Upper Devonian

System (period)		Series	Stage (age)	Lower boundary, Ma
Carboniferous	Mis.	Lower	Tournaisian	358.9±0.4
Devonian		Upper	Famennian	372.2±1.6
			Frasnian	382.7±1.6
		Middle	Givetian	387.7±0.8
			Eifelian	393.3±1.2
		Lower	Emsian	407.6±2.6
			Pragian	410.8±2.8
			Lochkovian	419.2±3.2
Silurian		Pridoli		older
Subdivisions and "golden spikes" according to IUGS as of September 2023

​ The Upper Devonian is the third and upper series of the Devonian system, corersponding to the Late Devonian epoch of the Devonian period. It lasted from 382.7 ± 1.6 Ma (million years ago) to 358.9 ± 0.4 Ma (IUGS 2023). It started after the Givetian age of the Middle Devonian and lasted until the Tournaisian age of the Mississippian (Carboniferous). During this epoch, numerous fish lived in the seas, and the ancestors of tetrapods evolved on the coasts. In the Late Devonian, three huge extinctions occurred, one of which, the Frasnian, is included to the six major extinctions of the Phanerozoic.

In the Late Devonian, comets repeatedly fell on Earth, causing tsunamis. Several significant sea level rises may have been associated with these impacts.

Definition

The Global Stratotype Section and Point (GSSP) of the Upper Devonian series and the Frasnian stage was ratified in 1986. The beginning of the Late Devonian is related to the first appearance of the conodont Ancyrodella rotundiloba. The type section, Col du Puech de la Suque, is located in Montage Noire, France.

Subdivisions

The Upper Devonian divided into two stages: Frasnian and Famennian. In geochronology, both correspond to the same ages.

Paleogeography

The sea level changed 18 times during this epoch, and some of the very high rises were probably caused by comet showers. The largest continent was Gondwana, located in Southern Hemisphere. In its northwestern part, it connected with Euramerica, in the central part of which there was a high mountain range. Between these continents, the narrow Rheic Ocean jutted out from the east, and to the northeast, in equatorial latitudes, there was a deep ocean called Paleotethys. Siberia was the largest continent in Northern Hemisphere.

Climate

The series of comet showers at the Frasnian-Famennian boundary led to the global cooling and the new glaciation in Southern Hemisphere. The cooling could have been enhanced by the appearance of trees, which released more oxygen into the atmosphere and reduced the amount of carbon dioxide. This was the beginning of the penultimate ice age of the Phanerozoic that ended only in the Permian period.

The level of atmospheric oxygen in the Late Devonian rised close to modern levels.

Late Devonian life

Titanichthys

Dunkleosteus

Cladoselache

Ichthyostega

During the Late Devonian, the active evolution of fish continued. Large filter feeders like Titanichthys and predators like Dinichthys and Dunkleosteus appeared among the armored fish (placoderms). The number and diversity of cartilaginous fish like Cladoselache increased. Very important events took place on the shores of fresh water bodies, where numerous ancestors of tetrapods already lived. These animals include Ichthyostega, Acanthostega, Tulerpeton, Ventastega and Hynerpeton. Lush forests in equatorial latitudes created ideal conditions for the life of early amphibians, which could move further and further from the water. The diversity of terrestrial arthropods also increased, although their fossils are extremely rare.

At the Frasnian-Famennian boundary, one of the mass extinctions occurred, affecting mainly marine species of low latitudes: many reef-forming sponges and corals, as well as reef-associated brachiopods and trilobites, disappeared. The placoderms survived, but the subsequent Fanemmian (end-Devonian) extinction wipe them out completely and marked the end of the Devonian Age of Fishes.

External links

• https://paleobiodb.org/classic/displayTimescale?interval=Late%20Devonian