Thursday, May 18, 2023

[Paleontology • 2023] Stelladens mysteriosus • A Strange New Mosasaurid (Squamata: Mosasauridae) from the Maastrichtian (Late Cretaceous) of Morocco

 Stelladens mysteriosus
 Longrich, Jalil, Pereda-Suberbiola & Bardet, 2023

Mosasaurids, a clade of specialized marine squamates, saw a major adaptive radiation in the Late Cretaceous, evolving a wide range of body sizes, shapes, and specialized tooth morphologies. The most diverse known mosasaurid faunas come from the late Maastrichtian phosphates of Morocco. Here, we report an unusual new mosasaurid, Stelladens mysteriosus, based on a partial jaw and associated tooth crowns from lower Couche III phosphatic deposits at Sidi Chennane, Oulad Abdoun Basin, Morocco. Stelladens is characterized by short, triangular tooth crowns with a series of strong, elaborate, and serrated ridges on the lingual surface of the tooth, functioning as accessory carinae. Morphology of the teeth and associated jaw fragment suggest affinities with Mosasaurinae. No close analogues to the unique tooth morphology of Stelladens are known, either extant or extinct. It may have had an unusual and highly specialized diet, a specialized prey-capture strategy, or both. The diversity of mosasaurid teeth is much higher than that of plesiosaurs, ichthyosaurs, or extant marine mammals, and likely reflects both the ecological diversity of mosasaurids and complex developmental mechanisms responsible for tooth formation in mosasaurines. Mosasaurid diversity continued to increase up to the Cretaceous–Paleogene boundary.

Keywords: Mosasauridae; marine reptiles; Cretaceous; Cretaceous–Paleogene mass extinction; Africa

Systematic Paleontology

Squamata Oppel, 1811

Mosasauridae Gervais, 1852
Mosasaurinae Gervais, 1852

Stelladens mysteriosus new genus and species.

Diagnosis. Mosasaurine mosasaurid characterized by the following unique character combination: low, triangular, weakly recurved crowns with a strong U-shaped cross-section; two prominent serrated carinae, the posterior one being more marked and pinched”from the main shaft; labial surface almost flat bearing 6–8 subtle low ridges; lingual surface strongly convex and bearing 2 to 4 very prominent, sharp and serrated ridges.

Holotype. MHNM.KHG.1436, partial left dentary and two associated teeth (Figure 3, Figure 4 and Figure 5).

Locality and Horizon. The holotype comes from Sidi Chennane phosphate mine, in the Oulad Abdoun Basin, Khouribga Province, Morocco. It was recovered from the lower part of Couche III (Figure 1 and Figure 2). Upper Couche III is dated to the late Maastrichtian on the basis of shark teeth [30], and to the latest Maastrichtian based on carbon and oxygen chemostratigraphy [27]. The age of lower Couche III is not well-constrained. Lower Couche III appears to contain a broadly similar fauna, but taxa are distinct at the species level, suggesting it is somewhat older than Upper Couche III.

Etymology. The genus’ name is from the Latin stella, ‘star’ + denstooth. The species’ name is from the Latin mysterium, ‘mystery’, because of the mysterious structure of the teeth.

A partial mosasaurid jaw and the associated teeth exhibit a highly unusual morphology, with two to four prominent, sharp, and serrated ridges on the lingual surface of the teeth. This unusual morphology diagnoses a new genus and species, Stelladens mysteriosus, and underscores the high morphological and ecological diversity of mosasaurids in the latest Cretaceous, especially among Mosasaurinae [Bardet, et al., 2015]. Stelladens presumably had a specialized feeding strategy, but the lack of any extinct or modern analogues makes it difficult to infer its ecology. As part of their radiation, mosasaurids experimented with unusual tooth morphologies, similar to dinosaurs and mammals. Mosasaurid diversity was high in the Maastrichtian and continued to increase prior to their extinction at the K-Pg boundary.

 Nicholas R. Longrich, Nour-Eddine Jalil, Xabier Pereda-Suberbiola and Nathalie Bardet. 2023. Stelladens mysteriosus: A Strange New Mosasaurid (Squamata) from the Maastrichtian (Late Cretaceous) of Morocco. Fossils. 1(1), 2-14. DOI: 10.3390/fossils1010002