Proterozoic eukaryotic macrofossils are rarely preserved with enough morphological detail to inform their phylogeny. This dataset includes the measurements and descriptions of three size classes of filamentous fossils from the Dolores Creek Formation of the Mackenzie Mountain Supergroup in the Wernecke Mountains, Yukon. This data was used to systematically describe and interpret the middle size class specimens as green macroalgae with an unbranching, uniseriate thallus (with uniform width throughout; n=304, width = 0.20 to 0.85 mm) and elliptical to globose anchoring holdfast. Fossils from the smaller size class (n = 90, width = 0.03 to 0.06 mm) retain too little morphological information to define properly. However, a third form is also documented, consisting of a ribbon-shaped thallus with a consistent width (n=19, width = 1.0 to 1.7 mm). The size range of these different, likely photoautotrophic, filaments supports the hypothesis of an increasing morphological complexity and overall diversification of macroalgae during the Tonian, setting the stage for dramatic changes to benthic marine ecosystems prior to the evolution of more complex ecosystems.

Measurements were collected using ImageJ.