Hypselosaurus (meaning 'highest lizard', from Greek ὑψηλός meaning 'high' or 'lofty' and σαυρος meaning 'lizard') was a titanosaurian sauropod that lived in southern France during the Late Cretaceous, approximately 70 million years ago in the early Maastrichtian. Hypselosaurus was first described in 1846, but was not formally named until 1869, when Phillip Matheron named it under the binomial Hypselosaurus priscus. The holotype specimen includes a partial hindlimb and a pair of caudal vertebrae, and two eggshell fragments were found alongside these bones. Because of the proximity of these eggshells to the fossil remains, many later authors, including Matheron and Paul Gervais, have assigned several eggs from the same region of France all to Hypselosaurus, although the variation and differences between these eggs suggest that they do not all belong to the same taxon. Hypselosaurus has been found in the same formation as the dromaeosaurids Variraptor and Pyroraptor, the ornithopod Rhabdodon, and the ankylosaurian Rhodanosaurus, as well as intermediate bones from other groups.
Discovery[]
In 1846, Pierre Philippe Émile Matheron, a french geologist and paleontologist, described several large bones from Provence, France.[1] In the spring of 1869, Matheron formally described these remains, including a partial femur, fibula and possible tibia and a pair of associated caudal vertebrae, as the holotype specimen of a new taxon, Hypselosaurus priscus.[2][3] Among the bones, portions of the femur shaft are not preserved, along with a majority of the tibia, while both the fibula and vertebrae are entirely preserved.[2] The layer the fossils came from is likely from the late Late Cretaceous, specifically 70 million years ago.[4][5]
Since its original description, several specimens have been referred to Hypselosaurus. One of these, originally described in 1957 by Albert de Lapparent, includes a caudal vertebra, as well as another vertebra described in 1960 by Bataller.[6] In 1993, a review of European sauropods stated that Hypselosaurus was a nomen dubium, and that its holotype could not be verifiably distinguished from other sauropods in the same, and many other, regions. Based on this, the material that was referred to Hypselosaurus by several other authors would have to be considered an intermediate titanosaur.[7]
In addition to the holotype skeleton, Matheron described two fragments of a spherical or ellipsoid fossil in 1869. These fragments were studied for some time by Matheron and his contemporary french paleontologists, and the only probable conclusion was that they were fragments of eggshells. The eggs were proposed to have been significantly larger than those of Aepyornis when complete, and Matheron suggested that they either were a very large bird egg, or belonged to Hypselosaurus.[2]
When originally named, Matheron proposed that Hypselosaurus was an aquatic crocodile, as was suggested by Richard Owen for taxa similar, like Pelorosaurus, Cetiosaurus, Streptospondylus and Steneosaurus. Matheron noted that the long bones, particularly the femur, lacked medullary bone, and thus proposed that it could not have been terrestrial like Iguanodon.
Description[]
Hypselosaurus was a proposed to be 15 m (49 ft) in length as a crocodilian, which would make it one of the largest of the group.[8][3] However, it has a complete femur length of about 80 cm (31 in), which is comparable in size to that of Neuquensaurus, at 75 cm (30 in).[3][9] Neuquensaurus is a smaller sauropod, measuring only 7.5 m (25 ft).[10]
The left femur of Hypselosaurus, at 80 cm (31 in) in length, is quite eroded, with both the femoral head and the distal condyles being eroded. The femur is slightly sinuous, and narrows antero-posteriorly, becoming a subquadrangular oval 17 cm (6.7 in) wide and only 7 cm (2.8 in) long. As preserved, the left tibia is largely incomplete, with only a small section of the shaft, just proximal to the distal condyles known. Few features can be identified, among those the dimensions and cross-section of the bone. The tibia is ovoid in cross-section, with the anterior diameter 11 cm (4.3 in) long, and 5.5 cm (2.2 in) wide. The fibula, at 55 cm (22 in) in length, corresponds well with the size of the femur and tibia. The fibula is approximately an equilateral triangle in cross-section, with the inner face concave and outer face convex.[2]
Two caudal vertebrae were preserved, and show that there would have been a very large number in the tail. Both bones are nearly identical in every feature, but the anterior one is slightly larger. The vertebrae are not compressed laterally, instead being compressed vertically to a width of 11 cm (4.3 in) and a height of 7 cm (2.8 in). Both vertebrae are procoelous, with the anterior articular face being concave, and the posterior face being convex.