Evidence of Simple Multicellarity in Tonian NeoProterozoic Fossils From China

Electron microscopy reveals evidence for simple multicellularity in the Proterozoic fossil Chuaria

Authors:

Tang et al

Abstract:

Multicellularity arose multiple times in the evolutionary history of eukaryotes, and simple multicellularity may have a deep history tracing back to the Paleoproterozoic. However, complex multicellular organisms with cellular and tissue differentiation did not appear in the fossil record until the Mesoproterozoic, and it is not until the Ediacaran Period (635–541 Ma) when diverse assemblages of complex multicellular eukaryotes evolved. In the intervening Tonian Period (ca. 1000–720 Ma), the fossil record of multicellular organisms is poorly documented. To address this knowledge gap, we investigated Chuaria and associated carbonaceous compression fossils from the Tonian Liulaobei Formation in North China. These fossils have been variously interpreted as unicellular or multicellular organisms. Our analysis using backscattered-electron scanning electron microscopy (BSE-SEM) revealed direct evidence for simple multicellularity in some of these fossils and suggests that Chuaria may have had a multicellular vegetative stage in its life cycle. This study demonstrates that BSE-SEM has the potential to unveil the hidden diversity of multicellular organisms in the Tonian Period, thus enriching our knowledge about the multiple origins of multicellularity in this critical geological period before Cryogenian glaciations.

Macroscopic (complex?) Eukaryotes From the Calymmian MesoProterozoic One Billion Years Before the Cambrian Explosion

Decimetre-scale multicellular eukaryotes from the 1.56-billion-year-old Gaoyuzhuang Formation in North China

Authors:

Zhu et al

Abstract:

Fossils of macroscopic eukaryotes are rarely older than the Ediacaran Period (635–541 million years (Myr)), and their interpretation remains controversial. Here, we report the discovery of macroscopic fossils from the 1,560-Myr-old Gaoyuzhuang Formation, Yanshan area, North China, that exhibit both large size and regular morphology. Preserved as carbonaceous compressions, the Gaoyuzhuang fossils have statistically regular linear to lanceolate shapes up to 30 cm long and nearly 8 cm wide, suggesting that the Gaoyuzhuang fossils record benthic multicellular eukaryotes of unprecedentedly large size. Syngenetic fragments showing closely packed ~10 μm cells arranged in a thick sheet further reinforce the interpretation. Comparisons with living thalloid organisms suggest that these organisms were photosynthetic, although their phylogenetic placement within the Eukarya remains uncertain. The new fossils provide the strongest evidence yet that multicellular eukaryotes with decimetric dimensions and a regular developmental program populated the marine biosphere at least a billion years before the Cambrian Explosion.

A new Burgess Shale-type Lagertatte From the Ediacaran NeoProterozoic Mongolia

A new Burgess Shale-type deposit from the Ediacaran of western Mongolia

Authors:

Dornbos et al

Abstract:

Preservation of soft-bodied organisms is exceedingly rare in the fossil record. One way that such fossils are preserved is as carbonaceous compressions in fined-grained marine sedimentary rocks. These deposits of exceptional preservation are known as Burgess Shale-type (BST) deposits. During the Cambrian Period, BST deposits are more common and provide a crucial view of early animal evolution. The earliest definitive fossil evidence for macroscopic animal-grade organisms is found in the preceding Ediacaran Period. BST deposits from the Ediacaran are rarer and lack conclusive evidence for animals. Here we report the discovery of a new Ediacaran BST deposit with exceptional preservation of non-mineralizing macro-organisms in thinly bedded black shale from Zavkhan Province, western Mongolia. This fossil assemblage, here named the Zuun-Arts biota, currently consists of two new species of probable macroscopic multicellular benthic algae. One species, Chinggiskhaania bifurcata n. gen., n. sp., dominates the biota. The other species, Zuunartsphyton delicatum n. gen., n. sp., is known from three specimens. SEM-EDS analysis shows that the fossils are composed of aluminosilicate clay minerals and some carbon, a composition comparable to fossils from the Cambrian Burgess Shale biota. This discovery opens a new window through which to view late Precambrian life.

pop sci link.

An Overview of the Revolutionary Nature of the NeoProterozoic

The Neoproterozoic

Author:

Butterfield

Abstract:

The Neoproterozoic era was arguably the most revolutionary in Earth history. Extending from 1000 to 541 million years ago, it stands at the intersection of the two great tracts of evolutionary time: on the one side, some three billion years of pervasively microbial ‘Precambrian’ life, and on the other the modern ‘Phanerozoic’ biosphere with its extraordinary diversity of large multicellular organisms. The disturbance doesn’t stop here, however: over this same stretch of time the planet itself was in the throes of change. Tectonically, it saw major super-continental reconfigurations, climatically its deepest ever glacial freeze, and geochemically some of the most anomalous perturbations on record. What lies behind this dramatic convergence of biological and geological phenomena, and how exactly did it give rise to the curiously complex world that we now inhabit?

