Youngibelus is a genus of belemnites, an extinct group of cephalopods.
Sexual dimorphism Youngibelus tubularis and Y. levis are two species from Toarcian aged rocks in Yorkshire. It has been suggested that these two species are actually morphs of the same species. The divergence in morphology occurs in the gerontic stage of development, characterised by differences in the rostrum. In Y. levis, the rostrum thickens, whilst in Y. tubularis, an epirostrum develops. Peter Doyle proposed that the epirostrum developed as either a counterbalance for a sexual adaptation, or for display in courtship.Doyle, Peter (1985). "Sexual dimorphism in the belemnite Youngibelus from the Lower Jurassic of Yorkshire". Retrieved 13 May 2020
References