The Eifelian is the first of two

faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by conven ...

s in the

Middle Devonian In the geological timescale, the Middle Devonian epoch (from 393.3 ± 1.2 million years ago to 382.7 ± 1.6 million years ago) occurred during the Devonian period, after the end of the Emsian age. The Middle Devonian epoch is subdivided into two ...

Epoch. It lasted from 393.3 ± 1.2 million years ago to 387.7 ± 0.8 million years ago. It was preceded by the

Emsian The Emsian is one of three faunal stages in the Early Devonian Epoch. It lasted from 410.62 ±1.95 million years ago to 393.47 ±0.99 million years ago. It was preceded by the Pragian Stage and followed by the Eifelian Stage. It is named after ...

Stage and followed by the Givetian Stage. North American subdivisions of the Eifelian Stage include Southwood, and part of Cazenovia (or Cazenovian).

Name and definition

The Eifelian is named after the Eifel Mountains of Western

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

, which exposed the

GSSP A Global Boundary Stratotype Section and Point (GSSP), sometimes referred to as a golden spike, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. ...

section at the Wetteldorf Richtschnitt outcrop. The base of the Eifelian is defined by the start of the '' Polygnathus partitus''

conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

zone. This layer lies within the Upper Heisdorf Formation, below the base of the Lauch Formation.

Major events

The earliest forest is known from the Eifelian stage.

Cladoxylopsid The cladoxylopsids are an extinct group of plants related to ferns and sphenopsids. They had a central trunk, from the top of which several lateral branches were attached. Fossils of these plants originate in the Middle Devonian to Early Carb ...

trees including '' Calamophyton'' and other plants have formed the forest landscape in what is now

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

Extinctions

The end of the Eifelian was marked by a biological crisis known as the Kačák Event, a two-part interval of extinction which led to ecological turnover among

ammonoids Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

conodonts Conodonts, are an extinct group of marine jawless vertebrates belonging to the Class (biology), class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning "cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known ...

, and other free-swimming animals. In deep marine waters, the event is indicated by

anoxic Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved ox ...

black shales. There is evidence for a major pulse of transgression (

sea level rise The sea level has been rising from the end of the last ice age, which was around 20,000 years ago. Between 1901 and 2018, the average sea level rose by , with an increase of per year since the 1970s. This was faster than the sea level had e ...

) and warming during the event. Warming and sea level rise through the Eifelian and beyond would have had major effects on diversity, likely leading to the downfall of several marine biogeographic realms. The cool-water Malvinoxhosan Realm (MXR), on the northwest edge of

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

, was decimated as rising temperatures eliminated suitably

temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

habitat. Fauna of the Eastern Americas Realm (EAR), which was restricted to a shallow basin in southwest Laurussia, were gradually replaced by aggressive cosmopolitan species of the Old World Realm (OWR), which invaded through a seaway cutting along a flooded continental arch on the western edge of Laurussia.

References

Middle Devonian {{geochronology-stub