Fossil Snake Snacks on Sauropods
The patchy and elusive nature of the fossil record offers us limited glimpses as to what life was like during ancient times. Often, details of behavior and interspecific interactions are left open to interpretation and speculation. But occasionally, a sudden catastrophe caught ancient animals by surprise, killing and preserving them in a moment of activity. This is rather unfortunate at the time, but proves a boon to inquisitive hominds all these years later. This is exactly the case a newly described snake, Sanajeh indicus. A new paper by Wilson et al. in PLoS Biology describes remains of a few unlucky Sanajeh that were fossilized in the act of raiding a Megaloolithus (sauropod) nest, preserved forever entwined amongst the eggs and hatchlings.
Some of the most celebrated fossils are those that preserve interspecies interactions. For example, the fighting dinosaur fossil consists of a Velociraptor and Protoceratops locked in what appears to be mortal combat. There are also “food chain” fossils, such as Repenomamus, the Cretaceous mammal that wowed the world by proving that mammals were not entirely subordinate to dinosaurs during the Mesozoic: the badger-sized animal was discovered with the remains of a baby Psittacosaurus in its stomach.
And now we have Sanajeh indicus. This amazing fossil features a 3.5 m long snake, which was found in the Lameta Formation. This Late Cretaceous fossil bed near Dholi Dungri, in western India has long been a fantastic source of preserved dinosaur eggs and nests. The Lameta Formation continues to yield incredible fossils that give insight into both intra- and interspecific interactions that took place on these nesting grounds.
As shown below, the snake is curled around a crushed titanosaur egg, and lies adjacent to a recent hatchling.
It gets better. The same site yielded multiple examples of these snakes lurking around Megaloolithus nests, indicating that this was a common interaction, and that the snakes posed significant risks to sauropod offspring.
In addition to giving insights into the Cretaceous food web, these finds are also have intriguing implications for our understanding of snake phylogeny and evolution. Snakes are thought to have arisen around 98 million years ago, towards the tail end of the dinosaur’s epic reign. Modern snakes are notorious for their expandable gapes, which allow them to consume prey items that are sometimes shockingly disproportionate to their head/body size. Snakes with these abilities, referred to as macrostomatans, are thought to be derived from more basal forms that had relatively constrained jaw capacity.
As is typical of many phylogenies, however, there is much controversy over the evolutionary path that snakes have taken, especially regarding the transition from narrow- to wide-gaped morphology. Wilson et al. show that Sanajeh was indeed a “gape limited” species relative to modern macrostomatans, but that it, along with two Australian genera (see below), was “phylogenetically intermediate between the narrow-gaped aniloids and the wide-gaped macrostomatans” (emphasis added). The authors suggest that early snakes compensated for their rather conventional jaws with large body size, allowing them to consume large prey (such as titanosaur eggs) without the need to unhinge their jaws as modern snakes do. It appears that they did have some degree of intraoral kinesis, similar to that found in modern snakes, yet did not have the “unhinging” abilities that wow us today.
Sanajeh’s intermediate cranial configuration places it as a sister taxon to two late Cenozoic snakes from Australia, Wonambi and Yurlunggu. This is fascinating, as it also appears to help sort out group of species several other large snakes from ancient South America, Africa, and Madagascar, which have previously been lumped together with Wonambi and Yurlunggu due to similarities in vertebral structure. Wilson et al. designate two South American genera, Dinilysia and Najash, as basal and not closely related to the Australian snakes.
The implications of this paper span a wide range of fascinating areas, from giving insights into food web structure to helping clear up some of the enigmas of snake phylogeny and evolution. This fossil is sure to stir excitment, and the paper is definitely a must-read.
Wilson JA, Mohabey DM, Peters SE, Head JJ (2010). Predation upon hatchling dinosaurs by a new snake from the Late Cretaceous of India. PLoS Biology, 8 (3) : http://10.1371/journal.pbio.1000322
Easter egg hunt clue: sfslasrlyaeerypilpeylq