The research history of Mosasaurus is extensive given its complicated taxonomic and cultural histories, with the earliest recorded fossil find dating back to 1764 in a chalk quarry located near Maastricht, Netherlands. A second, slightly more complete specimen, discovered in 1778 in the same locality, was captured by the French army after the siege of Maastricht in 1794, before being delivered to the French National Museum of Natural History in Paris the following year. Initially considered as fossils coming from crocodiles or whales, it was from 1800 that Adriaan Gilles Camper identified them as coming from a large marine reptile sharing affinities with monitor lizards, conclusions shared by Georges Cuvier in a 1808 study. This identification reinforces Cuvier in his conception of the notion of extinction which then appeared at this time. Long known as the “great animal of Maastricht”, it's in 1822 that William Conybeare proposed naming the new taxon as Mosasaurus in reference to its origin in fossil deposits near the Meuse River. The genus name, although later approved by Cuvier himself, remained without a specific epithet until 1829, from which a certain number of proposals appeared; later consensus suggesting the using of the name M. hoffmannii as first erected by Gideon Mantell, as well the designation of the second skull as the type specimen of this species.
After the true nature of the fossils was proven by Camper Jr. and Cuvier, many authors initially described the animal as a semi-aquatic marine reptile using webbed feet for walking, a view based after the misinterpretation of some bones. In 1854, Hermann Schlegel discovered that the animal had in fact flippers entirely made for the marine environment. His findings remained largely ignored until more complete North American mosasaur fossils were discovered during the 1870s. Historically, the type species M. hoffmannii was described via unclear diagnosis, leading the genus to become a wastebasket taxon containing up to fifty different species. A new description of the type specimen published in 2017 helps resolve the taxonomic problem and confirms that at least four other species belong to the genus, namely M. missouriensis, M. conodon, M. lemonnieri and M. beaugei. Another five species still nominally classified within the genus are planned to be reassessed.
First discoveries First skull
The first remains of Mosasaurus known to science are fragments of a skull discovered in 1764 at a subterranean chalk quarry under Mount Saint Peter, a hill near Maastricht, the Netherlands. It was collected by the French army Lieutenant Jean Baptiste Drouin in 1766 and was procured in 1784 by museum director Martinus van Marum for the Teylers Museum at Haarlem. In 1790, Van Marum published a description of the fossil, considering it to be a species of "big breathing fish" (in other words, a whale) under the classification Pisces cetacei. This skull is still in the museum's collections and is cataloged as TM 7424.
Second skull and historical capture
In 1778, a second more complete skull was discovered at the same quarry. The retired Dutch army physician named Johann Leonard Hoffmann took a keen interest in this specimen, who corresponded with the famous compatriot biologist Petrus Camper regarding its identification. Hoffmann, who had previously collected various mosasaur bones in the 1770s, the most complete of which a left lower jaw, presumed that the animal was a crocodile. He even intended to publish a treatise about the jaw but was dissuaded by Camper who, by showing Hoffmann a crocodile jaw to demonstrate its dissimilarity with the mosasaur one, wished to spare him the embarrassment of publicly retracting his initial opinion. The second skull, as the Teyler Museum's one, were first figured by the French naturalist Pierre-Joseph Buc'hoz in a 1782 work, in which he described them as representing the same lineage of an unknown animal. This same work represents the very first published scientific documentation about Mosasaurus, although the figures shown are upside down due to the lithographic process. In 1786, Camper concluded that the remains belonged to an "unknown species of toothed whale". He published his studies that year in the Philosophical Transactions of the Royal Society of London, the most prestigious scientific journal in the world at the time, giving the second skull international fame. During this time, the fossil was under the possession of canon Theodorus Joannes Godding, who owned the portion of the land it was discovered in. Godding was struck by its beauty and took every measure to conserve it, eventually displaying it to the public inside a grotto behind his house. This same cave would most likely correspond to a closed room of the "", which has since collapsed in 1916.
