Révision de la sous-famille Mercaticeratinae Guex, 1973 (Ammonitina, Hildoceratidae) du Toarcien moyen de la province nord-ouest européenne

Revision of the middle Toarcian subfamily Mercaticeratinae Guex, 1973 (Ammonitina, Hildoceratidae).- We here thoroughly compare the middle Toarcian Mercaticeratinae faunas from the NW European and the Mediterranean realms and show that these two faunas are significantly different. In turn, we erect a new genus for the Mercaticeratinae from the NW European realm, Pseudocrassiceras. This latter, whose first occurrence is in France and northern Spain at the base of the Variabilis Zone, is a very short-ranging taxon, as it went extinct without descendants before the end of the same zone. Although this new taxon indubitably originates from the Mediterranean Mercaticeratinae, we presently cannot identify the direct ancestor of Pseudocrassiceras bayani (Dumortier, 1874) n. gen., i.e., the most abundant and most cited species of the genus. The Mercaticeratinae occur in the Bifrons Zone both in Italy and Spain and therefore can have reached France from these two areas.