Inferring parrotfish (Teleostei: Scaridae) pharyngeal mill function from dental morphology, wear, and microstructure

Abstract

Morphology, occlusal surface topography, macrowear, and microwear features of parrotfish pharyngeal teeth were investigated to relate microstructural characteristics to the function of the pharyngeal mill using scanning electron microscopy of whole and sectioned pharyngeal jaws and teeth. Pharyngeal tooth migration is anterior in the lower jaw (fifth ceratobranchial) and posterior in the upper jaw (paired third pharyngobranchials), making the interaction of occlusal surfaces and wear-generating forces complex. The extent of wear can be used to define three regions through which teeth migrate: a region containing newly erupted teeth showing little or no wear; a midregion in which the apical enameloid is swiftly worn; and a region containing teeth with only basal enameloid remaining, which shows low to moderate wear. The shape of the occlusal surface alters as the teeth progress along the pharyngeal jaw, generating conditions that appear suited to the reduction of coral particles. It is likely that the interaction between these particles and algal cells during the process of the rendering of the former is responsible for the rupture of the latter, with the consequent liberation of cell contents from which parrotfish obtain their nutrients.

An Ancient Gene Network Is Co-opted for Teeth on Old and New Jaws

“…Second, all cichlids possess modified posterior pharyngeal arches, which act as a functional jaw (Figure 1 and 2; [6,7]). Cichlids, and a few other teleost lineages [6–9,12–14,48], feature fusion of the bilateral units of the lower pharyngeal jaw cartilages (LPJ) and a novel muscular sling that pulls the LPJ upward to contact the hinged upper pharyngeal jaw units. This formidable pharyngeal machinery for food processing can produce enough force in some species to crush hard prey such as shelled molluscs [6,7].…”

Ultrastructure and the importance of wear in the dentition of the halfbeak (Pisces: Hemiramphidae) pharyngeal mill

“…Descriptions of orientations followed Carr et al (2006). Pharyngeal teeth are composed of bundles of needle-like apatite crystals.…”

“…Vertically aligned crystals are preferentially aligned to resist cracking and failure due to vertically aligned tensile stresses (Carr et al, 2006). As no such stresses of high magnitude exist within the tooth, there is no need for vertically aligned crystals within the tooth.…”

“…Mineralized layers of fish teeth contain variously oriented apatite crystals within a protein matrix (Lund et al, 1992). The arrangement of these components differs among fish species and knowledge of tooth composition at the tissue level provides important insights into tooth function (Lund et al, 1992;Carr et al, 2006;Kemp and Barry, 2006). For example, tooth microstructure proved vital in explaining wear in parrotfish in which wear is fundamental to the development of a pharyngeal occlusal surface that enables the treatment of food bearing carbonate particles (Carr et al, 2006).…”

Dentition damage in parrotfishes feeding on hard surfaces at Fernando de Noronha Archipelago, southwest Atlantic Ocean

“…While doing so, parrotfishes usually break and ingest part of the hard substrata found on reefs (Bellwood & Choat 1990, Bruggemann et al 1996, indicating that they have a strong dentition (Bellwood & Choat 1990, Prostak et al 1991, Carr et al 2006 which enables them to continually access their main food source during their relatively long life. Furthermore, parrotfishes usually have a high feeding frequency; some species have been recorded delivering up to 5 bites min -1 against the substratum (Bellwood & Choat 1990, Bruggemann et al 1994a,b, Bonaldo et al 2006).…”