Data from: Emsian Ammonoidea and the age of the Hunsrück Slate (Rhenish Mountains, Western Germany)

The ammonoids from the well-studied German Fossillagerstätte of the Hunsrück Slate have the reputation of being the oldest known representatives of this cephalopod group. This material is of great interest not only because of the global scarcity of the earliest ammonoids, but also because it includes the first record of stratigraphically-controlled specimens, which could be assigned to the middle Kaub Formation in the Bundenbach/Gemünden area. Accordingly, some of the Hunsrück Slate ammonoids are indeed the stratigraphically oldest ammonoids because they are associated with the index dacryoconarid Nowakia praecursor and thus derive from the Nowakia zlichovensis Biozone of the early Emsian (Zlíchovian), while younger dacryoconarids and other ammonoid samples (Mimagoniatites fecundus, Mimosphinctes tripartitus) indicate the Nowakia barrandei to N. elegans biozones. In spite of this special importance, these Early Devonian cephalopods have never been revised comprehensively.Our study includesmore than 300 Hunsrück Slate specimens from both public and private collections. For the first time, ammonoids from the Altlay Hunsrück Slate in the Northern Hunsrück/Mosel region are reported, while all the materials from older collections derive from the middle Kaub Formation of the Central Hunsrück Basin (central Hunsrück, Taunus). These early ammonoids thus prove to be a valuable source of information for biostratigraphic correlation within the Hunsrück Slate and with early Emsian occurrences in other regions. Based on conch characters (geometry, ornament, suture lines) and ontogenetic traits, we describe the species Metabactrites fuchsi n. sp., Ivoites hunsrueckianus (Erben 1960), Ivoites schindewolfi n. sp., ?Ivoites sp., ?Ivoites opitzi n. sp., Anetoceras mittmeyeri n. sp., Erbenoceras advolvens (Erben 1960), Erbenoceras solitarium (Barrande 1865), Chebbites sp., Mimosphinctes primigenitus (Erben 1965), Mimosphinctes tripartitus Eichenberg, 1931, Gyroceratites heinricherbeni n. sp., ?Teicherticeras sp., and Mimagoniatites fecundus (Barrande 1865). Supposedly endemic species of the Hunsrück Slate such as “Anetoceras recticostatum Erben, 1962” and “Mimagoniatites falcistria (Fuchs 1915)” are here synonymized with the widely distributed species Erbenoceras solitarium and Mimagoniatites fecundus, both known to occur also outside Europe. Furthermore, we studied their taphonomy and assigned them to sevengroups of preservation.Theresults of this taphonomic study corroborate previous interpretations of the depositional environment and diagenesis. We also discuss the evolution of the shell in the earliest ammonoids and their closest relatives as well as structures (“Opitzian pits”) possibly caused by parasitic infestations of these early Emsian ammonoids.

产自研究程度较高的德国洪斯吕克板岩（Hunsrück Slate）化石产地（Fossillagerstätte）的菊石类（ammonoids），素来被认为是该头足类（cephalopod）类群已知最古老的代表类群。该化石材料不仅因早期菊石在全球范围内极为稀缺而备受关注，还包含了首批地层约束明确的标本记录，这些标本可归入本多巴赫/格明德（Bundenbach/Gemünden）地区的考布组（Kaub Formation）中段。据此，部分洪斯吕克板岩菊石确实是地层学意义上最古老的菊石：它们与标准化石竹节石类（dacryoconarid）先趋诺瓦克竹节石（Nowakia praecursor）伴生，产出层位属于早埃姆斯期兹利霍夫阶（Zlíchovian）的兹利霍夫诺瓦克竹节石生物带（Nowakia zlichovensis Biozone）；而伴生较年轻竹节石类群与其他菊石标本（如丰产拟角石Mimagoniatites fecundus、三分拟卷石Mimosphinctes tripartitus）的层位，则隶属于巴朗德诺瓦克竹节石生物带至优雅诺瓦克竹节石生物带。尽管这类早泥盆世头足类具有如此特殊的研究价值，但此前从未有学者对其开展过全面的修订研究。本研究涵盖了来自公共与私人馆藏的300余件洪斯吕克板岩菊石标本。本次研究首次报道了产自洪斯吕克北部/摩泽尔地区阿尔特莱（Altlay）洪斯吕克板岩的菊石类群，而此前所有馆藏标本均来自洪斯吕克中部盆地（洪斯吕克中部、陶努斯地区）的考布组中段。因此，这些早期菊石成为洪斯吕克板岩内部，以及与其他地区早埃姆斯期产出层位开展生物地层对比的宝贵研究资料。基于壳体特征（几何形态、装饰纹饰、缝合线（suture lines））与个体发育特征（ontogenetic traits），我们描述了以下物种：富克斯后杆菊石（Metabactrites fuchsi n. sp.）、洪斯吕克伊沃菊石（Ivoites hunsrueckianus (Erben 1960)）、辛德沃尔夫伊沃菊石（Ivoites schindewolfi n. sp.）、？伊沃菊石未定种（?Ivoites sp.）、？奥皮茨伊沃菊石（?Ivoites opitzi n. sp.）、米特迈耶阿内托角石（Anetoceras mittmeyeri n. sp.）、前伸埃尔贝角石（Erbenoceras advolvens (Erben 1960)）、独居埃尔贝角石（Erbenoceras solitarium (Barrande 1865)）、切贝菊石未定种（Chebbites sp.）、原始拟卷石（Mimosphinctes primigenitus (Erben 1965)）、三分拟卷石（Mimosphinctes tripartitus Eichenberg, 1931）、海因里希埃尔贝回旋角石（Gyroceratites heinricherbeni n. sp.）、？泰希特菊石未定种（?Teicherticeras sp.）、丰产拟角石（Mimagoniatites fecundus (Barrande 1865)）。此前被认为是洪斯吕克板岩特有种的"Anetoceras recticostatum Erben, 1962"与"Mimagoniatites falcistria (Fuchs 1915)"，本次研究将其分别归为广布种独居埃尔贝角石与丰产拟角石的同物异名，这两个物种在欧洲以外地区亦有发现记录。此外，我们还对这些菊石的埋藏学（taphonomy）特征开展了研究，将其划分为7类保存类型。该埋藏学研究结果佐证了此前关于沉积环境与成岩作用（diagenesis）的相关推断。我们还探讨了最早期菊石及其近缘类群的壳体演化，以及可能由这些早埃姆斯期菊石被寄生生物侵染所形成的结构——奥皮茨坑（Opitzian pits）。