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

REVISITING THE CRETACEOUS LUNGFISH <em>ATLANTOCERATODUS IHERINGI</em> (AMEGHINO 1898) FROM THE MATA AMARILLA FORMATION (ARGENTINA) WITH COMMENTS ON TOOTH PLATES HISTOLOGY

“…These similarities include the number of denticulations, the longer medial edge compared to the lingual edge, the curved lingual edge and the well-developed plateau area. The resemblance between North American and Patagonian species has been previously noted by other authors (Martin 1981(Martin , 1982Schultze 1991;Apesteguía et al 2007;Panzeri et al 2022b), and they may indicate a shared evolutionary history preceding the Jurassic era when these continents were communicated (Krause et al 2019). Regarding the tooth plates assigned to the genera Ptychoceratodus and Ferganoceratodus, the tooth plates of Argentinean species exhibit longer medial edges than lingual edges, with the lingual edges in pterygopalatine tooth plates being distinctly curved.…”

“…The anterior mediolateral bone has a longer-than-wide morphology, and its lateral edge shows a concave dorsal margin with the orbital process and the overlapping suture for the posterior mediolateral bone. These same structures are also present in other dipnoans, such as Rinconodus salvadori (Panzeri et al, 2022b), Ptychoceratodus serratus (Schultze, 1981), Ferganoceratodus martini (Cavin et al, 2007), and Arganodus atlantis Martin, 1979.…”

“…The histological description follows a combination of terms previously implemented in Panzeri et al 2022b (see references cited there). Briefly, in a horizontal histological section, pulp canals surrounded by circumdenteonal dentine can be identified, collectively forming a denteon (Fig.…”

“…The pulp canals are interconnected partially through the outer circumdenteonal dentine band and partially through elongated dentinal tubules, resulting in lines that resemble incremental lines. In the vertical section of M. baibianorum, the pulp canals are surrounded by a single band of circumdenteonal dentine, most of which are continuous, branching at specific points, and incremental lines can be seen on the interdenteonal dentine (Panzeri et al 2022b).…”

“…It follows the recent advancements in the study of the structural and anatomical variations in dipnoan morphology (e.g. Skrzycki 2015;Pawlak et al 2020;Panzeri et al 2020Panzeri et al , 2022a and histology (Denison 1974;Smith 1984;Campbell & Barwick 1998;Kemp 2001;Blaauwen et al 2006;Panzeri et al 2022b). Finally, the similarity with lungfish from other parts of the world and the taxonomic assignment of other species referred to this genus are discussed.…”