| System (period) | Series | Stage (age) | Lower boundary, Ma | |
|---|---|---|---|---|
| Ordovician | Lower | Tremadocian | 485.4±1.9 | |
| Cambrian | Furongian | Stage 10 | ~489.5 | |
| Jiangshanian |  ~494
| |||
| Paibian | ~497
| |||
| Miaolingian | Guzhangian | ~500.5
| ||
| Drumian | ~504.5
| |||
| Wuliuan | ~509
| |||
| Series 2 | Stage 4 | ~514 | ||
| Stage 3 | ~521 | |||
| Terreneuvian | Stage 2 | ~529 | ||
| Fortunian | 538.8±0.2
| |||
| Ediacaran | older | |||
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | ||||
Series 2 is an unnamed second series of the Cambrian system, corresponding to the Series 2 epoch of the Cambrian period. It lasted from ~521 Ma (million years ago) to approximately 509 Ma (IUGS 2023). It started after the Stage 2 age of the Terreneuvian epoch and lasted until the Wuliuan age of the Miaolingian. One of the most important events, the appearance of trilobites, is associated with the beginning of this epoch.
It is the only unnamed series/epoch in International Chronostratigraphic Chart.
Definition[]
The Global Stratotype Section and Point (GSSP) of the Series 2 and the Stage 3 is not established yet. The researchers propose using the first appearance of trilobites in the fossil record as a marker of the lower boundary of this subdivision.[2]
Subdivisions[]
Series 2 divided into two unnamed stages: the lower, Stage 3, and the upper, Stage 4. In geochronology, they correspond to the Stage 3 and Stage 4 ages, respectively.
Paleogeography[]
Series 2 epoch geography
Gondwana remained the largest continent surrounded by small islands and microcontinents. Parts of Kazakhstan, South China, North China, and the small continent of Avalonia broke away from Gondwana probably during this epoch. Baltic, Siberia and Laurentia (North America including Greenland) continued to drift west and northwest.
Life during Series 2 epoch[]
The green alga Cambroclavus lived in coastal waters off the northern and western parts of Gondwana. The small shelly fossils were still common. Various mobergellids (Hippoklosma), tommotiids (Lapworthella, Camenella), tubular hyolithelminthids (Hyolithellus) are knowm from this series. Demosponges (Choiaella, Allantospongia, Hazelia, Leptomitus) grew in shallow waters. Bivalves also lived on the seabed. Various priapulid worms (Mafangscolex, Tylotites, Banffia, Selkirkia,) inhabited the sea soil.
Fossil of Redlichia
Misszhouia
The beginning of the epoch is associated with the appearance of trilobites, marine arthropods that spread widely and became completely extinct only at the turn of the Paleozoic and Mesozoic eras. The oldest trilobites include Profallotaspis, Hupetina, Bigotina, Lunagraulos and other genera. Redlichia is a trilobite from the Series 2 sediments of Australia and China. Strenueva, Alanisia, Perrector, Saukianda and Eops have been found in Andalucia, Spain. Nektaspidids, the close relatives of trilobites, also appeared at the beginning of this interval. The oldest genera include Naraoia, Misszhouia, Buenaspis, Xandarella and Cindarella.
Pectocaris
Perspicaris
Pambdelurion, an arthropod or a close relative of arthropods, crawled along the bottom. Reaching a length of 55 cm, it was a dangerous predator and one of the largest animals of its time. Other arthropods hunted in the water column. Megacheirans, arthropods of unclear taxonomy, had many legs and two front appendages, with the help of which they searched for and grabbed food. Leanchoilia, Fortiforceps and Oestokerkus lived during this time. Radiodonts, another important arthropod group, also evolved during this epoch. The earliest radiodonts are known from China (Amplectobelua, Houcaris, Lyrarapax) and Greenland (Kerygmachela). Some radiodonts were predators, others fed on plankton, using a pair of frontal appendages to capture or filter food. Some arthropods, such as Pectocaris and Perspicaris, have developed broad shells to protect them from predators. Ostracod-like arthropods (Acanthomeridion, Phasoia,) are also known from this series.
Fossil of Myllokunmingia fengjiaoa
The first probable vertebrates are known from Stage 3. There are Haikouichthys and Myllokunmingia from Chengjiang biota in Yunnan, China. Conodonts, which may also be vertebrates, already inhabited the seas. Amphigeisina, Hertzina, Prooneotodus and Oneotodus existed in this epoch.
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.