Data from: New species of Franchia and Protozigzagiceras (Ammonoidea, Middle Jurassic): the phyletic origin of Zigzagiceratinae

Three genera and seven species belonging to the subfamily Zigzagiceratinae (family Perisphinctidae) are described from the Lower Bathonian of France and Saudi Arabia. Intraspecific dimorphism is recognized. A revision of the genus Franchia proposed by Sturani (1967), based on the syntypes and new specimens from south-east France, is presented. Franchia arkelli Sturani, Franchia subalpina sp. nov., Protozigzagiceras torrensi (Sturani), Protozigzagiceras tethycum sp. nov., Protozigzagiceras flexum sp. nov. and Protozigzagiceras densum sp. nov. are described from the Digne–Castellane region of south-east France. Megazigzagiceras subarabicum, gen. et sp. nov. is described from the Dharma region of Saudi Arabia. The successive Early Bathonian species of Franchia and Protozigzagiceras herein identified in West Tethyan areas, as members of the Mediterranean–Caucasian Subrealm, formed lasting separate peramorphoclines characterized by increasing hydrodynamic coiling of the shell. In contrast, rapid proterogenesis originated and diversified the earliest Bathonian zigzagiceratin lineages, giving paedomorphic members, commonly neotenic and more scarcely progenetic. Procerites–Siemiradzkia seems to be the oldest zigzagiceratin member in the French Subalpine, Iberian and Lusitanian basins, branched off by paedomorphosis from leptosphinctins at the Bajocian–Bathonian transition. The Mediterranean–Caucasian genera Franchia, Zigzagiceras, Zigzagites and Wagnericeras branched from successive species of Protozigzagiceras, in turn, a direct derivative of Procerites. The oldest lineages of the clade Zigzagiceratinae evolved by iterative, rapid, paedomorphic changes and additional, lasting, peramorphic modifications during the Early Bathonian.

本次研究记述了产自法国与沙特阿拉伯巴通阶下部（Lower Bathonian）的锯齿菊石亚科（Zigzagiceratinae，旋菊石科Perisphinctidae）下的3属7种，并确认该类群存在种内二态性。本文基于模式标本群（syntypes）以及法国东南部的新标本，对Sturani（1967）提出的弗兰菊石属（Franchia）进行了修订。产自法国东南部迪涅-卡斯泰讷（Digne–Castellane）地区的物种包括：阿克尔弗兰菊石（Franchia arkelli Sturani）、亚阿尔卑斯弗兰菊石（Franchia subalpina sp. nov.，新种）、托伦斯原锯齿菊石（Protozigzagiceras torrensi (Sturani)）、特提斯原锯齿菊石（Protozigzagiceras tethycum sp. nov.，新种）、弯曲原锯齿菊石（Protozigzagiceras flexum sp. nov.，新种）以及致密原锯齿菊石（Protozigzagiceras densum sp. nov.，新种）；产自沙特阿拉伯达尔马（Dharma）地区的阿拉伯巨锯齿菊石（Megazigzagiceras subarabicum, gen. et sp. nov.，新属新种）。本次研究在隶属于地中海-高加索亚区的西特提斯地区，识别出弗兰菊石属与原锯齿菊石属的连续巴通阶早期物种类群，该类群形成了持续独立的异时发育渐变群（peramorphoclines），其特征为壳体旋卷的流体动力学适配性逐步增强。与之相反，快速早熟发生（proterogenesis）事件催生并分化了巴通阶最早期的锯齿菊石亚科支系，产生了以幼态持续型（paedomorphic）为主的类群，这类类群通常兼具幼态延续（neotenic）特征，且较少出现早熟型（progenetic）演化。原旋菊石属-西美拉德茨菊石属（Procerites–Siemiradzkia）似乎是法国亚平宁、伊比利亚与卢西塔尼亚盆地中最古老的锯齿菊石亚科类群，其由薄旋菊石类（leptosphinctins）在巴柔阶-巴通阶过渡界线时期通过幼态演化分支而来。地中海-高加索亚区的弗兰菊石属（Franchia）、锯齿菊石属（Zigzagiceras）、扎格菊石属（Zigzagites）与瓦格纳菊石属（Wagnericeras）均起源于原锯齿菊石属的连续物种，而原锯齿菊石属本身则是原旋菊石属（Procerites）的直接衍生类群。锯齿菊石亚科（Zigzagiceratinae）演化支（clade）的最古老类群，在巴通阶早期经历了多次快速的幼态持续型演化改变，以及持续且持久的异时发育修饰过程。