Prosauropods were large semi-quadrupedal, herbivorous dinosaurs of the Triassic and Early Jurassic. Found on most continents, their fossils are considered to be some of the world's oldest discovered dinosaur bones. Their name "prosauropods" means "before the sauropods", and refers to the belief that this group is ancestral to the Sauropoda. They are usually classified as an infraorder of Sauropodomorpha, which includes the sauropods and belongs to the larger group Saurischia. The Prosauropods includes four families: Platesauride, Anchisauridae, Massospindylidae, and Melanorosauridae.
Although fossils of various Prosauropods have been found on most continents including Asia and the Americas, it is believed that Prosauropods primarily roamed the area now recognized as northern Europe. This is probably due to the fact that a large number of Prosauropod fossils have been unearthed in that area. Perhaps the most intriguing fossil discovery, however, has been found in present-day Madagascar. In October of 1999, a team of scientists uncovered fragmentary remains of Prosauropods believed to be the oldest dinosaur fossils discovered to date.
Even though a large number of Prosauropod fossils have been found, there are still several facts about these animals which remain unclear. For example, it is understood that at least twelve genera of Prosauropods exist, but this number may be upwards to eighteen because several groups are questionable. The diet of these large animals is also controversial albeit much of the evidence points to Prosauropods being herbivorous. Anchisaurids, one of the earliest known Prosauropods, was well-adapted for scavenger/predator type of diets, and even was initially thought to be carnivorous before scientists realized this animal was a herbivorous.
Morphological evidence also suggests Prosauropods were herbivores. Its muscular legs likely enabled them to stand on its two hind feet to reach and eat tall vegetation such as conifers. In addition, the dentition of Prosauropods more closely resembled that of herbivorous, rather than carnivorous, reptiles. Finally, these large grazing creatures were also thought to live and travel and in groups. This provided additional protection against potential predators, and is characteristic of large herbivorous mammals today, further propagating the notion of Prosauropods as being herbivorous creatures.
With a large concentration of Prosauropod fossils found in Europe, many have been found particularly in Germany. For example, one fossil find in Stugensandstein Southwest Germany has uncovered the Prosauropod Sellosaurus. The fossil specimens found revealed that they were the largest terrestrial animals of the Upper Triassic, and that they died when trapped in the quicksand of a floodplain.
Another significant Prosauropod fossil find occurred in the Antarctic on Mt. Kirkpatrick. This find was particularly important because the dinosaurs found in 1986 were among the first found on this extremely cold and unwelcoming continent. The fossil, a partial articulated foot, along with three theropod remains were found with the remains of a Tritylodont and a Pterosaur at this Jurrasic locality. Based on the features and size of the foot, some conclusions have been made such as the likelihood that it was probably one of the biggest Prosauropods that ever lived, and how it was related to Lufengosaurus (Early Jurassic, China) and Plateosaurids in general.
Fossils have also provided clues to the morphology of Prosauropods, and have shown that there were both quadrupedal (moving on all four limbs) and bipedal (walking on two feet) forms. The forelimbs were about half the length of the hind limbs. In the Prosauropods that were facultatively bipedal, the forelimbs had hoof-like structures that aided in gathering food. Some bipeds had a giant claw on their first digit that served as a weapon. In the quadrupeds, the Prosauropods walked with their weight on their second, third, and fourth digit. In addition to these podalic features, Prosauropods are distinctive because of their long necks and their long tails. Lengthwise, they averaged between 8 to 40 feet with their tails usually making up about half of their total length. The neck consisted of about ten elongated vertebrae. The Prosauropods had small heads and heavy limbs.
As mentioned before, the dentition of Prosauropods strongly suggests they were herbivores. Prosauropod teeth were not efficient for chewing; the mouth of the Prosauropod worked in a nutcracker-like fashion. In the remains of tooth crowns, there was no sign of wear, suggesting that the Prosauropods did not and could not chew resilient plant material. To supplement their inefficient mastication, Prosauropods had gastric mills in their stomach walls. The gastric mills are stones embedded in the stomach walls that grind and rip apart food. Despite the aid of the gastric mills, the digestive system of the Prosauropods made them inefficient herbivores, which is believed to have contributed to their extinction.
The following is a break down of the evolution of Prosauropoda. Please refer to the cladogram found as Appendix A at the end of this paper.
Today, most scientists support the idea that Prosauropods form a paraphyletic group (a common ancestor with only some of its descendants) because characteristics such as larger size, herbivory, and quadrupedality continue into the Sauropoda. There is also evidence, however, that Prosauropods are independent of the lineage leading to the more derived Sauropoda, which would make the Prosauropods monophyletic (a common ancestor with all its descendants). Scientists believe that Melanorosaurids are the transitional group between Prosauropods and Sauropods. However, there are differences (such as a reduced fifth metatarsal found in all Prosauropods, not in Sauropods) between the two groups that cause scientists to separate them. What do you think, paraphyletic or monophyletic? (skeleton of a Plateosaurus, a common herbivorous Prosauropod found in Europe)
For more information about Prosauropods:
Zoom Dinosaurs has several children's-level pages on Prosuropods, including: Massospondylus, Plateosaurus, Riojasaurus, and Thecodontosaurus.
Also check out the Sauropodomorpha page in the Dinosauricon, by Mike Keesey; it includes current classification hypotheses for the group as well as basic facts on each genus.
Cooper, M. R., 1980. The first record of the Prosauropod dinosaur Euskelosaurus from Zimbabwe: Its biology, mode of life and phylogenic significance. Arnoldia (Zimbabwe) 9: 1-17.
Discovery of oldest dinosaur bones reported in Science. Science Daily, 22 Oct 1999.
Flynn, John J., et al. 1999. A Triassic fauna from Madagascar, including early dinosaurs. Science 286: 763-765.
Galton, Peter M. 1984. Diet of prosauropod dinosaurs from the Late Triassic and Early Jurassic. Lethaia 18: 105-123.
Galton, Peter M. 1976. Prosauropod dinosaurs (Reptilia, Saurischia) of North America. New Haven: Peabody Museum of Natural History, Yale University.
Galton, Peter M. & P. E. Olsen, 1977. Triassic-Jurassic tetrapod extinctions: Are they real? Science 197: 983-986.
Hammer, William R. 1997. Antarctic Dinosaurs. in P. J. Currie & K. Padian, Encyclopedia of Dinosaurs. Academic Press.
Hungerbühler, A. 1998, Taphonomy of the prosauropod dinosaur Sellosaurus,and its implications for carnivore faunas and feeding habits in the Late Triassic. Palaeogeography, Palaeoclimatology, Palaeoecology 143: 1-29.
Lambert, David. 1980. Dinosaur Data Book: Facts and Fictions about the World's Largest Creatures. New York: Avon Books.
Internet Websites: http://www.kheper.auz.com/gaia/biosphere/vertebrates/dinosauria/Prosauropoda.html
