Valdosaurus - WikiHQ

Valdosaurus ("Weald lizard") is a genus of bipedal herbivorous dryosaurid dinosaur known from the Early Cretaceous of the Isle of Wight and elsewhere in England. Originally its remains were believed to belong to Hypsilophodon. In 1889, Richard Lydekker assigned them to Camptosaurus, alongside a partial lower jaw, and applied the name Camptosaurus valdensis. In the 1970s, Peter Galton reassigned these remains to a new species of Dryosaurus, then to an entirely new genus and species, that being Valdosaurus proper. The type and only species of Valdosaurus, named by Galton, is V. canaliculatus.

Numerous specimens have been assigned to Valdosaurus over the years. Some, namely those found in Niger (now Elrhazosaurus), have been reassigned to different genera, while others have simply been redesignated as indeterminate. With that said, additional specimens of V. canaliculatus have been discovered. The most complete is a specimen discovered in 2012 at Compton Bay on the Isle of Wight, which consists of a largely articulated rear half of the animal. Whereas the type specimens were very small, with a femur (thigh bone) length of just and an estimated body mass of , larger specimens such as the Compton specimen may have reached body lengths of around and body masses of roughly .

Discovery and naming

At some point in the 19th century, the Rev. William Fox collected two small femora (upper leg bones) near Cowleaze Chine on the south-west coast of the Isle of Wight. In 1888, these specimens, BMNH R184 and R185, were assigned to Hypsilophodon foxii by Richard Lydekker. The femora were associated with a tibia, and were subsequently assigned to the possible tyrannosauroid genus Calamosaurus. In 1889, Lydekker assigned them to Camptosaurus, alongside a partial mandibular ramus (half of a lower jaw), BMNH R180, applying the species name C. valdensis to all of these remains. The species name, valdensis derives from valdo, a modification of the Old English word weald ("a wood") which refers to the Weald area. In 1975, Galton re-examined the femora, and concluded that they did not belong to Camptosaurus. He therefore assigned them to Dryosaurus, and applied the name Dryosaurus canaliculatus. The specific name means "with a small channel" in Latin, referring to a distinct groove between the condyles of the lower femora. Two years later, Galton recognised that they were in fact morphologically distinct from Dryosaurus, and erected a new genus for them, Valdosaurus. The type species, D. canaliculatus, was thus renamed V. canaliculatus. Galton speculated that Valdosaurus might have been a direct descendant of Dryosaurus, based on the supposed ubiquity of that genus across Europe, Africa, and Asia. Furthermore, Galton reassigned BMNH R180 to Valdosaurus, after briefly and provisionally considering it a specimen of Vectisaurus.

Additional remains and reassigned species

A second species, V. nigeriensis, was described by Galton and Philippe Taquet from younger rocks from Niger in 1982. In 1998 William Blows inadvertently named another species, Valdosaurus dextrapoda, by including this name in a fauna list. This was an error, and the species has never been supported. In 2009, Galton reviewed the Valdosaurus material. He concluded that no fossils from outside England could be reliably referred to the genus. He thus gave V. nigeriensis its own genus: Elrhazosaurus. Even where many of the English specimens were concerned it was uncertain whether they belonged to Valdosaurus, including all cranial elements and teeth. Some hindlimb and pelvic bones from the Upper Weald Clay Formation (late Barremian) were referable to V. canaliculatus. Some material from the earlier Hastings Beds (Valanginian) were referred to a Valdosaurus sp. Galton established that Richard Owen had in 1842 been the first to describe Valdosaurus thighbones, specimens BMB 004297-004300, assigning them to Iguanodon. These rock units were deposited between the Berriasian and Barremian stages, between approximately 145 and 125 million years ago. V. canaliculatus would then be known from thigh bones, extensive additional postcranial elements, partial lower jaws, and teeth.thumb|left|Valdosaurus sp. [[ilium (bone)|ilia, NHM 2150, from the Upper Tunbridge Wells Sand of Cuckfield|alt=]]In 1888, Richard Lydekker described an ilium, BMNH R2150 from Sussex, assigning it to Hylaeosaurus. That specimen was subsequently assigned to Valdosaurus canaliculatus. by Nick Chase; the exact location of its discovery has been withheld to prevent attempts to steal material from the site. The specimen, since designated IWCMS 2013.175, is the most complete Valdosaurus yet found. It was found partly articulated and includes a partial dorsal (back) series, an almost complete caudal (tail) series, pelvic material, and both hind limbs. In life, the specimen would have been around long.

