Sauropodomorphs are among the most well known dinosaurs and the largest land animals that ever walked the surface of the Earth. As shown by their bones, tracks, and other fossils, they had a worldwide distribution that varied regionally but lasted from the Late Triassic to the end of the Cretaceous. Sauropodomorphs originally evolved at about the same time in the Late Triassic as the theropods, their sister clade within Saurischia. They apparently diverged into two clades early in their history, the Prosauropoda and the Sauropoda.
The Prosauropoda were distinguished by their anatomical adaptations toward possible facultative bipedalism and quadrupedalism, indicated by limb proportions and foot anatomy, as well as probable herbivory, discerned from their teeth and jaws, and fore-limb anatomy. They were certainly the largest herbivores of the Late Triassic and Early Jurassic, some reaching up to 11 meters in length (Riojasaurus). Prosauropods were relatively common by the end of the Triassic, and are most abundantly represented by the well-studied Plateosaurus. Prosauropods show the earliest known evidence for nesting of any dinosaur clade in Late Triassic deposits and they left distinctive tracks that correlate well with their skeletal foot anatomy. Despite nearly 50 million years of existence, prosauropods went extinct by the end of the Early Jurassic. Sauropods and other herbivorous dinosaurs that showed up in the geologic record at about that time probably filled their ecological niches as the first high-level browsers, but some sauropods were very likely low-level grazers as well.
Sauropods have a rich fossil record that continues to amaze paleontologists, who keep finding larger body parts of these dinosaurs that push the theoretical constraints on size for land-dwelling animals. Although their fossil record probably began in the Late Triassic, the diversification of sauropods apparently did not begin until the Early Jurassic. Their evolution resulted in some impressive forms adapted to carrying more massive bodies by the end of the Jurassic and continuing through the Cretaceous. Well-represented clades of sauropods include Diplodocidae (Diplodocus, Apatosaurus), Brachiosauridae (Brachiosaurus), Camarasau-ridae (Camarasaurus), and Titanosauridae (Argentinosaurus, Malawisaurus, Titanosaurus). Cetiosauridae was regarded as a loosely-held group containing sauropod species that did not fit well into the other clades, but is now considered a clade in its own right.
Sauropods were undoubtedly land-dwelling herbivores, as shown by their tracks, teeth, and gastroliths. Some may have been high-level browsers of Mesozoic forests, but recently acquired evidence (some anatomical, some botanical) suggests that some were better adapted for low-level grazing. At least some sauropods were social animals; their monospecific bone beds, nesting grounds, and trackways imply that they congregated and traveled in herds. Sauropods seem to have been healthy animals, and although they were on the menu of some theropods there is little evidence to support that they were the objects of predation more often than scavenging.
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