Fukuiraptor

History

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

As indicated by its slender phalanges, Fukuiraptor was a relatively lightly built animal, regardless of its maturity. The immature holotype is estimated to reach 4.2 m long and weigh 175 kg 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 250 kg. 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

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*.*

References

References

1. (2000). "A new carnosaur (Dinosauria: Theropoda) from the Lower Cretaceous of Japan". Canadian Journal of Earth Sciences.
2. (2006). "New specimens, including a growth series, of ''Fukuiraptor'' (Dinosauria, Theropoda) from the Lower Cretaceous Kitadani Quarry of Japan". J. Paleont. Soc. Korea.
3. (2009). "A tooth of ''Fukuiraptor'' aff. ''F. kitadaniensis'' from the Lower Cretaceous Sebayashi Formation, Sanchu Cretaceous, Japan". Bulletin of Tokyo Gakugei University, Division of Natural Sciences.
4. Paul, Gregory S.. (2010). "The Princeton Field Guide to Dinosaurs". Princeton University Press.
5. (2014-05-06). "Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage". PLOS Biology.
6. Molina-Pérez & Larramendi. (2016). "Récords y curiosidades de los dinosaurios Terópodos y otros dinosauromorfos". Larousse.
7. (2010). "A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic". Naturwissenschaften.
8. (2012). "Megaraptorans as members of an unexpected evolutionary radiation of tyrant-reptiles in Gondwana". [[Ameghiniana]].
9. (13 July 2016). "An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina". PLOS ONE.
10. (20 July 2016). "A New Megaraptoran Dinosaur (Dinosauria, Theropoda, Megaraptoridae) from the Late Cretaceous of Patagonia". PLOS ONE.
11. (2018-12-15). "Tyrannosauroids from the Southern Hemisphere: Implications for biogeography, evolution, and taxonomy". Palaeogeography, Palaeoclimatology, Palaeoecology.
12. (2003-04-11). "A new iguanodontian (Dinosauria: Ornithopoda) from the Lower Cretaceous Kitadani Formation of Fukui Prefecture, Japan". Journal of Vertebrate Paleontology.
13. (2010). "''Fukuititan nipponensis'', A New Titanosauriform Sauropod from the Early Cretaceous Tetori Group of Fukui Prefecture, Japan". Acta Geologica Sinica - English Edition.
14. (2015). "New basal hadrosauroid (Dinosauria: Ornithopoda) from the Lower Cretaceous Kitadani Formation, Fukui, central Japan". Zootaxa.
15. (2016-02-23). "A bizarre theropod from the Early Cretaceous of Japan highlighting mosaic evolution among coelurosaurians". Scientific Reports.
16. (2019-11-14). "An unusual bird (Theropoda, Avialae) from the Early Cretaceous of Japan suggests complex evolutionary history of basal birds". Communications Biology.