The enameloid microstructure of euselachian (Chondrichthyes) scales

Abstract

The enameloid microstucture of chondrichthyan teeth has been studied for decades and it has proven to be a useful taxonomic tool. Changes in enameloid organization have been related to the emergence of new trophic strategies and Mesozoic radiation of the neoselachian crown group. However, in contrast to the abundance of these data on tooth enameloid, descriptions of chondrichthyan scale enameloid are almost nonexistent. The topology and microstructure of scale enameloid in particular euselachian groups: fossil Mesozoic Hybodontiformes and living neoselachians, including batoids and sharks, are described. It is shown that a thick layer of single crystallite enameloid (SCE) covers all studied scales. Although the enameloid of scales clearly does not reach high levels of microstructural differentiation present in the dental enameloid of some neoselachians, we found some degree of organization, such as oriented crystallites, differentiation into sublayers, and the presence of poorly structured sets of densely arranged parallel crystallites. As scales lack feeding functions of teeth, we suggest that the emergence of microstructural organization/differentiation of chondrichthyan enameloid can be understood as consequence of a self organizing process rather than adap tive pressure.

Comparative anatomy study of teeth types in Barracauda and Tilapia fish

“…Also showed a visible part of the soft enamel texture which forms a thin layer covering the surface of the outer tooth (Figs.11 & 12). This description agrees with Manzanares et al (2014). The lower posterior side of the barracuda teeth showed series of similar teeth in size and shape.…”

A late Permian ichthyofauna from the Zechstein Basin, Lithuanian–Latvian Region

“…The morphotype 4 similar "tripod" shape of the crown was assigned to Hybodontidae denticles from late Triassic in the central Germany (Reig 1978). The morphotype 5 similar dermal denticle crown surface with these features was identified as a hybodontiform scale from the Middle Triassic in Spain (Manzanares et al 2014). The similar histological organisation of this morphotype has also been described in the dermal denticles of some Mesozoic Hybodontiformes and living neoselachians (Manzanares et al 2014); however, in the dermal denticles of the neoselachians, there appear to be two 'sublayers'; the outer sublayer is composed of compacted crystals and the inner sublayer has crystals showing a preferred orientation that is perpendicular to the crown's surface (Manzanares et al 2014).…”

“…The prepared polished fossils were coating with a gold-palladium alloy prior to photographing with the Hitachi S4800-FEG SEM at the Microscope Service at the University of Valencia. The polished sections technique used here has been described by Manzanares et al (2014).…”

The first microfossil record of ichthyofauna from the Naujoji Akmene Formation (Lopingian), Karpenai Quarry, northern Lithuania

“…5A, B). Manzanares et al (2014: fig. 1a) named sim i lar drop-like scales from the Mid dle Tri as sic in Spain as Glabrisubcorona-type hybodontiform scale based on their his tol ogy.…”