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 Arcovenator escotae

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PostSubject: Arcovenator escotae   Wed Oct 26, 2016 5:19 pm

Arcovenator escotae



Temporal range
: Late Cretaceous, 76-72Ma

Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Infraorder: Ceratosauria
Family: Abelisauridae
Subfamily: Majungasaurinae
Genus: Arcovenator Tortosa et al., 2013

Arcovenator ("Arc hunter") is a genus of abelisaurid theropod dinosaur hailing from the Late Cretaceous of France. The type and only described species is Arcovenator escotae.

Description

Though shallower, the nearly complete braincase of Arcovenator is otherwise of similar size to those of Majungasaurus and Carnotaurus, implying an animal about 5-6 m long. It has moderately thick frontals, as does Aucasaurus, thus less so than Rajasaurus, though more than Rugops, resulting in a slight dome. The parietal which borders the supratemporal fenestrae medially forms ridges on their respective anteromedial margins which as they approach the parietal eminence fuse into a sagital crest. The postorbital is intermediate between the plesiomorphic condition of Abelisaurus and the derived one of Carnotaurus. It has a thick rough-surfaced process dorsal to the eye socket that extended to the lacrimal, forming a bony brow ridge. Generally the external bone ornamentation is more subdued than that of Majungasaurus. The tall teeth (3-5.5 cm) have denticles on the apical portion of the mesial carina and along the length of the distal one, with varying density.

The caudal vertebrae of A. escotae are remarkably similar to those of Majungasaurus, though more dorso-ventrally compressed. The centra possess amphicoelous articulations with the pertinent facets of an intermediate nature between the circular ones of Ilokelesia and those of the elliptical persuasion of Rajasaurus and have neither pneumatic recesses nor accessory hyposphene-hypantrum articulations. The tranverse processes of the neural arches aren't as inclined as in Brachyrostra.

The cnemial crest of Arcovenator's the slender 51-cm tibia is well developed as is characteristic of abelisauroids. It has a proximal lateral condyle more prominent than the medial one and a noticeable distal longitudinal ridge. The nearly half-meter-long fibula possesses the typical anatomical characters of ceratosaurs.

Classification and systematics

Arcovenator is a theropod genus nested within the clade Abelisauridae, which in Linnaean taxonomy has the rank of family. This taxonomical group has as close relatives noasaurids within Abelisauroidea. The latter in turn along with Limusaurus and Ceratosaurus nests within Ceratosauria.

Distinguishing characters of abelisaurids are their short, tall, skulls with extensively sculptured external surfaces, the drastically reduced forelimbs, and the stout hindlimbs.

As with many dinosaur clades, the structure of the phylogenetic tree of Abelisauridae and which genus pertains to which subgroup is in a state of flux as more data is obtained. Arcovenator escotae, being the most complete and informative find since Genusaurus, suscitates readily the parallel interests of attempting to determine its position in relation to other genera, and ascertaining what its suite of characters resolves further of the relatedness between them.

Thus Thierry Tortosa and colleagues conducted a phylogenetic analysis, which is based on previously published works including both the newly discovered fossil remains and other described but unnamed French abelisaurs.

The study generally agrees with previous results, namely the one obtained by Diego Pol and Oliver W. M. Rauhut (2012) of a clade that includes at least Majungasaurus, Indosaurus and Rajasaurus being confirmed, and including Arcovenator at that. Tortosa et al. name this well-supported clade Majungasaurinae, ranking it as subfamily and defining it to contain all abelisaurids more closely related to Majungasaurus than to Carnotaurus. The members of this taxonomical group have various cranial characters in common including an elongated antorbital fenestra, and parietal with a sagittal crest that widens anteriorly into a triangular plate. Also of note is that, in partial agreement with some analyses, the more fragmentary French ceratosaur remains are placed within Abelisauridae, and contrary to others, Abelisaurus is recovered as a carnotaurin.

Discovery and naming

The fossil remains of A. escotae were found near both Pourrières, Var department, Provence-Alpes-Côte d'Azur region and the local stretch of the A8 motorway. The pertinent late Campanian strata (72 to 76 million years ago) of the Lower Argiles Rutilantes Formation are located in the Aix-en-Provence Basin of southeastern France. The holotype of Arcovenator escotae is made up of a fragmentary skull with teeth and associated lower leg bones and caudal vertebra found in a single stratum of fluvial sandstone. Caudal vertebra and teeth found close both in distance and depth were also referred to the species.

The genus name Arcovenator derives from the river Arc as the locality is set within its basin and the Latin word for 'hunter', venator. The specific epithet 'escotae' honors Escota, a motorway concession company, which since 2006 has provided the necessary funds to excavate the locality.

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