Crocodiles' Evolutionary Reversal: From Warm-Blooded to Cold-Blooded
Crocodiles' ancestors were warm-blooded, but an evolutionary reversal turned them into cold-blooded predators.
1Common Ancestor of Crocodiles and Birds
Modern crocodiles and birds share a common ancestor dating back to the Early Triassic period. Paleontologists call these ancestors archosaurs. Archosaurs are a group of reptiles that survived the harsh conditions following the Permian-Triassic extinction event, which occurred approximately 250 million years ago.
2The Warm-Blooded Misconception
Scientists previously believed that the evolutionary split of archosaurs began when birds became warm-blooded. However, new findings reveal that crocodile ancestors were also warm-blooded at one point. Fossil analyses indicate that crocodile ancestors remained warm-blooded until about 66 million years ago.
3Advantages of Cold-Bloodedness
The transition to cold-bloodedness slowed crocodiles' metabolism, allowing them to stay submerged in water for longer periods. This adaptation provided advantages such as ambushing prey and remaining underwater for extended durations. Cold-bloodedness became a crucial part of crocodiles' survival strategy.
4Clues from the Four-Chambered Heart
Crocodiles' four-chambered hearts are considered a sign of warm-bloodedness. This heart structure is also found in warm-blooded birds and mammals. Researchers highlight that this heart structure is a significant piece of evidence supporting the warm-blooded nature of crocodile ancestors.
5Evidence from Fossil Bones
Researchers examined holes in fossilized bones that once housed blood vessels. These holes are known to be larger in warm-blooded animals. The size of the holes in crocodile ancestors' bones was found to be consistent with warm-bloodedness.
6Blood Flow Rate Analysis
The diameter of blood vessel holes in fossil bones was measured to calculate blood flow rates. The blood flow rate of crocodile ancestors was found to be closer to that of high-metabolism reptiles and mammals living today. This finding supports the warm-bloodedness hypothesis.
7The Impact of Gigantic Size
Some paleontologists suggest that gigantic cold-blooded dinosaurs might have had high blood flow rates due to their massive size, a phenomenon known as 'gigantothermy.' However, microfracture analyses indicate that archosaurs led active lives.
8Cold-Bloodedness and Survival
Researchers propose that the transition to cold-bloodedness helped crocodile ancestors survive the aftermath of the Chicxulub asteroid impact. Cold-bloodedness slowed metabolism, increasing their chances of survival during this challenging period.
Original article: Gizmodo — Timsahların Evrimsel Geri Dönüşü: Sıcakkanlıdan Soğukkanlıya