Different environments, different customs: How animals feed differs not only in the type of food, but also depends highly on their habitat. While for many water-dwelling vertebrates the easiest way to “grab“ food is by simply opening the mouth, eating on land usually requires somewhat more complex movements and sophisticated "feeding techniques". Since the question of feeding is vital for all living creatures, the evolution of appropriate feeding behaviours for land-based vertebrates was therefore absolutely inevitable. However, how this adaptation proceeded in detail had not been researched in detail until now. An international team led by Dr. Daniel Schwarz and Prof. Dr. Rainer Schoch from the Natural History Museum in Stuttgart has now studied extant salamanders and used the results to draw conclusions about the feeding behaviour of early tetrapods.
In this context, salamanders are ideally suited as model organisms, as they switch from a water-based way of life in their larval stage to a life on land as adults. Additionally, their larval stage shows astonishing anatomical similarities to early tetrapods.
Forty species from nine of the ten salamander families were examined for the study. The feeding behaviour of the amphibians was observed during three developmental stages (larva, juvenile before metamorphosis and adult after metamorphosis). High-speed X-ray imaging was used to literally look into the mouths of the animals while they were feeding and to record the movements of the bone structures involved.
The results suggest that early terrestrial vertebrates may have already been able to eat on land, despite the lack of flexible tongues and even before leaving their aquatic habitat. Early stages of development that lived entirely in water could have already displayed complex chewing behaviours: The prey was probably either grasped with the jaw and dragged back into the water, where it was processed with chewing bites – or the prey was processed on land by a combination of shaking and biting and finally swallowed by fast forward movements or head turns while temporarily letting go of the prey. Therefore, feeding on land was probably already possible before vertebrates actually walked on land and before flexible tongues developed.