Description

Size

thumb|Size diagram of two Valdosaurus specimens: the [[holotype, BM R185, and an assigned specimen, IWCMS 2013.175]]

In his 2009 re-examination of Valdosaurus, Peter Galton emphasised that though the type femora were very small, in length, they came from a juvenile individual; an adult would have been a "medium-sized euornithopod", with femora reaching a length of something like , The fourth trochanter, the structure on the femur to which the caudofemoralis muscle would have attached, is on the proximal (closer) half of the femoral shaft. The lesser trochanter of the femur is rod-like, and is separated from the greater trochanter by a cleft. wherein it is paraphyletic. This definition of hypsilophodontids has been largely abandoned in favour of a more restrictive one. In 1972, before the proper naming of Valdosaurus, Galton suggested that it was the endpoint of a lineage starting with "Camptosaurus" leedsi (now Callovosaurus), and continued by Dysalotosaurus, Dryosaurus, and then Valdosaurus itself. A particularly close relationship with Elrhazosaurus from the Early Cretaceous of North Africa, (and which was formerly considered a species of Valdosaurus) has been proposed. Cladogram from Madzia, et al. 2020:

Palaeoenvironments

Hastings Beds/Lower Wealden

Whilst most remains assigned to Valdosaurus come from the Isle of Wight, remains from the Grinstead Clay Member of the Tunbridge Wells Sand Formation, part of the Lower Wealden (or Hasting Beds) of Sussex, have also been assigned to it, though have also been regarded as indeterminate dryosaurids.

Wessex Formation

thumb|alt=|[[Paleoart|Life restoration of Valdosaurus (midground, left) with contemporary dinosaurs: Eucamerotus (background), Baryonyx (left), two Neovenator (right), and Hypsilophodon (foreground).]]

The holotype of Valdosaurus heralds from the Wessex Formation, Sedimentological data suggests that the depositional environment of the Wessex Formation was a floodplain intersected by fluvial (river) and lacustrine (lake) deposits. Water levels likely varied throughout the year, due to there being more evaporation than precipitation, though precipitation was regardless quite high. The Wessex seems to have regularly experienced extreme storms Burned plant and insect material and fusain suggests that the environment experienced frequent wildfires, stifling for the most part the dense growth of gymnosperms. the thyreophorans Polacanthus and the ornithopods Brighstoneus, Comptonatus, Hypsilophodon, Iguanodon, and Vectidromeus. The pterosaur fauna of the Wessex Formation consists of Coloborhynchus, Caulkicephalus, Istiodactylus, Vectidraco, and Wightia; multiple unnamed pterosaur taxa, including a ctenochasmatid, are also known. and Vectisuchus. Limited evidence exists of elasmosaurids and leptocleidid plesiosaurs. The mammal fauna of the Wessex Formation includes the multituberculate Eobataar and the spalacotheriid Yaverlestes. Albanerpetontid amphibians are represented by Wesserpeton. The fish fauna of the Wessex Formation, both bony and cartilaginous, is extensive, including hybodontiform and modern sharks (Selachii), pycnodontiforms, Lepidotes and Scheenstia. Invertebrates are represented by an assortment of non-biting midges, hymenopterans (wasps) including multiple parasitoid taxa, coleopterans (beetles), the avicularoid spider Cretamygale, and the ostracod Cypridea.

References

External links

Valdosaurus at Dinosaur Isle
Valdosaurus at National History Museum
Valdosaurus at Dino Data