A team of scientists including Prof Anjali Goswami, research leader at the Natural History Museum have reconstructed what the ancestor of modern snakes may have looked like. The project itself is part of a larger work to create 3D reconstructions of how the skull evolved.
Incredibly, the team were able to delve so far into snake evolution that they were able to reconstruct the likely ancestral snake. Surprisingly the study points to the common ancestor being semi-fossorial, meaning it spent some of its life both above and underground and not in an aquatic environment, a habitat that was previously thought to have encouraged the evolution of the snake’s long thin body and unusual method of locomotion.
Prof Goswami says, ‘There is a lot of debate about how snakes evolved, but we think we have traced the ancestral skull shape. Lots of scientists have speculated that maybe snake ancestors lived in water, which made them lose their legs. So it’s surprising that the patterns we saw led us to a semi-fossorial animal.’
The squamates are an extremely diverse group which includes burrowing snakes, gliding lizards, and climbing chameleons. The animals in this group live all over the world, in a huge variety of habitats. These differences mean they have huge variation in their skull shapes making comparison a difficult task, with limited points for obvious comparison.
Prof Goswami explains, 'We capture lots of surface landmarks across the bones, to get a better 3D picture of the animal's skull.
'CT scanning and laser scanning in the Museum's Imaging and Analysis Centre are making this possible. The Museum is one of the best places in the world for these types of facilities, and it is shaping how science can be done differently.
'Once we have this nice dataset with 1,000 or more data points across the skull, we use various methods and computer programmes to examine how skull shape has changed through time.’
Akinobu Watanabe, Assistant Professor at New York Institute of Technology, who led the study said, ‘We used and developed brand new tools to collect and analyze this high-density skull dataset. This allowed us to reveal the evolutionary journey of how differences in the skull architecture of lizards and snakes arose from their common ancestors at an unprecedented scale and resolution.’
The team of collaborators also found that plant-eating lizards generally evolve faster, and semi-aquatic snakes that spend time in the water or underground were also quick evolvers.
More than 180 digitised specimens were used for this study, and they are now available for download, for free, anywhere in the world as part of the Phenome10k project, which is led by Prof. Goswami and involves digitisation and analysis of over 2000 vertebrate skulls.
Anjali adds, 'Truly open data is now becoming a reality, but it wasn't when we first started this project.
‘This study is also a great example of the benefits of digitised specimens. There is a big push to digitise Museum specimens, but then we are still working out what we can achieve with all the data. This is a high-density approach that we have been developing, and it means you can get more information about skull shape than you ever could before.’
