Biology subjects

Loron, C. C.

Publications and source records attributed to Loron, C. C..

3 recordsLinked to original sources

bioRxiv2026

Clade dynamics support an early origin of crown eukaryotes

The timing of the last eukaryotic common ancestor (LECA) remains a fundamental question in evolutionary biology and palaeontology. Unambiguous eukaryotic-grade fossils appear from 1780 Ma, but no crown-group supergroups are confidently identified before the end of the Mesoproterozoic (ca. 1050 Ma). The late LECA hypothesis suggests that this absence of crown-assignable fossils and biosignatures implies a late Mesoproterozoic origin of the crown. Here we show that this hypothesis is incompatible with the evolutionary dynamics of the eukaryote clade, even under the limited constraints of the fossil record. Studying stem-crown dynamics based on a birth-death model, we show that a late crown age requires diversification rates well below the minimum rate needed to generate observed living eukaryote diversity (~2.5 - 10 million species) for any plausible total group age. Our results suggest that only an early LECA can bridge evolutionary dynamics with the eukaryotic-grade fossil record, the living diversity, and the molecular clock estimates. Based on these constraints, we suggest a feasible minimum age estimate for LECA of ca. 1696 Ma, supported by current fossil evidence and supporting molecular clock estimates. These results also provide a fossil-testable prediction: crown-group eukaryotes likely exist in early Mesoproterozoic assemblages, albeit undetected with current morphology-based approaches.

paleontology↗

bioRxiv2025

Prototaxites was an extinct lineage of multicellular terrestrial eukaryotes

Prototaxites was the first giant organism to live on the terrestrial surface, reaching sizes of 8 metres in the Early Devonian. However, its taxonomic assignment has been debated for over 165 years1-7. Tentative assignments to groups of multicellular algae or land plants1,2,8-11 have been repeatedly ruled out based on anatomy and chemistry5,7,11-16 resulting in two major alternatives: Prototaxites was either a fungus5,6,17-22 or a now entirely extinct lineage 7,16,23. Recent studies have converged on a fungal affinity5-7,17-20,22. Here we test this by contrasting the anatomy and molecular composition of Prototaxites with contemporary fungi from the 407-million-year-old Rhynie chert. We report that Prototaxites taiti was the largest organism in the Rhynie ecosystem and its anatomy was fundamentally distinct from all known extant or extinct fungi. Furthermore, our molecular composition analysis indicates that cell walls of P. taiti include aliphatic, aromatic, and phenolic components most similar to fossilisation products of lignin, but no fossilisation products characteristic of chitin or chitosan, which are diagnostic of all groups of extant and extinct fungi, including those preserved in the Rhynie chert. We therefore conclude that Prototaxites was not a fungus, and instead propose it is best assigned to a now entirely extinct terrestrial lineage.

paleontology↗

bioRxiv2024

Optical photothermal infrared spectroscopy (O-PTIR): a promising new tool for bench-top analytical palaeontology at the sub-micron scale

The identification of preserved organic material within fossils is challenging. Well-established vibrational spectroscopy techniques, such as micro-FTIR (Fourier Transform Infra-Red spectroscopy), have been widely used to investigate organic fossils molecular composition. However, even when well-adapted to study objects several tens of micrometre across, they still suffer from limitations, notably regarding resolution and sample preparation requirements. Optical Photothermal Infrared Spectroscopy (O-PTIR), a recently developed technique, overcomes the challenges of bench-top FTIR spectroscopy. By combining an IR excitation laser with a 532 nm green probe laser, this technique allows molecular characterization at high spectral resolution (~2 cm-1) and with extremely fine spatial resolution (~500 nanometres). Additionally, problems linked with sample thickness, surface roughness and particle shape/size are mitigated when compared with FTIR or Atomic Force Microscopy-based nanoIR techniques. Here we show that O-PTIR can be used to easily and successfully map the molecular composition of small organic fossils preserved in silica matrix (chert) in petrographic thin sections. Our study reveals that O-PTIR resolves spatial heterogeneities in the preserved molecular composition of organic fossils (spores and plants) at a sub-micron scale, and that such heterogeneities occur in the cuticle in an early Devonian plant, where they suggest a structural organisation comparable to modern plants. These results on 400 million years old fossils, validate O-PTIR as a powerful and extremely promising new tool for nanoanalytical palaeontology.

paleontology↗