Famennian Stage 

What happened during this time?

Geophysical

• "Biotic crisis" decimates tropical marine environments at the beginning of the Famennian (Algeo and Scheckler 1998)

  • Land plants may have increased weathering of rocks and soils, producing an influx of minerals to the marine environment

  • Both an increase in root depth and penetration as well as the ability of seed plants to colonize drier, upland environments may have contributed to increased soil formation (pedogenesis)

  • Increased nutrient input on rivers creates eutrophic conditions in epicontinental seaways, "resulting in algal blooms, widespread bottom water anoxia, and high sedimentary organic carbon fluxes".

• An increase in plant biomass causes a draw-down of atmospheric CO2, and results in global cooling and glaciation.

• Volcanic eruptions have also been cited as a cause of the mass extinction (Racki et al. 2018)

Biological

Flora, spore-bearing

• Clubmosses continue to increase in size and dominate in lowland wetlands

  • Heterosporous lycopsids, such as Changxingia and Guangdedendron appear on the landscape (Wang et al. 2019)

  • Guangdedendron may be monocarpic and dioecious, showing the earliest stigmarian root

  • These forests may have contributed greatly to CO2 decline and coastal consolidation

• Horsetails begin to diversify

  • Sphenophyllophytes, woody horse-tail-like plants, appear in the under-story of wetland areas

  • Pseudoborniales, monopodial horsetail ancestors, may have populated drier upland areas

• Progymnosperms diversify in the uplands and lowland areas

  • Evidence for Archaeopteris tree at high latitudes by this time (Gess &  Berry, 2024)

Flora, seed-bearing

• Evidence of earliest known seed plants, Elkinsia polymorpha and Moresnetia zaleskyi

  • Very little is known about the vegetative portions of this plant

• Other seed plants, such as Latisemania, Hydrasperma, and Cosmosperma also on the landscape

• The earliest winged seed, Alasemenia tria from China, is found at this time (Wang et al., 2024)

• The appearance of many taxa of seeds during the Famennian indicates a possible adaptive radiation of spermatophytes