Aetosauria
Heavily armored Late Triassic reptiles related to crocodilians.
Wikipedia / Wikimedia Commons
Aetosaurs were heavily armored reptiles that lived only during the Late Triassic Period. They belong to the extinct order Aetosauria, whose name comes from Greek words meaning "eagle lizard." These animals were medium to large in size and were pseudosuchians—part of the archosaur lineage more closely related to modern crocodiles than to birds or non-avian dinosaurs. Depending on the species, they ate plants or a mix of plants and meat. In some Late Triassic rock layers, aetosaurs are among the most common fossil vertebrates found. Their bodies were covered with four rows of bony plates called osteoderms, and they had small heads, snouts that turned upward, and a semi-erect or pillar-erect stance, not fully upright like dinosaurs or mammals. Fossils have been discovered in Europe, North and South America, parts of Africa, and India. Because their armored plates preserve well and turn up in large numbers at certain sites, aetosaurs are important index fossils for the Late Triassic. Many species had broad geographic distributions but existed for only short stretches of geologic time, so finding a particular aetosaur can help date the rock layer precisely.
- Number of genera
- Around 10–15 valid genera
Lore & Background
Aetosaur remains were first discovered in the early 19th century, although the first remains that were described were mistaken for fish scales. They were later recognized as crocodile relatives, at which point they were interpreted as semiaquatic scavengers closely related to phytosaurs. Subsequent work has established that aetosaurs were entirely terrestrial animals, and were likely herbivorous to some extent. Some forms have characteristics that may have been adaptations to digging for food. Supposed nesting structures have also been referred to aetosaurs, but this connection is considered ambiguous.
Reader's Guide
Aetosaurs are significant as index fossils for the Late Triassic, because their armored plates are often preserved and abundant in certain localities, and many species had wide geographic ranges but short stratigraphic ranges. This allows the presence of particular aetosaurs to accurately date a site. Nearly all aetosaurs belong to the family Stagonolepididae, and two distinct subdivisions are recognized: Desmatosuchia and Aetosaurinae, based primarily on differences in skull morphology. Osteoderm structure is one of the most useful traits for inferring aetosaur relations. Among other archosaurs, aetosaurs are most closely related to Revueltosaurus, a small reptile originally known from teeth mistakenly referred to herbivorous dinosaurs. The study of aetosaurs has helped clarify the evolution of pseudosuchians and the terrestrial ecosystems of the Late Triassic. Their heavy armor and varied body forms—from broad, disc-shaped typothoracines to spiny desmatosuchines—illustrate adaptive radiation among herbivorous archosaurs before the end-Triassic extinction.
Did You Know?
- Aetosaurs are named from Greek words meaning 'eagle lizard'.
- Their first described remains were mistaken for fish scales.
- Aetosaurs are more closely related to crocodilians than to birds or non-avian dinosaurs.
- Some aetosaurs had a 'shovel'-shaped snout tip, similar to a pig's snout.
More in Extinct Archosaurs 1-24
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