Testing the occlusal relations between isolated upper and lower molars of an Eocene metatherian (Mammalia): The case of Xenocynus crypticus

Leonardo M Carneiro ^1,2, Hugo Bampi ³, Sérgio Lages ⁴

⁰Universidade Federal de Pernambuco, Centro de Tecnologia e Geociências, Departamento de Geologia, Programa de Pós-graduação em Geociências (PPGEOC), Av. Acadêmico Hélio Ramos, s/n, Cidade Universitária, 50740-530 Recife, PE, Brazil.

Anais Da Academia Brasileira De Ciencias +

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April 2, 2025

View abstract on PubMed

Summary

This study confirms the distinctness of Xenocynus crypticus fossil molars from Brazil using morphometric analyses. The findings support the species

Area Of Science

Paleontology
Mammalogy
Evolutionary Biology

Background

Xenocynus crypticus, an early Eocene metatherian from Brazil, was initially described from limited fossil dental remains.
The occlusal relationships and morphometric distinctiveness of Xenocynus crypticus molars have not been previously analyzed.
Fragmentary dental evidence poses challenges for taxonomic identification and species association in fossil mammals.

Purpose Of The Study

To analyze the morphometric parameters and infer occlusal relationships of Xenocynus crypticus upper and lower molars.
To assess the morpho-occlusal compatibility and taxonomic validity of Xenocynus crypticus.
To evaluate the utility of principal component analyses (PCA) for comparing isolated fossil mammal molars.

Main Methods

Inclusion of upper and lower molars assigned to Xenocynus crypticus and specimen AMNH 49805 in analyses.
Application of scatterplots and two principal component analyses (PCA) to assess morphometric parameters.
Inference of occlusal relationships to determine morpho-occlusal compatibility between upper and lower molars.

Main Results

Xenocynus crypticus molars are morphometrically distinct from sympatric taxa, with lower first molars (m1s) exhibiting proportionally shorter talonids.
Inferred occlusal compatibility was observed between the upper and lower molars of Xenocynus crypticus, showing similar talonid proportions.
Principal component analyses (PCA) reliably assessed morphometric similarity between isolated upper and lower metatherian molars.

Conclusions

The findings support the taxonomic validity of Xenocynus crypticus and the association of the studied lower molars with this species.
Morphometric analysis and PCA are valuable tools for taxonomic studies of fragmentary dental-based fossil taxa.
This research enhances our understanding of early Eocene metatherian diversity in the Itaboraí Basin.

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