“…The presence of a slender crown with three keels on its anterior surface and a narrow neck are common features in scales of PaleozoicMesozoic ctenacanthids, but are also common in euselachian chondrichthyans (Reif, 1978;Hansen, 1986;Rieppel et al, 1996;Johns et al, 1997;Derycke-Khatir et al, 2005;Ivanov et al, 2013). The Hydriot denticle compares favorably to the par-agenus Moreyella (Gunnell, 1933;Hansen, 1986), which has been tentatively affiliated with Carboniferous-Permian hybodontiform chondrichthyans (e.g., Derycke-Khatir et al, 2005). The Triassic paragenera Fragilicorona and Labascicorona (Johns et al, 1997) also display very similar, tricuspid distal crowns like the denticle in question, but their systematic affinities beyond the euselachian level have not been discussed (Ivanov et al, 2013).…”