Geniodect (lat.: Genyodectes) is a predatory theropod belonging to the infraorder Ceratosaurus (Ceratosauria) and lived in the Lower Cretaceous period in the territory of modern Argentina. Genyodectes serus is the only species in this genus.
Until now, only incompletely preserved bones of the muzzle found in the Argentine province of Chubut (Spanish) are known to science.: Chubut). They belong to the Aptian stage of the Lower Cretaceous period, and their age is about 112 million years.
The dinosaur fossils were found at the end of the 19th century by a local shepherd who later gave them to the Argentine palaeontologist Santiago Roth (Spanish).: Santiago Roth) during one of his expeditions to the Canyon Grande (Spanish.: Cañadón Grande), located in the Argentinean province of Chubut.
However, the exact location of the discovery of fossils, and, therefore, the exact geological age of the genus Geniodekt, is unknown. For a long time it was assumed that the remains found belong to the end of the Upper Cretaceous period, but recently many have attributed Geniodecta to abelisaurids (lat.: Abelisauridae).
Geniodect was scientifically described as early as 1901 by Arthur Smith Woodward.: Arthur Smith Woodward) and is thus the first described non-avian theropod of South America.
This genus is characterized in particular by the very long apices of the maxillary teeth. Fragment of the muzzle (holotype, specimen no. MLP 26-39), kept at the Museum of La Plata (Spanish).: Museo de La Plata), consists of the premaxilla, parts of both halves of the upper jaw, the right and left halves of the lower jaw, teeth, a fragment of the left half of the lamellar bone of the lower jaw, as well as parts of the alveolar processes of the upper jaw.
In 1901, the English paleontologist Arthur Smith Woodward described the fossils and assigned the Latin species name Genyodectes serus to the dinosaur they belonged to. The generic name “Genyodectes” is derived from the Greek words “genys” (“jaw”) and “dektes” (“biting”). The Latin specific epithet “serus” means “late”.
Fossils recorded as holotype no. MLP 26-39 were found between 1896 and 1898 in Cañado Grande Canyon in the Cerro Barcino Formation (Spanish.: Cerro Barcino) of the Aptian stage.
The upper and lower jaws of the holotype contain many teeth. The remains are poorly preserved, but until 1970 they represented the most extensive theropod bone material ever found in South America. It is assumed that the length of the skull of Geniodectus was approximately 30 centimeters, which indicates that it was a relatively small dinosaur with a body length of about 3 meters.
The lower jaw is characterized by a massive structure. Despite the small absolute size of the geniodect, its jaws clearly possessed excellent biting power and were probably adapted to hunting relatively large prey. The premaxilla of the dinosaur contained 8, the upper jaw probably 30, and the lower jaw probably 28 teeth.
The tips of the pair of longest teeth in the upper jaw of the holotype are 95 mm long, which means that when the mouth is closed, these teeth protrude beyond the lower edge of the lower jaw. Teeth recurved and strongly flattened. On the premaxilla, the teeth are overlapped, which is a unique feature of representatives of the suborder Theropoda (lat.: Theropoda) with the possible exception of Ceratosaurus.
Woodward attributed Geniodecta to megalosaurids (lat.: Megalosauridae), as at that time all theropods were generically designated. In 1932 the German paleontologist Friedrich von Huene.: Friedrich von Huene) classified it as a member of the Dinodontidae family (lat.: Dinodontidae), now known as “Tyrannosaurids” (Tyrannosauridae).
The basis for this classification was primarily the massive structure of the lower jaw. However, despite this, the geniodect has no external resemblance to tyrannosaurids. For this reason, and also in part because of the uncertainty of the exact location of the discovery of fossil remains, it was usually ranked among the late, derived representatives of this family. According to another point of view, the designation “geniodekt” was considered a dubious name (lat.: nomen dubium).
Thus, we can say that until recently this dinosaur was classified as a theropod with an indefinite position in the system (lat.: Theropoda incertae sedis).
However, in 2004 Oliver Rauhut (German).: Oliver Rauhut), using a new method of reconstructing fossil remains, on the basis of the unique structure of the skeleton of the geniodect, he singled it out as a separate taxon, which he attributed to the infraorder Ceratosaurus, and the fact that the premaxilla of the geniodectus contains not 6, but 8 teeth, made it possible to determine its belonging to basal ceratosaurids (lat.: Ceratosauridae). After determining the age of the remains, Rauhut agreed with the proposal of the American paleontologist Gregory Scott Paul (Eng.: Gregory Scott Paul) classify this dinosaur as an abelisaurid.
