How to eat a mouse whole; changes in skull shape in a large elapid snake

By Matt Patterson and Ash Wolfe. It’s not that easy to eat your food whole. Especially if you don’t have limbs to assist you. That’s what snakes have to deal with every day. The challenge is even harder for young snakes, which have to develop their abilities to handle and ingest their food.

The dugite (Pseudonaja affinis) is a venomous elapid common throughout Perth and the south-west Western Australia. These snakes are often painted in a negative light in the media as dangerous killing machines, but there is so much more to them than this ominous persona they have gained.

Dugites show a distinct size-related shift in their diet: the smallest individuals eat autotomised reptile tails and reptiles, medium-sized individuals predominantly eat mammals (mostly mice), while the largest individuals have the most diverse diet, including some very large reptiles. This sparked the question – how do these snakes change their ability to feed on increasingly large and bulky food items?

We studied the skulls of 46 dugites ranging in size from the smallest juvenile to adults about 1.8m in length. Using micro-CT scanning to create 3D reconstructions of their skulls, this allowed us to identify that the dugite skull completely alters as these animals grow.

The skulls of juveniles are smooth and simple in shape, protecting the snake’s brain but not being particularly specialised in terms of their jaws. By contrast, the skulls of adults have marked extensions for jaw muscle attachment, more robust jaw bones, and a well developed system to increase their gape (how wide they can open their mouths). One of the most fascinating patterns we found was that the jaw bones which play a role in feeding grow at different rates to each other, with certain bones growing faster than others.

3D models of skulls from juvenile (a) and adult (b) dugites with all the main jaw bones involved in feeding highlighted.

Understanding these changes in the anatomy of the skull and jaw bones has only been possible through the application of new scanning and computing methods. It demonstrates how micro-CT methods and shape analysis through Geometric Morphometrics can provide valuable insights into the morphology of animals and allow us to learn more about how these animals feed and how they adapt to different prey items.

This study has been accepted for publication in Evolutionary Ecology “Ontogenetic shift in diet of a large elapid snake is facilitated by allometric change in skull morphology”

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