Today, at a press conference, there was more clarity.
Mosasaurus hofmanni was the first mosasaur ever discovered amidst much publicity in the eighteenth century, also in Maastricht. The original fossil was stolen from Maastricht by French soldiers, and brought to the Paris museum where it still is.
A twitter message from the museum says that the skull of the newly discovered mosasaur (the only part of the animal recovered completely so far, though an important part) is about 10% bigger than the Paris specimen’s.
Dutch NOS TV says that probably, after the death of the mosasaur, scavenging sharks dispersed its remains. The search for other parts of the skeleton is still continuing.