The mystery of Mystriosaurus

Mystriosaurus life reconstruction

Investigating the Lower Jurassic marine crocodilian Mystriosaurus laurillardi

by Sven Sachs, Michela M. Johnson, Mark T. Young & Pascal Abel

Mystriosaurus laurillardi is one of the first marine crocodile fossils ever to be described. While it received its generic name in 1834, the three-dimensionally preserved skull was mentioned in the literature as early as 1776. The fossil that would later be named Mystriosaurus laurillardi was found in a quarry in Altdorf near Nuremberg in Southern Germany by Johann Friedrich Bauder. Bauder was an Altdorf-based merchant and avid naturalist, who was mayor of Altdorf from 1770 to 1776. The fossil was first mentioned in the scientific literature in an article by Johann Ernst Immanuel Walch (1776), who correctly referred to it as the skull of a crocodile. Johann Samuel Schröter (1780) was less convinced about the crocodylian nature of the find, suggesting that it might be the skull of an ant-eating animal.

Portraits of Johann Friedrich Bauder (1713-1791) (left), Johann Heinrich Merck (1741-1791) (middle) and Johann Jakob Kaup (1803-1873) (right). Source Wikipedia.
Portraits of Johann Friedrich Bauder (1713-1791) (left), Johann Heinrich Merck (1741-1791) (middle) and Johann Jakob Kaup (1803-1873) (right). Source Wikipedia.

Some years later the famous poet Johann Wolfgang von Goethe became aware of the Altdorf skull and told his friend, the wealthy Darmstadt-based naturalist Johann Heinrich Merck, about it. Apparently, Goethe had plans to purchase the fossil from Bauder but was beaten to it by Merck. After it came into his possession, Merck published a note about the skull and compared it to the Indian gharial (Merck, 1786). When Merck died in 1791 the fossil was purchased by landgrave Ludwig X in 1792, who added it to the Nature Cabinet at Darmstadt, which formed the foundation of today’s Hessisches Landesmuseum.

Mystriosaurus skull in side view
Mystriosaurus laurillardi holotype skull (HLMD V946-948) seen in side view. Top: as illustrated by Kaup in Bronn (1837). Bottom: photo of the fossil. [click to enlarge]

Various researchers, including Cuvier (1825), mentioned the skull before Johann Jakob Kaup, who was by then an assistant at the Nature Cabinet in Darmstadt, finally named it Mystriosaurus laurillardi. The specimen is now in collections at the Hessische Landesmuseum in Darmstadt and has the specimen number HLMD V946-948.

Steneosaurus bollensis skull
Skull of Steneosaurus bollensis (MMG BwJ 565, collection of the Senckenberg Naturhistorische Sammlungen Dresden) in dorsal view. [click to enlarge]

Mystriosaurus has been broadly accepted as a valid genus in numerous publications during the 19th and early 20th Centuries. However, in 1961 and 1962 the Tübingen based palaeontologist Frank Westphal published two revisions of Early Jurassic teleosauroids and concluded that Mystriosaurus laurillardi Kaup, 1834 was in fact a subjective junior synonym of Steneosaurus bollensis Jäger, 1828. This conclusion was largely based upon the characteristics named by Kaup in Bronn & Kaup (1842). Still, even Westphal found differences, mentioning that the ventrally protruding tip of the snout found in the Mystriosaurus type specimen is the most extreme case within Steneosaurus. Nevertheless Westphal’s (1961, 1962) conclusion was not questioned in any of the succeeding publications dealing with teleosauroids from the European Jurassic.

Mystriosaurus skulls seen from above
Skulls of Mystriosaurus on dorsal view. Top: type specimen (HLMD V946-948), bottom: referred specimen (NHMUK PV OR 14781). [click to enlarge]

In 2018, however, our team reinvestigated the Mystriosaurus type specimen at Darmstadt and come to very different conclusions which were now published the journal Acta Palaeontologica Polonica (Sachs et al., 2019).

Reassessment of Mystriosaurus

Comparison of nasal openings in Mystriosaurus and Steneosaurus
Comparison of the nasal openings in Mystriosaurus laurillardi (HLMD V946-948, left side top, NHMUK PV OR 14781, left side bottom) and Steneosaurus bollensis (RE 551.762.130 A 0248 - Ruhr Museum Essen, right side).

During our investigation we referred a second skull to Mystriosaurus. This specimen is another, yet more complete, three-dimensionally preserved skull from Whitby (Yorkshire, Great Britain) that is housed in the collection of the Natural History Museum London with the specimen number NHMUK PV OR 14781. This skull is also an old find; it was purchased by the British Museum in 1840, but it is unclear when and by whom it was discovered. The specimen was long referred to as Teleosaurus brevior, a manuscript name established by Richard Owen (see Blake, 1876, Woodward, 1885). In a study by Blake (1876), it was referred to the genus Steneosaurus and described as Steneosaurus brevior (Blake, 1876).

The German and English skulls share a number of key features, including: a similar length of the rostrum; four teeth in the premaxilla; and an identical, forwardly facing nasal opening, a character that rarely occurs in crocodylomorphs as nearly all fossil and extend forms have the nasal openings at the top of the snout.

Mystriosaurus skull in side view
Mystriosaurus laurillardi referred specimen (NHMUK PV OR 14781), initially described as Steneosaurus brevior. The fossil was found in Whitby (Yorkshire, UK). [click to enlarge]

In addition to these characters, the specimen also displays: extreme ornamentation on several bones forming the rostrum and skull roof; the presence of numerous large neurovascular foramina on the premaxillae, maxillae and dentaries; and unique antorbital and temporal fenestrae. These features are also diagnostic for Mystriosaurus and distinguish it from all other crocodilians, including Steneosaurus bollensis.

Skull reconstruction of Mystriosaurus
Reconstruction of the skull of Mystriosaurus laurillardi in dorsal (top) and ventral (bottom) views. Artwork by Julia Beier (Hamburg). [click to enlarge]


Mystriosaurus laurillardi is a marine crocodylomorph with a mesorostrine skull (having a snout that is between 70 and 55% of the total skull length). It lived during the early Toarcian of the Early Jurassic (approximately 182 million years ago), patrolling the coasts of what is today Germany and England. It can be distinguished from contemporary species such as Steneosaurus bollensis by a number of characters, which includes the forwardly facing nasal openings.

Mystriosaurus skull at the Urweltmuseum Hauff in Holzmaden
Skull of ?Mystriosaurus sp. from Holzmaden (Germany). Collection of the Urweltmuseum Hauff in Holzmaden. [click to enlarge]

Besides the holotype specimen and the Whitby skull (‘S. brevior holotype), we can tentatively attribute another specimen from Holzmaden in Southern Germany to Mystriosaurus. This specimen is a complete skull embedded in a slab of Posidonia Shale that is shown at the Urweltmuseum Hauff in Holzmaden.

Now, after a 250-year mystery, of the validity of Mystriosaurus, a more than 4 m long marine crocodilian, has been resolved.

Life reconstruction of Mystriosaurus
Life reconstruction of Mystriosaurus. Artwork by Julia Beier (Hamburg). [click to enlarge]



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Sachs, S., Johnson, M.M., Young, M.T., & Abel, P. (2019) The mystery of Mystriosaurus: Redescribing the poorly known Early Jurassic teleosauroid thalattosuchians Mystriosaurus laurillardi and Steneosaurus brevior. Acta Palaeontologica Polonica 64 (3), 565–579.

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