Reconstructed skeleton and holotype fossils on the lower right
Thetype specimen is a partial skeleton (designatedFPDM-V97122) discovered in theKitadani quarry nearKatsuyama in theFukui prefecture. It is thought that this specimen was not mature and an adult may have been larger. The remains of many other individuals have been found in the quarry, with numerous humeri, femurs, and teeth being assigned to this species.[2] However, the other individuals recovered from the same locality are mostly juveniles that were smaller than theholotype (Currie & Azuma, 2006), in the smallest case less than a quarter of the holotype's size. A tooth (NDC-P0001) discovered in a block ofconglomerate from theSebayashi Formation has been referred toFukuiraptor as well.[3]
As indicated by its slender phalanges,Fukuiraptor was a relatively lightly built animal, regardless of its maturity.[1] The immature holotype is estimated to reach 4.2 metres (14 ft) long and weigh 175 kg (386 lb) in its initial description.[1] In 2010Gregory Paul gave a length of 5 meters (16 ft) and a weight of 300 kg (660 lbs).[4] In 2014, its body mass was estimated up to 250 kilograms (550 lb).[5] Molina-Pérez and Larramendi estimated a length of 4.3 meters (14.1 ft) and a weight of 590 kg (1,300 lbs) in 2016.[6]
The distinctive teeth ofFukuiraptor show similarities with bothcarcharodontosaurids (being very compressed and blade-like, as well as having wrinkled enamel) andtyrannosaurids (having oblique blood grooves near the serrations).[2] The holotype also had very large and flat manual unguals (hand claws), which played a role in its initial classification as a dromaeosaurid (as the hand claws were mistaken for foot claws) as well as its current classification as a megaraptoran.[7]
Initially considered a member of theDromaeosauridae when first discovered, its initial describers considered it acarnosaur, related toAllosaurus. More recent studies consider it a megaraptoran, an enigmatic group which may have been part of the familyNeovenatoridae.[7] However, more recently, another analysis has proposed that allmegaraptorans are actuallytyrannosauroids, which would reclassifyFukuiraptor as atyrannosauroidcoelurosaur.[8] Recent cladistic analysis of the theropodGualicho has suggested thatFukuiraptor and other megaraptorans are eitherallosauroids, or non-tyrannosauroid basal coelurosaurs.[9]
It has been suggested thatFukuiraptor is a close relative to the Australian megaraptoran known asAustralovenator,[10] however a subsequent study has placedAustralovenator as amegaraptorid megaraptoran alongside other derived South American taxa, whileFukuiraptor remains a megaraptoran outside of Megaraptoridae.[11]
Below is a cladogram reconstructing the position ofFukuiraptor in the Megaraptora as per Delcourt and Grillo, 2018.[11]
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