Description. Genotype Lepthoplites falcoides Spath, 1926. The definition of the genus by Spath and the justifications for its creation are not clear. Cooper & Owen (2011a) thus refined the diagnosis. The juvenile whorls are those of Anahoplites. Then, with growth, Lepthoplites differs from Anahoplites by having stronger ribs on the flanks, smaller and more numerous ventrolateral tubercles that give a crenulated appearance to the ventrolateral shoulder, a raised to fastigiate venter, rather evolute outer whorls, and suture lines with a narrower and non-flared first lateral lobe. Lower Cretaceous, late Albian (fallax, perinflatum, and briacensis zones, i.e., the Vraconian substage). Found in England, France (Paris Basin, Gard, Hautes-Alpes), and Kazakhstan (Mangystau). The photo shows a Lepthoplites cantabrigiensis Spath, 1926, from Salazac in Gard (Jattiot et al., 2021).
Frequent confusions. The genus Lepthoplites is often confused with Callihoplites and Pleurohoplites, which are found alongside it in some deposits. Lepthoplites is distinguished from Callihoplites by its sinuous ribs, which originate in pairs or trios at the umbilical bullae and terminate in small crenulations on the ventrolateral shoulder. A few pairs of lautiform ribs may be present, but they are a small minority. In contrast, all Callihoplites exhibit paired ribs that meet at stronger ventrolateral clavi. Pleurohoplites is generally thicker, with flatter, more convergent flanks, a distinctly fastigiate venter, and stronger, fewer ribs that extend slightly beyond the ventrolateral bullae.
Remarks. The genus Lepthoplites was challenged after Spath. Juignet & Kennedy (1976) wrote the following about the last Anahoplitidae of the terminal Albian: "the genera Lepthoplites, Pleurohoplites, Arrhaphoceras and some Callihoplites, commonly used, are certainly only variants of a single unispecific genus from which Schloenbachia originated in the Cenomanian". According to Amédro (1992), the range of variation of these ammonites extends from Lepthoplites falcoides Spath, 1925 (the most compressed) to Pleurohoplites (Pleurohoplites) renauxianus (medium form) and to Pleurohoplites (Arrhaphoceras) studeri (Pictet & Campiche, 1860) (the thickest). Wright (1996) takes a less extreme position: he recognizes all four genera, except Lepthoplites, which he relegates to the rank of junior synonym of Anahoplites. The recent trend is to rehabilitate the genus Lepthoplites, for example Kennedy et al. (2008), Cooper & Owen (2011a), Gale et al. (2011) and Jattiot et al. (2021).
Lepthoplites was reported only in England for a long time. In 1984, Amédro revised the Barrois collection at the Gosselet Museum in Lille: the "Ammonites renauxianus" from Barrois (current name Pleurohoplites renauxianus) from the Gaize d'Argonne at Chatel, Montblainville and Varennes-en-Argonne (Meuse) are in fact Lepthoplites. The genus was subsequently retrieved in Mangystau (Kennedy et al., 2008), at the Col de Paluel near Rosans in the Hautes-Alpes (Gale et al., 2011), and at Salazac in Gard (Jattiot et al., 2021). It has not been discovered in Aube so far.
| Lepthoplites (1) | cantabrigiensis |