Description
The head is small relative to the large body, and quite distinctive in shape, being flat and blunt at the front, like the snout of a pig. Some teeth are chisel-shaped, small and leaf-like, indicating a probable herbivorous diet, although peg-like teeth and a keratinous snout have been considered possible adaptations in some species for feeding on colonial insects. A study of the braincase of Stagonolepis robertsoni has shown that there are similarities between it and those of crocodylomorphs, which may indicate a close relationship.
Aetosaurs had a "pillar-erect" erect limb posture similar to that seen in Rauisuchia, a related group of Triassic archosaurs. A pillar-erect limb posture is one where the femur articulates vertically with the acetabulum of the hip, which is angled downward, so that the leg is positioned beneath the body and acts as a pillar bearing weight. While the limb posture is similar to rauisuchians, the feet resemble those of phytosaurs (crocodile-like semiaquatic crurotarsans) in the retention of primitive characteristics. Although the forelimbs are much smaller than the hind limbs, all aetosaurs were quadrupeds.
Aetosaurs were very heavily armored (most certainly as a defense against predators), with large quadrangular, interlocking bony plates, or osteoderms, protecting the back and sides, belly, and tail. In life, these plates were probably covered in horn. Dorsal osteoderms, which are found on the backs of aetosaurs, are often ornamented with radial grooves. Dorsal paramedians, those found along the midline of the animal, are often wide and quadrangular with a small boss called a dorsal eminence on the dorsal surface of each plate. In aetosaurs, paramedian plates often have raised or depressed anterior edges where the plates articulate with the ones in front of them. If the anterior edge is raised, the area is called an anterior bar, while if it is depressed, the area is called an anterior lamina. In lateral plates, which are positioned on either side of the paramedian plates, the dorsal eminence is often enlarged into a prominent spike. This spike is especially noticeable in desmatosuchines such as Longosuchus and Desmatosuchus. Osteoderms are useful in diagnosing aetosaur taxa, and aetosaur species can often be identified from individual scutes based on their ornamentation pattern.
Primitive genera, like the widespread Norian genus Aetosaurus and the Carnian Coahomasuchus, tended to be small, about a metre (3.2 ft) in length. However, more advanced forms were larger - about 3 metres (9.8 ft) in length - with some taxa, such as Typothorax and Paratypothorax, possessing broad turtle-like bodies, and others, like Desmatosuchus, a narrow-bodied genus at least 4 metres (13 ft) long, equipped with large spines over the shoulders, which added to the animal's defensive armament.
Read more about this topic: Aetosaurs
Famous quotes containing the word description:
“Once a child has demonstrated his capacity for independent functioning in any area, his lapses into dependent behavior, even though temporary, make the mother feel that she is being taken advantage of....What only yesterday was a description of the child’s stage in life has become an indictment, a judgment.”
—Elaine Heffner (20th century)
“As they are not seen on their way down the streams, it is thought by fishermen that they never return, but waste away and die, clinging to rocks and stumps of trees for an indefinite period; a tragic feature in the scenery of the river bottoms worthy to be remembered with Shakespeare’s description of the sea-floor.”
—Henry David Thoreau (1817–1862)
“The Sage of Toronto ... spent several decades marveling at the numerous freedoms created by a “global village” instantly and effortlessly accessible to all. Villages, unlike towns, have always been ruled by conformism, isolation, petty surveillance, boredom and repetitive malicious gossip about the same families. Which is a precise enough description of the global spectacle’s present vulgarity.”
—Guy Debord (b. 1931)