Life history and autecology of an Ediacaran index fossil: Development and dispersal of Cloudina

Abstract

Cloudina is the best-known biomineralizing metazoan and a potential index fossil in the late Ediacaran Period, yet many aspects of its biology remain poorly understood. Previous reports have shown that Cloudina tubes grow from a basally closed funnel (or apical element), with occasional dichotomous branching. New material from the Ediacaran Beiwan Member of the Dengying Formation, South China, includes two distinct morphotypes-tubes with rounded versus pointed conical apices. In branching specimens, one of the daughter branches tends to have a conical apex. It is hypothesized that cloudinids with a spherical apex were derived from sexual reproduction, with their spherical termination representing the embryonic shell, whereas those with a conical apex are daughter branches detached from their parent tubes through asexual reproduction. These interpretations imply that Cloudina could reproduce both sexually and asexually, producing spherical embryonic shells and conical propagules, respectively. This strategy may have served to enhance dispersal, which was critical for the ecological success of early gregarious and sedentary animals such as Cloudina.

Environmental context for the terminal Ediacaran biomineralization of animals

“…550-541 Ma) sedimentary successions worldwide (Conway Morris et al, 1990;Sour-Tovar et al, 2007;Gaucher & Germs, 2009;Cortijo et al, 2010;Zhuravlev et al, 2012). This animal, which is suggested to be an ancient cnidarian-grade (Grant, 1992;Cortijo et al, 2010) or lophotrochozoan animal (Hua et al, 2005;Zhuravlev et al, 2015), constructed a high-Mg calcitic tubular shell with nested funnels, had an epibenthic lifestyle with its apex attached to the substrate (Grant, 1990;Zhuravlev et al, 2012;Cai et al, 2014), and may have had both sexual and asexual reproductive strategies to aid in its broad ecological dispersal (Cortijo et al, 2015). Cloudina was associated with microbial reefs and may have been a reef builder like modern-day corals that inhabit oligotrophic shelf environments where they band together in search of hard substrates and for protection against predators (Penny et al, 2014;.…”

Intraspecific variation in an Ediacaran skeletal metazoan: Namacalathus from the Nama Group, Namibia

“…The terminal Ediacaran (~550–541 Ma) skeletal taxa Cloudina (Cortijo et al, ; Hua et al, ) and Namacalathus (Zhuravlev et al, ) reproduced clonally through budding, but their broad geographic distribution suggests that like many extant benthic invertebrates, they also possessed a dispersive, planktonic larval stage (Zhuravlev, Liñán, Vintaned, Debrenne, & Fedorov, , fig. 7; Cortijo, Cai, Hua, Schiffbauer, & Xiao, ). Size distributions, and bedding plane‐scale spatial distributions have further been used to distinguish reproductive styles.…”

Ultrastructure of Ediacaran cloudinids suggests diverse taphonomic histories and affinities with non-biomineralized annelids

“…It has been argued that reports of basal terminations 3,59 and branching/budding in Cloudina 3 would rather support a cnidarian affinity for the cloudinids 6,28 . Bulbous and conical basal terminations have been documented from phosphatized specimens from South China 3,59 and interpreted as evidence of direct development of a tubular structure from a rounded embryo and propagation via released daughter tubes with pointed terminations 59 . However, these developmental sequences do not exist in modern Cnidaria, where there is always a motile planula larva that hatches from an embryo, and tubular exoskeletons are only developed after larval settlement.…”