| 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 Lochkovian is a lower stage of the Lower Devonian series and the whole Devonian system, corresponding to the Lochkovian age of the Early Devonian epoch of the Devonian period. It lasted from approximately 419.2 Ma to around 410.8 Ma (million years ago). It is preceded by the Pridoli epoch of the Silurian and is followed by the Pragian age of the Early Devonian.
Definition[]
The GSSP of the Lochkovian stage, the Lower Devonian series and the whole Devonian system was ratified in 1972. The lower boundary is fixed within Bed 20 in Klonk, near Prague, Czech Republic, and related to the first appearance of the graptolite species Monograptus uniformis.[2]
Lochkovian life[]
As before, many brachiopods lived in shallow sea waters. Huge numbers of their genera including Leptaenisca, Strophonella, Leptostrophia, Skenidioides, Meristina and Howellella, are found in coastal Lochkovian sediments of Nevada, USA. Bivalves (Panenka, Nuculites etc.) lived in the similar ecosystems, although they are mollusks, unrelated to brachiopods. Cephalopods continued to hunt in the water column, although their diversity had noticeably decreased and there were no longer large forms among them. Graptolites, including Monograptus and Linograptus, were still widespread in the seas.
Trilobite numbers declined, although they still remained important components in some ecosystems. Trilobites of the orders Odontopleurida (Kettneraspis, Dicranurus, Ceratonurus), Phacopida (Lochkovella, Kainops, Paciphacops) and Proetida (Cyphaspis, Cordania, Otarion) are known from the Lochkovian sediments of Oklahoma, USA. The flowering of euchelicerates continued. Various chasmataspidids (Skrytyaspis, Dvulikiaspis, Heteroaspis) and eurypterids (Pterygotus, Parahughmilleria) lived in the sea in Siberia. Jaekelopterus, the largest eurypterid and the largest arthropod of all time, appeared in North American seas in this age. Eurypterids are often called sea scorpions due to their claws and similar body type, although true scorpions are descended from other euchelicerates. In the Lochkovian, scorpions had already reached high numbers and, most likely, were the main land predators. Reaching a length of up to 1 m, Brontoscorpio and Praearcturus existed during this age. Other scorpion genera of the time include Acanthoscorpio, Branchioscorpio and Hydroscorpius. Finally, spider-like trigonotarbids gradually spread on land. Arianrhoda is a trigonotarbid from the Lochkovian of Tredomen, Wales. The evolution of another group of arthropods, Hexapoda, is shrouded in mystery. Some researchers suggest that insects had long existed by this time, but their fossils are unknown from this or earlier ages.
Cardipeltis
Cephalaspis fossil
Uranolophus fossil
Vertebrates still lived in water, and among them conodonts reached large numbers. The study of Pyrenean conodonts revealed that during Lochkovian two extinctions of these animals happened.[3] Despite this, conodonts continued to exist. Lochkovian conodont genera include Ancyrodelloides, Lanea, Kimognathus and Icriodus.[3] The Devonian period is called the "age of fishes" because during this time fishes reached their greatest diversity. Many groups that emerged in the Silurian continued to flourish during Lochkovian. Various jawless pteraspidomorphs (Steinaspis, Cardipeltis, Pteraspis, Protaspis, Lampraspis, Cosmaspis, Errivaspis) and cephalaspidiforms (Cephalaspis) inhabited coastal waters, as well as bays and estuaries. Many of these fishes acquired armor covering the front of their bodies to protect them from predators. True armored fishes (placoderms) are assigned to Gnathostomata (jawed fishes). Among placoderms, arthrodires reached the greatest numbers. Lochkovian arthrodire genera include Simblaspis, Aethaspis, Heightingtonaspis and Wheathillaspis. The seas were also home to many cartilaginous fish (Chondrichthyes), although their fossil remains consist mainly of teeth and dorsal fin spines. In their lifestyle, some of them probably already resembled modern sharks. Onchus and Nodonchus were found in the Lochkovian strata of Besom Farm Quarry in the United Kingdom. Very important events occurred in the evolution of bony fishes. Some species that lived in fresh waters adapted to breathing atmospheric air, and this feature allowed them to survive when small lakes dried up. Uranolophus is one of such lungfishes. Its fossils were found in the Lochkovian and Emsian deposits of Wyoming, USA.
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.
- ↑ 3.0 3.1 José Ignacio Valenzuela-Ríos; Jau-Chyn Liao (2024). "Biodiversity and evolutionary phases of Lochkovian (Lower Devonian) conodonts in the Pyrenees: A comparative study". Marine Micropaleontology vol. 187. https://doi.org/10.1016/j.marmicro.2023.102326