Development of the nasal capsule in Emydura subglobosa (Testudines: Pleurodira) with a comparison to other turtles

Abstract

Abstract Extant turtles occupy freshwater, marine, and terrestrial habitats, and their nasal region provides important evidence for the evolution of respiration‐ and sensory‐related cranial morphology. However, developmental data on the turtle nasal capsule remain limited, particularly in Pleurodira. Here, we describe nasal capsule development in the pleurodiran turtle Emydura subglobosa based on histological cross‐sections of five distinct developmental stages and three‐dimensional reconstructions. The nasal capsule underwent marked reorganization between Emyd. subglobosa developmental stages 4− and 5− (ES 4− and ES 5−), during which its basic architecture became established. Several features are notable. First, the nasal entrance shows distinctive pleurodiran specializations, including a processus supranarinus communis formed by medial fusion of the paired processus supranarini and a dorsally projecting processus rostralis medialis formed from the paired processus infranarini. In addition, Emyd. subglobosa possesses a fenestra rostralis at the nasal entrance, a feature not identified in other turtles examined to date. Second, the floor of the nasal capsule exhibits the expanded solum nasi complex characteristic of turtles, including the lamina transversalis anterior, pars paraseptalis, and pila supraglandularis, together with a canalis praepalatinus and a posteriorly facing fenestra basalis. Third, the pars ectochoanalis differs between the two major turtle clades: in pleurodires, it extends only slightly caudally, whereas in cryptodires it typically extends farther caudally and forms the ventral margin of the ductus nasopharyngeus. These findings provide a developmental framework for interpreting pleurodiran nasal morphology and a broader comparative framework for understanding turtle nasal evolution.