Bruno GonÃalves Augusta & Hussam Zaher (2019)
Enamel dentition microstructure of Mariliasuchus amarali (Crocodyliformes, Notosuchia), from the Upper Cretaceous (TuronianâSantonian) of the Bauru Basin, Brazil.
Cretaceous Research (advance online publication)
Highlights
Mariliasuchus amarali presents four distinct tooth morphotypes in its dentition.
It is the only known reptile to bear both true and false denticles in the same tooth.
Adults and juveniles probably occupied very similar ecomorphological niches.
Dental anatomy and microstructure support the ziphomorph condition.
Abstract
Advanced notosuchians represent a diverse clade of highly heterodont crocodyliforms that were endemic to the South American landmass during the Cretaceous. Mariliasuchus amarali is an advanced notosuchian from the Upper Cretaceous (TuronianâSantonian) of the Bauru Basin, south-central Brazil, and it is known from several well-preserved specimens in distinct ontogenetic stages. Previous functional analyses of the dentition of M. amarali suggested generalist feeding habits. However, microscopic patterns of the enamel, such as crystallite micromorphology and microwear variation along the dental series, have not been investigated in detail so far. Our results evidence that M. amarali enamel is unique among crocodyliforms, and that heterodonty in this species is even more complex than previously thought. External crown morphology, macrowear position, microwear orientation, and enamel crystallite micromorphology support the recognition of four tooth morphotypes, each of these presenting a combination of features never seen before. M. amarali is the first described reptile bearing both true and false denticles in the same tooth, a condition up to now autapomorphic for the taxon that supports its classification into a distinct dental category (ziphomorph). Ontogenetic trends of dentition reveal that heterodonty was kept through the entire life of M. amarali, and that adults and juveniles occupied very similar ecological niches. Hypothesis of M. amarali presenting omnivorous feeding habits, with the inclusion of hard items in its diet, is supported here. The unique combination of dental features in the taxon could have provided an important adaptive advantage in a low resource environment, as it has been postulated for the Bauru Basin.
Daniel Madzia (2019)Â
Dental variability and distinguishability in Mosasaurus lemonnieri (Mosasauridae) from the Campanian and Maastrichtian of Belgium, and implications for taxonomic assessments of mosasaurid dentitions.
Historical Biology (advance online publication)
DOI: 10.1080/08912963.2019.1588892
Mosasaurus lemonnieri is a mosasaurine mosasaurid first unearthed from the lower Maastrichtian of the Mons Basin, southern Belgium. Even though numerous well-preserved specimens have been attributed to the taxon, the knowledge of its anatomy is surprisingly poor and merely limited to some general characteristics. Here I describe the morphology of the marginal dentition of M. lemonnieri based on the holotype and 14 referred individuals originating from the upper Campanian and Maastrichtian of Belgium. The dental variability is assessed through linear discriminant analyses aimed to appraise the tooth crown distinguishability between (1) individuals, (2) tooth-bearing elements (premaxillae, maxillae, and dentaries), and (3) within particular jaw regions (anterior, middle, and posterior). The overall dental distinguishability between individuals was, expectedly, poor though the rates of correctly classified teeth differed for particular specimens, which can have taxonomic implications. The premaxillary and maxillary teeth were inferred to be more distinguishable than the dentary teeth. The dental distinguishability of M. lemonnieri is further compared to that of other sympatric and potentially sympatric taxa. The use of mosasaurid dental measurements substantially facilitates the comparisons of mosasaurid teeth on both inter- and intraspecific scale, increasing the accuracy of the studies appraising the patterns of mosasaurid dental evolution.
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