The South American dipnoan Metaceratodus baibianorum (Dipnoi, Ceratodontidae) from the Upper Cretaceous La Colonia Formation, Patagonia, Argentina: an approach from the histology of the tooth plates

Abstract

Lungfish remains are a frequent component of the Upper Cretaceous deposits of Patagonia; they are mainly represented by tooth plates fused or not to the jaw bones. Here, we describe the histology of the tooth plates of Metaceratodus baibianorum from the La Colonia Formation, Patagonia. The present study is the first of its kind to be carried out in Argentinian dipnoans. Under the petrographic microscope, the tooth plates show two distinct arrangements of calcium hydroxyapatite crystals in the interdenteonal dentine (cross birefringent pattern and monorefringent pattern), which differ from the one present in the circumdenteonal dentine (lamellar birefringent pattern). The tissue arrangement of M. baibianorum tooth plates is more similar to that of other Mesozoic and Cenozoic species (such as neoceratodontids) than it is to that present in Paleozoic species (such as Dipterus valenciennesi). At the same time, incremental lines in vertical sections are observed. The nature of incremental lines in the interdenteonal dentine and their use in estimating the minimum age of the specimen are discussed.