that it may belong to Zephyrosaurus, from a similar time and place, as no femur was known from that taxon. Fossils from other locations, especially from the mainland of southern Great Britain, Portugal and Spain, have once been referred to Hypsilophodon. However, in 2009 Galton concluded that the specimens from Great Britain proper were either indeterminable or belonged to Valdosaurus, and that the fossils from the rest of Europe were those of related but different species. This leaves the finds on Isle of Wight, off the south coast of England, as the only known authentic Hypsilophodon fossils. The fossils have been found in the Hypsilophodon Bed, a one-metre thick marl layer surfacing in a 1200 metre long strip along the Cowleaze Chine parallel to the southwest coast of Wight, part of the upper Wessex Formation and dating to the late Barremian, about 126 million years old. Reports that Hypsilophodon would be present in the later Vectis Formation, Galton in 2009 considered as unsubstantiated. Description Hypsilophodon was a relatively small dinosaur, though not quite as small as, for example, Compsognathus. For Hypsilophodon often a maximum length of is stated. This has its origin in a study of 1974 by Galton, in which he extrapolated a length of based on specimen BMNH R 167, a thigh bone. However, in 2009, Galton concluded that this femur in fact belonged to Valdosaurus and downsized Hypsilophodon to a maximum known length of , the largest specimen being NHM R5829 with a femur length of 202 millimetres. Typical specimens are about long. In 2010, Gregory S. Paul estimated a weight of for an animal in length. Like most small dinosaurs, Hypsilophodon was bipedal: it ran on two legs. Its entire body was built for running. Numerous anatomical features aided this, such as: light-weight, minimized skeleton, low, aerodynamic posture, long legs, and stiff tail — immobilized by ossified tendons for balance. In light of this, Galton in 1974 concluded it would have been among the ornithischians best adapted to running. Despite living in the last of the periods in which non-avian dinosaurs walked the earth, the Cretaceous, Hypsilophodon had a number of seemingly "primitive" features. For example, there were five digits on each hand and four on each foot. With Hypsilophodon the fifth finger had gained a specialised function: being opposable it could serve to grasp food items. Cranial anatomy In an example of primitive anatomy, although