Crocodiles can’t fly. Birds can. Scientists have finally figured out why

Scientists have recently discovered why crocodiles cannot fly while birds can. Both crocodiles and birds are classified as archosauriforms, a group of species that originated around 250 million years ago during the early Triassic period. Over time, this group split into two lineages: one evolved into crocodiles (Pseudosuchia) and the other into dinosaurs and birds (Avemetatarsalia). This means there is a significant 500 million years of evolutionary difference between modern birds and crocodiles.

Crocodiles are ectothermic, meaning their body temperatures are determined by the environment, and they have low metabolic rates. They are generally sluggish, only occasionally exhibiting bursts of powerful activity when hunting or fighting. Birds, on the other hand, are endothermic, with high metabolic rates that allow them to generate heat and maintain stable body temperatures, enabling them to perform sustained, strenuous exercise like flying. Birds do not tire or fall from the sky.

The conventional belief has been that the common ancestor of crocodiles and birds was more similar to a crocodile than a bird. However, recent research suggests the opposite may be true. The study found that modern crocodiles possess four-chambered hearts, a feature exclusive to warm-blooded animals such as birds and mammals. These hearts are crucial for maintaining high blood flow rates and pressures to accommodate the high metabolic demands of warm-blooded creatures.

The researchers hypothesize that both the crocodile and dinosaur-avian lineages originally possessed warm-blooded metabolisms, but the crocodiles later reverted to a cold-blooded lifestyle. The crocodiles' unique heart structure suggests that their ancestors had evolved for warm-blooded life at some point. Moreover, analysis of fossil leg bones from various species, including dinosaurs and ancient archosaurs, revealed larger blood vessels that indicate a higher metabolic rate, further supporting the theory that both lineages were warm-blooded until relatively recently.

The researchers believe that the transition from warm-blooded to cold-blooded lifestyles in crocodiles may have been a response to changes in their behavior and environment. As ambush predators in water, modern crocodiles have adapted to conserve energy by holding their breath for longer periods, allowing them to remain hidden while waiting for prey.

This low metabolic rate is an advantage for ambush predators, but it is incompatible with the water-based lifestyle of warm-blooded animals, which cannot hold their breath for extended periods. Additionally, the extinction of most dinosaur lineages around 66 million years ago, likely caused by an asteroid impact, may have been due to the crocodile lineage reverting to a cold-blooded metabolic system, which better suited their aquatic habitat and helped them survive the mass extinction event.