“The ancient aquatic crocs developed unusual inner ears after modifying their skeletons to become better swimmers. Whales also changed their ears in a similar way, but did it soon after entering the water. It seems like the crocs and whales took similar, but different, evolutionary routes from land to water.”Dr Steve Brusatte School of GeoSciences
Researchers from the School of Geosciences at Edinburgh University have published details about a crocodile which swam the world’s seas in ancient times. Inner ear sensory system changes as extinct crocodylomorphs transitioned from land to water
Today, salt water crocodiles live in the brackish and freshwater regions of eastern India, Southeast Asia, and northern Australia. They are excellent swimmers and have often been spotted far out at sea.
The ancient crocodiles – called thalattosuchians – evolved from their land-living ancestors to become fast swimming predators by adapting their limbs into flippers, streamlining their bodies and forming fluked tails for powerful swimming.
The animals adapted a part of the inner ear, responsible for balance and equilibrium, as they gradually adjusted to their new ocean home 170 million years ago.
Paleontologists analysed CAT scans of more than a dozen fossil skulls to examine the vestibular system of the inner ear, which comprises of three looping semicircular canals and helps with balance and spatial awareness.
Their ear canals became markedly fatter and smaller – a shape that made the sensory system less sensitive and one shared with dolphins and whales.
Scientists say this canal shape is better suited to life in the oceans, where buoyancy can hold up an animal, as compared to land, where animals need a highly sensitive sense of balance to cope with gravity and complex landscapes.
A similar change occurred independently in whales. It is thought that each species mimicked each other’s changes during this period of adaptation.
Experts say the findings also show that the crocodiles’ sensory systems evolved in response to their new deep-water environment, rather than driving them into it.
” thalattosuchians and cetaceans became secondarily aquatic in different ways and at different paces, showing that there are different routes for the same type of transition.”
The study, published in Proceedings of the National Academy of Sciences (USA), was supported by a grant from the Leverhulme Trust, and involved a team of scientists from around the world, including from the National Museum of Scotland.