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''Deltadromeus'' (meaning "delta runner") is an extinct genus of controversial
theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...
dinosaurs from the Aoufous Formation (
Kem Kem Beds The Kem Kem Group (commonly known as the Kem Kem beds) is a geological group in the Kem Kem region of eastern Morocco, whose strata date back to the Cenomanian stage of the Late Cretaceous. Its strata are subdivided into two geological formations ...
) of Morocco. The genus contains a single species, ''Deltadromeus agilis'', known from multiple partial skeletons from the mid-
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
period (mid-
Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...
age), about 95
million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...
. The classification of ''Deltadromeus'' has been in flux since its original description. In 2016, the South American
megaraptora Megaraptora is a clade of carnivorous theropod dinosaurs. Its derived members, the Megaraptoridae are noted for their large hand claws and powerfully-built forelimbs, which are usually reduced in size in other large theropods. Although undoubt ...
n ''
Gualicho ''Gualicho'' (named in reference to the gualichu) is an enigmatic genus of theropod dinosaurs. The type species is ''Gualicho shinyae''. It lived in what is now northern Patagonia, on what was then a South American island continent split off fro ...
'' was noted to have many similarities with ''Deltadromeus''. Other studies have considered it a
ceratosauria Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlies ...
n, potentially as a member of the family
Noasauridae Noasauridae is an extinct family of theropod dinosaurs belonging to the group Ceratosauria. They were closely related to the short-armed Abelisauridae, abelisaurids, although most noasaurids had much more traditional body types generally simila ...
. It may be a junior synonym of the contemporary ''
Bahariasaurus ''Bahariasaurus'' (meaning " Bahariya lizard") is an enigmatic genus of large theropod dinosaur. The genus contains a single species, ''Bahariasaurus ingens'', which was found in North African rock layers dating to the Cenomanian age of the Lat ...
''.


Discovery

The
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
of ''Deltadromeus agilis'' (museum catalogue number SGM-Din2) is a partial skeleton. A number of specimens (catalogued under IPHG 1912 VIII) from the
Bahariya Formation The Bahariya Formation (also transcribed as Baharija Formation) is a List of fossiliferous stratigraphic units in Egypt, fossiliferous Formation (stratigraphy), geologic formation dating back to the early Cenomanian, which outcrops within the Baha ...
of Egypt were originally considered by
Ernst Stromer Ernst Freiherr Stromer von Reichenbach (born on 12th of June, 1871 in Nürnberg, died on 18th of December, 1952 in Erlangen) was a German paleontologist best remembered for his expedition to Egypt, during which the discovery of the first kno ...
to be conspecific with ''
Bahariasaurus ''Bahariasaurus'' (meaning " Bahariya lizard") is an enigmatic genus of large theropod dinosaur. The genus contains a single species, ''Bahariasaurus ingens'', which was found in North African rock layers dating to the Cenomanian age of the Lat ...
'',Stromer (1934). "Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wüsten Ägyptens." II. Wirbeltierreste der Baharije-Stufe (unterstes Cenoman). 13. Dinosauria. Abh. Bayer. Akad. Wiss., Math.-Nat. Abt., (n. s.) 22 1-79, 3 pls. but were referred to ''Deltadromeus'' by
Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago who has discovered several new dinosaur species on several continents, including at sites in Inner Mongolia, Argentina, Morocco and Niger. ...
and colleagues in 1996 based on extreme similarities between them.


Description

The holotype is estimated to have measured long. The weight of the living animal was estimated to have been around 1,050 kilograms, slightly more than an
imperial ton The long ton, also known as the imperial ton, displacement ton,Dictionary.com - ''"a unit for measuring the displacement of a vessel, equal to a long ton of 2240 pounds (about 1016 kg) or 35 cu. ft. (1 cu. m) of seawater."'' or British ton, is a ...
. Assigned specimens from the Bahariya Formation come from a much larger individual, with a
femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...
(upper leg bone) length of , compared to the femur of the holotype. These referred specimens, if legitimately would indicate that members of the genus could grow up to in length, approximately the size of a ''
Tyrannosaurus rex ''Tyrannosaurus'' () is a genus of large theropoda, theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It live ...
''.


