Asyrnmetry in Two Rhynchonellid Species from the Jurassic Formations of Kutch, Western India

Sphenorhynchia asymmetrica (Kitchin) from the upper and upper middle Macrocephalus Beds of Middle Callovian age and Rhactochynchia pseudoinconstans (Kitchin) from the Lower Patcham Beds of Upper Bathonian age of Kutch, Western India, show typical asymmetry in their shell development. This is particularly noticeable at the anterior commissure. This is compared with similar asymmetric features exhibited by other brachiopod species from different parts of the world. On the basis of the nature of asymmetry in the two Kutch species, the strength of numerical observation in them and on a consideration of the reproductive mechanisms in brachiopods, it is suggested that the asymmetric developments in these two species has led to an easily recognisable dimorphism which possibly is reminiscent of sexual dimorphism.