Ancient crocodilians represent a diverse group of reptiles that thrived throughout Earth’s history, long before and alongside the dinosaurs. Their deep evolutionary roots extend back millions of years, establishing them as a long-reigning lineage of predators and other ecological roles. This group encompassed a far greater variety of forms and lifestyles than the relatively uniform crocodilians seen today.
A World of Ancient Crocodilians
Ancient crocodilians displayed a wide range of body plans and behaviors, exceeding the semi-aquatic generalists of today. Some lineages evolved into fully marine predators, possessing streamlined bodies and paddle-like limbs similar to modern dolphins. Other forms were nimble, swift-running terrestrial predators, unlike the typical slow-moving crocodilian. Certain ancient species even adopted herbivorous diets, a stark contrast to their modern relatives.
This diversity was reflected in their skeletal structures, with variations in limb arrangements, jaw morphologies, and skull shapes. Adaptations allowed them to exploit different environments, from open oceans to dense forests, and to consume a wide array of food sources. Changes in skull and jaw structures enabled them to occupy these new ecological niches. The fossil record reveals forms adapted for crushing prey, slicing flesh, or processing plant material.
Key Ancient Crocodilian Lineages
Among the giant aquatic predators was Sarcosuchus imperator, “SuperCroc,” which lived during the Early Cretaceous period, 130 to 112 million years ago, in what is now Africa and South America. This massive crocodyliform reached lengths of 9 to 9.5 meters (29.5 to 31.2 feet) and weighed between 3.45 to 4.3 metric tons. Its long snout, comprising about 75% of its skull length, and overbite suggest it was a generalist predator in ancient river systems.
Deinosuchus riograndensis was another aquatic giant, inhabiting North America during the Late Cretaceous, 83 to 72 million years ago. Reaching lengths of 10.6 meters (35 feet), Deinosuchus possessed robust teeth designed for crushing and a back covered in thick, hemispherical osteoderms. Its bite force was estimated to be immense, ranging from 18,000 N to over 100,000 N, enabling it to prey on large dinosaurs. These estuarine predators had a secondary bony palate, allowing them to breathe while submerged.
Terrestrial forms showcased adaptations. Kaprosuchus saharicus, the “boar croc” from the Late Cretaceous of Niger, was a fast-running land-dweller with tusk-like teeth that projected from its jaws. Its short, deep skull and large fangs had a powerful bite, adapted for a predatory lifestyle on land. Baurusuchus pachecoi, found in Late Cretaceous deposits of Brazil, was another terrestrial crocodyliform with a deep skull and serrated, blade-like teeth, indicating it was an active predator in its environment.
Marine ancient crocodilians, known as metriorhynchids, were specialized for life in the open ocean. Genera like Metriorhynchus, from the Middle to Late Jurassic, possessed dolphin-like bodies with flippers instead of legs and a tail fin for propulsion. They had slender, pointed teeth for catching fish and other marine prey. These fully aquatic forms represent a departure from the semi-aquatic body plan of modern crocodilians.
Evolutionary Trajectories
The evolutionary journey of crocodilians began in the Triassic period, 240 million years ago, with their emergence as pseudosuchians. This group diversified after the Permo-Triassic mass extinction, 252.2 million years ago, becoming dominant terrestrial vertebrates. Early crocodylomorphs, though small and less common, survived the end-Triassic extinction event, which eliminated many other pseudosuchian groups. Their ability to adapt to diverse diets, including being generalists, contributed to their survival.
Crocodilians underwent adaptive radiations throughout the Mesozoic Era. Different lineages rose, occupying a variety of ecological roles, from aquatic hypercarnivores to terrestrial herbivores. Marine thalattosuchians and various neosuchian lineages diversified in aquatic and semi-aquatic environments during the Jurassic and Early Cretaceous. The Cretaceous also saw a second diversification event with notosuchians in terrestrial habitats.
The Late Cretaceous period saw a decline in crocodylomorph diversity, with many ecologically diverse lineages disappearing. Crocodilians demonstrated resilience, surviving the Cretaceous-Paleogene mass extinction event 66 million years ago, which wiped out the non-avian dinosaurs. The semi-aquatic generalists, similar to modern crocodilians, were among the survivors. This persistence highlights their adaptability to endure environmental changes, allowing a few lineages to continue and give rise to the crocodilians we see today.