Danian

System (period)	Series	Stage (age)	Lower boundary, Ma
Neogene	Miocene	Aquitanian	23.03
Paleogene	Oligocene	Chattian	27.82
		Rupelian	33.9
	Eocene	Priabonian	37.71
		Bartonian	41.2
		Lutetian	47.8
		Ypresian	56.0
	Paleocene	Thanetian	59.2
		Selandian	61.6
		Danian	66.0
Cretaceous	Upper	Maastrichtian	older
Subdivisions and "golden spikes" according to IUGS as of September 2023

Wyoming rock wich with the Iridium geochemical anomaly (light intermediate claystone layer), that indicates the base of the Danian stage.

The Danian is a lower stage of the Paleocene series, the Paleogene system and the whole Cenozoic erathem, corresponding to the Danian age of the Paleocene epoch of the Paleogene period of the Cenozoic era. It lasted from approximately 66.0 Ma to around 61.6 Ma (million years ago). It is preceded by the Maastrichtian age of the Late Cretaceous and is followed by the Selandian age of the Paleocene. The beginning of the Danian corresponds to the mass Cretaceous–Paleogene (K–Pg) extinction event that killed pterosaurs, non-avian dinosaurs and numerous other terrestrial and aquatic animals.

Definition

The GSSP of the Danian stage and the whole Cenozoic system was ratified in 1991. The lower boundary is a reddish layer at the base of the dark boundary clay of the section by west of El Kef, Tunisia, and related to the Iridium geochemical anomaly that associated with a major extinction horizon.

Paleogeography

In the Danian, the Western Interior Seaway ceased to exist. It is assumed that the land bridge arose in the central part of North America, connecting Laramidia and Appalachia. In the central part of southern Canada there remained the Cannonball Sea connected to the Hudson Seaway.

Danian life

Baculites

The K–Pg extinction has caused severe damage to the earth's ecosystems. There were almost no large animals left, however, as before, a variety of molluscs, including bivalves (Venericardia, Ostrea, Cucullaea) and gastropods (Turritella, Mesalia, Calyptraphorus), lived in the seas. Cephalopods also experienced extinction, although most ammonites disappeared. Baculites, one of the latest ammonites, still existed in Danian seas, but very soon these animals became completely extinct. Nautiloids, other hard-shelled cephalopods, were luckier and several of their genera (Hercoglossa, Eutrephoceras, Cimomia, Teichertia, Pseudocenoceras) are known from this age. The reasons why nautiluses, unlike ammonites, survived are not precisely known, although it is assumed that the baby ammonites lived in near-surface waters and were more vulnerable.

Otodus obliquus jaws

The diversity of fish was generally not affected, although some orders (Pachycormiformes, Ichthyodectiformes) became completely extinct. With the disappearance of large piscivores, the time of dawn has come for fish. Such bony fishes as lepisosteiforms (Lepisosteus), aulopiforms (Chlorophthalmus), gadiforms (Palaeomorrhua, Protocolliolus), and siluriforms (Arius) have become more numerous. Ellimmichthyiforms (Gasteroclupea) also survived extinction, but during Paleogene their numbers gradually declined. Ceratodus, a lungfish, escaped the disaster and survived in isolated reservoirs. We know that coelacanthiforms also survived the disaster. Their fossils are unknown from this age, but two of their species still live in the depths of the Indian and western Pacific oceans. Cartilaginous fish continued to occupy an important place in ecosystems. Edaphodon, a chimaeriform, is known from the Danian of New Jersey, USA. Lamniform sharks became the apex predators in the seas. Odontaspis, a modern genus, already existed in this age. Otodus obliquus, the earliest species of its genus, probably reached 8-9 m in length and was likely the largest animal that survived the extinction. Later, in the Neogene, its descendants became even larger.

Amphibians (caecilians, caudates and anurans) survived extinction and have changed little since then to the present day.

Thoracosaurus

Kupoupou

The most noticeable changes occurred among sauropsids. The mass extinction wiped out sauropterygians and mosasaurs, although their relatives, snakes and lizards, survived. Most of the turtles also survived, although large protostegids became extinct. Several choristoderes (Champsosaurus) and crocodylomorphs (Borealosuchus, Thoracosaurus) survived the extinction and continued to hunt in Cenozoic rivers for several million years. Pterosaurs and non-avian dinosaurs became completely extinct. However, birds, the only surviving group of dinosaurs, became the dominant group of flying vertebrates. Some of the modern orders of birds like Gruiformes (cranes), Anseriformes (ducks) and probably Galliformes (chicken) had long existed at that time, although their early members are poorly studied. In Danian, some of the birds lost the ability to fly and occupied completely different ecological niches. Hesperornithiforms had become extinct by this time and new birds appeared, well adapted to life in the sea, penguins. The oldest of them, Kupoupou, lived in the coastal waters of New Zealand.

Cimolestes

Purgatorius

Numerous mammals, such as such as Cimolestes and Procerberus, survived extinction, and after the disappearance of sauropsid land predators, large forms began to appear. Half a million years later, Wortmania appeared, weighing 20 kg. Another two million years later, Psittacotherium, a taeniodont, emerged with a mass of 50 kg. Both of these animals ate primarily plants. A primitive group of Multituberculata (Hainina, Boffius) still existed in the Danian. The group Eulipotyphla appeared in the Mesozoic, and its memvers were largely small predators. Quadratodon, one of such mammals, is known from the Danian sediments of Belgium. The direct ancestors of some modern orders of mammals appeared in this age. Ravenictis and Pappictidops related to carnivorans. Purgatorius, an early primate-like mammal, existed in the Danian. In Australia, isolated from the rest of the world, marsupialiforms (Roberthoffstetteria) and true marsupials (Khasia, Tiulordia) evolved.

External links

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