SLITHERY STALKER: Eagerly waiting in the egg clutch, the 3.5-meter-long snake would snatch the tiny titanosaurs as they hatched. Image: Sculpture by Tyler Keillor and original photography by Ximena Erickson; image modified by Bonnie Miljour
An extraordinary set of fossils recovered from Cretaceous period rocks in western India has offered a rare glimpse into a baby dinosaur's first—and last—day on Earth about 67 million years ago. The frightful scene, fossilized by a rapid flow of debris, reveals a titanosaur hatchling's unlikely predator—a snake.
"The new fossils provide the first evidence, to our knowledge, of snake predation on hatchling dinosaurs and a rare example of non-dinosaurian predation on dinosaurs," says Jeff Wilson, a paleontologist from the University of Michigan at Ann Arbor and the lead author of the study, published March 1 in PLoS Biology. Wilson and his team describe the partial skeleton of a new 3.5-meter-long snake named Sanajeh indicus—Sanskrit for "ancient gape (mouth opening) from India"—fossilized in what appears to have been a titanosaur nest. Coiled around one of three eggs, the snake was frozen in time with its jaws facing the remains of the 50-centimeter-long hatchling.
The deadly dealings captured in the fossils occurred sometime during the relatively short 35-million-year-period of overlap between the two species. "Snakes were extraordinarily late in the dinosaur era. There was a long stretch when there were dinosaurs but no snakes," Wilson says.
Snakes and sauropods bracket the reptilian body-mass range, at 1.4 grams and 38,000 kilograms, respectively. But at birth a sauropod started out as small as one fortieth its adult size. "We now have evidence that these snakes were capable of taking down the biggest animals to have ever lived. Small birth size was really the Achilles heel of these big animals," Wilson says. This early puniness might have given sauropods a compelling reason to grow quickly from an evolutionary perspective. But it also gave snakes a reason to evolve. Sanajeh couldn't open up wide enough to nab the hatchling in one gulp. Instead, it displaced its upper jaw to slowly cram the baby body down inch by inch. "It didn't have the big gape but it had the jaw mobility—it was on the way to becoming something that could feed on bigger things," Wilson says.
Dhananjay Mohabey of the Geological Survey of India discovered the fossil specimen in 1987 and described it as a sauropod nest. A preserved chain of bones was assumed to belong to a hatchling. But when Wilson took a close look at the fossils in 2001 he saw something that he never expected. "I was stunned," he says. "I thought: that's awesome, it's a snake!" After agreeing to properly describe the specimen together, Wilson and Mohabey "put it in a backpack and brought it to Michigan" where they spent a year cleaning it grain by grain. "What we revealed was extraordinary—not only was there an egg and a chain of bones, but the bones were in a coil and there was a skull there," Wilson recounts. "We hardly have any good snake skeletons with a head and a body. This was a truly amazing fossil."
Now, nearly a decade later, Wilson and Mohabey, along with Shanan Peters of the University of Wisconsin–Madison and Jason Head of the University of Toronto Mississauga have described a new species of snake and a novel predatory relationship. "We really wanted to put together the complete story," Wilson says. "Sometimes it's worth the wait." Working closely with the researchers, University of Chicago–based paleoartist Tyler Keillor has re-created the scene in a life-size cast. The team will donate the cast to the Geological Survey of India at a formal function in Mumbai on March 12.