| Neovenator | |
|---|---|
 | |
| Reconstructed skeleton in Japan | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | †Allosauria |
| Clade: | †Carcharodontosauria |
| Family: | †Neovenatoridae |
| Genus: | †Neovenator Hutt,Martill &Barker, 1996 |
| Species: | †N. salerii |
| Binomial name | |
| †Neovenator salerii Hutt, Martill & Barker, 1996 | |
Neovenator (nee-o-ven-a-tor meaning "new hunter") is agenus ofcarcharodontosauriantheropoddinosaur. It is known from several skeletons found in theEarly Cretaceous (Hauterivian-Barremian)Wessex Formation on the south coast of theIsle of Wight, southern England. It is one of the best known theropod dinosaurs from the Early Cretaceous of Europe.
The first bones ofNeovenator were discovered in the summer of 1978, when a storm made part of theGrange Chine collapse. Rocks containingfossils fell to the beach ofBrighstone Bay on the southwestern coast of the Isle of Wight. The rocks consisted ofplant debris bed L9 within the variegatedclays andmarls of theWessex Formation dating from theBarremian stage of theEarly Cretaceous, about 125 million years ago. They were first collected by the Henwood family and shortly afterwards by geology student David Richards. Richards sent the remains to the Museum of Isle of Wight (nowDinosaur Isle) and theBritish Museum of Natural History. In the latter institutionpaleontologistAlan Jack Charig determined that the bones belonged to two kinds of animal:Iguanodon and a theropod. The "Iguanodon", later referred toMantellisaurus and ultimately made the separate genusBrighstoneus, generated the most interest and in the early 1980s a team was sent by the BMNH to secure more of its bones. On that occasion an additional theropod tail vertebra was discovered.
Several amateur paleontologists, among them Keith and Jenny Simmonds, now began to search for additional remains of the predator. Ultimately, the total of secured bones included the snout, teeth, a front lower jaw, most of the vertebral column, ribs, belly ribs, chevrons, the left shoulder girdle, pelvis bones and a hindlimb. These were accessioned under numbers BMNH R10001 and MIWG 6348. They equalled approximately 70% of the skeleton. In 1985, excavations undertaken bySteve Hutt of the MIWG revealed two vertebrae of a second individual, specimen MIWG.5470. In 1987, Jenny Simmonds found a third skeleton, containing vertebra and pelvic bones, specimen MIWG.6352. A fourth individual found by Nick Oliver is represented by specimen IWCMS 2002.186,[1] consisting of a lower jaw, parts of the cervical vertebrae and limb elements. In 1990 the material, then considered a possible new species ofMegalosaurus, was provisionally described by Hutt. Having mistaken the ischium of MIWG 6352 for a pubic bone, Hutt suggested this specimen represented a separate species.[2]
In 1996, Steve Hutt,David Martill andMichael Barker named and described thetype speciesNeovenator salerii. The generic nameNeovenator means "new hunter" from the Greekneo~, "new" andLatinvenator, "hunter". Thespecific namesalerii honours the land owners of the site, the Salero family. In view of the large number of individuals involved in the discovery process, it was considered improper to single out one of them as discoverer. Theholotype is the skeleton accessioned as BMNH R10001 and MIWG 6348.[3]
In 1999, Hutt dedicated his (unpublished) master thesis toNeovenator.[4]
In 2008,Stephen Louis Brusatte,Roger Benson and Hutt redescribed the species in great detail.[5]
In 2012, teeth indistinguishable from those of the holotype ofNeovenator were found in the Angeac lignitic bone bed, France, dating to theBarremian.[6]
Neovenator measured approximately 7 metres (23 ft) in length, and was of a gracile build, weighing 1 metric ton (1.1 short tons).[7] Specimen MIWG 4199 indicates an individual with a possible length of about 10 metres (33 ft), but it only consists of a toe phalanx and its position inNeovenator is dubious.[8][9]
The various scientific descriptions ofNeovenator have indicated some distinguishing traits. The nostril is twice as long as it is high. Thepraemaxilla in the snout bears five teeth. Themaxilla is pierced by a large maxillaryfenestra, the diameter of which equals a sixth of the length of the tooth row. The tooth crown equals a quarter of the tooth length, thus including the root. The toe claws have a groove on top.[3] Both praemaxillae are connected by an extra pen-in-socket connection.[10] The front joint surface of the intercentrum of the axis, the second neck vertebra, is transversely widened. The odontoid process of the axis has small openings along the side edge of the front facet. The neural process of the axis has a single small opening in the side. The rear neck vertebrae are fused with their neck ribs. On the eighth and ninth neck vertebrae, at the parapophysis, the lower rib joint facet, the internal camellate structure of the bone is visible. At the front neck vertebrae the undersides are formed as sharp keels which are not inset from the lateral sides. At the front back vertebrae, the hypapophyses, the lower swellings of the front facet edges, are formed like low mounds. On the rear back vertebrae the facets of the joint processes are continued sideways as curved flanges. The shoulder joint is wider transversely than long, measured from the front to the rear. The notch on the underside of the front blade of the ilium has a shelf at the inner side. The ilium in Neovenator is highly pneumatized.