DOI:10.1127/0077-7749/2009/0252-0361 0077-7749/09/0252-0361 $ 4.00 ©2009 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart N. Jb. Geol. Paläont. Abh. 2009, vol. 252/3, p.361–376, Stuttgart, June 2009, published online 2009 Anetoceratinae (Ammonoidea, Early Devonian) from the Eifel and Harz Mountains (Germany), with a revision of their genera Kenneth De Baets, Christian Klug, Zürich, and Dieter Korn, Berlin With 5 figures DE BAETS,K.,KLUG,C.&KORN, D. (2009):Anetoceratinae (Ammonoidea, Early Devonian) from theEifelandHarzMountains(Germany),witharevisionoftheirgenera.–N.Jb.Geol.Paläont.Abh., 252:361–376;Stuttgart. Abstract: “Cyrtoceratites arduennensis”, one of the stratigraphically oldest ammonoids and type speciesoftheambiguouslydefinedgenus Anetoceras,wasfirstdescribedfromtheEifelMountains. It has been misinterpreted several times and is here re-described, based on the holotype and additionalmaterialfromthetypearea. Anetoceras arduennense (STEININGER,1853)hasacrioconical conch with whorls almost touching the preceding volution. The revision of the subfamily Aneto- ceratinae leads to the result that only five genera (Metabactrites, Borivites, Ivoites gen. nov. as a replacement name for Teneroceras, Anetoceras, and Erbenoceras) can be regarded valid, which probablyrepresentaphyleticseries. Key words: Emsian,Agoniatitina,systematics,Germany,coiling,morphometrics. 1. Introduction TheoldestammonoidsareknowntobeofearlyEmsi- an (Early Devonian) age. It is generally accepted that they originated from the bactritids (SCHINDEWOLF 1934; ERBEN 1960, 1966; DZIK 1984; DOGUZHAEVA 1999; Korn 2001; KLUG &KORN 2004; KRÖGER & MAPES 2007), and that the transformation from straighttocoiledconchshappenedalongthephyloge- netic lineage Bactrites – Lobobactrites –“Tenero- ceras”(ERBEN 1966;KRÖGER &MAPES 2007). Some authors (SPATH 1933, 1936; BÖHMERS 1936) con- sidered the earliest ammonoids to have evolved from nautiloids, a hypothesis that has now been rejected. Earlyammonoidswerethusoftendescribedasand/or confused with bactritoid and nautiloid genera such as Cyrtoceras, Cyrtoceratites, Kokenia, “Gyroceras”, and Trochoceras. The first, loosely coiled ammonoids are assigned to the paraphyletic subfamily Anetoceratinae; they exhibit several plesiomorphic characters (arched ammonitella, large umbilical window, simple septal morphology, low whorl expansion rate) and are regarded as the forms closest related to the am- monoid ancestor (CHLUPÁ ˇ C &TUREK 1983; KLUG 2001a). This subfamily is restricted to the early Emsian. The early Emsian ammonoids (inclusive the Anetoceratinae; see Fig. 2) quickly reached a nearly cosmopolitan distribution (HOUSE 1981) with the exceptionofpolartosubpolarwaters. “Cyrtoceratites arduennensis STEININGER, 1853” from the Eifel Mountains in Germany was the first anetoceratin described. Subsequently, several in- complete specimens from localities in the Harz (Schneckenberg near Harzgerode) and Eifel Moun- tains (‘Auf dem Lauzert’near Niederstadtfeld, Sankt Johann,Zendscheid)inGermanyhavebeenattributed tothisspecies(KUTSCHER 1933;SCHINDEWOLF 1934; SOLLE 1951; ERBEN 1954, 1960). Recently, a suite of previouslyunpublishedorpoorlyknownspecimensof