Ontogeny and homology of cranial bones associated with lateral‐line canals of the Senegal Bichir,Polypterus senegalus(Actinopterygii: Cladistii: Polypteriformes), with a discussion on the formation of lateral‐line canal bones in fishes

Abstract

The association between lateral‐line canals and skull bones in fishes has been the subject of several studies and raised a series of controversies, particularly with regard to the hypothesized role of lateral‐line organs (i.e. neuromasts) in osteogenesis and the consequences for hypotheses of homology of the bones associated with lateral‐line canals. Polypteridae, a group of freshwater fishes that occupies a key phylogenetic position as the most basal extant lineage of ray‐finned fishes (Actinopterygii), provides an interesting model for the study of the relationships between lateral‐line canals and skull bones. We describe the development of bones associated with lateral‐line canals in the Senegal Bichir, Polypterus senegalus, and use these data to re‐address previous hypotheses of homology of skull bones of polypterids. We demonstrate that the lateral‐line canals constitute a separate component of the dermatocranium that may interact with a membranodermal component, thereby forming compound bones in the adult. Differences in the interactions between these components determine the characteristics of the development of each independent bone in the skull of adult P. senegalus. Our results shed light on long‐standing controversies about the identity of skull bones such as the rostral, preopercle, and sphenotic in Polypteridae, and suggest the presence of an ancestral two‐component pattern of formation of bones associated with lateral‐line canals in bony fishes. These findings reveal the need to re‐address previous hypotheses of homology of bones associated with lateral‐line canals in different groups of bony fishes, especially fossil taxa.

Osteohistology of Greererpeton provides insight into the life history of an early Carboniferous tetrapod

“…However, unlike modern amphibians, Greererpeton did not metamorphose and maintained its lateral line system into adulthood. This retention of a lateral line system does not necessarily preclude temporary terrestrial excursions as experimental and developmental evidence suggests extensive flexibility in lateral line system development and function (Gayer, 2018; Rizzato et al, 2020) and that aquatic vertebrates with lateral line systems can survive days to years in aerial settings (Davenport & Abdul Matin, 1990; Healy, 1975; Schoch, 2001; Standen, Du & Larsson, 2014). Moreover, recent functional analyses have revealed that although primarily aquatic in habit, Greererpeton limb morphology had adaptations supporting at least limited terrestrial capabilities (Dickson et al, 2021).…”

Feroxichthys yunnanensis gen. et sp. nov. (Colobodontidae, Neopterygii), a large durophagous predator from the Middle Triassic (Anisian) Luoping Biota, eastern Yunnan, China

“…However, Feroxichthys gen. nov. slightly differs from luganoiids in that the lacrimo-maxilla does not contribute to the composition of the anterior margin of the orbit. Outside of the Neopterygii, an infraorbital/maxilla fusion is present in the living Polypterus , in which the sixth and seventh infraorbitals are fused with the maxilla ( Rizzato et al, 2020 ).…”

Cranial morphology of the Stellate Sturgeon, Acipenser stellatus Pallas 1771 (Acipenseriformes, Acipenseridae), with notes on the skulls of other sturgeons

“…The left and right series of rostral canal bones meet together at the rostral canal commissure. On either side of this commissure is a distinctly shaped, tripartite canal bone, the lateral rostral bone (Hilton, 2002), which is homologous to the antorbital of other basal actinopterygians (Warth et al., 2017; Rizzato et al., 2020).…”

“…The branching pattern between the trunk lateral‐line sensory canal, the occipital sensory canal, and the supratemporal sensory canal was first used as a character in a phylogenetic analysis of Acipenseridae by Findeis (1997: character 56) (Figures 8 and 18). He found the conjunction of these canals within the lateral extrascapular to be a synapomorphy of Pseudoscaphirhynchus (note that these canals correspond to the postotic [= supratemporal] and supratemporal [= occipital and trunk lateral line] of Rizzato et al., 2020, but we are using the terminology used by Findeis and others for Acipenseriformes). Indeed, Scaphirhynchus , Huso and most Acipenser species have this branching in the posttemporal, whereas Pseudoscaphirhynchus has it in the lateral extrascapular as described by Findeis (1997; Figure 18).…”

“…The dermosphenotic is intercalated between the supraorbital and the postorbital, which is a robust, irregularly rectangular bone; the postorbital forms the posterior margin of the orbit and carries the infraorbital sensory canal from the dermosphenotic ventrally to the jugal. For consistency with other recent studies of the osteology of sturgeons, we use the term jugal herein for this bone, although as shown by Rizzato et al, 2020, this bone is likely not homologous to the jugal of other osteichthyans. The jugal of Acipenser stellatus has a relatively small dorsal arm (relative…”