Aetosauria Translation and Pronunciation Guide

Introduction

Ben Creisler

Aetosaurs ("eagle lizards") might be the answer to a riddle: "What looks like an armadillo but is named for a bird?" Members of this group of archosaurs somewhat resembled modern armadillos, and filled a role during the Late Triassic assumed in later ages by ankylosaurs and glyptodonts--a low-slung quadrupedal herbivore, with a prickly, bite-proof suit of armor to deter predators. Such comparisons notwithstanding, the name Aetosauria means "eagle lizards," and perpetuates an old, misleading idea: the name-sake genus Aetosaurus was first described as having a birdlike skull.

Aetosaurs were the among the earliest archosaurs to adapt to a diet of plants. The recent discovery of a small aetosaur from Texas that had recurved saber-like teeth--indicating a carnivorous diet--may shed new light on the still murky origin of the group. Later aetosaurs were characterized by pointed pig-like snouts with a toothless tip expanded in a small shovel-like ridge, likely designed to dig up roots and tubers. Further back along the upper jaw lay a number of weak leaf-shaped teeth. The slipper-shaped lower jaw was also toothless at the tip, with a few teeth along the dentary.

The top of the head was solid, as might be expected in an armored animal. Somewhat surprisingly, though, the orbit, antorbital fenestra, nostril and other lateral openings were quite large and deeply excavated, lightening the skull in a somewhat birdlike manner--thus inspiring the unlikely name "eagle lizard" for Aetosaurus. The mandible also had a large lateral opening. Armor covered the neck, and the upper and under sides of both the trunk and the tail, and was particularly developed over the back with large interlocking bony plates and, in many forms, heavy spikes along the neck and flanks. The short, robust limbs had a crocodile-like tarsus and moved in a semi-sprawl (unlike ankylosaurs, which had erect limbs brought close to the body). The manus was small and broad, and lacked large claws that might be expected in an apparent digging animal.

Aetosaurs ranged in size from the unnamed carnivorous form from Texas at 0.9 m. (3 ft.) to Desmatosuchus, at up to 5 m. (16.5 ft.). Most (Stagonolepis, Desmatosuchus) retained a rather narrow crocodile-like body, but Typothorax and Paratypothorax had a broad turtle-like midsection, probably expanded to contain a large fermenting gut in the manner of ankylosaurs. Aetosaurs currently are known from the Late Triassic of North America, Western Europe and South America. A supposed genus from China, Fukangolepis Yang 1978, based on fragmentary material, has been reidentified as a dicynodont (= Sinokannemeyeria) (Lucas & Hunt, 1993).