Katian

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

The Katian is a second stage of the Upper Ordovician series, corresponding to the Katian age of the Late Ordovician epoch. It lasted from approximately 453.0 Ma to around 445.2 Ma (million years ago). It is preceded by the Sandbian and is followed by the Hirnantian. The last astrapidiforms are known from this stage.

Definition

The GSSP of the Katian stage was ratified in 2006. The lower boundary is fixed at 4.0 m above the base of the Bigfork Chert of Black Knob Ridge Section in Oklahoma, USA, and related to the first appearance of the graptolite species Diplacanthograptus caudatus.

Katian life

The continents remained lifeless, although primitive plants were already growing on the coasts. These plants probably provided food for some gastropods and arthropods that spent some time on land.

Cameroceras

Life flourished mainly in the seas. Crinoids (Gaurocrinus, Plicodendrocrinus) grew on the seabed far from the shore. Graptolites (Mastigograptus, Climacograptus, Orthograptus, Geniculograptus, Glossograptus) also lived on the open sea. Brachiopods, shelled animals that buried themselves in the sand when predators approached, lived in shallow water. Katian genera include Sphenosphaera, Rafinesquina, Heterorthina, Zygospira and Megamyonia. Brachiopods are similar to bivalves, but differ from them in the position of the valves. They are not mollusks and are more closely related to hyoliths, animals with a cone shell, also common at that time. Among the mollusks, bivalves (Breviorthonota, Modiolodon, Ambonychia, Cyrtodontula), gastropods (Liospira, Loxoplocus, Carinaropsis, Sphenosphaera) and cephalopods predominated. Some endocerids, such as Endoceras and Cameroceras, reached gigantic sizes, over 4 m in shell length, and were the largest predators of the time. Other cephalopods of the Katian seas include orthocerids (Ephippiorthoceras, Orthoceras, Kionoceras), pseudorthocerids (Spyroceras), actinocerids (Lambeoceras, Gonioceras) and other groups.

Isotelus rex fossil

Lunataspis aurora

Megalograptus ohioensis

Arthropods were probably already the most numerous group at that time. Marine sediments contain many ostracods, small animals that still remain an important element of plankton in seas and fresh waters. Eoleperditia, Tetradella, Leperditella, Aparchitella and Paraschmidtella were among the numerous ostracods thal lived in the Katian seas. Another common group were trilobites. Small and large trilobites of different orders lived during this age. Isotelus rex, the largest complete trilobite known to date, is known from the Churchill River Group in Manitoba, Canada. Like other asaphid trilobites, such as smaller Onchometopus, it had prominent eyes, which could indicate a predatory lifestyle. Phacopid (Eomonorachus, Ceraurus, Ceraurinus, Monorakos, Carinopyge), lichid (Amphilichas), olenid (Triarthrus), corynexochid (Bumastus, Stenopareia) and proetid (Proetus) trilobites were also discovered in the Katian strata. Horseshoe crabs (xiphosurans) of that time have survived almost unchanged to this day. Lunataspis from the Katian of Manitoba looks very similar to modern species. It was found in peritidal sediments and probably laid eggs on the shore. Eurypterids are close relatives of xiphosurans and probably also bred on the coasts. Among these arthropods, very large forms are known, but in the Katian, mainly small and medium-sized members existed. Megalograptus and Echinognathus are known from the Katian of the United States, while Paraeurypterus, a eurypterid on uncertain taxonomy, has been found in Sort Tepe Formation of Turkey.

Astraspis

Conodonts remained one of the most numerous groups of vertebrates. Drepanodus, Oulodus, Pristognathus, Eodinobolus, Paltodus, Zygognathus and many other genera are known from the Katian sediments. Pteraspidomorphs continued to evolve. These primitive fishes have armor to protect them from predators. Some of these vertebrates, however, became extinct in the Ordovician. Astraspis and Eriptychius, the last known astrapidiforms, lived in deep waters in the territory of modern Wyoming.

External links

• https://paleobiodb.org/classic/displayTimescale?interval=Katian