Until recently, Smilosuchus gregorii and all other phytosaurs were classified as the earliest group in Crurotarsi, the evolutionary branch containing modern crocodiles and their extinct relatives (1, 2). There is still support for this grouping, but new evidence suggests that this long-held relationship may not be accurate. According to Nesbitt (3), phytosaurs may not be archosaurs at all, but an evolutionary offshoot prior to the common ancestor between crocodiles and birds. This leads to the collapse of Crurotarsi as a useful grouping, as it was previously defined with the inclusion of phytosaurs and would therefore include dinosaurs as well after the phylogenetic rearrangement (1).
S. gregorii has also had its share of taxonomic reshuffling. Leptosuchus is another genus of phytosaur, and there has been much discussion on whether Leptosuchus is congeneric with Smilosuchus. If they are, all species withing the genus Leptosuchus and all species within the genus Smilosuchus would need to be combined under one genus name (4). The crested snout of S. gregorii is not possessed by any Leptosuchus members, leading to them being them being definined as differente genera (5). However, the redefining of S. gregorii is still a matter of some debate, and not accepted by all researchers. Some still classify the taxon as Leptosuchus gregorii and argue that the nose crest was independently developed (4).
- 1. Sereno, Paul C. "Basal archosaurs: phylogenetic relationships and functional implications." Journal of Vertebrate Paleontology 11.S4 (1991): 1-53.
- 2. Brusatte, Stephen L., et al. "The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida)." Journal of Systematic Palaeontology 8.1 (2010): 3-47.
- 3. Nesbitt, Sterling J. "The early evolution of archosaurs: relationships and the origin of major clades." Bulletin of the American Museum of Natural History (2011): 1-292.
- 4. Nesbitt, Sterling J., William G. Parker, and Randall B. Irmis. "The vertebrate fauna of the Upper Triassic Chinle Formation in northern Arizona."
- 5. Long, Robert A., and Phillip Anthony Murry. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science, 1995.
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