| 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] | ||||
The Fortunian is a lower stage of the Terreneuvian series, the Cambrian system, the Paleozoic erathem and the Phanerozoic eonothem, corresponding to the Fortunian age of the Terreneuvian epoch of the Cambrian period of the Paleozoic era of the Phanerozoic eon. It lasted from approximately 538.8 Ma to around 529 Ma (million years ago). It is preceded by the Ediacaran period of the Neoproterozoic era and is followed by the Stage 2 age of the Terreneuvian epoch. The beginning of the Fortunian age is associated with the Cambrian explosion, when the number and diversity of living organisms sharply increased.
Definition[]
Trichophycus pedum, a marker of the base of the Fortunian
The GSSP of the Fortunian stage and the whole Phanerozoic eonothem was ratified in 1992. The lower boundary is fixed in Fortune Head on the island of Newfoundland near the continental Canada and related to the first appearance of the ichnospecies Trichophycus pedum.[2]
Fortunian life[]
The vast majority, if not all, of the animals of this age lived in water. Numerous invertebrate fauna of a more complex organization than Precambrian animals appeared in shallow sea waters. Even then, scyphozoans (true jellyfish) like Hexaconularia, Cambrotubulus, Arthrochites and Carinachites swam in the water column. Punctatus, a small, cone-shaped organism, is probably related to such cnidarians as Olivooides.[3] Platysolenites, a foraminiferan genus, still lived on the seabed. Calcified microbes like Tarthinia and Korilophyton began to form the first reefs.
Anabarites fossils
An important indicator of the Cambrian explosion is the appearance of small shelly fossils. The classification of some of these animals (such as Anabarites) is questionable. The earliest hyoliths are known from this age. A characteristic feature of hyoliths is their conical shells, which some cephalopods also had, but it has also been suggested that hyoliths are more closely related to brachiopods. Fortunian hyolith genera include Ladatheca and Lophotheca. True brachiopods probably also appeared around this time. The first mollusks appeared in this age. Purella belongs to the extinct family Maikhanellidae in the class of Monoplacophora, while helcionelloids like Aldanella, Barskovia, Securiconus, Bemella, and Latouchella looked like modern snails and likely belong to gastropods. Other shelled prganisms include cambroclavids, that lived on the surface of the water. Their classification is difficult because their fossils are likely to belong to different phyla of animals. One of them, Paracarinachites, is known from the Fortunian sediments of Shaanxi, China.
In the Fortunian, the first arthropods most likely already existed, although their exact time of origin remains questionable. The earliest chordates probably also appeared around this time. Hertzina, the oldest known conodont, is known from the Nemakit-Daldynian stage of Siberia, which cover a slightly longer interval than Fortunian, indicating that vertebrates could appear as early as at the beginning of the Cambrian.
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.
- ↑ Fang Chen, Xi-ping Dong (2008) "The internal structure of Early Cambrian fossil embryo Olivooides revealed in the light of Synchrotron X-ray Tomographic Microscopy". Chinese Science Bulletin 53 (24): pp. 3860-3865. DOI:10.1007/s11434-008-0452-9