| System (period) | Series | Stage (age) | Lower boundary, Ma | |
|---|---|---|---|---|
| Devonian | Lower | Lochkovian | 419.2±3.2 | |
| Silurian | Pridoli |  423.0±2.3
| ||
| Ludlow | Ludfordian | 425.6±0.9
| ||
| Gorstian | 427.4±0.5
| |||
| Wenlock | Homerian | 430.5±0.7
| ||
| Sheinwoodian | 433.4±0.8
| |||
| Llandovery | Telychian | 438.5±1.1
| ||
| Aeronian | 440.8±1.2
| |||
| Rhuddanian | 443.8±1.5
| |||
| Ordovician | Upper | Hirnantian | older | |
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | ||||
The Aeronian is a second stage of the Llandovery series, corresponding to the Aeronian age of the Llandovery epoch. It lasted from approximately 440.8 Ma to around 438.5 Ma (million years ago). It is preceded by the Rhuddanian and is followed by the Telychian.
Definition[]
The GSSP of the Aeronian stage was ratified in 1984. The lower boundary is fixed in Trefawr Track Section, Trefawr Formation, in Wales, UK, and related to the first appearance of the graptolite subspecies Monograptus austerus sequens.[2]
Aeronian life[]
Numerous rugose and tabulate corals formed extensive reefs in the shelf zone. Reef ecosystems of this age include a diverse fauna. Brachiopods (Eostropheodonta, Eoplectodonta, Mendacella) lived on the bottom. Orthocerid cephalopods (Orthoceras, Aptychopsis) hunted in water column. Tentaculites, a shelled animal probably related to molluscs, also lived near reefs. Numerous graptolites also lived in the seas. Aeronian genera include Climacograptus, Diplograptus, Rastrites and Monograptus.
A large number of arthropods is known from this age. Trilobites of the orders Odontopleurida (Acidaspis), Trinucleida (Asaphus), Phacopida (Phacops, Encrinurus, Cheirurus, Calymene), Proetida (Proetus) and Harpetida (Harpes) as well as agnostids (Dawsonia) were found in the Aeronian strata of the Stockdale Shales, Lake District, UK. Chasmataspidids and eurypterids like Pterygotus were active nektobenthic carnivores. The seas were also inhabited by malacostracans such as Peltocaris and Discinocaris. There is an assumption that hexapods or true insects, the relatives of malacostracans, already existed then, but their fossils of this age are unknown.
There was an active evolution of fish. Jawless (Kalanaspis) and jawed (Pentlandia) fish lived in the ocean.
References[]
- ↑ "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. https://stratigraphy.org/chart#latest-version.
- ↑ "GSSP Table - Paleozoic Era". https://timescalefoundation.org/gssp/index.php?parentid=77.