An official website of the United States government
ABSTRACT A three‐dimensional tubular fabric known as “vermiform microstructure” in Phanerozoic and Neoproterozoic carbonate microbialites has been hypothesized to represent the body fossil of nonspicular keratose demosponges. If correct, this interpretation extends the sponge body fossil record and origin of animals to ~890 Ma. However, the veracity of the keratose sponge interpretation for vermiform microstructure remains in question, and the origin of the tubular fabric is enigmatic. Here we compare exceptionally well‐preserved microbialite textures from the Upper Triassic to channel networks created by modern microbial biofilms. We demonstrate that anastomosing channel networks of similar size and geometries are produced by microbial biofilms in the absence of sponges, suggesting the origin for vermiform microstructure in ancient carbonates is not unique to sponges and perhaps best interpreted conservatively as likely microbial in origin. We present a taphonomic model of early biofilm lithification in seawater with anomalously high carbonate saturation necessary to preserve delicate microbial textures. This work has implications for the understanding of three‐dimensional biofilm architecture that goes beyond the current micro‐scale observations available from living biofilm experiments and suggests that biofilm channel networks have an extensive fossil record.
more »
« less
The Neoproterozoic Emergence and Environmental Consequences of Biomineralized Sponge-Grade Animals
While molecular clock studies suggest a Tonian-Cryogenian (~800–635 Ma) emergence of the Porifera, convincing fossil evidence of sponges is seen only as far back as ~530 Ma. The >100 Ma lacuna for sponges represents a critical missing piece of the Neoproterozoic puzzle. Assembling an evolutionary framework requires that Poriferan antiquity be understood in terms of sponge form and function, and the emergence of suspension-feeding amid profound environmental and climatic change. Here we report newly discovered biomineralized fossils of sponge-grade animals in Neoproterozoic carbonates of Siberia, Australia, and Brazil. Using a wide range of petrographic, eProbe, µXRF, µCT, and serial grinding techniques, the sponge-grade fossils are shown to be remarkably preserved in three dimensions, displaying broad morphological characters associated with early experiments in biomineralization such as siliceous spicules and external carbonate shells. Reconstructions of their bauplan reveal forms evolutionarily equipped for a suspensionfeeding lifestyle, well-prepared for pumping seawater through their bodies. As ecosystem engineers that clarified the water column and allowed for greater depths of photosynthetic activity, the emergence (and dominance) of sponge-grade animals in shallow marine carbonate reefs had the potential to drive environmental change that is arguably recorded during extremes in the Neoproterozoic carbon cycle. With their global distribution, these animals would link the planktic and benthic realms for the first time in Earth history and represent a sink for the photosynthetically derived organic matter that impacted the oxidation state of the oceans and atmosphere. Notably, most of these fossils are archived in carbonates preserving global expressions of profoundly negative δ13C perturbations. These include the Ediacaran Period Shuram Excursion, which foreshadowed the widespread appearance of the Ediacara biota, and the terminal Cryogenian Period Trezona Anomaly, which immediately preceded the Marinoan snowball Earth.
more »
« less
- Award ID(s):
- 2242732
- PAR ID:
- 10523531
- Publisher / Repository:
- Papers on Paleontology
- Date Published:
- Journal Name:
- Papers on paleontology
- Volume:
- 39
- ISSN:
- 0148-3838
- Format(s):
- Medium: X
- Location:
- Ann Arbor, Michigan
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Three-dimensional tubular microfabrics known as ‘vermiform microstructure’ in Phanerozoic and Neoproterozoic carbonate microbialites have been hypothesized to represent the body fossil of nonspicular keratosan demosponges. If correct, this interpretation extends the sponge body fossil record to ~890 Ma, in good agreement with molecular clock estimates for the emergence of metazoans. However, the veracity of the keratose sponge interpretation for tubular microstructures remains in question and the origin of the microtubule texture is enigmatic. Here, we compare exceptionally preserved microbialite textures from Upper Triassic microbialites to channel networks created by modern microbial biofilms. We demonstrate that anastomosing channel networks of similar size and geometries to ‘vermiform microstructure’, are produced by microbial biofilms in the absence of sponges, suggesting the origin for the three-dimensional tubular microfabric in ancient carbonates is not unique to sponges and perhaps best interpreted conservatively as likely microbial in origin. We present a taphonomic model of early biofilm lithification in seawater with anomalously high carbonate supersaturation necessary to preserve delicate microbial textures. This work has implications for the understanding of three-dimensional biofilm architecture that goes beyond the current micro-scale observations available from living biofilm experiments and suggests that biofilm channel networks have an extensive fossil record.more » « less
-
