Riojasuchus

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Not to be confused with the sauropodomorph dinosaur, Riojasaurus
Riojasuchus
Temporal range: Late Triassic, 217–215Ma
Riojasuchus BW.jpg
Riojasuchus tenuiceps
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Pseudosuchia
Family: Ornithosuchidae
Genus: Riojasuchus
Bonaparte, 1969
Type species
Riojasuchus tenuisceps
Bonaparte, 1969

Riojasuchus is an extinct genus of quadrupedal crurotarsan archosaur. Riojasuchus is a member of Ornithosuchidae, a family of facultatively bipedal carnivores that were geographically widespread during the Late Triassic. Two other genera, Ornithosuchus and Venaticosuchus, are currently known. The holotype specimen is PVL 3827. It was found in the Los Colorados Formation.

Discovery and naming[edit]

The holotype specimen is PVL 3827, consisting of a mostly complete crania and a partial postcrania. A majority of the postcranial material was preserved. The skeleton was found with others in the upper section of the Los Colorados Formation. Other that the holotype, it is known from three skeletons[1]

Description[edit]

The skull of the type specimen is 25 centimetres (9.8 in) long, and has a large, partially preserved, curved mandible. The preserved mandible is made up of the maxilla and the premaxilla.[1]

Distinguishing characteristics[edit]

Many characteristics were identified by Bonaparte in 1969. They are listed below:[1]

  • a preorbital vacuity well bordered by protruding edges of the smaller preorbital opening, found in Ornithosuchus;
  • an outgoing lateral lacrimal edge;
  • an infratemporal fenestra present in the shortest adult skull with mandibular fenestra;
  • the top of the surangular laterally pointed, and with a small prearticular process;
  • short atlas and cervical vertebrae, all with a ventral keel;
  • an ilium, pubis and femur, with the talus and calcaneus of the type of Ornithosuchus
  • and median orbits with a higher bottom than in Ornithosuchus.

Classification[edit]

Riojasuchus is a member of Ornithosuchidae, a family of facultatively bipedal carnivores that were geographically widespread during the Late Triassic.[1] Two other genera, Ornithosuchus and Venaticosuchus, are currently known. The group was originally considered to be related to dinosaurs, before many phylogenetical analysises.[2]

Below is a phylogenetic cladogram by Butler et al. in 2011 showing the cladistics of Archosauriformes, focusing mostly on Pseudosuchia:[3] Clade names follow Nesbitt 2011.[4]


Mesosuchus




Prolacerta


Archosauriformes

Proterosuchus




Erythrosuchus




Vancleavea



Proterochampsia

Tropidosuchus



Chanaresuchus





Euparkeria



Phytosauria

Parasuchus




Smilosuchus



Pseudopalatus




Archosauria
Pseudosuchia
Ornithosuchidae

Riojasuchus



Ornithosuchus



Suchia

Gracilisuchus



Turfanosuchus




Revueltosaurus


Aetosauria

Aetosaurus




Stagonolepis



Longosuchus







Ticinosuchus


Paracrocodylomorpha
Poposauroidea

Qianosuchus



Ctenosauriscidae

Arizonasaurus



Xilousuchus



Hypselorhachis



Ctenosauriscus



Waldhaus Taxon






Poposaurus gracilis H



Poposaurus gracilis Y





Lotosaurus


Shuvosauridae

Sillosuchus




Shuvosaurus



Effigia








Loricata

Prestosuchus




Saurosuchus




Batrachotomus




Fasolasuchus



Rauisuchidae

Rauisuchus




Polonosuchus silesiacus



Postosuchus alisonae



Postosuchus kirkpatricki




Crocodylomorpha

CM 73372




Hesperosuchus agilis



Hesperosuchus "agilis"



Dromicosuchus



Alligator














Avemetatarsalia










Paleoecology[edit]

Fossils of Riojasuchas are found in the Los Colorados Formation, a Late Triassic unit in Argentina,[1] and date to approximately 217 to 215 million years ago.[2] At that age, it is the youngest ornithosuchid known.[2] It lived alongside the protosuchid Hemiprotosuchus; the sphenosuchid Pseudohesperosuchus; the stagonolepidid Neoaetosauroides; the melanorosaurid Strenusaurus; and the riojasaurid Riojasaurus.[1]

References[edit]

  1. ^ a b c d e f Bonaparte, J. F. (1969). "Dos Nuevas 'faunas' de reptiles triásicos de Argentina". First Gondwana Symposium (in Spanish) 2: 283–306. 
  2. ^ a b c von Baczko, M. B.; Ezcurra, M. D. (2013). "Ornithosuchidae: a group of Triassic Archosaurs with a unique ankle joint". In Nesbitt, S. J.; Desojo, J. B.; Irmis, R. B. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and Their Kin. The Geological Society. pp. 183–195. ISBN 978-1-86239-361-5. 
  3. ^ Butler, R. J.; Brusatte, S. J.; Reich, M.; Nesbitt, S. J.; Schoch, R. R.; Hornung, J. J. (2011). "The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation". In Farke, Andrew A. PLoS ONE 6 (10): e25693. doi:10.1371/journal.pone.0025693. 
  4. ^ Nesbitt, S. J. (2011). "The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades". Bulletin of the American Museum of Natural History 352: 189. doi:10.1206/352.1. ISSN 0003-0090. 

External links[edit]