5/16/2023 0 Comments Heteromorph ammoniteThe authors declare that they have no competing interest. We nevertheless have chosen to study of this material because (1) the taphonomic characteristics of the specimens and the Disclosure of interest We initially faced two difficulties: (1) the studied material is from “historical” collections and has not been bed-by-bed sampled and (2) most of the studied specimens are fragmentary. In the present work, we have studied a sample of 54 Ancyloceras specimens from the Argiles à Plicatules Formation (lower Aptian of the Paris Basin), including the lectotype of A. The specimens discarded from the statistical analysis are fragments of proversum and spiral that share Systematicsġ842 Ancyloceras varians sp. The results of the statistical analysis allow us to consider the study sample as homogeneous for the following reasons: (1) the distributions of H and W are unimodal and do not depart from normality and (2) the distribution of R is considered ‘more or less’ unimodal because the small pick for the high values of R is not considered to be significant as it is only determined by two specimens. Only H and W are linked by isometric function and are thus regarded as ‘dependent’ variables (see Bersac and Bert, 2015 for Homogeneity of the study sample The results of the bivariate analysis are given in Fig. The value of Ds is 50.6 mm and the ratio between Ds and L is 22.6% for the specimen No. The total length L of the two subcomplete specimens is respectively 149.8 and 224 mm (respectively Fig. The results of the univariate analysis are given in Table 1. These collections contain numerous specimens (generally fragmentary) of heteromorph ammonites from the Univariate and bivariate analyses The studied material is composed of ‘historical’ specimens collected during the Nineteeth Century in the Argiles à Plicatules Formation and deposited in the following French public institutions: the Pierre et Marie Curie University (UPMC – Paris, ex Sorbonne's collection), the Natural History National Museum (MNHN – Paris) and the Municipal Museum of Saint-Dizier (Haute-Marne department). No outcrop of the Argiles à Plicatules Formation is Material frequently quoted in the literature) ammonite species such as Deshayesites deshayesi (d’Orbigny, 1841), Cheloniceras cornuelianum (d’Orbigny, 1841), Toxoceratoides royerianum (d’Orbigny, 1842), Pseudosaynella bicurvata (Michelin, 1838), etc. They are the type stratum of several ‘classical’ (i.e. The Argiles à Plicatules are a lower Aptian plurimetric clayey formation of the eastern Paris Basin (NE France, Fig. The objective of the present work is to conduct such a study on a sample of Ancyloceras from the Argiles à Plicatules, a lower Aptian formation of the north-east of France, by determining the taxonomic diversity of these Ancyloceras and the patterns of intraspecific variability of the recognized species. Despite this, the evolutionary patterns and the intraspecific variability of the species nowadays assigned to the genus Ancyloceras remain little known, especially because no population study has ever been conducted. Ancyloceras is the type genus of the family Ancyloceratidae Gill, 1871 and its type species is Ancyloceras matheronianum d’Orbigny, 1842 (Haug, 1889).Īncyloceras is one of the most iconic ammonite genera of the Lower Cretaceous and it is frequently cited in the literature (Klein et al., 2007). Its ornamentation typically consists of trituberculate main ribs alternating with smooth intercalaries on the spiral and the proversum, and of strong ribs on the flexus and the retroversum. 1 for an illustration of the various parts of the Ancyloceras shell). Nowadays, the genus Ancyloceras is generally restricted to lower Aptian (Lower Cretaceous) medium to large-sized heteromorph ammonites composed of a spiral, a proversum, a flexus and a retroversum (Kakabadze and Hoedemaeker, 2004 and see Fig. Thereafter, ’the name Ancyloceras was apt to be applied to any hooked-shaped heteromorph, whether of Jurassic or Cretaceous age’ (Casey, 1960, p. 491) introduced the genus Ancyloceras d’Orbigny, 1842 to name Jurassic and Lower Cretaceous planispiral heteromorph ammonites composed of a spiral and a hook.
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