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.