Genyodectes

Taxobox|
name = "Genyodectes"

fossil_range = Early Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Theropoda
infraordo = Ceratosauria
familia = ?Ceratosauridae
genus = "Genyodectes"
species = "G. serus"
binomial = "Genyodectes serus"
binomial_authority = Woodward, 1901

"Genyodectes" (Woodward, 1901) is a genus of ceratosaurian theropod dinosaur from the Lower Cretaceous of South America. The holotype material (MLP 26-39, Museo de La Plata, La Plata, Argentina) was collected from the Cañadón Grande, Departamento Paso de Indios in the Chubut Province of Argentina and consists of an incomplete snout, including the premaxillae, portions of both maxillas, the right and left dentary, many teeth, a fragment of the left splenial, and parts of the supradentaries. These elements are generally poorly preserved and some are in articulation. The premaxilla of "Genyodectes" (Greek "genys" = "jaw" and "dektes" = "biter") possesses relatively large and protruding teeth, and it is for this feature that the genus was named.

Taxonomy and phylogeny

The taxon has long been considered a nomen dubium, owing to its fragmentary nature and some doubt as to its precise geographic and stratigraphic origins (see Tykoski et Rowe, 2004, p. 50).Tykoski, R.S., and Rowe, T. (2004). Ceratosauria. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (Eds.). "The Dinosauria" (2nd edition). University of California Press:Berkeley. ISBN 0-520-24209-2.] However, a recent redescription of the type material by Rauhut (2004) has shed some light on these questions and seems to establish the taxonomic validity of "Genyodectes serus", the only species referred to the genus.Rauhut, O.W.M. (2004). Provenance and anatomy of "Genyodectes serus", a large-toothed ceratosaur (Dinosauria: Theropoda) from Patagonia. "Journal of Vertebrate Paleontology" 24(4):894-902.] English paleontologist Sir Arthur S. Woodward described "Genyodectes" in 1901,Woodward A. S. 1901. On some extinct reptiles from Patagonia, of the genera "Meiolania", "Dinilysia", and "Genyodectes". "Proceedings of the Zoological Society of London" 1901:169-184.] and, after "Loncosaurus" (Ameghino, 1899; "nomen dubium"),Ameghino, F. (1899). Nota preliminar sobre el "Loncosaurus argentinus", un representante de la familia de los Megalosauridae en la Republica Argentina. "Anales de la Sociedad Cientifica Argentina" 47:61-62.] it is the second non-avian dinosaur described from the South American continent, and it remained the most completely South American theropod until the 1970s. Over the last decade, the holotype has been variously referred to as a megalosaurid, a tyrannosaurid, Theropoda "incertae sedis", and a possible abelisaurid (perhaps even a senior synonym of "Abelisaurus"). However, fossil the recent removal of the holotype from "artificial matrix" in which is had long been displayed (see photo) has permitted a reevaluation of the specimen. Rauhut (2004, p. 900) concluded that the specimen lacks important abelisaurid and tyrannosaurid synapomorphies, but found many neoceratosaurian traits. This would seem to imply "Genyodectes" was closer to "Ceratosaurus" than the more derived abelisaurs (that also decended from animals like "Ceratosaurus"). Also, by studying historical records and preservation of the bones, Rauhut (2004, p. 894) concluded that the specimen was likely collected from the Cerro Castaño Member of the Cerro Barcino Formation (Aptian-Albian).

Diagnosis

Rauhut (2004, p. 895-896) diagnoses "Genyodectes serus" as follows: "Differs from all theropods with the possible exception of "Ceratosaurus" in that the premaxillary teeth are arranged in an overlapping "en-echelon" pattern and the longest maxillary tooth crowns are longer apicobasally than the minimal dorsoventral depth of the mandible. Differs from "Ceratosaurus" in the presence of four, as opposed to three, premaxillary teeth."

References