Crocodiles and lizards are both reptiles, but a common misconception exists regarding their biological relationship. Despite superficial similarities, these animals belong to distinct evolutionary lineages. This article clarifies their biological standing and explores why this confusion often arises.
The World of Crocodiles
Crocodiles are large, semi-aquatic predatory reptiles found in tropical and subtropical regions across the Americas, Africa, Asia, and Australia. They include true crocodiles (family Crocodylidae), alligators and caimans (family Alligatoridae), and gharials (family Gavialidae). These animals are characterized by robust bodies, armored skin with bony plates called osteoderms, and powerful jaws with conical teeth designed for gripping prey. Their eyes, ears, and nostrils are positioned on top of their flat heads, allowing them to remain largely submerged while stalking.
Crocodilians inhabit freshwater environments like rivers and lakes, and some species tolerate brackish and saltwater. They are carnivorous, preying on fish, birds, mammals, and other vertebrates. Their evolutionary history is ancient, with members of the crocodilian group appearing around 250 million years ago in the Early Triassic period, making them close living relatives of birds.
The World of Lizards
Lizards are a highly diverse group of reptiles, with over 5,500 species found on every continent except Antarctica. They display a wide range of forms, from small geckos to the large Komodo dragon. Most lizards feature scaly skin, four limbs, movable eyelids, and external ear openings, though some species have lost limbs or eyelids.
Lizard skin is covered in overlapping scales, which provide protection and reduce water loss. Many species can shed their tails as a defense mechanism, a process called autotomy. Lizards occupy diverse habitats, including terrestrial, arboreal, and semi-aquatic environments, with diets varying from insectivorous to herbivorous or carnivorous. They belong to the order Squamata, which also includes snakes, and are classified under the suborder Lacertilia (or Sauria).
Distinct Biological Classifications
Crocodiles are not lizards; they represent distinct branches of the reptile evolutionary tree. While all reptiles belong to the class Reptilia, crocodiles are placed in the order Crocodilia, and lizards are in the order Squamata. This taxonomic distinction reflects their separate evolutionary paths; crocodilians are more closely related to birds than to lizards. Both crocodiles and birds share a common ancestor within the Archosauria group, while lizards belong to the Lepidosaur lineage, which also includes snakes.
Anatomical and physiological differences further distinguish these groups. Crocodiles possess a four-chambered heart, similar to birds and mammals, which efficiently separates oxygenated and deoxygenated blood. Most lizards, conversely, have a three-chambered heart. Crocodilians also feature a unique secondary bony palate, allowing them to breathe while their mouths are full of water or prey, a structure absent in lizards. Crocodilian scales are plate-like osteoderms that do not overlap, whereas lizard scales are typically smaller, more flexible, and overlapping. Their locomotion differs as well; crocodilians can adopt a “high walk” with their bodies lifted from the ground, unlike the sprawling gait of most lizards.
Why the Misconception Persists
The common confusion between crocodiles and lizards stems from several superficial resemblances. Both are cold-blooded reptiles with scaly skin and a generally elongated body shape, leading to a misleading visual similarity. Their shared reptilian appearance, including four limbs and a tail, contributes to the perception of a close relationship. Many people broadly categorize any large, scaly, four-legged reptile as a “lizard,” overlooking precise biological classifications.
Both groups often inhabit similar warm, tropical environments, further blurring distinctions. Despite these outward similarities, their underlying biological structures and evolutionary histories confirm that crocodiles and lizards are distinct groups.