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|(unranked)||Crurotarsi
Family Prestosuchidae
Family Rauisuchidae
Family Poposauridae
Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters) Triassic archosaurs. Originally it was believed that they were related to Erythrosuchids (Sill, 1974), but it is now known that they are crurotarsans (Benton 2004). Three families are generally recognised: Prestosuchidae , Rauisuchidae , and Poposauridae , as well as a number of forms (e.g. those from the Olenekian of Russia) that are too primitive and/or poorly known to fit in any of these groups. There is no doubt that the group as currently defined is paraphyletic, representing a number of related lineages independently evolving and filling the same ecological niche of medium to top terrestrial predator. The group may even be something of a "wastebasket taxon ". Determining exact phylogentic relationships is difficult because of the scrappy nature of a lot of the material. However, recent discoveries and studies such as those of Batrachotomus (Gower, 2002; Benton & Walker 2002) are shedding light on the evolutionary relationships of this poorly known but fascinating group.
Jose Bonaparte and following him Mike Benton argue (Bonaparte 1981, Benton, 1984) that rauisuchians such as Saurosuchus developed an erect stance independently of and differently to dinosaurs, by means of having the femur vertical and angling the acetabulum ventrally, rather than having an angled neck or curve in the femur. They refer to this as the pillar-erect posture.
The erect gate indicates that these animals were clearly active, agile predators, with locomotor superiority over the Kannemeyerid Dicynodonts and abundant Rhynchosaurs on which they fed. They were succesful animals, the largest with skulls a meter or more in length, and continued right until the end of the Triassic, when, along with many other large archosaurs, they were killed off by the end Triassic extinction event. With their demise, theropod dinosaurs were able to emerge as the sole large terrestrial predators; meat-eating dinosaur footprints are suddenly increase in size at the start of the Jurassic, when rauisuchians are absent (Olsen et al. 2002)
Well known Rauisuchians include Ticinosuchus of the Middle Triassic of Europe (Switzerland and Northern Italy), Saurosuchus of the late Triassic (Late Carnian ) of South America (Argentina), and Postosuchus of the late Triassic (Late Carnian to Early Norian ) of North America (SW USA). On Rauisuchian, Teratosaurus , was for a long time even considered an early theropod|theropod dinosaur!
External links
References
- Benton, MJ (1984), Rauisuchians and the success of dinosaurs. Nature 310: 101
- Benton, M. J. (2004), Vertebrate Paleontology, 3rd ed. Blackwell Science Ltd
- Benton, MJ & AD Walker (2002), Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland, Zool. J. Linn. Soc. 136: 25-47.
- Bonaparte, JF (1984) Locomotion in rauisuchid thecodonts. J. Vert. Paleont. 3(4):210-218
- Carroll, RL (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co.
- Gower, DJ (2002), Braincase evolution in suchian archosaurs (Reptilia: Diapsida): evidence from the rauisuchian Batrachotomus kupferzellensis, Zool. J. Linn. Soc. 136: 49-76
- Olsen, P.E., Kent, D.V., H.-D.Sues,, Koeberl, C., Huber, H., Montanari, E.C.Rainforth, A., Fowell, S.J., Szajna, M.J., and Hartline, B.W., (2002) Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary. Science, vol. 296, p. 1305-1307.
- Sill, WD (1974). The anatomy of Saurosuchus galilei and the relationships of the rauisuchid thecodonts. Bull. Mus. Comp. Zool. 146: 317-362
