The oldest holocephalan (Chondrichthyes) from the Middle Devonian of the Boulonnais (Pas-de-Calais, France)

The Couderousse Member of the Blacourt Formation in the Banc-Noir quarry, Ferques inlier, Boulonnais (Pas-de-Calais, France) has yielded a tooth plate whose morphology is similar to that of Synthetodus, which is considered a holocephalan. Its histology is made of an outer enameloid-like tissue, and an inner trabecular dentine. Its occlusal surface shows a bean-shaped bulge. This tooth plate was prepared from a limestone that is dated from the Middle–Upper varcus Conodont Zone, that is lower upper Givetian. This limestone has also yielded a Pokorninella bricae–Rothpletzella–Tentaculites assemblage, which is indicative of an environment of the inner to middle marine platform boundary. This specimen appears to be the oldest confirmed holocephalan (‘bradyodont’) tooth plate for which the name Melanodus loonesi nov. gen. et sp. is erected.