The diets of snakes diversified massively in the aftermath of the mass extinction event that wiped out the non-bird dinosaurs, contributing to the existence of the 4000 snake species we know today.
Three-quarters of all species on the planet, famously including all the dinosaurs except birds, were killed off in what is known as the K-T extinction event 66 million years ago. For the surviving species, the event gave rise to extreme changes to their surroundings, as well as less competition for food and living space.
While the evolutionary diets of birds and mammals following this event are well known, the diets of snakes have been poorly studied until now.
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In one of the most comprehensive studies on the diets of snakes, at the University of California, Los Angeles, and at the University of Michigan analysed 34,060 historical records of snake diet relating to 822 extant snake species. The records were taken from publicly available databases.
鈥淥ne of the unique things about our study is that we鈥檙e able to use聽ecological information on snake聽diets that聽comes聽from analysing stomach contents of preserved museum聽specimens,鈥� says Grundler.
They then plotted the dietary data from each species on a snake evolutionary tree, calibrated against geological time. This allowed the two researchers to estimate when particular prey types 鈥� mammals for instance 鈥� began to be eaten by snakes.
Before the K-T extinction event, snakes tended to have a diet of insects. However, the two researchers found that after the event, snake diets expanded to include birds and mammals. This may be because these animals became more abundant after the disappearance of non-bird dinosaurs, some of which ate birds and mammals.
What鈥檚 more, as the continents continued to drift, snake species were exposed to new and different environments, also offering new opportunities to change diet. Grundler and Rabosky found the fastest increase in snakes鈥� dietary changes to be in tropical and arctic regions spurred by the emergence of different animals and plants in these regions.
Following initial sharp increases of diversity of snake diets and species, the rate of change slowed over time, suggesting the extreme ecological events caused by the K-T extinction were important for shaping snake diets.
鈥淥ur work helps to show how ecological opportunities can shape evolutionary fortunes,鈥� says Grundler. 鈥淪ometimes those opportunities are created by extinctions, such as the one that wiped out the dinosaurs. Sometimes it鈥檚 caused by an ancestor dispersing to a new landmass, as happened when some ancient snakes colonised South America.鈥�
at the University of the Western Cape in South Africa says: 鈥淯nderstanding snake diets likely holds the key to understanding not only the ecological functions of snakes in ecosystems, but also the evolution of snake venoms, and the associated impacts on humans.鈥�
PLoS Biology
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