| 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 Gorstian is a lower stage of the Ludlow series, corresponding to the Gorstian age of the Ludlow epoch. It lasted from approximately 427.4 Ma to around 425.6 Ma (million years ago). It is preceded by the Homerian age of the Wenlock epoch and is followed by the Ludfordian age of the Ludlow epoch. The earliest placoderms are known from this stage.
Definition[]
The GSSP of the Gorstian stage was ratified in 1980. The lower boundary is coincident with the base of the Lower Elton Formation near Ludlow, UK, and related to the first appearance of the graptolite species Saetograptus (Colonograptus) varians.[2]
Gorstian life[]
The seas were inhabited by many species of brachiopods, shelled animals very similar to bivalves, but with upper and lower valves instead of right and left. Gorstian brachiopod genera include Gypidula, Microsphaeridiorhynchus, Isorthis and Dalejina. Bivalves belonging to the phylum Mollusca also reached large numbers. Sedgwickia, Orthonota, Ptychopteria, Actinopteria and other bivalves were found in the Gorstian strata of Bringewood Beds, England. Other molluscs of the time include benthic gastropods (Ulrichospira, Prosolarium, Euomphalus) and nektonic cephalopods like Kionoceras and Cyrtocycloceras.
Dalmanites fossil
Among arthropods, trilobites, a bit like woodlice, reached large numbers, but lived in the ocean and left no descendants. Most trilobites like Proetus, Dalmanites and Encrinurus lived on the seabed, but other members like Calymene could swim in the water column. Predatory eurypterids like Eurypterus hunted at the seabed and in the water column. Their relatives, scorpions, already lived on land at that time, along with myriapods.
The diversity of fishes increased noticeably. Jawless fish like Oeselaspis and Tremataspis are known from sediments of this age, but jawed fishes competed more and more actively with them. Among jawed fishes, a new group, placoderms, appeared. The front of their body was covered with hard plates that protected them from the claws of eurypterids. One of the earliest placoderm is Silurolepis from the Gorstian sediments of Junnan, China.
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.