Angeac ornithomimosaur

The “Angeac ornithomimosaur” is a naked genus of ornithomimosaur that lived in France during the Early Cretaceous.

## Description

The genus is known from many specimens, accounting for much of the body, Originally thought to have been Hauterivian-Barremian, the species was dated correctly based on palynology to be Berriasian-Valanginian-aged. It is found the the Aquitaine Basin near Angeac, France. Some remains were described by Allain et al. in 2014. This animal was toothless. It has been speculated the remains attributed to the Angeac specimen belong to a ceratosaur, based on morphology of the arms and shoulder girdle. Of the Angeac-Charente locality, ~3800 macroremains attributable to ornithomimosaurs have been discovered, equating to ~50% of all identified vertebrate material at the site. At minimum, ~70 individuals have been recovered (based on the distal end of the left tibiae), and are most concentrated at the CG1 AND CG3 localities, where they represent ~70% of identified remains. This has been suggested to be a mass-mortality event in a herd, but little articulated remains have been found due to intense dinoturbation. The only articulated remains are from the CG9 plot, including the zeugopod and autopod of the forelimb. Maxillary and palate bones recovered have not been identified due to damage. Aside from those elements, this new taxon is virtually complete. The taxon is very similar to Limusaurus, is part of an unknown clade and may be the oldest ornithomimosaur.

With Limusaurus, it shares an external mandibular fenestra, short forelimbs and manual digit reduction. Since the ornithomimosaur/ceratosaur connection is often disputed, and many taxa (probably including the Angeac taxon) have no prominent features to specify their relations, it is difficult to tell what the Angeac ornithomimosaur is. It has weak longitudinal curvature in the pedal unguals, exhibits reduction in the flexor tubercle to a ventral platform (seen in ornithomimosaurs and abelisaurs), having a slender triangular cross-section with one ventral groove (seen in ornithomimosaurs). The centrum in the middle and distal caudal vertebrae is long and low, with the anterior and posterior slightly wider than they are tall and bearing a reniform contour. The ventral surface is adorned with a broad and shallow sulcus and is laterally delimited by two noticeable ridges. These are all in ornithomimosaurs but also in Elaphrosaurus. Seen in ornithomimosaurs, the robust tongue-shaped prezygapophyses elongates anteroposteriorly, up to 3/4 of the centrum's length. They direct horizontally. The proximal end of the tibia is very different from Ceratosaurus, Masiakasaurus, Carnotaurus, Majungasaurus, Afromimus and Elaphrosaurus. It has a fibular crest that is definitively from the proximal articular surface, closer to tetanurans. The elliptical scars present in some ceratosaurs are not present in the Angeac taxon, but this taxon does bear expanded flat articular surface on the astragalus.

The medial buttress present in many tetanurans is not present. On the medial face of the fibular bears a deep, proximodistally elongate elliptical fossa that opens medial and is anteriorly-posteriorly bounded by sharp rims. This fits the musculus popliteus. This feature is in colurosaurs and Elaphrosaurus, but is very different in coelophysoids and ceratosaurs. The tibia and fibula is similar to the astragalus in coelurosaurs and very different to ceratosaurs. The astragalus fuses to the calcaneum. The height and blade of the astragalus is 2x the height of the astragalar body and a process arises from the astragalar' complete body breadth. On the lateral side, the fibular facet is very reduced.