430: Proterozoic Rise: Steady Diversification of Crown Eukaryotes

Sandin MM et al., Proceedings of the National Academy of Sciences - Molecular clocks and diversification models applied to a 75,975-OTU rDNA dataset, including long-read environmental sequences and 77 fossil calibrations, indicate crown-group eukaryotes diversified steadily from the mid‑Proterozoic with Archaeplastida dominating early diversity. Key terms: eukaryote evolution, Proterozoic diversification, Archaeplastida, molecular clock, environmental sequencing.

Study Highlights:
The study assembled 75,975 nonredundant rDNA OTUs combining long-read environmental metabarcoding and reference sequences and calibrated 32 timetrees with 77 fossil constraints. Molecular dating places LECA at ~1775 Ma and finds most eukaryotic supergroups originating across the Mesoproterozoic. Diversification analyses (ClaDS, BAMM) show steady accumulation of crown-group diversity through the Proterozoic, with Archaeplastida exhibiting an early rapid diversification likely tied to plastid endosymbiosis. Results suggest crown eukaryotes were ecologically and taxonomically diverse long before clear crown-group fossils appear.

Conclusion:
Integrating extensive environmental sequencing with molecular dating and diversification models reveals that crown-group eukaryotes were diversifying steadily from the mid‑Proterozoic, overturning the notion of a biologically stagnant “boring billion” and indicating early ecological interactions and endosymbioses drove diversification.

Music:
Enjoy the music based on this article at the end of the episode.

Article title:
Environmental phylogenetics supports a steady diversification of crown eukaryotes starting from the mid-Proterozoic

First author:
Sandin MM

Journal:
Proceedings of the National Academy of Sciences

DOI:
10.1073/pnas.2600283123

Reference:
Sandin MM, Burki F, Cohen PA, Morlond H (2026) Environmental phylogenetics supports a steady diversification of crown eukaryotes starting from the mid-Proterozoic. PNAS 123(29):e2600283123. doi:10.1073/pnas.2600283123

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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Episode link: https://basebybase.com/episodes/environmental-phylogenetics-steady-diversification-crown-eukaryotes

QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-07-23.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music
- transcript coverage: Audited transcript segments covering LECA dating and molecular clock; environmental sequencing (OTUs and 18S-28S rDNA); Archaeplastida endosymbiosis and early diversification; Proterozoic diversification dynamics and the 'boring billion' reinterpretation; predator–prey dynamics and fossil evidence; and limitations/samp
- transcript topics: LECA dating and molecular clock; Environmental metabarcoding and OTU dataset (75,975 OTUs); Archaeplastida diversification and plastid endosymbiosis; Proterozoic diversification vs. 'boring billion' narrative; Predation, defense, and ecosystem dynamics (fossil evidence); Sampling limitations and diversification modeling (ClaDS, BAMM)

QC Summary:
- factual score: 10/10
- met...