| System (period) | Series | Stage (age) | Lower boundary, Ma | |
|---|---|---|---|---|
| Silurian | Llandovery | Rhuddanian | 443,8±1,5 | |
| Ordovician | Upper | Hirnantian |  445.2±1.4
| |
| Katian | 453.0±0.7
| |||
| Sandbian | 458.4±0.9
| |||
| Middle | Darriwilian | 467.3±1.1
| ||
| Dapingian | 470.0±1.4
| |||
| Lower | Floian | 477.7±1.4
| ||
| Tremadocian | 485.4±1.9
| |||
| Cambrian | Furongian | Stage 10 | older | |
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | ||||
The Lower Ordovician is the first series of the Ordovician system, corersponding to the Early Ordovician epoch of the Ordovician period. It lasted from 485.4 ± 1.9 Ma (million years ago) to 470.0 ± 1.4 Ma (IUGS 2023). It started after the 10th age of the Cambrian and lasted until the Dapingian age of the Middle Ordovician. During this epoch there was an explosion of species diversity, known as the Great Odrovician Biodiversification Event.
Definition[]
The Global Stratotype Section and Point (GSSP) of the Lower Ordovician series and the Tremadocian stage was ratified in 2000. The beginning of the Early Ordovician is related to the first appearance of the conodont Iapetognathus fluctivagus. The type section, Green Point, is located on the island of Newfoundland near the continental Canada.[2]
Subdivisions[]
The Lower Ordovician divided into two stages: Tremadocian and Floian. In geochronology, both correspond to the same ages.
Climate[]
At the beginning of the epoch, the surface water temperatures of the equatorial seas were extremely high, much higher than today's equatorial temperatures. However, the climate gradually cooled, which should have affected the processes of evolution.
Early Ordovician life[]
During this epoch, fast processes of evolution occurred among all living organisms. For some time, typical Cambrian species still existed in shallow waters, but gradually they were replaced by new groups, many of which still exist. Sponges and echinoderms began to form coral reefs further and further from the coast. Ecosystems gradually became more complex, large filter feeders (Aegirocassis) appeared, and straight-shelled cephalopods like Buenoceras and Clarkoceras became the main predators. The diversity of trilobites increased, Early Ordovician genera include Falanapis, Lapidaria, Niobe, Symphysurus and Euloma. Numerous graptolites like Phyllograptus, Tetragraptus, and Didymograptus also lived in the seas. Based on graptolites, stratigraphic zones are distinguished in various areas. Conodonts were also abundant. Pircanchaspis, a primitive agnathan fish, lived in the open ocean with the graptolites.
Some researchers suggest that the first insects may have appeared around 479 Ma, although their fossils of this age are not yet known.[3]
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.
- ↑ Misof, Bernhard; Liu, Shanlin; Meusemann, Karen; Peters, Ralph S.; Donath, Alexander; Mayer, Christoph; Frandsen, Paul B.; Ware, Jessica; Flouri, Tomáš; Beutel, Rolf G.; Niehuis, Oliver (2014). "Phylogenomics resolves the timing and pattern of insect evolution". Science. 346 (6210): 763–767. DOI:10.1126/science.1257570