Tooth serration morphologies in the genus Machimosaurus(Crocodylomorpha, Thalattosuchia) from the Late Jurassic of Europe

Abstract

Machimosaurus was a large-bodied durophagous/chelonivorous genus of teleosaurid crocodylomorph that lived in shallow marine and brackish ecosystems during the Late Jurassic. Among teleosaurids, Machimosaurus and its sister taxon ‘Steneosaurus’ obtusidens are characterized by having foreshortened rostra, proportionally enlarged supratemporal fenestrae and blunt teeth with numerous apicobasal ridges and a shorter anastomosed ridged pattern in the apical region. A recent study on ‘S.’ obtusidens dentition found both true denticles and false serrations (enamel ridges which contact the carinae). Here, we comprehensively describe and figure the dentition of Machimosaurus, and find that Machimosaurus buffetauti and Machimosaurus hugii have four types of serration or serration-like structures, including both denticles and false denticles on the carinae. The denticles are irregularly shaped and are not always discrete units, whereas the false denticles caused by the interaction between the superficial enamel ridges and the carinae are restricted to the apical region. Peculiarly, the most ‘denticle-like’ structures are discrete, bulbous units on the apicobasal and apical anastomosed ridges of M. hugii. These ‘pseudo-denticles’ have never, to our knowledge, previously been reported among crocodylomorphs, and their precise function is unclear. They may have increased the surface area of the apical region and/or strengthened the enamel, both of which would have been advantageous for a durophagous taxon feeding on hard objects such as turtles.

The taxonomic content of Machimosaurus (Crocodylomorpha, Thalattosuchia)

“…This was recently confirmed by Young et al (2014b) who did not notice major differences between the studied specimens, despite the presence of intra-individual morphological variations. Further work at the level of Teleosauridae is pending and may prove useful for their taxonomy (Schaefer, 2012).…”

The oldest durophagous teleosauroid (Crocodylomorpha, Thalattosuchia) from the lower Bathonian of central High Atlas, Morocco

“…D) as in Machimosaurus hugii von Meyer, (Young et al . ). In Machimosaurus buffetauti Young et al ., , the ridges are ‘wavy’ and could closely resemble serrations (Young et al .…”

“…(Young et al . ) cannot be excluded. The surface of the middle region of the crown is abraded, but the carina seems to be slightly developed, being not thicker than the ridges on lingual and lateral surfaces.…”

Occurrence of Torvoneustes (Crocodylomorpha, Metriorhynchidae) in marine Jurassic deposits of Oaxaca, Mexico

“…Now, the tooth enamel ornamentation of Torvoneustes is also known in IGM 9026 ( Figures 2A-B); consequently, this specimen is reassigned to the genus Torvoneustes. Similar tooth enamel ornamentations are present in at least two teleosaurids, Machimosaurus von Meyer, 1837, and "Steneosaurus" obtusidens Geoffroy Saint-Hilaire, 1825; in these semiaquatic crocodylomorphs, the tooth carinae are heterogeneous because its denticles, although true and isomorphic, are poorly defined and discontinuously distributed (Young et al, 2014b. The carinae pattern found in these teleosaurids contrasts with IGM 9026, because in the latter the homogeneous carinae have true, well-defined, isomorphic and continuously distributed denticles.…”