Sinuses prevented prehistoric relatives of crocodiles from diving to great depths like whales and dolphins. This was shown by a study by scientists from the University of Southampton published in the journal. Royal Society Open Science.
Scientists studied a group of Thalattosuchians, crocodile-like reptiles that lived during the time of the dinosaurs. Some species resembled modern gharials and probably lived on the coast. But there were also other species adapted to life in the sea. They had streamlined bodies, fin-like limbs, and tail fins. All this made them resemble dolphins. Scientists decided to test whether the sinuses of these animals are adapted in the same way as dolphins.
Biologists used CT scans to compare the sinuses in the skulls of 11 Thalattosuchian skulls, 14 living crocodile species, and six other fossil species. They found that the sinuses of thalattosuchians shrank during the transition to an aquatic lifestyle, just like in whales and dolphins. This helped them swim, dive and find food. However, when Thalattosuchia turned completely into water, its sinuses grew larger. This prevented them from being as good divers as whales and dolphins. They probably felt pain when diving deep and could even damage their skulls.
The authors suggest that Thalattosuchians “had to enlarge” their sinuses due to a defective excretory system. Whales and dolphins have highly efficient kidneys that filter salt from seawater. Marine reptiles and birds use special glands for this. It is likely that the large and complex nasal sinuses of thalattosuchians helped them secrete salt, as in modern marine iguanas.
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