Classification


As an avetheropod

The original description of ''Deltadromeus'' in 1996 regarded it as a basal
coelurosaur Coelurosauria (; from Greek, meaning "hollow-tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, ty ...
, only slightly more derived than the
Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...
genus ''
Ornitholestes ''Ornitholestes'' (meaning "bird robber") is a small theropod dinosaur of the late Jurassic ( Brushy Basin Member of the Morrison Formation, middle Kimmeridgian age, about 154 million years agoTurner, C.E. and Peterson, F., (1999). "Biostratigrap ...
''. In 2016, an analysis of ''
Gualicho ''Gualicho'' (named in reference to the gualichu) is an enigmatic genus of theropod dinosaurs. The type species is ''Gualicho shinyae''. It lived in what is now northern Patagonia, on what was then a South American island continent split off fro ...
'', a South American theropod considered to belong to the
allosauroid Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...
family
Neovenatoridae Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...
, found ''Deltadromeus'' to be a possible
sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
of ''Gualicho''. 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 the 2016 description of ''
Aoniraptor ''Aoniraptor'' is an extinct genus of megaraptoran theropod dinosaurs from the Late Cretaceous Huincul Formation of Argentina. The genus contains a single species, ''Aoniraptor libertatem'', known from a partial skeleton. Discovery and naming ...
'', ''Deltadromeus'' was speculated to potentially form a clade with ''Aoniraptor'' and ''
Bahariasaurus ''Bahariasaurus'' (meaning " Bahariya lizard") is an enigmatic genus of large theropod dinosaur. The genus contains a single species, ''Bahariasaurus ingens'', which was found in North African rock layers dating to the Cenomanian age of the Lat ...
'' ('Bahariasauridae') within
Megaraptora Megaraptora is a clade of carnivorous theropod dinosaurs. Its derived members, the Megaraptoridae are noted for their large hand claws and powerfully-built forelimbs, which are usually reduced in size in other large theropods. Although undoubt ...
, distinct from the
Megaraptoridae Megaraptora is a clade of carnivorous theropod dinosaurs. Its derived members, the Megaraptoridae are noted for their large hand claws and powerfully-built forelimbs, which are usually reduced in size in other large theropods. Although undoubt ...
. The cladogram below follows the 2016 ''Gualicho'' analysis by Sebastián Apesteguía, Nathan D. Smith, Rubén Juarez Valieri and Peter J. Makovicky.