[11] The "feet" of the ischia are connected at their fronts but diverge at their rears. The head of the thighbone is obliquely directed to the front, to above and to the inside. On the thighbone the lesser trochanter has a robust ridge on its outer side. On the thighbone the fourthtrochanter has a depression in the form of a thumbprint located to the outside of its upper limit. The front underside of the thighbone is nearly flat, only showing a short vertical groove between the lowercondyles. The lower shinbone shows an oval rough area at the inner side. The top of the outermalleolus of the shinbone is pinched from the front to the rear. The outer front bulge of the top surface of the shinbone has a spur pointing to below. In the foot, the outer side of the secondmetatarsal has a hollow surface to contact the third metatarsal.[5]
Several traits that once were thought to be unique orapomorphic forNeovenator, subsequent research showed to have been shared by other theropods. The nostrils are large but not uncommonly so. Having pneumatised rear back vertebrae is normal for carcharodontosaurids. Elevated paired nasal crests are shared withAllosaurus. Denticles continuing over the tooth apex are today known from other species.[5]
In 2015, it was reported that the front of the snout ofNeovenator contains a complex system of neurovascular canals, functioning as sensory organs. This trait is also known fromSpinosauridae and was there explained as an adaptation for searching prey in water. It was doubted, however, whetherNeovenator used its system for the same purpose.[12]
At the time that it was described, by Steve Hutt, Martill and Barker in 1996, it was considered the only knownallosaurid in Europe. However, further studies suggested it had more in common with the advancedcarcharodontosaurid group of allosaurs, and several studies including a detailed examination of the species by Benson, Carrano and Brusatte in 2010 suggest that it is closely related to the Carcharodontosauridae (in a group calledCarcharodontosauria), but is actually closer to themegaraptorans, together with them forming the familyNeovenatoridae.[11] Other studies have supportedNeovenator being a carcharodontosaurid, and megaraptorans beingtyrannosauroids.
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Thecladogram below follows the 2010 analysis by Benson, Carrano and Brusatte.[11]
| Neovenatoridae |
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Cladogram after Novaset al., 2013[13]
Chris Barker and colleagues suggested thatNeovenator may have possessed integumentary sensory organs on its snout, much as modern waterfowl and crocodilians use to find food in muddy water, based on neurovascular structures found on the skull. AsNeovenator is believed to be completely terrestrial, unlike the modern species, it is assumed that these sensory organs were used for other purposes, such as sensitivity to pressure and temperature, controlling jaw pressure and precision feeding. In support of this, the tooth wear forNeovenator seems to indicate that it avoided eating or biting into bone while it fed. Additionally,Neovenator might have used these integumentary sensory organs in courtship and sensing nest conditions, a technique seen today in most species of crocodilians and megapode birds. Though such structures are known for another theropod, thetyrannosauridDaspletosaurus horneri,Neovenator's neurovascular structures that likely supported these organs are the best preserved and most complete in any known theropod yet discovered.[14][15] However, a more recent study reviewing the evolution of the trigeminal canals among sauropsids notes that a much denser network of neurovascular canals in the snout and lower jaw is more commonly encountered in aquatic or semiaquatic taxa (e.g.,Spinosaurus,Halszkaraptor,Plesiosaurus), and taxa that developed a rhamphotheca (e.g.,Caenagnathasia), while terrestrial taxa such as tyrannosaurids andNeovenator may have had average facial sensitivity for non-edentulous terrestrial theropods, although further research is needed.[16]
The holotype ofNeovenator salerii had many pathologies. The authors of the genus list them as "midcaudal vertebrae fusions, healed fractures of mid-caudal vertebra transverse processes;osteophytes affecting pedal phalanges, healedgastralia rib fractures, some formingfalse joints... [and] scapula fracture."[17]
Fossil remains ofNeovenator have been found on theIsle of Wight off southernEngland, and were first discovered in the 20th century.Neovenator perhaps existed alongside other dinosaurs found in the Wessex Formation of the earlyCretaceous period, such asCeratosuchops,Riparovenator,Baryonyx,Polacanthus,Iguanodon andEotyrannus. The holotype bones were mixed with those of the herbivorous iguanodontianBrighstoneus and in the dig site also remains of fishes, amphibians, lizards, pterosaurs andGoniopholididae were present.Neovenator was likely theapex predator of its ecosystem.
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