| Afrovenator | |
|---|---|
 | |
| Reconstructed skeleton in Japan | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Megalosauridae |
| Genus: | †Afrovenator Sereno et al. 1994 |
| Species: | †A. abakensis |
| Binomial name | |
| †Afrovenator abakensis Sereno et al. 1994 | |
Afrovenator (/ˌæfroʊvɪˈneɪtər/; "African hunter") is agenus ofmegalosauridtheropod dinosaur from theMiddle orLate JurassicTiourarén Formation and maybe theIrhazer II Formation of theSahara region of Niger in western Africa.Afrovenator represents the only named definitive Gondwanan megalosaur, with proposed material of the group present in theTacuarembó Formation of Uruguay and theTendaguru Formation of Tanzania, both dated to the Late Jurassic.[1]
The remains ofAfrovenator were discovered in 1993 in theTiourarén Formation of the department ofAgadez inNiger. The Tiourarén was originally thought to represent theHauterivian toBarremian stages of the earlyCretaceous Period, or approximately 132 to 125 million years ago (Sereno et al. 1994). However, re-interpretation of the sediments showed that they are probably Middle to Late Jurassic in age, datingAfrovenator to theBathonian toOxfordian stages, between 167 and 161 mya.[2] ThesauropodJobaria, whose remains were first mentioned in the same paper which namedAfrovenator, is also known from thisformation.
Afrovenator is known from a single relatively complete skeleton,holotype UC OBA 1, featuring most of theskull minus its top (likewise themandible, or lower jaws, are lacking apart from theprearticular bone), parts of thespinal column, partial forelimbs, a partialpelvis, and most of the hind limbs. This skeleton is housed at theUniversity of Chicago.
The generic name comes from theLatinafer, "African", andvenator, "hunter". There is one namedspecies,Afrovenator abakensis. The generic name refers to its predatory nature, and its provenance from Africa. Thespecific name refers toAbaka, theTuareg name for the region of Niger where thefossil was found. The original short description of both genus and species is found in a 1994 paper which appeared in the prestigious journalScience. The primary author was well-knownAmericanpaleontologistPaul Sereno, withJeffrey Wilson, Hans Larsson,Didier Dutheil, andHans-Dieter Sues as coauthors.[3]
Recent discoveries in the region include referred teeth (MUPE HB-118, 125, 142) from the underliyingIrhazer II Formation[4] and TP4-12, a rostral part of left maxilla from the Tiourarén Formation at NE Tadibene.[5] New semiarticulated specimens, including previously unknown sections of the skeleton, were also recovered from the locality of Tawachi.[6]
Judging from the one skeleton known, this dinosaur was about 8 meters (26 feet) long, from snout to tail tip, and had a weight of about 1 tonne according toGregory S. Paul.[7]Thomas R. Holtz Jr. estimated it at 7.6 meters (25 feet) in length and 453–907 kg (999–2,000 lb) in weight.[8] In 2016 it was given a lower estimation of 6.8 meters (22 feet) in length, 1.9 meters (6.2 feet) tall at the hips and 790 kg (1,740 lb) in weight.[9] Sereno stressed that the general build was gracile and that the forelimbs and the lower leg were relatively long: thehumerus has length of forty centimetres and the tibia and fourth metatarsal measure 687 and 321 millimetres respectively, as compared to a thighbone length of seventy-six centimetres.[3]
Severalautapomorphies have been established, traits that distinguishAfrovenator from its nearest relatives. The depression in which theantorbital fenestra is located, has a front end in the form of a lobe. The third neck vertebra has a low rectangular spine. The crescent-shaped wrist bone is very flat. The first metacarpal has a broadly expanding contact surface with the second metacarpal. The foot of thepubic bone is notched from behind.[10]
In general the skull is rather flat, its height being less than three times its length, which cannot be exactly determined because thepraemaxillae are lacking. Themaxilla, which has a long front branch, bears fourteen teeth, as can be deduced from the tooth sockets: the teeth themselves have been lost. There is a small maxillary fenestra, which does not reach the edge of the antorbital depression and is located behind a promaxillary fenestra. Thelacrimal bone has a distinctive rounded horn on top. The lower branch of thepostorbital bone is transversely wide. Thejugal bone is short, deep and pneumatised.[3] The teeth wear distinctive proximodistally subrectangular distocentral denticles and a sigmoidal shape in distal view, seen also onTorvosaurus.[11]Afrovenator had a flexible, S-shaped neck and probably had well-developed neck muscles, allowing for stronger side-to-side and up-and-down movements, as well more power for feeding thanAllosaurus, but not as strong asSpinosaurus and other spinosaurids.[12] New specimens uncovered recently have record an updated premaxillae that shows a nasal process with a less steep angle than previously thought, givingAfrovenator a slightly larger nostril.[6]
Limb material from new specimens revelated hindlimbs shorter than the holotype, with a proportional larger tibia. Based on a new nearly complete foot,Afrovenator had better running adaptations thanAllosaurus but not as good asAucasaurus, lacking some features for fast running seen in abelisaurids.[6]
Most analyses placeAfrovenator within theMegalosauridae, which was formerly a "wastebasket family" which contained many large and hard-to-classify theropods, but has since been redefined in a meaningful way, as asister taxon to the familySpinosauridae within theMegalosauroidea.
A 2002 analysis, focused mainly on thenoasaurids, foundAfrovenator to be abasal megalosaurid. However, it did not includeDubreuillosaurus (formerlyPoekilopleuron valesdunensis), which could affect the results in that region of thecladogram (Carrano et al. 2002). Other more recent and more comprehensive cladistic analyses have recoveredAfrovenator in a group of Megalosauridae withEustreptospondylus andDubreuillosaurus. This group is either calledMegalosaurinae (Allain 2002) orEustreptospondylinae (Holtz et al. 2004). The latter study also includesPiatnitzkysaurus in this clade. A study byMatthew Carrano from 2012 placedAfrovenator in the megalosaurid cladeAfrovenatorinae.[10]
A few alternative hypotheses have been presented forAfrovenator's relationships. In Sereno's original description,Afrovenator was found to be a basal spinosauroid (he at the time used the name "Torvosauroidea"), outside of Spinosauridae and Megalosauridae (which he called "Torvosauridae").[3]
In their 2023 redescrpition of the spinosauridIrritator, Schade et al. recoveredAfrovenator as megalosauroid in a clade excludingDubreuillosaurus,Magnosaurus,Eustreptospondylus, andStreptospondylus, which were instead placed close to the Spinosauridae. These results are displayed in thecladogram below:[13]
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