Did Multicellularity in Cyanobacteria Help Drive the Great Oxidation Event?

Cyanobacteria and the Great Oxidation Event: evidence from genes and fossils

Authors:

Schirrmeister et al

Abstract:

Cyanobacteria are among the most ancient of evolutionary lineages, oxygenic photosynthesizers that may have originated before 3.0 Ga, as evidenced by free oxygen levels. Throughout the Precambrian, cyanobacteria were one of the most important drivers of biological innovations, strongly impacting early Earth's environments. At the end of the Archean Eon, they were responsible for the rapid oxygenation of Earth's atmosphere during an episode referred to as the Great Oxidation Event (GOE). However, little is known about the origin and diversity of early cyanobacterial taxa, due to: (1) the scarceness of Precambrian fossil deposits; (2) limited characteristics for the identification of taxa; and (3) the poor preservation of ancient microfossils. Previous studies based on 16S rRNA have suggested that the origin of multicellularity within cyanobacteria might have been associated with the GOE. However, single-gene analyses have limitations, particularly for deep branches. We reconstructed the evolutionary history of cyanobacteria using genome scale data and re-evaluated the Precambrian fossil record to get more precise calibrations for a relaxed clock analysis. For the phylogenomic reconstructions, we identified 756 conserved gene sequences in 65 cyanobacterial taxa, of which eight genomes have been sequenced in this study. Character state reconstructions based on maximum likelihood and Bayesian phylogenetic inference confirm previous findings, of an ancient multicellular cyanobacterial lineage ancestral to the majority of modern cyanobacteria. Relaxed clock analyses provide firm support for an origin of cyanobacteria in the Archean and a transition to multicellularity before the GOE. It is likely that multicellularity had a greater impact on cyanobacterial fitness and thus abundance, than previously assumed. Multicellularity, as a major evolutionary innovation, forming a novel unit for selection to act upon, may have served to overcome evolutionary constraints and enabled diversification of the variety of morphotypes seen in cyanobacteria today.

Did Something PaleoMagnetically Strange Happen to the Earth's Ediacaran NeoProterozoic Poles?

A paleomagnetic and U-Pb geochronology study of the western end of the Grenville dyke swarm: Rapid changes in paleomagnetic field direction at ca. 585 Ma related to polarity reversals?

Authors:

Halls et al

Abstract:

A paleomagnetic study of the western end of the ∼585 Ma Grenville dyke swarm shows that individual dykes are characterized by high coercivity and unblocking temperature magnetizations that can differ in direction by as much as 90°. Field tests including baked contact studies and the continuity of paleomagnetic direction along dyke strike, suggest that the magnetizations are primary. Precise U-Pb baddeleyite dating on these dykes indicates that changes in magnetization direction of ∼90° occur in less than 4 million years, and their close temporal association with reversals of the axial dipole field suggest that certain dykes are recording an equatorial dipole field as a transitional field between opposite polarity states. The documented instability in the Earth's field occurs less than 10 Myr before the first recorded appearance of macroscopic multi-cellular organisms on Earth, inviting speculation that an extended period of frequent magnetic reversals may play a part in faunal evolution.

Complex Life During the Rhyacian PaleoProterozoic From the Francevillian Biota

The 2.1 Ga Old Francevillian Biota: Biogenicity, Taphonomy and Biodiversity

Authors:

El Albani et al

Abstract:

The Paleoproterozoic Era witnessed crucial steps in the evolution of Earth's surface environments following the first appreciable rise of free atmospheric oxygen concentrations ~2.3 to 2.1 Ga ago, and concomitant shallow ocean oxygenation. While most sedimentary successions deposited during this time interval have experienced thermal overprinting from burial diagenesis and metamorphism, the ca. 2.1 Ga black shales of the Francevillian B Formation (FB2) cropping out in southeastern Gabon have not. The Francevillian Formation contains centimeter-sized structures interpreted as organized and spatially discrete populations of colonial organisms living in an oxygenated marine ecosystem. Here, new material from the FB2 black shales is presented and analyzed to further explore its biogenicity and taphonomy. Our extended record comprises variably sized, shaped, and structured pyritized macrofossils of lobate, elongated, and rod-shaped morphologies as well as abundant non-pyritized disk-shaped macrofossils and organic-walled acritarchs. Combined microtomography, geochemistry, and sedimentary analysis suggest a biota fossilized during early diagenesis. The emergence of this biota follows a rise in atmospheric oxygen, which is consistent with the idea that surface oxygenation allowed the evolution and ecological expansion of complex megascopic life.

Keep in mind Rettalack also claims complex terrestrial life in the Rhyacian PaleoProterozoic (100 million years after the critters from the above).