A 3.5-metre-long snake that lived 67 million years ago made a habit of eating baby sauropods as they first scrambled out of their eggs, say paleontologists writing in PLoS Biology. The conclusion is based on the discovery in India of a nearly complete fossilized skeleton of the primitive snake Sanajeh indicus coiled inside a dinosaur nest.

The fossils were first found in 1987 by dinosaur egg expert Dhananjay Mohabey from the Geological Survey of India, in rocks of the Lameta Formation in Gujarat, a state in western India known for its rich fossil record of dinosaurs and their eggs. Originally identified as a hatchling dinosaur, the fossils were recognized to include a snake by dinosaur paleontologist Jeff Wilson from the University of Michigan and Mohabey in 2001.

The snake lacked the wide-jawed gape seen in modern snakes such as pythons and boas, which would have prohibited it from eating rigid dinosaur eggs. But baby dinosaurs would have been just the right prey size for a large snake, says Jason Head, a paleontologist and assistant professor in the Department of Biology at the University of Toronto Mississauga.

"Living primitive snakes are small animals whose diet is limited by their jaw size, but the evolution of a large body size in Sanajeh would have allowed it to eat a wide range of prey, including dinosaur hatchlings," says Head. "This is the first direct evidence of feeding behavior in a fossil primitive snake, and shows us that the ecology and early evolutionary history of snakes were much more complex than we would think just by looking at modern snakes today."

This is a life-sized reconstruction of the moment just before preservation. The scales and patterning of Sanajeh’s skin is based on modern relatives of the fossil snake. The hatchling dinosaur is reconstructed from known skeletal materials, but its color is conjectural. The eggs are based directly on the fossils.

(Photo Credit: Sculpture by Tyler Keillor and original photography by Ximena Erickson; image modified by Bonnie Miljour)

Sanajeh indicus, which means "ancient gape from India", is represented by a nearly complete skull and lower jaws along with vertebrae and ribs coiled around a crushed titanosaur egg, next to the remains of a 0.5-metre-long titanosaur hatchling. These dinosaurs, part of a larger group called sauropods, were long-necked, four-legged plant-eaters that grew to weigh up to 100 tonnes, and Wilson says they likely grew quickly in their first year, beyond the reach of predators like Sanajeh.

The findings—along with two other similar snake-egg pairings, suggest that snakes fed on titanosaur hatchlings when they emerged from their eggs. "The eggs were laid in loose sands and covered by a thin layer of sediment. We think that the hatchling had just exited its egg, and its movement attracted the snake," explains Mohabey. "It would have been a smorgasbord," says Head. "Hundreds or thousands of defenseless baby sauropods could have supported an ecosystem of predators during the hatching season."

Wilson et al., 'Predation upon Hatchling Dinosaurs by a New Snake from the Late Cretaceous of India', March 2010, PLoS Biol 8(3): e1000322; doi:10.1371/journal.pbio.1000322