A one-billion-year-old multicellular chlorophyte

Abstract

Chlorophytes (which represent a clade within the Viridiplantae and a sister group of the Streptophyta) probably dominated marine export bioproductivity and played a key role in facilitating ecosystem complexity before the Mesozoic diversification of phototrophic eukaryotes such as diatoms, coccolithophorans, and dinoflagellates. Molecular clock and biomarker data indicate that chlorophytes diverged in the Mesoproterozoic or early Neoproterozoic, followed by their subsequent phylogenetic diversification, multicellular evolution, and ecological expansion in the late Neoproterozoic and Paleozoic. This model, however, has not been rigorously tested with paleontological data because of the scarcity of Proterozoic chlorophyte fossils. Here we report abundant millimeter-sized, multicellular, and morphologically differentiated macrofossils from ~1,000 Ma rocks. These fossils are described as Proterocladus antiquus new species and are interpreted as benthic siphonocladalean chlorophytes, suggesting that chlorophytes acquired macroscopic size, multicellularity, and cellular differentiation nearly a billion years ago, much earlier than previously thought.

Towards a new geological time scale: A template for improved rock-based subdivision of pre-Cryogenian time

“…Current fossil and molecular evidence agree that crown group Archaeplastida (a group that includes the red, green and glaucophyte algae) emerged during the Mesoproterozoic Era (Butterfield, 2000;Eme et al 2014), or possibly even earlier in non-marine environments (Sánchez-Baracaldo et al, 2017). Multicellular eukaryotic algae appear before 1.0 Ga in the form of isolated examples of red algae (Bangiomorpha pubescens at c. 1.05 Ga) and green algae (Proterocladus antiquus at c. 1.0 Ga) (Butterfield et al, 1994;Tang et al, 2020), although see possibly earlier examples of red algae from India (Rafatazmia chitrakootensis and Ramathallus lobatus) at c. 1.6 Ga (Bengtson et al, 2017). Ornamented acritarchs are more common eukaryote-grade fossils and some may prove useful for biostratigraphy, e.g.…”

“…Cohen and Macdonald, 2015;Butterfield, 2015;Xiao and Tang, 2018). Latest Mesoproterozoic and earliest Neoproterozoic rocks are the first to preserve fossils with clear similarities to particular modern eukaryotic clades, including red and green algae, fungi, amoebozoans, and stramenopiles (Butterfield et al, 1994;Butterfield, 2004;Porter et al, 2003;Nagovitsin, 2009;Loron et al, 2019b;Tang et al, 2020), though the affinities of most early Neoproterozoic fossils remain enigmatic. A number of eukaryotic innovations also appear in the record during this time, including scales, tests, biomineralization, and eukaryovory (Porter and Knoll, 2000;Cohen and Knoll, 2012;Cohen et al, 2017a,b;Porter, 2016).…”

The Nonesuch Formation Lagerstätte: a rare window into freshwater life one billion years ago

“…For example, a probable Proterocladus (Fig. 4c), with its diagnostic sub-septal branching pattern (Tang et al 2020), may indicate that siphonaceous green algae were present at this time. Other non-septate forms show simple branches in tubes with a very rough wall structure that does not reveal an underlying cellular structure (Fig.…”

The Coral of Plants

“…Geological time is another important factor: Plant material is scarce when we reach the older strata. For example, from the Proterozoic (>541 mya), which was the era of important events in archaeplastid evolution and diversification, only a few fossils of rhodophytes (e.g., Bangiomorpha pubescens) and green algae (e.g., Proterocladus antiquus) have been described, and the interpretation of some remnants as plants is sometimes doubtful (Tang et al, 2020). Monosporangiates appear first as fossilized spores; those of liverworts in the Paleozoic (~450 mya) and of hornworts only putatively in the Mesozoic (~140 mya).…”