| System (period) | Series (epoch) | Stage (age) | Lower boundary, Ma | |
|---|---|---|---|---|
| Paleogene | Paleocene | Danian | 66,0 | |
| Cretaceous | Upper (Late) | Maastrichtian |  72.1±0.2
| |
| Campanian | 83.6±0.2
| |||
| Santonian | 86.3±0.5
| |||
| Coniacian | 89.8±0.3
| |||
| Turonian | 93.9
| |||
| Cenomanian | 100.5
| |||
| Lower (Early) | Albian | ~113.0
| ||
| Aptian | ~121.4 | |||
| Barremian | 125.77* | |||
| Hauterivian | ~132.6
| |||
| Valanginian | ~139.8 | |||
| Berriasian | ~145.0 | |||
| Jurassic | Upper | Tithonian | older | |
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] *A golden spike is seen in chart but not ratified yet. | ||||
The Aptian is a fifth stage of the Lower Cretaceous series, corresponding to the Aptian age of the Early Cretaceous epoch. It lasted from approximately 121.4 Ma to around 113.0 Ma (million years ago). It is preceded by the Barremian age and is followed by the Albian age.
The Aptian partly overlaps the upper part of the regionally used (in Western Europe) stage Urgonian.
Definition[]
As of 2024, there is no GSSP defining the base of the Aptian stage. A candidate is a section in Umbria-Marche, central Italy, and the base of Chron M0r near the base of Paradeshayesites oglanlensis ammonite zone define the base of this stage.[2]
Aptian life[]
Cephalopods of various orders and families lived in the seas around the world. Ammonites (Aptian genera include Deshayesites, Australiceras, Cheloniceras, Epancyloceras and Tonohamites) looked a lot like nautilids. Both groups are characterized by curled external shells, but nautilids, unlike ammonites, still live today. Aptian nautilids include genera Cymatoceras and Eucymatoceras discovered in the Ferruginous Sands, England. Ichthyosaurs of the Ophthalmosauridae family such as Leninia still inhabited the oceans and hunted cephalopods and small fish. Pliosaurids like Kronosaurus were the apex predators in marine ecosystems.
Artist's impression of Tupuxuara leonardii (left) and T. longicristatus (right)
Irritator and anhanguerids
Rising sea levels gradually led to desalination of the ocean, and, as a result, many marine groups of animals began to adapt to life along the coasts and near river mouths. Various coastal animals have been foun in the Aptian sediments of Santana Group of Romualdo Formation, Brazil. Fossils include cartilagenous (Rhinobatos, Tribodus) and bony fish (Lepidotes, Obaichthys, Microdon and Oshunia), turtles (Brasilemys) and crocodylomorphs (Araripesuchus, Caririsuchus). But these deposits are best known for their numerous fossils of pterosaurs. Members of several families are known from the Santana Group. Primitive anhanguerids, Maaradactylus and Tropeognathus, are easily recognizable due to the rounded crests at the end of both upper and lower jaws. TThese were large pterosaurs: Maaradactylus had a wingspan of 6 m, and Tropeognathus up to 8 m. Santanadactylus also had a wingspan of almost 6 m but it is a relative of later pteranodontid pterosaurs. Some pterosaurs of that time, such as Tupuxuara and Kariridraco of the Thalassodromidae family, lost teeth as a result of evolution. On the heads of these animals there was a prominent crest, probably used in mating rituals. Tapejarids like Tapejara and Tupandactylus also have a crest but at the front part of the snout. Tapejarids were probably herbivores, which makes them unique among pterosaurs. Further from the ocean, in fresh waters, lived predatory Cladocyclus, members of the order Ichthyodectiformes, which reached large diversity later, in the Late Cretaceous. Irritator, a spinosaurid theropod, hunted Cladocyclus and other fish.
Unusual forms began to appear among dinosaurs at this time. Nigersaurus, a small sauropod with numerous teeth, and Ouranosaurus, an ornithopod with high dorsal vertebrae, lived in what is now Niger in northern Africa. Microraptor, a four-winged dromaeosaurid, hunted lizards on the territory of Liaoning, China. Birds, which are essentially avian dinosaurs, had already reached noticeably high numbers. Jianchangornis and Zhongjianornis are known from the Aptian sediments of Jiufotang Formation where Microraptor ald lizards Yabeinosaurus and Indrasaurus have also been found. Ankylosaurs like Polacanthus and Hoplitosaurus displaced their stegosaurid relatives. Covered with sharp lateral spines, they occupied the same ecological niche as aetosaurs in the Triassic period.
The direct ancestors of modern marsupials, marsupialiforms, probably appeared in this age. Adinodon was found in the Aptian-Albian strata of British Columbia, Canada. At that time, monotremes such as the Australian Teinolophos already existed.
References[]
- ↑ "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. https://stratigraphy.org/chart#latest-version.
- ↑ "GSSP Table - Mesozoic Era". https://timescalefoundation.org/gssp/index.php?parentid=35.