A new Middle Jurassic (Bajocian) homolodromioid crab from northwest France; the earliest record of the Tanidromitidae

A new homolodromioid, Tanidromites maerteni, the earliest member of the genus and family, is recorded from the lower upper Bajocian (Niortense Zone) of Calvados, northwest France. It is noted that carapace morphologies of other Jurassic brachyuran taxa within the family Prosopidae are closely similar to those of tanidromitids, and that diagnoses of recently erected Jurassic families and genera partially overlap or have conflict among them. Thus, the taxonomy of the earliest brachyuran groups appears to be less stable than currently thought. In recent years, knowledge of primitive extinct brachyurans has greatly benefitted from findings made by amateur collectors, the present paper included.