Redescription of the ammonite Himalayites treubi and taxonomic implications for Jurassic–Cretaceous Himalayitidae

This study presents the first comprehensive revision and illustration of the type material of the himalayiatid ammonite Himalayites treubi, preserved as a plastoholotype of the lost original type specimen from Upper Jurassic strata of the Sula Islands in Indonesia. Detailed comparisons with closely related members of the Himalayitidae allow clear taxonomic distinctions. Himalayites treubi is closely allied with the Himalayites seideli–hollandi group from the Indo-Pacific Sub-realm. A phyletic connection between those Himalayites taxa and the neocomitid genus Blanfordiceras is hypothesized, as the diagnostic ornamental stage of Himalayites likely represents a derived innovation originating from a neocomitid morphology. Our analysis indicates that Indo-Pacific Himalayitidae do not exhibit clear phyletic links with the Suaritidae Cantú-Chapa, from the Caribbean Sub-realm, either in shell morphology, ontogeny, or ribbing pattern. The same applies to the newly proposed families Micracanthoceratidae fam. nov., predominantly known from the Mediterranean–Caucasian Sub-realm with occasional Tethyan occurrences; and Windhauseniceratidae fam. nov., which were mainly distributed along the southern margin of the Indo-Pacific Sub-realm. Several of their representatives were long assigned to the Himalayitidae. Yet, phylogenetic evidence indicates they derive from the Ataxioceratidae ancestral lineage. Finally, the genus Birobagoczkyceras gen. nov. is introduced herein based on Ammonites tripartitus, to recognize a group of upper Berriasian taxa from the Indo-Pacific Sub-realm that have long been conflated with Himalayites. Pseudohimalayites gen. nov. is also formally established to accommodate Himalayites nieri, which ranged across the Berriasian–Valanginian boundary in the Mediterranean Tethys. Both genera are assigned to the Neocomitidae based on ontogenetic development and suture-line characteristics.Camille Frau [camille_frau@hotmail.fr], Palaeo-Expertise, 8 Rue du Moulin, 65350 Cabanac, France; ICUB Fellowships for Young Researchers, University of Bucharest, Romania.