Palatoquadrate and its ossifications: Development and homology within osteichthyans

Abstract

The palatoquadrate and associated dermal bones have significant evolutionary transformations among teleostomes and provide numerous features that characterize teleostomian subgroups. The palatoquadrate forms the upper part of the mandibular arch and is present as a single cartilaginous element in the early ontogeny of teleostomes, except for some advanced teleosts such as siluroids where it is divided into pars autopalatina and pars pterygoquadrata. During ontogeny, the palatoquadrate may ossify as a unit, with a pars autopalatina (absent in Acanthodii), pars quadrata, and pars metapterygoidea in teleostomes (e.g., primitive acanthodians and actinopterygians, onychodonts, and rhipidistians). However, the palatoquadrate may remain cartilaginous (e.g., chondrosteans) or it may ossify as separate elements (e.g., autopalatine, metapterygoid, and quadrate) as occurs in advanced acanthodians, Polypterus and advanced actinopterygians, and advanced actinistians. From the single-unit pattern, separate autopalatine, metapterygoid, and quadrate evolve in parallel in the three teleostomian subgroups. Therefore, it is necessary to distinguish between actinopterygian and actinistian autopalatines and among acanthodian, actinopterygian, and actinistian metapterygoids and quadrates. A palatoquadrate fused with the neurocranium occurs in parallel in dipnoans. There are differences in the timing of ossification of the autopalatine, metapterygoid, and quadrate. The autopalatine ossifies late in ontogeny in Polypterus, Amia, and primitive teleosts (absent in lepisosteids and osteoglossmorphs), whereas both metapterygoid and quadrate ossify early in ontogeny. The early ossification of the autopalatine is characteristic of clupeocephalan teleosts. During ontogeny, tooth plates (not forming a separate dermometapterygoid) fuse with the metapterygoid in actinopterygians. Pars autopalatina, pars metapterygoidea, and pars quadrata are regions at the three corners of the single-unit palatoquadrate present in primitive teleostomes; there are no clear limits among these regions, but they may be identified by their processes, articular facets, and topographical relationships with surrounding bones and the orbit. Autopalatine, metapterygoid, and quadrate are chondral bones, perichondrally ossified. Dermal elements such as dermopalatine(s), entopterygoid, ectopterygoid, and tooth plates may cover the palatoquadrate medially. The predermopalatine that originates in front of pars autopalatina in Cladistia and the "dermopalatine" that lies medial to the ectopterygoid in Ginglymodi are specializations of these groups. A dermopalatine fused with the autopalatine is characteristic of clupeocephalan teleosts. Highly specialized tendon bone pterygoids are found in some teleosts (e.g., siluroids). The presence of both maxilla and lacrimal lateral to the pars autopalatina is synapomorphous of osteichthyans. The eye supported by the bony palatoquadrate is a teleostomian synapomorphy. Dermal elements support the eye in actinopterygians, the entopterygoid in...

Development of the pharyngeal arch skeleton in Catostomus commersonii (Teleostei: Cypriniformes)

“…The posterior end of the autopalatine conforms to its cartilage model and remains rodlike. A dermopalatine does not form, as is typical for ostariophysans (Fink and Fink, 1981;Arratia and Schultze, 1991).…”

“…We follow the terminology of Nelson (1969) for the branchial arches and Arratia (1992) and Arratia and Schultze (1991) for the mandibular and hyoid arches. We have applied the term ''post-ceratobranchial cartilage'' to the midline cartilage extending posterior to ceratobranchial five elements in Catostomus commersonii.…”

The genetic basis of modularity in the development and evolution of the vertebrate dentition

“…When considered as a group, bony ¢shes may possess teeth in the oral cavity on the marginal dermal bones of the mandibular arch and any of the dermal bones forming the palatal surface (Gosline 1971). Teeth may also be found on toothplates (with bony bases presumed to be homologous to bone of attachment, Smith & Hall 1993) attached to endochondral bones of the palate (Arratia & Schultze 1991) or free in the skin between palatal bones (e.g. the primitive teleost Elops, Nybelin 1968).…”

An Experimental Study of Intraspecific Variation, Developmental Timing, and Heterochrony in Fishes

“…Dermal bones are generally reported to develop before cartilage bones in fishes (Arratia and Schultze 1990;Vandewalle et al 1992;Schultze 1993;Mabee and Trendler 1996) as well in other vertebrates: some amphibians (Wiens 1989;Hanken et al 1992) though only as a derived condition (J. Hanken, pers.…”

“…Finding intraspecific variability in development in turn requires a large sample size, which is difficult or impractical to obtain in developmental studies of many organisms. Thus, in studies where the relative timing of developmental events is examined, typically a single, linear (with respect to time) developmental sequence is reported for a species (e.g., Trueb 1985;Arratia 1990Arratia , 1992Arratia andSchultze 1990, 1991;Kobayakawa 1992;Hanken et al 1992;Clark and Smith 1993;Smith 1997). Although the lack of reported variability may be due to small sample size, in a number of studies in which a moderate number of specimens have been examined Hall 1984, 1988;Hanken et al 1992), variability in ossification sequence appears to be low.…”