Maastricht, an important Dutch fortress city at the time, was captured during the French Revolutionary Wars by the armies of General Jean-Baptiste Kléber in November 1794. Four days after the conquest, the fossil was looted from Godding's possession by French soldiers due to its international scientific value under Kléber's orders, carried out by political commissar . According to an account by Godding's niece and heiress Rosa, Frécine first pretended to be interested in studying the famous remains and corresponded with Godding via letter to arrange a visit to his cottage to personally examine it. Frécine never visited, and instead sent six armed soldiers to forcefully confiscate the fossil under the pretext that he was ill and wanted to study it at his home. Four days after the seizure, the National Convention decreed that the specimen was to be transported to the National Museum of Natural History, France (MNHN). By the time it arrived at the museum, various parts of the skull were lost. In an 1816 reclamation request, Rosa claimed that she still possessed two missing parts that were not taken by Frécine. However, the fate of these bones is unknown, and some historians believe that Rosa mentioned them in hopes of negotiating indemnity. The French government refused to return the fossil but recompensed Godding in 1827 by exempting him from war taxes.
When the second specimen was finally incorporated into the Paris Museum, it was first exhibited in the Gallery of Mineralogy and Geology. As the chair of palaeontology did not yet exist at the time (it was only created in 1853), the vertebrate fossils housed in this gallery were placed under the authority of the chair of animals, which had become the chair of comparative anatomy in 1802 under the French naturalist Georges Cuvier. It is for this precise reason that the second skull has since been numbered as MNHN AC 9648. Despite its notoriety, the specimen was not displayed when the museum’s first paleontological gallery opened in 1885, where only around thirty fossils were exhibited. It was only with the inauguration of the Gallery of Paleontology and Comparative Anatomy in 1898 that it was finally placed on public display, where it remains today. In 2009, the MNHN temporarily loaned the specimen to the Maastricht Natural History Museum as part of an event entitled Darwin, Cuvier and the Great Animal of Maestricht.
Cultural legend concerning second skull
There is a popular legend regarding Godding's ownership of the second skull and its subsequent acquisition by the French, which is based on the account of geologist Barthélemy Faujas de Saint-Fond (one of four men that arrived in Maastricht in January 1795 to confiscate any public objects of scientific value for France) in his 1799 publication Histoire naturelle de la montagne de Saint-Pierre de Maestricht (Natural history of the mountain of Saint-Pierre of Maastricht). According to Faujas, Hoffmann was the original owner of the specimen, which he purchased from the quarrymen and helped excavate. When the news of this discovery reached Godding, whom Faujas painted as a malevolent figure, he sought to take possession of the greatly valuable specimen for himself and filed a lawsuit against Hoffmann, claiming his rights as landowner. Due to Godding's position as a canon, he influenced the courts and was able to force Hoffmann to relinquish the fossil and pay the costs of the lawsuit. When Maastricht was attacked by the French, the artillerymen were aware that the famous fossil was stored at Godding's house. Godding did not know his house was spared and he hid the specimen in a secret location in town. After the city's capture, Faujas personally helped secure the fossil while Frécine offered a reward of 600 bottles of good wine to anyone who would locate and bring to him the skull undamaged. The next day, twelve grenadiers brought the fossil safely to Frécine after assuring full compensation to Godding and collected their promised reward.
Historians have found little evidence to back up Faujas' account. For example, there is no evidence that Hoffmann ever possessed the fossil, that a lawsuit involved him and Godding, or that Faujas was directly involved in acquiring the fossil. More reliable but contradictory accounts suggest that his narrative was mostly made up: Faujas was known to be a notorious liar who commonly embellished his stories, and it is likely that he falsified the story to disguise evidence of looting from a private owner (which was a war crime), to make a propaganda for the French army, or to simply impress others. Nevertheless, the legend created by Faujas' embellishment helped elevate the second skull into cultural fame.
Fate of the first skull Unlike its renowned contemporary, the first skull TM 7424 was not seized by the French after the capture of Maastricht. During Faujas and his colleagues' mission in 1795, the collections of Teylers Museum at Haarlem, although famous, were protected from confiscation. The four men may have been instructed to protect all private collections unless its owner was declared a rebel. However, this protection may have also been due to Van Marum's acquaintance with Faujas and the botanist André Thouin (another of the four men) since their first meeting in Paris in July 1785.
Identification Early hypotheses as a crocodile or cetacean