Shallow marine Rostroconchia (Mollusca) from the latest Devonian (Strunian) and their significance for rostroconch life style and evolution

Abstract

ABSTRACT. The rostroconch fauna of the uppermost part of the Devonian (Strunian, "Etroeungt") comes from a sand-/siltstone succession of the northern flank of the Velbert Anticline, western Germany. The few specimens most probably represent one species of the Hippocardioidea and one of the Conocardioidea without definite determination. The material confirms the difficulties in recognizing different shell layer architecture in conocardiid rostroconchs. The presence of rostroconchs in the Strunian documents a continuous evolutionary lineage from the abundant Middle Devonian rostroconch assemblages to the even more abundant rostroconch associations of the Mississippian. Three hippocardiid specimens are preserved in former life position with the anterior part of the conch oriented almost vertically within the sediment and the hood almost parallel with the former sediment surface, thus, perfectly confirming earlier suggestions on hippocardiid life style.

Bohemicardia hainense (Maurer) revisted: insights into ontogeny and variability of a Devonian hippocardiid rostroconch (Conocardiida: Hippocardiidae)

“…In this study, this relation is used with reservation, as it is adulterated by abrasion and loss of the outer shell layer. Amler (1986Amler ( , 2016, Richter and Amler (1994), Gierse (2003), Schröder-Rogalla (2005, Amler and Rogalla (2013) and Balik (2018) For details of the general palaeobiology and morphology of conocardiid rostroconchs used for the descriptions, we refer to Amler (1996Amler ( , 2016Amler ( , 2018, Rogalla et al ( , 2003, Schröder-Rogalla (2005), Amler and Rogalla (2013) and Amler et al (2020).…”

“…The wide range of basic morphologies in rostroconchs as well as palaeobiological constraints derived from the basic molluscan bauplan lead to the assumption that several lifestyles were realised for the occupation of different niches, e.g. reef margin, soupy mud or unstable sand (Richter and Amler 1995;Rogalla and Amler 2005a, b;Amler and Rogalla 2013;Amler 2016). Thus, the morphology of many Conocardiida reflects their life habits, such as mobile epibenthic crawling, immobile semi-endobenthic sediment sticking, and the loss of the hood in advanced conocardiids indicates a rather mobile, almost endobenthic life position (Runnegar 1978;Pojeta 1987;Richter and Amler 1995;Amler and Richter 1997;Schröder-Rogalla 2005;Amler and Rogalla 2013).…”

“…Accordingly, hippocardiids most probably obtained a specific life position relative to the sediment surface. With respect to mobility, stable position within 1) the substrate and efficient orientation of the posterior surface of the hood, only one life position is able to meet each of the demands properly, a rather horizontal orientation of the rostral area parallel with the surface of the substrate (Amler 2016).…”

Late Ordovician rostroconchs (Mollusca) from fluvial erratics in northwestern Europe

“…Pseudo lunulae are always with the convex side towards the umbo and the concave side towards the ventral orifice (Rogalla 2005). Amler (2016) coined the term lunulazone for this band in a pseudobigaleaiid, which emphasizes a feature of the primary carina and as such is a supplement to the descriptive morphology (primary carina channel in Wagner 1997, Schleppenrinne in Rogalla 2005. However, the name does not necessarily replace 'primary carina', which is the term preferred herein for the sharp ridge; Pojeta & Runnegar (1978) and Pojeta (1987) defined the carina as an angulation of the umbo or a sharply defined rib associated with the umbonal ridge.…”

“…Rostroconchs are presumed to have occupied infaunal to semi-infaunal habitats (Pojeta & Runnegar 1976, Runnegar 1978, Pojeta 1987, Mazaev 2012, Amler 2016. The infaunal mode of life is reflected in the often narrow, elongated body shape, a recurring morphological theme among Palaeozoic infaunal molluscs called scaphopodization by Peel (2006).…”