| System (period) | Series (epoch) | Stage (age) | Lower boundary, Ma | ||
|---|---|---|---|---|---|
| Carboniferous | Mis. | Lower | Tournaisian | 358.9±0.4 | |
| Devonian | Upper (Late) | Famennian |  372.2±1.6
| ||
| Frasnian | 382.7±1.6
| ||||
| Middle | Givetian | 387.7±0.8
| |||
| Eifelian | 393.3±1.2
| ||||
| Lower (Early) | Emsian | 407.6±2.6
| |||
| Pragian | 410.8±2.8
| ||||
| Lochkovian | 419.2±3.2
| ||||
| Silurian | Pridoli | older | |||
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | |||||
The Givetian is a second and upper stage of the Middle Devonian series, corresponding to the Givetian age of the Middle Devonian epoch. It lasted from approximately 387.7 Ma to around 382.7 Ma (million years ago). It is preceded by the Eifelian age of the Middle Devonian and is followed by the Frasnian age of the Late Devonian.
The oldest coelacanthiforms, pseudoscorpiones and related to spiders arachnids are known from this stage.
Definition[]
The GSSP of the Givetian stage was ratified in 1994. The lower boundary is fixed in the base of Bed 123 in Jebel Mech Irdane, Morocco, and related to the first appearance of the conodont species Polygnathus hemiansatus.[2]
Givetian life[]
The seas still contained a wide variety of echinoderms. The diversity of tentaculites (Nowakia) was preserved. The number of cephalopods declined, but bivalves and gastropods were still widespread. The number of trilobites was declining, although various groups of them still existed in this age. Eldredgeops is a member of the order Phacopida while Otarion belongs to the order Proetida. Eurypterids were few in number, and their fossils of this age are almost unknown. Quite numerous arthropods already lived on land. Attercopus, the earliest known animal related to spiders, and Dracochela, the oldest known pseudoscorpion, were found in the Givetian strata of Schoharie County, New York, USA. Various myriapods (Devonobius, Crussolum), trigonotarbids (Gilboarachne, Aculeatarbus) and acariforms (Archaeacarus) and indeterminate agnathan insects lived with them, near the sea coast.
Among vertebrates, conodonts were still numerous. Givetian genera include Ozarkodina, Palmatolepis, Icriodus and especially Polygnathus whose species P. hemiansatus is used as a marker of the beginning of the age. A variety of fish lived in the seas and fresh waters. Cartilaginous (Phoebodus, Omalodus, Diplacanthus), placoderm (Asterolepis, Coccosteus, Homosteus) and bony fish (Gyroptychius, Onychodus, Cheirolepis) were found in the Givetian delta plain sediments of Karksi, Estonia. Miguashaia, the earliest known coelacanthiform, lived in rivers flowing through the territory of modern Latvia. Hamodus, a close relative of tetrapodomorphs, was capable of breathing both underwater and atmospheric air. True tetrapodomorphs like Kenichthys from the Givetian of China or Tinirau from the same age of Nevada, USA, remained aquatic forms.
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.