|Fossil Range||Mid Triassic - |
Prosauropoda, meaning 'before the lizard-footed', were a genus of early herbivourous dinosaurs that lived during the Triassic and early Jurassic periods. As a group of the earliest dinosaurs in their lineage, they were frequently the dominant herbivores in their environment, reaching sizes of 6 to 10 meters in length. While relatively small compared to its later relatives, their size was considerable in such an early period of the dinosaurs. Like their relatives during later periods, the prosauropods had a long neck and small head. However, as these creatures predated the era of the sauropodomorphs, and had not yet evolved into quadrupedal creatures, they were still mainly bipedal, and had forelimbs shorter than their hindlimbs. The prosauropods also had a large claw for defence on their thumbs. Originally thought of as ancestors to the sauropods, as implied by their given name, the prosauropods are no considered to be a parallel lineage.
The prosauropods were originally defined as the early, bipedal, Triassic ancestors of the great sauropod dinosaurs. However, more recent studies have suggested that the prosauropods are of a sister group to the sauropods, evolving on a parallel lineage.
Prosauropods first appeared on the supercontinent of Pangaea as small animals during the middle or late Carnian age, which was the earliest part of the Late Triassic. Fossil records of the creatures have been located in Brazil, Madagascar, and Morocco.
The prosauropod skull was approximately half the length of the femur, while their jaw articulation was slightly below the level of the maxillary tooth row. Their teeth were small and relatively weak, and bore the shape of a spoon, similar to other related clades. The marginal serrations along the teeth allowed for a modest ability to grind and chew tough fauna or plant life. Prosauropods retained the same body plan as ancestral species, but by the later Early or Early Middle Norian age, the prosauropods had doubled in linear dimensions, growing as large as 4 to 6 meters in length in the case of the Plateosaurus gracilis found in Germany. This animal in turn gave rise to other species of Plateosaurus,which gave rise to a dominant creature of the era. Meanwhile, in Argentina, an even larger prosauropod, Riojasaurus, served a similar role. This animal was one of the first fully quadrupedal prosauropods, as it is large size forced it to walk on all fours. Curiously, in southern Africa at this time, the megaherbivore niche was taken not by prosauropods, but by basal sauropods, as indicated by Euskelosaurus, Melanorosaurus and Blikanasaurus, and Antetonitrus. Interestingly, while sauropodomorphs dominated the Norian and Rhaetian large herbivore niche, the large carnivore niche continued to be ruled by the Crurotarsi, for example the Ornithosuchids and 'rauisuchians'.
The end-Triassic extinction killed off the basal sauropodomorphs like Thecodontosaurus, Riojasaurus and species more closely related to sauropods such as Melanorosaurs and Blikanasaurus. However, 'prosauropod' species such as Anchisaurus survived, as did true sauropods. While the first sauropods diversified, the early Jurassic prosauropods radiated out in a number of medium sized megaherbivores like Massospondylus, Lufengosaurus and Yunnanosaurus and were as successful as their Late Triassic predecessors.
The prosauropod reign came to an end in the late Early Jurassic. Although three genera of prosauropods survived into the Middle Jurassic, they were no longer the dominate terrestrial megaherbivores, as the sauropods had continued their massive growth.
- Suborder Sauropodomorpha
- Infraorder Prosauropoda