Implications of the ‘hemihoplitid-like’ ammonites iterative morphology in the context of the late Tethyan Barremian (Early Cretaceous)

• Published in: Cretaceous Research
• Main Authors: Bert, Didier, Bersac, Stéphane, Canut, Léon
• Other Authors: Géosciences Rennes (GR), Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Laboratoire du Groupe de recherche en Paléobiologie et biostratigraphie des Ammonites (GPA), Geological National Nature Reserve of Haute-Provence, Alpes de Haute-Provence, G.P.A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: ammonites; Pareto-optimal solution; systematics; competition; homeomorphy; Early Cretaceous; [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology; Austral; Antarc*
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-02283637; https://hal-insu.archives-ouvertes.fr/insu-02283637/document; https://hal-insu.archives-ouvertes.fr/insu-02283637/file/Bert-CretRes-2019.pdf; https://doi.org/10.1016/j.cretres.2019.104239

International audience Hemihoplitidae evolution is well documented in the north-west Tethyan margin at the lower upper Barremian. In this context, the genus Lenicostites gen. nov. (L. rusticus), with ‘hemihoplitid-like’ morphology, is unexpected because of its age older than the earliest Hemihoplites and its evolutionary stasis that contrasts with the rapid changes of the Hemihoplitidae. Data show no connection between Hemihoplitidae and Lenicostitidae fam. nov. and the resemblance is homeomorphy. The numerous reported occurrences of Hemihoplitinae over the world are reviewed. Their critical revision shows that some of them are contradictory with the evolutionary history of the group. The ‘hemihoplitid-like’ morphology is iterative in several taxa without any phyletic links (homeomorphy). Reasons could be linked to the morphospace occupation in the zone of maximum equilibrium between different constraints (a Pareto-optimal solution), making such morphology effortless to reproduce. The Austral Homeomorphitinae subfam. nov. (with Homeomorphites aguirreurretae gen. nov. et sp. nov.) are assigned to the Neocomitidae. A phyletic link between Shasticrioceras and Antarcticoceras is suggested (Shasticrioceratidae fam. nov.). Until proven otherwise, there is no Hemihoplitinae outside the north and west margins of the Tethys (including the Essaouira Basin). Homeomorphy between Hemihoplitinae and Lenicostitidae fam. nov. is explored and convergence seems the most convincing hypothesis. The further appearance of Camereiceras (Hemihoplitinae) could establish favorable conditions for interspecific competition, and the disappearance of Lenicostites gen. nov. could be interpreted as a complete competitive replacement. In this hypothesis Lenicostites gen. nov. is a victim of the Gause Principle as it lost the Red Queen race.