Morphological variability in response to palaeoenvironmental change – a case study on Cretaceous ammonites

Abstract

Changes in ammonite morphology during the earliest Early Aptian (Cretaceous) of an epicontinental sea in northern Germany were investigated based on new and rich material of Deshayesites (Deshayesitidae). This is a globally distributed genus and one of the most important ammonites of the Cretaceous with respect to biostratigraphy and abundance. The purpose of our study was to describe changes in morphology over few hundred thousand years and to discuss their relationships to major palaeoenvironmental perturbations. Our material is derived from four different horizons, and the studied stratigraphical interval includes a sea‐level change, a period of warming and an oxygen depletion event. We observe variable patterns in the occurrence of different morphological groups through time, probably indicating that morphotypes were individually impacted by environmental change. These morphological groups, unequivocally attributed to Deshayesites, cannot be fit into the existing species classification system. The greatest morphological disparity in Deshayesites is multi‐causal. It may be the result of: (1) an invasion of two morphogroups new to the habitat, which thus immediately face considerably greater competition in an environment just recovered from low‐oxygen conditions in parts of the water column during an early interval within Oceanic Anoxic Event 1a (OAE 1a); or, (2) it may be due to a rise in sea level with a simultaneous invasion of competitors of Tethyan origin. This sheds new light on the current concept for high morphological variability within ammonite species and poses challenges to our current ideas about ammonite diversity and the use of well‐established index‐species in supraregional correlations.

Patterns of intraspecific variation through ontogeny: a case study of the Cretaceous nautilid Eutrephoceras dekayi and modern Nautilus pompilius

“…Landman & Waage ; Kawabe ; Wilmsen & Mosavinia ; Ikeda & Wani ; Lehmann et al . ). Taking the habitat into consideration, the two taxa we studied appear to have occupied different water depths: E. dekayi examined in this study probably inhabited a relatively shallow water environment in the Western Interior (<50 m; Landman et al .…”

Fluctuations of the oxygen minimum zone at the end of Oceanic Anoxic Event 2 in the Gulf of Mexico and the response of ammonites

“…Bold all-over response, light response of the species P. flexuosum (summarized from Ifrim 2006Ifrim , 2013Stinnesbeck 2007, 2008;Ifrim et al 2011a) These studies, summarized by Ifrim (2013), do not interpret similar ecologies for the same morphotypes. The impact of environmental changes such as sea-level change, warming and the OAE1a on a persisting ammonoid population and related modifications in ornament and shell dimensions were described by Lehmann et al (2015), but a response of the morphology to the environmental changes was not observed at Vallecillo. Other case studies deal with the interpretation of particular Upper Cretaceous species (Tanabe 1979;Tsujita and Westermann 1998;Wiese and Schulze 2005;Ifrim and Stinnesbeck 2010, Wilmsen and Mosavinia 2011), but they are not from stratigraphic levels coeval to those of Vallecillo.…”

A Dufrenoyia (Ammonoidea, Deshayesitidae) fauna from Germany: Evidence for D. furcata Zone deposits at the lower–upper Aptian boundary

“…Nowadays, there is hardly any outcrops left. This is the main reason why only 15 papers illustrating ammonites from in situ occurrences from the Aptian in North Germany were published in the past 50 years (Kemper, 1971a(Kemper, , 1973aKemper and Zimmerle, 1978;Gaida et al, 1978;Kemper, 1976Kemper, , , 1982aKemper, , , 1995Weber, 1996;Mutterlose, 1996; Owen in Mutterlose et al, 2003;Hoffmann and Mutterlose, 2011;Vespermann, 2006;Mutterlose and Wiedenroth, 3 2009;Lehmann et al, 2012;Lehmann et al , 2016). Among those, ammonite systematic is only addressed in a couple of contributions (Owen in Mutterlose et al, 2003;Hoffmann and Mutterlose, 2011) and thus each further account is reasonable.…”