Infraclass Archosauromorpha

The ruling reptiles, or archosaurs, constitute a spectacular assemblage of reptiles — the dinosaurs, pterosaurs and crocodiles (see pp. 90-169). They arose from a group of primitive diapsid reptiles, the archosauromorphs (meaning "ruling reptile types") in the Late Permian period — quite a different evolutionary line from the lizards/snakes.

Most archosauromorphs were well-adapted land animals, with their long legs placed more directly under the body than in other reptiles. Associated with this change in stance were improvements in the feet, particularly in the articulation of the ankle joints and flexibility of the "big toes."

The carnivorous protorosaurs are the earliest-known members of this group, ancestral to the ruling reptiles. The plant-eating rhynchosaurs are a later group that thrived in the Mid-Triassic.

name: Protorosaurus time: Late Permian locality: Europe (Germany) size: up to 6 ft 6 in/2 m long

This lizard-type reptile is the earliest-known archosauromorph. It lived in the deserts of Europe toward the end of the Permian period. Its long legs were tucked in under its body, allowing it to chase after fast-moving prey — mainly insects. Its neck was made up of 7 large and greatly elongated vertebrae.

name: Tanystropheus time: Middle Triassic locality: Asia (Israel) and Europe

(Germany and Switzerland) size: 10 ft/3 m long

The long necks characteristic of the protorosaurs reached an extreme in this member of the group. Tanystropheus' neck was longer than its body and tail combined. Yet, only 10 vertebrae made up the neck — only 3 more than in Protorosaurus (above) — but each bone was greatly elongated. In fact, when these neck bones were first discovered, they were thought to be leg bones.

So bizarre is Tanystropheus' shape that some paleontologists believe it must have lived in water to support its long neck. But it shows no specific adaptations to an aquatic life. Perhaps it lived on the shoreline, dipping its head into the water after fish or shellfish, and crushing them with its peglike teeth.

name: Hyperodapedon time: Late Triassic locality: Asia (India) and Europe

(Scotland) size: 4 ft/1.3 m long Hyperodapedon was a member of the rhynchosaur group of early reptiles. They were all heavy, barrel-shaped plant-eaters, which thrived from the Middle to Late Triassic. They were the most abundant reptiles of the day, especially in South America and Africa.

The success, though short-lived, of Hyperodapedon and its rhynchosaur relatives can be attributed to their teeth. There were 2 broad tooth plates on each side of the upper jaw. Each plate contained several rows of teeth, and a groove ran down the middle. The 2 single tooth rows of the lower jaws fitted into this groove when the mouth was closed, to give a chopping action.

Rhynchosaurs would have feasted on seed ferns, everywhere abundant during the Triassic. But these plants died out at the end of that period, and were replaced by conifers. The rhynchosaurs died out, too, and their herbivorous niche was taken by the newly evolved, plant-eating dinosaurs. The "Age of Ruling Reptiles" had begun.

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