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The taxonomic status of the genus Hubertoceras Spath: A new light on sexual dimorphism from the Callovian ammonites of Kutch, India
Published in Texas A and M University
Volume: 20
Issue: 2
The genus Hubertoceras was described under the subfamily Proplanulitinae from the middle to upper Callovian (Middle Jurassic) beds of Kutch. Recently we revisited the Kutch Proplanulitinae and proposed a new endemic subfamily Sivajiceratinae for them. The new subfamily consists of the genera Sivajiceras, Kinkeliniceras, Obtusicostites and Hubertoceras. Development of sexual dimorphism was widespread in Jurassic ammonite families and at the same time, there was a significant increase (especially from the Callovian) of isolated sexual variants, which could not easily be paired up. In the present endeavour, we have explored the status of Hubertoceras in the light of sexual dimorphism. The genus Hubertoceras is characterised by small adult size, evolute shell with biplicate ribs and well-preserved lappets, which speak for its microconchiate nature. We have also made an attempt to identify the probable antidimorph of Hubertoceras from the contemporary large genera with evolute shells described from Kutch. Detailed morphological and morphometrical analyses indicated that Obtusicostites is likely the macroconchiate counterpart of Hubertoceras. The Hubertoceras-Obtusicostites pair satisfied all the paleobiological as well as geological prerequisites to form antidimorphs. Evolutionary trends between macroconchs and microconchs within the Sivajiceratinae lineage also showed parallelism. Most of the Callovian ammonite genera of Kutch were strongly dimorphic. Intense competition for food, habitat and mates perhaps forced these genera to undergo character displacement. While the macroconchs remained less diverged being uniformly large, evolute and strongly ornate; the microconchs showed wide interspecific variation in the shape of lappets, some even lacked peristomal modifications. Different types of lappet or absence of it perhaps facilitated easy mate recognition system among other functions. © August 2017 Palaeontological Association.
About the journal
JournalPalaeontologia Electronica
PublisherTexas A and M University
Open AccessNo