Genyodectes
Encyclopedia
Genyodectes is a genus
of ceratosaurian theropod dinosaur from the Lower Cretaceous
(Aptian
) 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 premaxilla
e, portions of both maxilla
s, 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.
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). 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. English paleontologist Sir Arthur S. Woodward described Genyodectes in 1901, and, after Loncosaurus
(Ameghino
, 1899; nomen dubium), it is the second non-avian
dinosaur described from the South American continent
, and it remained the most completely known 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, the recent removal of the holotype from the "artificial matrix" in which it had long been displayed 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 descended 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
).
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."
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of ceratosaurian theropod dinosaur from the Lower Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
(Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
) of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
material (MLP 26-39, Museo de La Plata, La Plata
La Plata
La Plata is the capital city of the Province of Buenos Aires, Argentina, and of La Plata partido. According to the , the city proper has a population of 574,369 and its metropolitan area has 694,253 inhabitants....
, Argentina) was collected from the Cañadón Grande, Departamento Paso de Indios in the Chubut Province of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
and consists of an incomplete snout, including the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
e, portions of both maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
s, the right and left dentary, many teeth, a fragment of the left splenial
Splenial
The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side between the angular and suprangular....
, and parts of the supradentaries. These elements are generally poorly preserved and some are in articulation. The premaxilla of Genyodectes (Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean 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 taxonTaxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
has long been considered a nomen dubium
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
, owing to its fragmentary nature and some doubt as to its precise geographic and stratigraphic origins (see Tykoski et Rowe, 2004, p. 50). 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. English paleontologist Sir Arthur S. Woodward described Genyodectes in 1901, and, after Loncosaurus
Loncosaurus
Loncosaurus was a genus of ornithopod dinosaur from the Upper Cretaceous of Provincia de Santa Cruz, Argentina. The type species is Loncosaurus argentinus, described by the famous Argentinian paleontologist Florentino Ameghino, but is considered a dubious name...
(Ameghino
Florentino Ameghino
Florentino Ameghino was an Argentine naturalist, paleontologist, anthropologist and zoologist.Born in Luján, son of Italian immigrants, Ameghino was a self-taught naturalist, and focused his study on the lands of the southern Pampas...
, 1899; nomen dubium), it is the second non-avian
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
dinosaur described from the South American continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
, and it remained the most completely known South American theropod until the 1970s. Over the last decade, the holotype has been variously referred to as a megalosaurid
Megalosaurid
Megalosauridae was a family of relatively primitive tetanuran theropod dinosaurs, order Saurischia. They were small-to-large carnivores with sharp teeth and three claws on each hand. Some members of this group were Megalosaurus, Eustreptospondylus, Streptospondylus and Torvosaurus...
, a tyrannosaurid, Theropoda incertae sedis
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
, and a possible abelisaurid (perhaps even a senior synonym of Abelisaurus
Abelisaurus
Abelisaurus is a genus of abelisaurid theropod dinosaur from the Late Cretaceous Period of what is now South America. It was a bipedal carnivore that probably reached 7 to 9 meters in length, although it is known from only one partial skull.The generic name recognizes Roberto Abel as the...
). However, the recent removal of the holotype from the "artificial matrix" in which it had long been displayed 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 descended 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
Cerro Barcino Formation
The Cerro Barcino Formation is a geological formation in South America whose strata span the mid-late Cretaceous period. Dinosaur remains are among the fossils that have been recovered from the formation....
(Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
-Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
).
Diagnosis
Rauhut (2004, p. 895-896) diagnoses Genyodectes serus as follows: "Differs from all theropods with the possible exception of CeratosaurusCeratosaurus
Ceratosaurus meaning "horned lizard", in reference to the horn on its nose , was a large predatory theropod dinosaur from the Late Jurassic Period , found in the Morrison Formation of North America, in Tanzania and Portugal...
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."