranial nerves. Scale bars equal 2 cm.
Figure 4
Figure 4. Precloacal vertebrae of S. indicus, n. gen. n. sp.
Half-tone drawing of the four articulated vertebrae at the base of the block GSI/GC/2903. fos, fossa; ns, neural spine; poz, postzygapophysis; prz, prezygapophysis; ri, rib; zs, zygosphene. Scale bar equals 2 cm.
Figure 5
Figure 5. Titanosaur sauropod hatchling and egg.
(A) Photograph of block GSI/GC/2904, showing elements of the anterior thorax and forelimb of the hatchling. The images at right are radial (B) and tangential (C) sections through an eggshell fragment removed from titanosaur egg 3 (from block GSI/GC/2905). External is towards the top in (B). hu, Humerus; il, incremental lines; n, node; pc, pore canal; ra, radius; ri, rib; sc, scapula; su, shell unit. Scale bar equals 2 cm for (A) and 500 µm for (B and C).
Figure 6
Figure 6. Calibrated phylogeny of snakes and evolution of wide-gape feeding.
Adams consensus of the single most parsimonious trees derived from analyses employing Amphisbaenia and Varanoidea as outgroups. Topologies were identical except for the position of Najash relative to Scolecophidia and Dinilysia. Numbers at nodes indicate decay values greater than 1; where decay indices differ between analyses, both are reported (separated by a “/”). Trees rooted with Amphisbaenia have stronger support at basal nodes (see Text S6 for additional details). Half-tone drawings at right illustrate three innovations in the evolution of large gape in snakes. Basal alethinophidians such as Sanajeh acquired a prominent median ventral keel on the basioccipital and parabasisphenoid (1) and an elongate posterior dentary process (2), which suggest increased intraoral mobility. Macrostomatans evolved an elongate supratemporal bone (3) that increases gape by positioning the jaw joint well posterior of the occipital condyle. Geographic distributions (gray rectangles) indicate Gondwanan affinities for basal snakes, including an Indo-Australian distribution for the clade including Sanajeh, Wonambi, and Yurlunggur. Scolecophidia and Macrostomata possess a cosmopolitan distribution, and outgroup distributions are primarily Laurasian . The taxonomic composition of Macrostomata follows and . Stars indicate first occurrences based on stem-group fossils ,. Abbreviations: AF, Africa; AS, Asia; AU, Australia; IN, India; NA, North America; SA, South America.
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