Crocodilian Ancestors’ Sinuses Limited Deep Diving Evolution, Study Finds

Scientists have determined that the sinuses of ancient crocodilian relatives hindered their development into deep-diving creatures comparable to whales and dolphins. Researchers from Southampton and Edinburgh Universities conducted a comparison between thalattosuchians, marine reptiles that coexisted with dinosaurs, and the evolutionary precursors of cetaceans, including whales. The scientists elaborated that cetaceans originated from terrestrial mammals. Over a period spanning 10m years, their bone-encased sinuses diminished, and they subsequently formed sinuses and air sacs external to their skulls. This adaptation enabled dolphins to descend to depths of hundreds of metres and whales to thousands of metres beneath the ocean surface without skull damage. Dr. Mark Young, the lead author and a researcher at the University of Southampton, stated that thalattosuchians went extinct during the Early Cretaceous period, a timeframe between 145m years ago and 100.5m years ago. He commented, “We’ll never know for sure if given more evolutionary time they could have converged further with modern cetaceans or whether the need to mechanically drain their salt glands was an impassable barrier to further aquatic specialisation.” The research team conducted scans of the sinuses in 11 thalattosuchian skulls, alongside skulls from 14 contemporary crocodile species and six additional fossil species. Their findings indicated that brain-case sinuses decreased throughout thalattosuchian evolution as these creatures adapted to a more aquatic lifestyle, mirroring a similar trend observed in whales and dolphins, potentially aiding in diving and feeding. However, the team also observed that after thalattosuchians achieved a fully aquatic existence, their snout sinuses enlarged in comparison to their ancestral forms. The findings of the team were published in the journal Royal Society Open Science.