Frasnian Age

Rise of Woody Plants

The Frasnian Age (382-372 Ma) is the first stage of the Late Devonian epoch, which occurred after the Givetian Age, and before the Famennian Age.

Above: Reconstruction of a Frasnian landscape, showing cladoxylopsid "trees" with Tetraxylopteris in the understory

Below: Early aquatic tetrapod, such as Tiktaalik, emerging under a Archeopteris forest

Flora, spore-bearing

Cladoxylopsid ferns found to dominate some areas
- Xinicaulis with a complex pattern of anatomy and "poles" of secondary xylem grew to over 8 meters
Herbaceous rhyniophytes and zosterophylls became rare to absent
Lycopsid trees remain on the landscape
- Lycopsids forests are still present near the equator (Berry and Marshall 2015)
Woody plants, lignophytes appear on the landscape in the form of progymnosperms
- Aneurophytales (progymnosperms) declined in abundance, but Tetraxylopteris was still present
- Archaeopteridales (progymnosperms) appear and increase in abundance and diversity
  - The landscape was altered drastically by the subsequent rise of Archaeopteris forests
  - Dominance-diversity changes have been attributed to the same factors that ultimately caused the Frasnian- Famennian marine extinctions (Scheckler 1986a), possibly climatic change associated with the onset of Gondwanan glaciation (Veevers and Powell 1987; Crowley and North 1988).
  - The decline in diversity and major shifts in dominance patterns continued into the late Frasnian

Flora, seed-bearing

There is no evidence of seed plants on the landscape, although seeds appear in the next epoch, the Fammenian.

Fauna

Tiktaalik roseae, a fish-like amphibian (fishapod) lived in shallow waters
In marine environments, there are ammonoids and fishes
There are lobe-finned fishes (sarcopterygia), and one taxon of actinopterygian ray-finned fishes (e.g.Cheirolepis).
There are ancestral fishes, such as placoderms, acanthodians, the earliest-known osteostracan jawless fishes (e.g. Escuminaspis), as well as anapsid-like naked jawless fishes (Endeiolepis and Euphanerops)
The Frasnian-Famennian boundary is marked by a global extinction (Zhang et al., 2021), with widespread anoxic-ocean conditions (the Upper Kellwasser Event) in Europe and elsewhere around the world.
- There is an abrupt loss of aquatic biota, possibly in several steps (e.g., Schindler, 1993; Geldsetzer et al., 1993; McGhee, 1996; Joachimski, 1997; Casier et al., 1998; Joachimski et al., 2001; Bond et al., 2004; Bond and Wignall, 2005; Yatsu et al., 2010)

Geophysical

Major mountain deformation and uplift spread across the Appalachian-Caledonian mountain chain in North America and Europe. This later helped form a single continent called Laurussia.
On the northeastern margin of Laurussia, mountainous uplifts occurred in the Ural mountains,
The Central Asian mountains buckled and uplifted in the collision of the Siberian crustal block.
In the south, the Variscide mountain chain extended into northern Africa on the giant southern supercontinent Gondwana
There might have been active mantle-plume volcanism, in which a giant plume of magma rises from deep in the Earth’s mantle and erupts in huge volumes of basaltic lava (Courtillot and Renne 2003; Courtillot et al. 2010; Bond and Wignall 2014).
Such weathering could extract huge volumes of carbon dioxide from the atmosphere and cause global cooling
There is a "charcoal gap" in the fossil record, marking lack of evidence of wildfires, even though there is abundant plant material
- Atmospheric oxygen levels were below 13 percent, which is the minimum necessary to sustain wildfires

Page updated

Google Sites

Report abuse