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. 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). Neuquensaurus is a smaller sauropod, measuring only 7.5 m (25 ft).
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.
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.
Eggs attributed to Hypselosaurus by Matheron and Paul Gervais have been found in France since 1846, and were the earliest dinosaur eggs actually discovered, although they were not recognized as being dinosaurian for several decades. The eggs are unusually large; measuring at around 1-foot (0.30 m) in length. Age determination studies performed on the fossilized remains have been inconclusive, with results ranging from a few decades to several hundred years.
Eggs with abnormally thin shells have been attributed to Hypselosaurus priscus. Some experts have speculated that this was the cause of the species' extinction, with vegetation changes, climatic change and overcrowding being the original impetus for the shell thinning. However, there are alternative explanations for the thin eggshell not dependent on pathology. Later researchers found evidence that the eggs in question successfully hatched. Some researchers postulated that the thinner "Hypselosaurus priscus" eggshells came from different taxa than the thicker eggshells, and subsequent researchers have come to support this idea. Another potential explanation for variation in eggshell thickness is that the thinner eggs were laid by younger individuals than the thicker shell eggs laid by older individuals or that it was a consequence of natural variations of eggshell thickness within a single species.
Hypselosaurus has been found only in the Grès à Reptiles Formation, in the Provence region of southern France. This formation, dating to the early Maastrichtian approximately 70 mya, has provided fossils of several different groups of dinosaurs. The theropods Variraptor and Pyroraptor, both considered to be within the family Dromaeosauridae, have been found in the Grés á Reptiles Formation, in addition to the nodosaurid ankylosaurian Rhodanosaurus (a dubious genus); a bone fragment potentially belonging to Abelisauridae; and the rhabdodontid ornithopod Rhabdodon. Although the material between Variraptor and Pyroraptor cannot be compared, and they may in fact belong to the same taxon, there are at least two separate dromarosaurids present in the formation. In addition, a new titanosaur, Atsinganosaurus was described from the formation, based on several dorsal vertebrae. It is possible that this titanosaur represents the same taxon as Hypselosaurus, but as the latter is likely a nomen dubium, and no material overlaps, Atsinganosaurus can be separated for now.
In The Land Before Time
A teal Hypselosaurus briefly appears in The Land Before Time II: The Great Valley Adventure, where it is seen wading in a river in a wide shot of the Great Valley.