Identifying North African (Moroccan) mosasaur teeth

George Corneille (Ireland)

I have been a collector of marine reptile and dinosaur fossils for many years and started to sell on a small scale a few years ago. This editorial is specifically to help collectors identify teeth that they may have in their collections and to better understand these giant ocean going reptiles that dominated the oceans from the middle to late Cretaceous.

Many mosasaur species have been identified by isolated teeth. This is extremely difficult, because, ideally, to describe a new taxon, you need skull elements, jaw hinges, flipper digits and so on. This fossil material is of course not easily available for the most part and we have to rely on isolated teeth. However, both French palaeontologist, Camille Arambourg, and Belgian palaeontologist, Louis Dollo, have relied on isolated teeth to identify a new taxon.

The first mosasaur was discovered in Holland in 1780 by Dr Johann Leonard Hoffman. Since that time, at least another 40 species have been identified worldwide from Sweden to Africa and Israel to New Zealand as well as the USA, especially in Kansas.

Mosasaurs dominated the world’s oceans at the end of the Cretaceous. Here, we concentrate on the Moroccan species, specifically from the Oulad Abdoun Basin and Sidi Daoui in the Moroccan Sahara.

There are currently six identified species of mosasaur from the marine deposits in Morocco. Arambourg (1952) was the last comprehensive study of marine fossils. In Mosasaurus beaugei (Arambourg 1952), the tooth crowns are described as robust with both carinae (cutting edges) having fine visible serrations, the most noticeable feature is the very distinctive and pronounced longitudinal prism-shaped facets on the tooth crown. The teeth are almost triangular in cross section and the facets can also be even more pronounced. It was a giant that grew to approximately 12m long and is one of the largest identified species from Morocco.

Leiodon anceps (Owen 1841) is the one that seems to cause the greatest confusion. This species is very common in the Moroccan marine deposits. The tooth crowns are laterally compressed with smooth enamel and fine serrations may be present on both labial and lingual carinae. They are much less robust than M. beaugei.

The anterior teeth of Leiodon anceps are more elongated as can be seen from the jaw section (Fig. 2). Note the tooth left by a shark feeding on the mosasaur carcass.

Prognathodon giganteus (Dollo 1904) and later described by Arambourg in 1952 as Mosasaurus (leiodon) anceps is what has caused so much confusion amongst mosasaur fossil collectors.

What Arambourg described was a species already known as Prognathodon giganteus. The teeth are described as having large robust crowns with a triangular shape when looked at in lateral view. They are finely serrated, which is visible to the naked eye. They are sub-circular in cross section and the prism facets are absent with both carinae being serrated. They bear no resemblance to Leiodon anceps teeth.

Platycarpus ptychodon is an uncommon mosasaur that has interesting and unusual teeth. The crowns are small, being laterally compressed and again the anterior teeth are more elongated. They have very distinctive vertical striations, which are more numerous on the lingual side. These were mid-sized mosasaurs that grew to 18.5m in length, with teeth approximately 25mm long.

The large jawbone shows the erupting teeth which replaced damaged teeth when the mosasaur was alive. This is a common trait with all mosasaur species as are pterogoid teeth (throat teeth), with the exception of Globidens aegypticus. You can see the erupting teeth at the bottom of the teeth sockets in Fig. 6. This specimen now in the collection of Terry Boudreaux.

Globidens aegypticus has the most distinctive of all teeth. Described as globe-shaped with the anterior teeth becoming more peg shaped. It is the rarest in the Moroccan deposits. Globidens was a heavy, robust species, closely related to Prognathodon. It fed on molluscs and other shellfish on the bottom of shallow Cretaceous seas, with teeth having an unusual crenulated appearance on their crowns.

Halisaurus (Marsh 1869) has teeth described as being small slender and abruptly recurved close to the mid-point of the crown. They have a circular basal cross section and both carinae have minute serrations. Adult teeth are very small, being approximately 20mm in height.

There may be another tooth so far not described in Morocco. This tooth is in my collection (Fig. 9) and was found in the Sidi Daoui Oulad Abdoun Basin. The tooth is a monster with the crown alone measuring over 7.5cm and is the equivalent of a 17.5cm Carcharocles megalodon shark tooth in size comparison. The carinae have flared edges, which disappear at the crown midpoint. This tooth is the biggest tooth I have ever seen and any opinion on the tooth would be appreciated. I believe the tooth to be an undescribed species of Prognathodon.

Acknowledgements

I would like to thank Maarten Haverkamp in Holland, Jim Dodrill in Australia and Terry Boudreaux in the USA for being so helpful. Also Mike Everhart for answering my emails so eloquently.