Hypselosaurus was scientifically described by geologist Pierre Émile Philippe Matheron in 1846 and formally named in 1869, on the basis of fragmentary remains from the Late Cretaceous of the Provence region of France. Matheron thought the animal was a gigantic crocodile.
The legs of Hypselosaurus were proportionally robust. Eggs attributed to it 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.