Flourishing Sponge-Based Ecosystems after the End-Ordovician Mass Extinction

Abstract

The Late Ordovician (Hirnantian, approximately 445 million years ago) extinction event was among the largest known, with 85% species loss [1]. Post-extinction survival faunas are invariably low diversity, especially benthic communities [2], but ecological structure was restored relatively rapidly [1]. This pattern, however, reflects organisms with robust skeletons, as only one exceptionally preserved Hirnantian fossil biota was previously known [3, 4]; in particular, almost no Hirnantian sponges have been recorded. Our study reveals an extraordinarily diverse, sponge-dominated community thriving immediately after the Hirnantian extinction in Zhejiang, South China. Several contemporaneous sites preserve a total diversity of over 75 sponge species, many with preserved soft tissues, in pronounced contrast to normal survival and early recovery faunas. This diversity is unprecedented for any Hirnantian fossil group, and the fauna provides a unique window into a post-extinction ecosystem. The sponges are often large and structurally complex and represent numerous different lineages that survived the extinction. Layers with abundant sponge remains were deposited after other mass extinctions [5, 6], suggesting a general pattern of sponge abundance during collapse of Phanerozoic marine ecosystems. It is possible that the conditions of ecological collapse increase the particulate food sources for sponges, while they themselves are relatively unaffected by the crises. Furthermore, the abundance of sponges in the Hirnantian sequence of South China may have aided post-extinction ecosystem recovery by stabilizing the sediment surface, allowing sessile suspension feeders such as brachiopods, corals, and bryozoans to recover rapidly.

Lipidomics of the sea sponge Amphimedon queenslandica and implication for biomarker geochemistry

“…By contrast, C 28 / 29 steranes (the diagenetic alteration products of precursor sterols) in rocks are overwhelmingly algal, as microalgae together with photosynthetic prokaryotes (which do not produce sterols) are the major contributors to modern marine organic matter. However, community ecology and structure have changed significantly over deep time, and sponges might have provided a significant contribution to the environmental lipid signal following mass extinction events (Botting et al, 2017;Ritterbush, Rosas, Corsetti, Bottjer, & West, 2015), or in Neoproterozoic/early Phanerozoic rocks prior to the evolution of some algal lineages. In these scenarios, the possible contribution of sponges to the geochemical record should be considered.…”

A candidate stem-group rossellid (Porifera, Hexactinellida) from the latest Ordovician Anji Biota, China

“…This foreland basin or Kwangsian synorogenic basin lies between the Cathaysian Oldland to the southeast and the Yangtze Platform to the northwest, with most of the sediment input originating from Cathaysia. High sedimentation rates and thick sandstone deposits characterise the Hirnantian lowstand, with the Anji Biota preserved in a 10-m-thick black mudstone interval within the largely sandstone Wenchang Formation deposited during the post-glacial transgression in the mid to upper Metabolograptus persculptus Biozone (Botting et al 2017a). This mudstone interval is exposed in several sections across a distance of 10 km ( Fig.…”

“…The central parts of most sections contain the darkest-coloured and finest-grained sediment intervals, which are also the richest sponge-bearing horizons, and are presumed to represent the maximum water depth. There are differences in the preserved faunas and taphonomic signatures between sections, with more condensed, graptolite-rich grey siltstones that are found in the basal and upper parts of the fossiliferous interval yielding only articulated skeletons of a relatively small range of taxa (see Botting et al 2017a). The most common sponge species in the deepest-water, black mudstone sediments are widespread across all sections, implying broad ecological continuity.…”

“…The Anji Biota is a latest Ordovician Konservat-Lagerstätte in Zhejiang Province, China (Botting et al 2017a). The assemblage represents a relatively deep-water postextinction community (mid to late Metabolograptus persculptus Biozone) that was dominated by planktonic graptolites and a hyper-diverse assemblage of sponges, over 75 species as estimated on material available so far, with only rare examples of other taxa.…”

“…Localities: ZWK -Zhuwukou (30° 30.507´ N, 119° 22.712´ E); SGS -Shangangshan (30° 35´ 48.64˝ N, 119° 27´ 05.62˝ E); TFC -Tianfucun (30° 38.215´ N, 119° 28.824´ E). For lithological logs of these sections, refer toBotting et al (2017a).…”