Mamíferos da Guimarota na SVP de Los Angeles

Deixamos aqui o resumo de uma das comunicações apresentadas no encontro anual da Society of Vertebrate Paleotology que se debroçou sobre o registo fóssil português, e teve como autores  Janka Brinkkötter e Thoma Martin da Universidade de Boon (Alemanha). Este encontro teve lugar na cidade americana de Los Angeles no passado mês de Novembro. O trabalho em questão focou-se no estudo de uma numerosa amostra de dentes de Haldanodon proveniente dos sedimentos do Kimmeridgiano (Jurássico Superior) da Mina da Guimarota em Leiria.

"In the history of mammalian evolution a talonid-like crushing zone in the lower molars convergently evolved up to three times before the appearance of the Tribosphenida. The most basal group with such “pseudotribosphenic” teeth are the docodonts. They possess a fairly derived dentition with a mesially situated “pseudotalonid”. To examine the dental function of Haldanodon, a large number of isolated teeth and upper and lower tooth rows from the Kimmeridgian of the Guimarota coal mine in Portugal were studied by SEM, synchrotron, and micro-CT. Wear facets were mapped and their striation recorded which served together with 3D models as the basis for an analysis of the chewing cycle with the Occlusal Fingerprint Analyser (OFA). By OFA analysis, the occlusal relationships of Haldanodonmolars were reconstructed in detail. Previous models with an occlusion of the upper molars in between the lower molars and contact of the mesial part of the upper molar with the distal part of the lower molar were confirmed. The distal part of the upper molar contacts the mesial part of the following lower molar. This implies that the “pseudoprotocone” actually occludes mesiolingually of the “pseudotalonid”. Therefore the amount of crushing occurring in the “pseudotalonid” is actually quite small. Instead, the majority of the crushing function is conducted in the distally situated “pseudotrigon” of the upper molar by cusp b of the lower molar. The OFA-analysis also revealed a considerable “overbite” in the molars of Haldanodon, with main cusp a of the lower molar occluding beyond the dental crownroot-boundary of the upper molar. This overbite is compensated by grooves in the maxilla between the upper molars. Noteworthy is also a change from mesially heavier worn molar tooth rows in juvenile specimens to distally heavier worn molar tooth rows in older specimens probably due to a distally shifted chewing focus, a relatively thin enamel layer and highly abrasive food."

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Referência:

• Brinkkötter, J., Martin, T. (2013). Molar morphology and function of Haldanodon exspectatus (Docodonta, Mammaliaformes). Journal of Vertebrate Paleontology, Program and Abstracts, 2013, 94.
• Foto: Castorcauda, membro do grupo Conodonta, que foi encontrado na China em sedimentos do Jurássico Médio.