"the specimen is no longer in existence. It was extremely fragile and at some point shortly after its discovery it apparently crumbled and fell apart. Such a fate is not uncommon for some kinds of fossils where exposure to the air or being freed from the supporting matrix can lead to specimens disintegrating but this was before the development of glues that could help consolidate and preserve fragile specimens, and it is also likely that no one immediately realised this was a risk.

...this leaves some frustrating gaps in our knowledge – there are suggestions that the original fossils may have actually been more than one different species that were mixed up together. Without the specimens to hand that is hard to say either way. At least in the case of Spinosaurus we have now found various new specimens but working out the taxonomy of this genus is complicated by the fact that the original material on which the name was based no longer exists. There are suggestions that there are multiple spinosaurs living at this time and working out which may be which is inevitably complicated by the absence of this critical material.

Plenty of other famous fossil specimens have also been lost. Other dinosaurs were also lost during the World Wars including some of the original bones of Thecodontosaurus, a small dinosaur from Bristol. While many survived, important fossils were lost through Axis bombing of Bristol in 1940. Various Canadian dinosaur specimens en route to the UK were lost when the ship they were on was sunk by the German Navy. And it’s not just dinosaurs, the famous hominid fossils of the original went missing from a train in the fog of war of 1941."

[theguardian.com]