| Oplosaurus | |
|---|---|
 | |
| Illustration of the holotype tooth in multiple views | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Genus: | †Oplosaurus Gervais, 1852 |
| Species: | †O. armatus |
| Binomial name | |
| †Oplosaurus armatus Gervais, 1852 | |
Oplosaurus (meaning "armed or weapon lizard" or "armoured lizard"; see below for discussion) was agenus ofsauropoddinosaur from theLower Cretaceous (Barremian stage)Wessex Formation of theIsle of Wight, England. It is known from a single tooth usually referred to the contemporaneous "wastebasket taxon"Pelorosaurus, although there is no solid evidence for this.
In 1852geologistThomas Wright reported the find of a large reptilian tooth from theWealden Clay nearBrixton Bay on Wight. Wright had presented the find to several experts, among themRichard Owen,David Forbes,George Robert Waterhouse andSamuel Pickworth Woodward but onlyGideon Mantell came with a useful suggestion pointing to a similarity with the teeth of the dinosaurHylaeosaurus. Not convinced by this, Wright concluded that the tooth, in view of its sharpness, belonged to a carnivorous reptile of unknown affinities.[1]
Wright had also asked the French paleontologistPaul Gervais for his opinion on the fossil. Gervais in 1852 based thetype speciesOplosaurus armatus on it. The generic name would normally read as "armoured lizard" from the Greekhoplon, "body armour". The usual story about the — given the fact thatOplosaurus is not known to be armoured — odd choice of name is that Gervais named this large, well-preserved tooth (holotype BMNH R964) under the mistaken belief that its owner was an armoured dinosaur likeHylaeosaurus following Mantell's suggestion.[2] However,recent researchArchived 2017-05-02 at theWayback Machine by Ben Creisler shows that Gervais compared it toMosasaurus, notHylaeosaurus, and that the name may have been intended as "armed lizard", with the teeth as the weapons of acarnivore, ashoplon can also mean "weapon" (although this would make thespecific name redundant, asarmatus too means "armed" inLatin).[3]
Richard Lydekker (1888) suggested that amaxilla with a tooth (BMNH R751), also from the Isle of Wight, was another exemplar of this animal, but this opinion has not been substantiated.[4] Lydekker also used the improved spelling "Hoplosaurus" but the originalOplosaurus has priority.
The tooth is large, 85 mm (3.35 in) tall in total, with aspatulate crown 52 mm (2.05 in) tall, comparable toBrachiosaurus; it has a pointed tip, a slightly compressed form "cheek" totongue, a slightconvexity to the base of the tongue-facing side, and wear facets.[2][3] It is vaguely like aBrachiosaurus tooth, which is why the genus has for a time been referred to theBrachiosauridae.[5] Earlier,Oplosaurus was typically referred toPelorosaurus following an opinion ofFriedrich von Huene in 1909, althoughPelorosaurus is based on fragmentary remains that do not include teeth, making it impossible to prove the identity. (See Naish and Martill (2001) for a good review ofOplosaurus andWealden sauropods in general;here is a more recent informal summation of the state of work.)
Given how poor thePelorosaurusholotype material is, and that it doesn't include teeth, recent reviews have retainedOplosaurus as a potentially valid but poorly known genus.[6]Darren Naish, aBritishpalaeontologist familiar with Wealden sauropods, hassuggested informally that the genus may be aturiasaur but also co-authored an article concluding it was a member of theCamarasauridae.[7] In any case, it likely belongs to the more generalMacronaria.[8] A 2022 review considered it to be a potential turiasaur, echoing Naish's suggestion.[9]
As Naish and Martill point out, the tooth is comparable in size to that ofBrachiosaurus, indicating that the owner was a large sauropod;[2] as a possible turiasaur, the size should not change drastically. It would have been aquadrupedalherbivore, possibly around 25 m (82 ft) long.[2]
