The term “galloping crocodile dinosaur” often appears in discussions about prehistoric life. This phrase combines aspects of two distinct groups of ancient reptiles: the crocodilian lineage and the dinosaur lineage. The creatures typically associated with this description are neither true dinosaurs nor true crocodiles, but rather a fascinating group of their own. This article explores what this popular, yet often misapplied, term refers to in the fossil record.
Identifying the Creature
The creature most commonly linked to the “galloping crocodile dinosaur” concept is Postosuchus, a large, quadrupedal archosaur that lived in North America during the Late Triassic period. Postosuchus was a member of the Pseudosuchia, a diverse group of archosaurs that includes modern crocodilians, making them more closely related to today’s crocodiles than to dinosaurs or birds. Pseudosuchians were dominant terrestrial megafauna during the Triassic. Postosuchus could reach lengths of 5 to 6 meters (16 to 20 feet) and possessed a robust skeleton with a deep skull and a long tail.
Anatomy and Locomotion
The physical characteristics of these ancient archosaurs offer insights into the “galloping” idea. Unlike modern crocodiles, whose legs sprawl out to the side, pseudosuchians like Postosuchus had limbs positioned more directly underneath their bodies, allowing for an upright stance. This gait provided a more efficient way of moving on land.
Evidence suggests Postosuchus may have been bipedal, with its forelimbs significantly shorter than its hind limbs. Other primitive crocodiles from later periods also exhibited bone structures suggesting they were capable of “galloping” across plains. This upright leg posture allowed for a more agile, bounding movement over land compared to the belly-crawling of modern crocodiles.
Its Role in the Ancient World
During the Triassic period, creatures like Postosuchus occupied the role of apex predators in terrestrial environments. They were larger than the early dinosaur predators of their time, such as Coelophysis. Their diet likely consisted of large, bulky herbivores, including dicynodonts, and various smaller creatures. Fossil discoveries have revealed a diverse array of ancient crocodilians that coexisted with dinosaurs. Some of these, like Kaprosuchus saharicus (“BoarCroc”), were large predators with dagger-like tusks and armored snouts. Others, such as Laganosuchus thaumastos (“PancakeCroc”), were ambush predators that would lie motionless in water with open jaws, waiting for prey.
Evolutionary Connections
Pseudosuchians are one of the two major divisions within Archosauria, often referred to as “crocodilian-line archosaurs.” This lineage is distinct from Avemetatarsalia, which includes all archosaurs more closely related to birds, such as dinosaurs and pterosaurs. Despite sharing a common archosaur ancestor, the pseudosuchian line diverged early on from the lineage that led to dinosaurs and birds. Pseudosuchians were highly diverse, from marine forms to agile speedsters and armored tanks. While they were the dominant terrestrial megafauna during the Triassic period, many groups of pseudosuchians went extinct around the Triassic-Jurassic extinction event. This event paved the way for dinosaurs to rise to prominence, though one group, the crocodylomorphs, survived and diversified, eventually leading to modern crocodiles.