New multicellular marine macroalgae from the early Tonian of northwestern Canada

Abstract

Molecular phylogenetic data suggest that photosynthetic eukaryotes first evolved in freshwater environments in the early Proterozoic and diversified into marine environments by the Tonian Period, but early algal evolution is poorly reflected in the fossil record. Here, we report newly discovered, millimeter- to centimeter-scale macrofossils from outershelf marine facies of the ca. 950–900 Ma (Re-Os minimum age constraint = 898 ± 68 Ma) Dolores Creek Formation in the Wernecke Mountains, northwestern Canada. These fossils, variably preserved by iron oxides and clay minerals, represent two size classes. The larger forms feature unbranching thalli with uniform cells, differentiated cell walls, longitudinal striations, and probable holdfasts, whereas the smaller specimens display branching but no other diagnostic features. While the smaller population remains unresolved phylogenetically and may represent cyanobacteria, we interpret the larger fossils as multicellular eukaryotic macroalgae with a plausible green algal affinity based on their large size and presence of rib-like wall ornamentation. Considered as such, the latter are among the few green algae and some of the largest macroscopic eukaryotes yet recognized in the early Neoproterozoic. Together with other Tonian fossils, the Dolores Creek fossils indicate that eukaryotic algae, including green algae, colonized marine environments by the early Neoproterozoic Era.

New Species of Macroalgae from Tamengo Formation, Ediacaran, Brazil

“…nov. is a very simple macroalga difficult to attribute a major group, can be compared to Chinggiskhaania bifurcata (Dornbos et al 2016) due to its a thin filament with an average width of 0.45 mm, does not densely assemble and without distal tapering in width, but lacks a longitudinal striation. Macroalgae from Dolores Creeks Formation, Canada (Maloney et al, 2021), presents a longitudinal division but have septa along the fossil, structure that our specimen does not have; the aspects differentiating L. veinosa are the corrugated edges and the thick longitudinal structure in the center of the thallus.…”

“…They still are defined as eukaryotic multicellular organisms capable of doing photosynthesis, megascopic with a size larger than 1 mm, and possible to see with the naked eye, whose oldest fossil record dates to the Neoproterozoic (Xiao and Dong, 2006;Tang et al, 2020). Their complexity and diversity have records in China (Xiao et al, 1998), India (Srivastava, 2012), the United States (Rowland and Rodriquez, 2014), Russia (Nagovitsin et al, 2015), Mongolia (Dornbos et al, 2016), and Canada (Maloney et al, 2021). Interacting with other organisms of their time, the macroalgae form biotas, which serve as protection sites or creating oxygen niches (Xiao et al, 2002;Zhao et al, 2004).…”

New Material of Carbonaceous Compressions from the ∼1.5 Ga Singhora Group, Chhattisgarh Supergroup, India, and their Interpretation as Benthic Algae

“…However, most of the fossil record supports their evolution in marine environments (Yan and Liu, 1997;Rai and Singh, 2006;Sharma, 2006;Bengtson et al, 2017;Qu et al, 2018). They extended into marine environments in the Tonian Period due to dramatic changes in the marine biological pump, food webs, and benthic habitats (Sanchez-Baracaldo et al, 2017;Del Cortona et al, 2020;Tang et al, 2020;Maloney et al, 2021).…”

“…In addition, these studies also support the molecular clock analyses that suggest the divergence of Phaeophyta, Rhodophyta, and Viridiplantae in the Palaeoproterozoic-Mesoproterozoic Eras. Further, the crown-group Chlorophyta diverged during the late Mesoproterozoic to early Neoproterozoic eras; however, siphonous, multicellular, and siphonocladous chlorophytes evolved repeatedly in the late Neoproterozoic and Palaeozoic (Tang et al, 2020;Maloney et al, 2021).…”

A stem group Codium alga from the latest Ediacaran of South China provides taxonomic insight into the early diversification of the plant kingdom

“…While the Ediacaran “Doushantuo” material—otherwise well-known for providing insights into a cryptic Ediacaran diversity of derived eukaryotes arguably including some metazoans [ 13 , 14 ]—and the Mesoproterozoic fossil Bangiomorpha pubescens have provided some constraint on red algae affinities with extant lineages [ 4 , 5 , 15 ], the classification of Precambrian potential chlorophytes has been more tentative. Proterocladus Butterfield from the Svanbergfjellet Formation has been formally classified as a siphonocladalean Ulvophyceae [ 2 , 16 ], and a large number of fossil green algae from the Neoproterozoic have been regarded as Ulvophyceae [ 3 , 15 , 17 ]—notably Beltanelliformis brunsae , which has been interpreted by some as a structure similar to the gametophyte of the Bryopsidales Derbesia [ 12 ]—but most chlorophyte taxa remain in a floating state of taxonomy, in part due to the lack of information on internal microstructures or even fine analyses of surface morphology [ 18 ].…”