The sexual dimorphism in the Tithonian, Jurassic, simoceratid ammonite Lytogyroceras

Abstract

The family Simoceratidae Spath, 1925, lumps various formsbelonging to lineages with different roots and is clearlyparaphyletic. One of its genera is Lytogyroceras Spath, 1924,which stands apart from the typical forms of the familybearing strong ribbing and tubercles. The sexual dimorphismof Lytogyroceras was supposed to be based only onadult size differences. Here we describe a recently collectedlappeted microconch of Lytogyroceras subbeticum (Olóriz,1978) from the Ponti Zone of Carchelejo (southern Spain).This microconch shows that the sexual dimorphism in thegenus Lytogyroceras is not only characterized by differentadult size of the sexes as formerly assumed, but also by differentadult peristome morphology.