Alligators and crocodiles, though often confused due to their similar appearances, are distinct creatures. Despite sharing the order Crocodilia, fundamental biological and ecological differences prevent them from successfully mating and producing viable offspring.
Distinctive Characteristics
A primary difference between alligators and crocodiles lies in their snout shape. Alligators have a broad, U-shaped snout, suited for crushing hard-shelled prey. In contrast, crocodiles have a more pointed, V-shaped snout, effective for catching fish and fast-moving aquatic prey.
Another distinguishing feature is tooth visibility. An alligator’s upper jaw is wider, hiding lower teeth when its mouth is shut. Crocodiles have similarly sized jaws, leaving their large fourth lower tooth visible, creating a “toothy grin.” Alligators also have darker, grayish-black skin, while crocodiles are lighter, often olive or tan. Crocodiles are also larger; some species, like the saltwater crocodile, reach 20 feet, compared to the American alligator’s 15 feet.
Divergent Lifestyles
Their differing habitats also contribute to their separation. Alligators inhabit freshwater environments like swamps, rivers, and lakes, found mainly in the southeastern United States and China. Their lack of functional salt glands limits their ability to thrive in saline conditions.
Crocodiles tolerate broader salinity, inhabiting freshwater, brackish, or saltwater environments globally in tropical and subtropical regions. Specialized salt glands allow them to excrete excess salt, enabling life in coastal and marine environments. Though they coexist in some regions, like the Florida Everglades, their distinct environmental preferences usually keep them geographically isolated. Temperamental differences also separate them; alligators are more docile unless provoked, while some crocodile species are more aggressive.
The Genetic Barrier
The primary reason alligators and crocodiles cannot produce viable, fertile offspring is their genetic incompatibility. A species is defined as a group of organisms that can naturally interbreed and produce fertile offspring. They belong to different families within the order Crocodilia—Alligatoridae and Crocodylidae—indicating significant evolutionary divergence.
Their common ancestors diverged 80 to 100 million years ago. This extensive divergence led to distinct genetic makeups. For instance, alligators (Alligator mississippiensis and Alligator sinensis) have 32 chromosomes. Crocodile species, however, vary, with some Crocodylus species having 30 to 34 chromosomes. These chromosomal differences make successful fertilization and embryonic development highly improbable, or would result in infertile hybrid offspring, similar to a mule.