Origin of the Tethyan Hemihoplitidae tested with cladistics (Ancyloceratina, Ammonoidea, Early Cretaceous): an immigration event?

Abstract

Abstract:The Late Barremian Hemihoplitidae (Ancyloceratina, Ammonoidea) are widely known in the northern Tethyan Margin and the Essaouira-Agadir Basin (Morocco). Their rapid evolution and diversification make them one of the key groups for that period, but their origin remains poorly known and several competing hypotheses have been published. These hypotheses are tested here with cladistic analysis in order to reject those receiving the least support and discuss those well supported. The analysis discards the Crioceratitidae, Emericiceratidae (Emericiceras and Honnoratia) and Toxancyloceras as stem-groups of the Hemihoplitidae (Gassendiceras). The Toxancyloceras appear instead to be a sister-taxon of the Moutoniceras, so we propose the latter to be classified with the Ancyloceratidae rather than with the Heteroceratidae. The best supported hypothesis assumes that the Hemihoplitidae first appeared suddenly in the Essaouira-Agadir Basin at the end of the Early Barremian from small populations of Boreal Paracrioceras. These latter could have migrated southward episodically before invading the northern Tethyan margin at the beginning of the Late Barremian. As a consequence, the Paracrioceratidae fam. nov. is proposed to include the Boreal groups Fissicostaticeras / Paracrioceras / Parancyloceras, and Gassendiceras essaouirae sp. nov. is proposed as a new name for the Moroccan endemic "Barrancyloceras" maghrebiense sensu COMPANY et al., 2008, non IMMEL, 1978 Key Words: Ammonites; Hemihoplitidae; Barremian; cladistics; allopatry; founder effect; palaeobiogeography. Résumé : L'origine des Hemihoplitidae téthysiens testée par la cladistique (Ancyloceratina, Ammonoidea, Crétacé inférieur) : un événement migratoire ?.-Les Hemihoplitidae du Barré-mien supérieur (Ancyloceratina, Ammonoidea) sont connus sur la plus grande partie de la marge Nord Téthysienne et dans le Bassin de Essaouira-Agadir (Maroc). Leur évolution et leur diversification rapide en font un des groupes clés pour cette période, mais leur origine reste peu connue et plusieurs hypothèses contradictoires ont été développées dans la littérature. Ces hypothèses sont testées ici par une analyse cladistique afin d'écarter les moins étayées d'entre elles et de discuter les meilleures. L'analyse écarte les Crioceratitidae, les Emericiceratidae (Emericiceras et Honnoratia) et les Toxancyloceras en tant que groupe-souche pour les (Gassendiceras). D'autre part, les Toxancyloceras apparaissent être taxon-frêre des Moutoniceras, aussi est-il proposé de classer ces derniers parmi les Ancyloceratidae plutôt que dans les Heteroceratidae. L'hypothèse la mieux soutenue suggère que les Hemihoplitidae seraient initialement apparus soudainement à la fin du Barrémien inférieur dans le Bassin d'EssaouiraAgadir à partir de petites populations de Paracrioceras boréaux. Ces derniers auraient pu migrer épisodiquement vers le Sud avant d'envahir la marge Nord-Téthysienne au début du Barrémien supérieur. En conclusion, la Famille des Paracrioceratidae fam. nov. est proposée pour individ...

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

“…6 -Valanginian to Aptian, see references in Klein et al, 2007), some of them being contradictory with the evolutionary history of the group. Thus, a critical review is essential to understand the geographic and stratigraphic distribution of the group, which appears in all probability in the late Tethyan Barremian (Bert and Bersac, 2014). Klein et al, 2007) that seems to confirm the depiction of Kotetishvili (1970) and the stratigraphic distributions given by Kotetishvili et al (2005, p. 417).…”

“…vandenheckei Subzone, at the same time as the first Gassendiceras of the G. cf. essaouirae Bert and Bersac, 2014 group that migrate to the northwestern Tethyan margin from Moroccan representatives (see Bert and Bersac, 2014;Company et al, 2008). There is no argument to indicate a link between Gassendiceras and Lenicostites gen. nov., which have a very different morphology, and above all a very different ontogeny (see the discussion of the genus Lenicostites gen. nov.).…”

“…However, the variation observed between robust and gracile morphologies seems here to concern only the strength of the ornamentation and the presence of intercalated ribs. Considering the general laws of intraspecific variation in ammonites (see Bert, , 2014, this isolated character is not taken here to be the result of a species differentiation.…”

“…In our view, these taxa are close to the Parancyloceras of the P. aegoceras (Von Koenen, 1902) and P. bidentatum (Von Koenen, 1902) group from the P. bidentatum Zone (Boreal uppermost Barremian) because of their very particular morphology (paucituberculate in P. brevispina and with weaker tubercles in P. trispinosum). Consequently, they are assigned here to the boreal genus Parancyloceras (Paracrioceratidae Bert and Bersac, 2014).…”

“…1). In the context of the North Tethyan margin, this family develops three major trends, materialized into three subfamilies: (1) the Gassendiceratinae Bert et al, 2006 appear in the Toxancyloceras vandenhenckei Subzone and represent the stem of the whole group (following Bert and Bersac, 2014, this subfamilly actually would appear in the early Barremian in the proto-Altantic context of the Essaouira Basin, Morocco, with Gassendiceras essaouirae Bert and Bersac, 2014); (2) the Peirescinae Bert et al, 2006, which connect with the Douvilleiceratoidea Parona and Bonarelli, 1897 (spanning the Gassendiceras alpinum to Imerites giraudi subzones); and (3) the Hemihoplitinae Spath, 1924a, which are derived from the genus Gassendiceras Bert et al, 2006 (Gassendiceratinae) at the top of the Gassendiceras alpinum Subzone. The older Hemihoplitinae species [Camereiceras breistrofferi (Sarkar, 1955) and C. marchandi Bert et al, 2006] retain some characters from the Gassendiceras: (1) the ontogenetic stages (the Heberti, Barremense and Camereiceras stages -see for an extensive description); (2) ornamentation with differentiated ribs; (3) trituberculate main ribs; (4) general morphology with uncoiled shell.…”