Deltadromeus

Deltadromeus (meaning "delta runner") is a genus of theropod dinosaur from Northern Africa. It had long, unusually slender hind limbs for its size, suggesting that it was a swift runner. The skull is not known. One fossil specimen of a single species ("D. agilis", or "agile delta runner") has been described, found in the Kem Kem Beds, which date to the mid Cretaceous Period (mid Cenomanian age), about 95 million years ago. It may be a junior synonym of the contemporary "Bahariasaurus". The classification of "Deltadromeus" has been in flux since its original description. In 2016, a South American theropod known as "Gualicho shinyae" was found to possess many similarities with "Deltadromeus". Depending on the phylogenetic position of "Gualicho", "Deltadromeus" may have been a neovenatorid carnosaur, a tyrannosauroid, or a basal coelurosaur if its close relation to "Gualicho" is legitimate. Other studies have considered it a ceratosaurian, more specifically a member of the family Noasauridae.
Description.
The holotype of "Deltadromeus agilis" (museum catalogue number SGM-Din2) is a partial skeleton of an animal which is estimated to have measured 8 meters (26.24 feet) long. The weight of the living animal was estimated to have been around 1050 kilograms, slightly more than an imperial ton.
A number of specimens (catalogued under IPHG 1912 VIII) were originally considered by Ernst Stromer to be conspecific with "Bahariasaurus", but were referred to "Deltadromeus" by Paul Sereno in 1996. They were thought to come from a much larger individual, with a femur (upper leg bone) length of 1.22 meters (4 feet), compared to the 0.74 meter (2.46 foot) long femur of the holotype. These referred specimens, if legitimately assigned to "Deltadromeus", would have indicated that members of the genus could grow up to 12.2 meters (40 feet) in length, approximately the size of a "Tyrannosaurus rex". However, the referral of the coracoid, pubes, and hindlimb material catalogued under IPHG 1912 VIII to "Deltadromeus" has been questioned because the remains came from different horizons and localities in the Bahariya Formation, and actually exhibit notable differences from the holotype of "Deltadromeus".
The "Deltadromeus" skeleton has been found in the same formation as those of the giant theropods "Carcharodontosaurus", "Spinosaurus", and "Bahariasaurus", which may be synonymous with "Deltadromeus". No skull material has been found for either "Deltadromeus" or "Bahariasaurus", and though carnivore teeth labelled as "Deltadromeus" are sold in rock shops, there is no way of knowing if they actually come from this animal.
Classification.
"Deltadromeus" as a ceratosaur.
Many studies published since the original description of "Deltadromeus" have considered it to be a ceratosaur, although different studies disagree on what kind of ceratosaur. One 2003 study suggested it was a member of the Noasauridae, though others have found it to be more primitive, possibly related to the primitive ceratosaurs "Elaphrosaurus" and "Limusaurus". A more comprehensive study of noasaurid relationships published in 2016 found that both of these interpretations were essentially correct, with "Deltadromeus", "Limusaurus", and "Elaphrosaurus" all found to be within the Noasauridae. A 2017 paper describing ontogenetic changes in "Limusaurus" and the effect of juvenile taxa on phylogenetic analyses placed "Deltadromeus" as a noasaurid in every analysis regardless of which "Limusaurus" specimen was used, although the analyses did not include "Gualicho" or "Aoniraptor". According to the writers of the paper, resolving the phylogenetic positions of "Gualicho, Aoniraptor, Deltadromeus," and megaraptorans is one of the most critical issues presently facing theropod systematics. "Deltadromeus" was also considered a noasaurid in a 2020 review of the Kem Kem Group geology and fauna.
The cladogram below follows a 2016 analysis by Oliver Rauhut, and Matthew Carrano.
"Deltadromeus" as an avetheropod.
The original description of "Deltadromeus" in 1996 found that it was a fairly basal coelurosaur, only slightly more advanced than the Late Jurassic genus "Ornitholestes". In 2016, an analysis of "Gualicho", a South American theropod considered to belong to the allosauroid family Neovenatoridae, found "Deltadromeus" to be "Gualicho"'s probable sister taxon. However, the analysis also noted that "Deltadromeus" shared many features with ceratosaurs and that if "Gualicho" was removed from the analysis, "Deltadromeus" would resolve to a member of Ceratosauria. In an analysis of "Aoniraptor", which may be the same animal as "Gualicho", "Deltadromeus" was found along with "Aoniraptor" and "Bahariasaurus" to probably form a still poorly known clade of megaraptoran tyrannosauroids different from the Megaraptoridae. A 2018 study by Porfiri et al. has supported the idea that "Gualicho" and megaraptorans were basal coelurosaurs, outside of both Neovenatoridae and Tyrannosauroidea. However, this study did not include "Deltadromeus".
The cladogram below follows the 2016 "Gualicho" analysis by Sebastián Apesteguía, Nathan D. Smith, Rubén Juarez Valieri, and Peter J. Makovicky.