Stagonosuchus

Stagonosuchus is an extinct genus of loricatan, or possibly a species of Prestosuchus. Fossils have been found from the Late Triassic Manda Formation in Tanzania that are Anisian in age.

Stagonosuchus
Temporal range: Anisian
~247–242 Ma
↓
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Family: †Prestosuchidae
Genus: †Stagonosuchus
Huene, 1939
Species
  • †S. nyassicus Huene, 1939 (type)

Unlike other rauisuchians, which have a prominent ridge on the illium called the supra-acetabular buttress that overlies the femur, Stagonosuchus possesses only a slight thickening on the surface of the bone.[1][2] In Stagonosuchus, the pubis is broad and plate like, while in other genera it is narrower and may have a prominent "foot" like that of some theropod dinosaurs.[3]

The centra of the vertebrae are constricted to some extent, though not as much as in other rauisuchians such as Saurosuchus. In the vertebrae, the neural canals (through which the spinal cord would pass) extend into the centra, forming deep concavities.[4] A wide articulation between the hyposphene and hypantrum in successive vertebrae prevented any lateral movement of the spine. A small accessory neural spine projects near the larger main spine, possibly as an extra attachment for bracing ligaments. Stagonosuchus also has many laminae, or ridges of bone on the vertebrae.[5]

Friedrich von Huene, who named the genus in 1938, first classified Stagonosuchus as a rauisuchid.[6] In 1967, Alfred Romer placed Stagonosuchus in the newly erected family Prestosuchidae.[7] However, this was likely due to the close similarities shared between the two families which made classification difficult. Stagonosuchus has since been considered a rauisuchid. A 2010 study on archosaurian phylogeny found Stagonosuchus to be outside both Rauisuchidae and Prestosuchidae in a more basal position within Rauisuchia. The study erected the name Rauisuchoidea to include it and other basal taxa that were closely related to rauisuchids and prestosuchids, including Ticinosuchus (traditionally thought to be a prestosuchid) and Arganasuchus and Fasolasuchus (previously considered rauisuchids).[8] A 2011 study found Ticinosuchus to be the closest relative of Stagonosuchus despite a conspicuous difference in size between the two forms (Ticinosuchus is much more gracile than the larger Stagonosuchus).[5] A 2020 study argued that Stagonosuchus was a second species of Prestosuchus, Prestosuchus nyassicus.[9]

References
  1. Gower, D. J. (2000). "Rauisuchian archosaurs (Reptilia:Diapsida): An overview" (PDF). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 218 (3): 447–488. doi:10.1127/njgpa/218/2000/447.
  2. Sulej, T (2005). "A new rauisuchian reptile (Diapsida: Archosauria) from the Late Triassic of Poland". Journal of Vertebrate Paleontology. 25 (1): 78–86. doi:10.1671/0272-4634(2005)025[0078:ANRRDA]2.0.CO;2.
  3. Bonaparte, J. F. (1984). "Locomotion in rauisuchid thecodonts". Journal of Vertebrate Paleontology. 3 (4): 210–218. doi:10.1080/02724634.1984.10011976.
  4. Dawley, R. M.; Zawiskie, J. M.; Cosgriff, J. W. (1979). "A rauisuchid thecodont from the Upper Triassic Popo Agie Formation of Wyoming". Journal of Paleontology. 53 (6): 1428–1431.
  5. Lautenschlager, Stephan; Julia Brenda Desojo (2011). "Reassessment of the Middle Triassic rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus". Paläontologische Zeitschrift. 85 (4): 357–381. doi:10.1007/s12542-011-0105-1.
  6. Huene, F.v. (1936). "Übersicht über Zusammensetzung und Bedeutung der Thecodontia". Zentralblatt für Mineralogie, Geologie und Paläontologie. 1936: 162–168.
  7. Romer, A. S. (1967). Vertebrate Paleontology. Chicago: University of Chicago Press. p. 468.
  8. Brusatte, S.L.; Benton, M.J.; Desojo, J.B.; Langer, M.C. (2010). "The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida)" (PDF). Journal of Systematic Palaeontology. 8 (1): 3–47. doi:10.1080/14772010903537732.
  9. Desojo, Julia Brenda; Baczko, María Belén von; Rauhut, Oliver W. M. (2020-02-18). "Anatomy, taxonomy and phylogenetic relationships of Prestosuchus chiniquensis (Archosauria: Pseudosuchia) from the original collection of von Huene, Middle-Late Triassic of southern Brazil". Palaeontologia Electronica. 23 (1): 1–55. doi:10.26879/1026. ISSN 1094-8074.


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