Morphological plasticity in the dentition of the lungfish Gnathorhiza from the Permian of Brazil: A population‐level geometric morphometric analysis

Dental plates are pivotal in the lungfish paleontological record, constituting highly mineralized structures resilient to diagenetic processes. This study provides a detailed description and quantitative shape analysis of 95 newly discovered Gnathorhiza sp. dental plates from the Middle–Late Permian Corumbataí Formation, Brazil. The analyzed sample comprises both upper and lower dentition morphotypes, sharing diagnostic generic features such as straight, sharp, and narrow conical ridges, an obtuse angle between the first and last ridges, a slightly conical lingual border, deep sulci, and an occlusal surface displaying reticulated ornamentation with distinct petrodentine cores. Taphonomic systematization suggests distinct preservation histories for each morphotype, explaining the overrepresentation of upper plates relative to lower ones. To quantitatively evaluate structural variation, landmark‐based geometric morphometrics was applied to both upper and lower tooth plates; however, due to a significantly larger sample size, the upper dentition yielded the most robust and biologically significant results. The geometric morphometric analyses revealed substantial morphological variance, particularly localized in the first ridge and first sulcus of the upper plates. Rather than resulting from strict ontogenetic developmental paths or sexual dimorphism, we hypothesize that these predominant morphological differences reflect high phenotypic plasticity within this isolated population. This study confirms the high abundance of Gnathorhiza in the Corumbataí Formation, provides a rigorous assessment of key morphological features in late Paleozoic dipnoan dental plates, and offers insights into the population dynamics of these specialized durophagous predators within a complex Permian mega‐lake paleoenvironment.