Animals originated and evolved during a unique time in Earth history—the Neoproterozoic Era. This paper aims to discuss (1) when landmark events in early animal evolution occurred, and (2) the environmental context of these evolutionary milestones, and how such factors may have affected ecosystems and body plans. With respect to timing, molecular clock studies—utilizing a diversity of methodologies—agree that animal multicellularity had arisen by ∼800 million years ago (Ma) (Tonian period), the bilaterian body plan by ∼650 Ma (Cryogenian), and divergences between sister phyla occurred ∼560–540 Ma (late Ediacaran). Most purported Tonian and Cryogenian animal body fossils are unlikely to be correctly identified, but independent support for the presence of pre-Ediacaran animals is recorded by organic geochemical biomarkers produced by demosponges. This view of animal origins contrasts with data from the fossil record, and the taphonomic question of why animals were not preserved (if present) remains unresolved. Neoproterozoic environments demanding small, thin, body plans, and lower abundance/rarity in populations may have played a role. Considering environmental conditions, geochemical data suggest that animals evolved in a relatively low-oxygen ocean. Here, we present new analyses of sedimentary total organic carbon contents in shales suggesting that the Neoproterozoic ocean may also have had lower primary productivity—or at least lower quantities of organic carbon reaching the seafloor—compared with the Phanerozoic. Indeed, recent modeling efforts suggest that low primary productivity is an expected corollary of a low-O2 world. Combined with an inability to inhabit productive regions in a low-O2 ocean, earliest animal communities would likely have been more food limited than generally appreciated, impacting both ecosystem structure and organismal behavior. In light of this, we propose the “fire triangle” metaphor for environmental influences on early animal evolution. Moving toward consideration of all environmental aspects of the Cambrian radiation (fuel, heat, and oxidant) will ultimately lead to a more holistic view of the event.more » « less
-
Abstract Reports of diverse vermiform and peloidal structures in Neoproterozoic to Mesozoic open marine to peritidal carbonates include cases interpreted to be keratose sponges. However, living keratose sponges have elaborate, highly elastic skeletons of spongin (a mesoscopic end‐member of a hierarchical assemblage of collagenous structures) lacking spicules, thus have poor preservation potential in contrast to the more easily fossilized spicule‐bearing sponges. Such interpreted fossil keratose sponges comprise diverse layered, network, amalgamated, granular and variegated microfabrics of narrow curved, branching, vesicular–cellular to irregular areas of calcite cement, thought to represent former spongin, embedded in microcrystalline to peloidal carbonate. Interpreted keratose sponges are presented in publications almost entirely in two‐dimensional (thin section) studies, usually displayed normal to bedding, lacking mesoscopic three‐dimensional views in support of a sponge body fossil. For these structures to be keratose sponges critically requires conversion of the spongin skeleton into the calcite cement component, under shallow‐burial conditions and this must have occurred prior to compaction. However, there is no robust petrographic–geochemical evidence that the fine‐grained carbonate component originated from sponge mummification (automicritic body fossilsviacalcification of structural tissue components) because in the majority of cases the fine‐grained component is homogenous and thus likely to be deposited sediment. Thus, despite numerous studies, verification of fossil keratose sponges is lacking. Although some may be sponges, all can be otherwise explained. Alternatives include: (i) meiofaunal activity; (ii) layered microbial (spongiostromate) accretion; (iii) sedimentary peloidal to clotted micrites; (iv) fluid escape and capture resulting in bird's eye to vuggy porosities; and (v) moulds of siliceous sponge spicules. Uncertainty of keratose sponge identification is fundamental and far‐reaching for understanding: (i) microfacies and diagenesis where they occur; (ii) fossil assemblages; and (iii) wider aspects of origins of animal clades, sponge ecology, evolution and the systemic recovery from mass extinctions. Thus, alternative explanations must be considered.more » « less
-
Heterotrophic protists are vital in Earth’s ecosystems, influencing carbon and nutrient cycles and occupying key positions in food webs as microbial predators. Fossils and molecular data suggest the emergence of predatory microeukaryotes and the transition to a eukaryote-rich marine environment by 800 million years ago (Ma). Neoproterozoic vase-shaped microfossils (VSMs) linked to Arcellinida testate amoebae represent the oldest evidence of heterotrophic microeukaryotes. This study explores the phylogenetic relationship and divergence times of modern Arcellinida and related taxa using a relaxed molecular clock approach. We estimate the origin of nodes leading to extant members of the Arcellinida Order to have happened during the latest Mesoproterozoic and Neoproterozoic (1054 to 661 Ma), while the divergence of extant infraorders postdates the Silurian. Our results demonstrate that at least one major heterotrophic eukaryote lineage originated during the Neoproterozoic. A putative radiation of eukaryotic groups (e.g., Arcellinida) during the early-Neoproterozoic sustained by favorable ecological and environmental conditions may have contributed to eukaryotic life endurance during the Cryogenian severe ice ages. Moreover, we infer that Arcellinida most likely already inhabited terrestrial habitats during the Neoproterozoic, coexisting with terrestrial Fungi and green algae, before land plant radiation. The most recent extant Arcellinida groups diverged during the Silurian Period, alongside other taxa within Fungi and flowering plants. These findings shed light on heterotrophic microeukaryotes’ evolutionary history and ecological significance in Earth’s ecosystems, using testate amoebae as a proxy.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Proceeding:
- The DOI is not currently available.
