Fukuiraptor

Fukuiraptor ("thief of Fukui") is a genus of medium-sized megaraptoran theropod dinosaur of the Early Cretaceous epoch (either Barremian or Aptian) that lived in what is now Japan. Fukuiraptor is known from the Kitadani Formation and possibly also the Sebayashi Formation. Fukuiraptor may have been one of the most basal members of Megaraptora or it could be a sister taxon to Australovenator.

History

File:フクイラプトルの全身骨格化石.jpg

Reconstructed skeleton and holotype fossils on the lower right

The type specimen is a partial skeleton (designated FPDM-V97122) discovered in the Kitadani quarry near Katsuyama in the Fukui 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. However, the other individuals recovered from the same locality are mostly juveniles that were smaller than the holotype (Currie & Azuma, 2006), in the smallest case less than a quarter of the holotype's size. A tooth (NDC-P0001) discovered in a block of conglomerate from the Sebayashi Formation has been referred to Fukuiraptor as well.

Description

File:Fukuiraptor scale diagram.png

Size comparison

As indicated by its slender phalanges, Fukuiraptor was a relatively lightly built animal, regardless of its maturity. The immature holotype is estimated to reach long and weigh in its initial description. In 2010 Gregory Paul gave a length of 5 meters (16 ft) and a weight of 300 kg (660 lbs). In 2014, its body mass was estimated up to . 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.

The distinctive teeth of Fukuiraptor show similarities with both carcharodontosaurids (being very compressed and blade-like, as well as having wrinkled enamel) and tyrannosaurids (having oblique blood grooves near the serrations). 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.

Classification

Initially considered a member of the Dromaeosauridae when first discovered, its initial describers considered it a carnosaur, related to Allosaurus. More recent studies consider it a megaraptoran, an enigmatic group which may have been part of the family Neovenatoridae. However, more recently, another analysis has proposed that all megaraptorans are actually tyrannosauroids, which would reclassify Fukuiraptor as a tyrannosauroid coelurosaur. Recent cladistic analysis of the theropod Gualicho has suggested that Fukuiraptor and other megaraptorans are either allosauroids, or non-tyrannosauroid basal coelurosaurs. It has been suggested that Fukuiraptor is a close relative to the Australian megaraptoran known as Australovenator, however a subsequent study has placed Australovenator as a megaraptorid megaraptoran alongside other derived South American taxa, while Fukuiraptor remains a megaraptoran outside of Megaraptoridae.

Below is a cladogram reconstructing the position of Fukuiraptor in the Megaraptora as per Delcourt and Grillo, 2018.

Palaeoecology

File:Fukuivenator skeleton and stratigraphy.jpg

Stratigraphic positions of the non-avialan dinosaurs of the Kitadani Formation, Japan.

File:ティラノミムスを狩るフクイラプトル.jpg

Life restoration of Fukuiraptor hunting Tyrannomimus .

In the Kitadani Formation, where fossils of Fukuiraptor have been recovered, fossils of other vertebrates have been preserved. Among the species that have been properly described and named are Fukuisaurus tetoriensis, a styracostern ornithischian, Fukuititan nipponensis, a titanosauriform sauropod, Koshisaurus katsuyama, a hadrosauroid ornithischian, Fukuivenator paradoxus, a possible therizinosaurian theropod, and Fukuipteryx prima, an avialan as defined by the authors.

External links

• Image of the holotype skeleton, published by the twitter account of Thomas Holtz