A study from the University of Southampton, published in the journal Royal Society Open Science, shows that the nasal sinuses of Thalattosuchians helped keep these crocodile relatives from diving to the great depths reached by whales and dolphins.
Thalattosuchians were crocodile like reptiles that lived during the age of the dinosaurs. Some species resembled modern gharials and probably lived on the coast. But there were also other species adapted to life at sea. They had streamlined bodies, fin like limbs, and tail fins, all features that made them resemble dolphins. Scientists tested whether the sinuses of these animals were adapted in the same way as dolphins by studying skulls with CT scans.
Biologists used CT scans to compare the sinuses in the skulls of 11 Thalattosuchian specimens, 14 living crocodile species, and six other fossil relatives. They found that the sinuses of thalattosuchians shrank during the shift to an aquatic lifestyle, just as happens in whales and dolphins. This helped them swim, dive, and find food. However, when Thalattosuchia became fully aquatic, its sinuses grew larger. This prevented them from diving as deeply as whales and dolphins. They probably felt pain when diving deep and could even damage their skulls.
The researchers suggest that Thalattosuchians had to enlarge their sinuses because their excretory system was not optimized for seawater. Whales and dolphins have highly efficient kidneys that filter salt from seawater. Marine reptiles and birds rely on specialized glands for this task. It is likely that the large and complex nasal sinuses of thalattosuchians helped them secrete salt, similar to the mechanism seen in modern marine iguanas.
Earlier work in paleontology also touched on unrelated topics, including notes about giant marsupial mice and their relevance to conservation concerns such as poaching.