As a ceratosaur

Many studies published since the original description of ''Deltadromeus'' have considered it to be a
ceratosaur Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with ''Ceratosaurus'' than with birds. The oldest known ceratosaur, ''Saltriovenator'', dates to the earliest ...
, although different studies disagree on what kind of ceratosaur. A 2003 study suggested it was a member of the
Noasauridae Noasauridae is an extinct family of theropod dinosaurs belonging to the group Ceratosauria. They were closely related to the short-armed Abelisauridae, abelisaurids, although most noasaurids had much more traditional body types generally simila ...
, though others have found it to be more primitive, possibly related to the more ancestral ceratosaurs ''
Elaphrosaurus ''Elaphrosaurus'' ( ) is a genus of ceratosaurian Theropoda, theropod dinosaur that lived approximately 154 to 150 million years ago during the Late Jurassic, Late Jurassic Period in what is now Tanzania in Africa. ''Elaphrosaurus'' was a medium- ...
'' and ''
Limusaurus ''Limusaurus'' is a genus of theropod dinosaur that lived in what is now China during the Late Jurassic, around 161 to 157 million years ago. The type and only species ''Limusaurus inextricabilis'' was described in 2009 from specimens ...
''. A more comprehensive study of noasaurid relationships published in 2016 effectively agreed with both of these interpretations, with ''Deltadromeus'', ''Limusaurus'' and ''Elaphrosaurus'' all found to be within the Noasauridae.Rauhut, O.W.M., and Carrano, M.T. (2016). The theropod dinosaur ''Elaphrosaurus bambergi'' Janensch, 1920, from the Late Jurassic of Tendaguru, Tanzania. ''Zoological Journal of the Linnean Society'', (advance online publication) 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 wuthors, resolving the phylogenetic positions of ''Gualicho, Aoniraptor, Deltadromeus'' and
megaraptora Megaraptora is a clade of carnivorous theropod dinosaurs. Its derived members, the Megaraptoridae are noted for their large hand claws and powerfully-built forelimbs, which are usually reduced in size in other large theropods. Although undoubt ...
ns is a critical issue facing theropod systematics. ''Deltadromeus'' was also considered a noasaurid in a 2020 review of the
Kem Kem Group The Kem Kem Group (commonly known as the Kem Kem beds) is a geological group (stratigraphy), group in the Kem Kem region of eastern Morocco, whose strata date back to the Cenomanian stage of the Late Cretaceous. Its strata are subdivided into two ...
geology and fauna. The roughly contemporaneous theropod ''
Bahariasaurus ''Bahariasaurus'' (meaning " Bahariya lizard") is an enigmatic genus of large theropod dinosaur. The genus contains a single species, ''Bahariasaurus ingens'', which was found in North African rock layers dating to the Cenomanian age of the Lat ...
'', some of the bones of which have been referred to ''Deltadromeus'', has been suggested to be synonymous with the latter taxon.Holtz, Thomas R. Jr. (2008) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages'
Supplementary Information
/ref> In a 2010 analysis of the
Ceratosauria Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlies ...
, Carrano and Sampson noted that the differences between ''Deltadromeus'' and ''Bahariasaurus'' were partily due to misidentified bones in the former, and that other distinctions were subtle and insufficient to distinguish the two. In 2020, Ibrahim and colleagues acknowledged similarities between the two genera, but considered it unlikely that ''Deltadromeus'' represents a specimen of ''Bahariasaurus'' due to perceived differences in the pelvic bones. They further regarded ''Bahariasaurus'' as a ''
nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...
'' without explanation. In 2024, Andrea Cau published a comprehensive theropod
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
framework that could be used to identify immature specimens of other taxa. He included the ''
Bahariasaurus ''Bahariasaurus'' (meaning " Bahariya lizard") is an enigmatic genus of large theropod dinosaur. The genus contains a single species, ''Bahariasaurus ingens'', which was found in North African rock layers dating to the Cenomanian age of the Lat ...
'' type specimen in his analyses and recovered it within the
ceratosaur Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with ''Ceratosaurus'' than with birds. The oldest known ceratosaur, ''Saltriovenator'', dates to the earliest ...
clade
Abelisauroidea Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with ''Ceratosaurus'' than with birds. The oldest known ceratosaur, ''Saltriovenator'', dates to the earliest ...
in a
polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...
including ''Deltadromeus''. The following year, Cau and Paterna used an updated version of this dataset to reanalyze the relationships of ''Bahariasaurus'', ''Deltadromeus'', and other Cretaceous theropods from Africa. They determined that the variation observed between specimens of ''Deltadromeus'' and ''Bahariasaurus'' was the result of individual and
ontogenetic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...
variation, as the former is known from immature remains. They further reidentified specimen SNSB-BSPG1912VIII82—incorrectly recognized as a indeterminate theropod pubis by Stromer in his 1934 description of ''Bahariasaurus''—as a complete . The authors observed anatomical characters that the bone shares with the less complete ischia of the holotypes of both ''Bahariasaurus'' and ''Deltadromeus'', which they used to strengthen their argument. They concluded that ''Deltadromeus'' should be regarded as a
junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...
of ''Bahariasaurus''. The results of their
phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...
are displayed in the
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
below, with ''Bahariasaurus'' (including ''Deltadromeus'') indicated in the so-called "abelisauroid clade 1".


Paleobiology

''Deltadromeus'' specimens are known from the same formation as the giant theropods ''
Carcharodontosaurus ''Carcharodontosaurus'' (; ) is a genus of large carnivorous theropod dinosaur that lived in Northwest Africa from about 100 to 94 million years ago during the Cenomanian age of the Cretaceous. Two teeth of the genus, now lost, were first des ...
'', ''
Spinosaurus ''Spinosaurus'' (; ) is a genus of large spinosaurid theropod dinosaurs that lived in what now is North Africa during the Cenomanian faunal stage, stage of the Late Cretaceous Period (geology), period, about 100 to 94 annum, million year ...
'', and ''Bahariasaurus'' (which may be synonymous with ''Deltadromeus''). No skull material has been found for either ''Deltadromeus'' or ''Bahariasaurus''. However, they may be omnivorous or herbivorous if abelisauroid affinities are supported, implying
niche partitioning In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for e ...
in the large theropods in these localities.


References

{{Taxonbar, from=Q131629 Ceratosauria Dinosaur genera Cenomanian dinosaurs Dinosaurs of Egypt Dinosaurs of Niger Fossil taxa described in 1996 Taxa named by Paul Sereno