Can a snake prey on a dinosaur? The answer is yes.

Remains of a snake and dinosaur fossil, and dinosaur eggs provide unequivocal evidence that a particular species of snake that lived in Dholi Dungri village, about 130 km from Ahmedabad, Gujarat about 67 million years ago devoured sauropod dinosaurs.

The snake did not eat fully-grown sauropod dinosaurs; it preyed on dinosaurs just as they were hatching from the eggs. The snake used its long body to coil around its prey to kill it and then swallow it. “We infer that the crushed egg encircled by the snake was exited by the sauropod hatchling found adjacent to it,” notes the paper published online today (March 02) in PLoS Biology journal.

Modern day pythons use the same technique — coil around their prey quickly and tighten the grip so that the prey suffocates and dies. They then swallow the prey. Pythons are not poisonous.

The new snake fossil discovered in Gujarat — named Sanajeh indicus (Sanaj means ancient, jeh means gape) — from the Late Cretaceous rocks is 3.5-metre long and is found in a coiled position around a broken egg. There are other broken pieces of eggs and two other unbroken eggs lying nearby, and fossil remains of a 0.5-metre-long hatchling dinosaur lying next to the snake.

Importance of the study

The study is important as the nearly complete remains of the snake preserved in the nest of a sauropod dinosaur, and feeding on the hatchling dinosaur provide unequivocal evidence of its eating habits.

The authors have interpreted the snake coiled around a broken egg, two unbroken eggs and a dinosaur lying nearby as “ethofossil” preservation of the snake’s feeding behaviour. It also provides evidence of the evolutionary transition from basal snakes to modern-day derived macrostomatans like pythons.

Why wide gape matters

One of the most important features that enable macrostomatans (like pythons) to prey on animals bigger than deer is their wide gape (the extent to which the mouth can be opened).

Fully grown pythons, for instance, can have a gape as wide as 60 cm. “The gape of Sanajeh indicus is approximately 16 cm,” said Dr. Dhananjay M. Mohabey, Director of Palaeontology Division, Geological Survey of India (GSI), Nagpur. Dr. Mohabey is one of the authors of the paper; he had discovered the fossil way back in 1984.

The evolution of large-gape snakes (macrostomatans) capable of feeding on large prey and their ancestral habitat has remained controversial. Modern-day pythons have excellent jaw adaptations and elongated skull; fully grown pythons have a gape as wide as nearly 60 cm. Among other changes, macrostomatans have really long lower jaws and increased mobility of jaws compared with S. indicus.

“The lower jaw of S. indicus is 12 cm long… it’s a fairly long jaw,” said Dr. Mohabey. “There are other morphological features that make the jaws highly mobile and flexible… and give a wide gape of 16 cm.”

Mobility of jaws

For instance, unlike the jaws of basal snakes that open like a hinge, the upper and lower jaws of S. indicus can be moved laterally as well. This lateral movement gives the jaw the mobility. The combination of jaw mobility along with its 12 cm-long jaw size provides the snake with a wide gape and the ability to swallow its prey.

“It had a large body-size… it was able to manipulate the jaws to swallow large dinosaurs,” said Dr. Mohabey. However, dinosaurs older than one year were free of risk from S. indicus as even today’s macrostromatans of lengths comparable to the fossil snake prey on animals weighing less than 10 kg.

Not a transitional fossil

Discussing about the evolutionary transition, Dr. Mohabey said: “It’s a primitive snake with some advanced features.” However, it is surely not the transitional fossil between the basal and derived macrostomatans. “… [S. indicus] lacks specializations of modern egg eaters and of macrostromatans, [and the other features] place it in intermediate position in snake phylogeny,” notes the paper.

“There will be other more primitive [ones] between this [snake] and the basal snake, and more advanced ones between this [S. indicus] and the derived macrostomatans,” he said.

According to him, the nest was along a riverside and the dinosaurs were burying their eggs in the sand. “Some sort of smell or sound during hatching used to alert the snakes, which then preyed on the hatchlings,” he said.

No transportation of the eggs, snake

The presence of two unbroken eggs and broken pieces of eggs, the coiled position of the snake, along with the snake-dinosaur association clearly shows that they were buried and killed instantaneously with little transportation from another locality. In other words, the snake-dinosaur and egg association is not an accidental co-deposition phenomenon.

Along with the unbroken eggs, “the excellent preservation of delicate cranial elements… is indicative of relatively rapid and deep burial,” notes the paper.

According to Dr. Mohabey, there must have been some storm induced flooding event that resulted in debris flow, and there should have been hardly any time for the snake to escape.

This is not the first instance of snake fossils found in association with sauropod dinosaur eggs.