Assessing the evolutionary history of the class Synurophyceae (Heterokonta) using molecular, morphometric, and paleobiological approaches.
PREMISE OF THE STUDY
Heterokont algae of the class Synurophyceae, characterized by distinctive siliceous scales that cover the surface of the cell, are ecologically important in inland waters, yet their evolutionary history remains enigmatic. We explore phylogenetic relationships within this group of algae relative to geologic time, with a focus on evolution of siliceous components.


METHODS
We combined an expansive five-gene and time-calibrated molecular phylogeny of synurophyte algae with an extensive array of fossil specimens from the middle Eocene to infer evolutionary trends within the group.


KEY RESULTS
The group originated in the Jurassic approximately 157 million years ago (Ma), with the keystone genera Mallomonas and Synura diverging during the Early Cretaceous at 130 Ma. Mallomonas further splits into two major subclades, signaling the evolution of the V-rib believed to aid in the spacing and organization of scales on the cell covering. Synura also diverges into two primary subclades, separating taxa with forward-projecting spines on the scale from those with a keel positioned on the scale proper. Approximately one third of the fossil species are extinct, whereas the remaining taxa are linked to modern congeners.


CONCLUSIONS
The taxonomy of synurophytes, which relies extensively on the morphology of the siliceous components, is largely congruent with molecular analyses. Scales of extinct synurophytes were significantly larger than those of modern taxa and may have played a role in their demise. In contrast, many fossil species linked to modern lineages were smaller in the middle Eocene, possibly reflecting growth in the greenhouse climatic state that characterized this geologic interval.
['Siver|Peter A|PA|', 'Jo|Bok Yeon|BY|', 'Kim|Jong Im|JI|', 'Shin|Woongghi|W|', 'Lott|Anne Marie|AM|', 'Wolfe|Alexander P|AP|']
D001483:Base Sequence D005075:Biological Evolution D002138:Calibration D048429:Cell Size D005580:Fossils D019684:Magnoliopsida D010163:Paleontology D010802:Phylogeny D013997:Time Factors
evolutionary history Synurophyceae scales phylogeny Mallomonas Synura morphology Synurales bristles fossil synurophytes