On the enameloid microstructure of Archaeobatidae (Neoselachii, Chondrichthyes)

Purpose In this study, we present new data regarding the enameloid microstructure of the oldest batoid family, Archaeobatidae. Methods First, all the teeth were etched superficially with HCl 10% for 5 s and photographed in the SEM. Afterwards, the same teeth were embedded in Canadian Balsam, polished and etched again with HCl 10% in order to reveal the enameloid microstructure before being photographed a second time. Results The enameloid layer of Archaeobatidae consists on a superficial single crystallite enameloid (SCE) with a parallel bundled enameloid (PBE) in all the taxa studied, but only in Toarcibatis and Cristabatis there exists a tangled bundled enameloid (TBE) under it. Conclusions The structural complexity and diversity found in Archaeobatidae are comparable to that recently described in others fossil batoids. Our data suggest a general trend to “simplification” in batoid enameloid up till the homogeneous single crystallite enameloid that is present in the majority of current batoids; which contrasts with the increasing structural complexity present in selachimorphs.