Selandian

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

The Selandian is a second stage of the Paleocene series, corresponding to the Selandian age of the Paleocene epoch. It lasted from approximately 61.6 Ma to around 59.2 Ma (million years ago). It is preceded by the Danian and is followed by the Thanetian. During Selandian, large birds and specialized mammals began to appear.

It was named after the island of Zealand (Danish: Sjælland) by Rozenkrantz in 1924.

Definition

The GSSP of the Selandian stage was ratified in 2008. The lower boundary is fixed in Zumaia section, northern Spain, and related to the base of the red marls of Itzurun Formation. The GSSP of the upper Thanetian stage has been established in the same section.

Selandian life

Ecosystems continued to recover from the mass extinction. Sea levels were higher than today, and Marengo and Wilcox counties in Alabama, USA, were covered with seawater. The shallow zone in this area supported a variety of bivalves (Cucullaea, Nuca, Venericardia, Lirodiscus) and gastropods (Turritella, Orthosurcula, Aragonia, Scaphella, Pseudolatirus). The seas were still inhabited by cephalopods, although the diversity had noticeably decreased by this time. Ammonites became extinct completely, and from the Selandian the only shelled cephalopods remained nautilids, such as Cimomia, Hercoglossa and Eutrephoceras from Denmark. Brachiopod genera of this age include Televratula, Telebratulina and Rhynchonella. The abundance of arthropods remained. Marine crustaceans were almost no different from modern ones. Costacopluma, a retroplumid decapod, is known from the coastal sediments of Venezuela. On land, the number of insects continued to increase, some of them, especially butterflies and hymenopterans, adapted to close coexistence with flowering plants.

Among vertebrates, fishes reached noticeably large numbers. As in the Mesozoic, cartilaginous fish had a significant impact on ecosystems. Numerous myliobatiform rays (Ishaquia, Heterobatis, Myliobatis, Archaeomanta, Rhombodus), orectolobiforms (Metlaouia, Palaeorhynchodon, Ginglymostoma, Hologinglymostoma), carcharhiniforms (Khouribgaleus, Triakis, Palaeogaleus, Scyliorhinus, Microscyliorhinus) and lamniforms (Isurolamna, Otodus) inhabited Selandian seas.

Presbyornis

Gastornis

Various sauropsids lived along the coasts. Some of reptiles, such as pleurodiran turtles (Bothremys), choristoderes (Champsosaurus) and crocodylomorphs (Borealosuchus), survived from the Maastrichtian. Lizards like Camptognathosaurus and Parasauromalus lived in warm places. Birds, the only surviving dinosaurs, partially occupied the ecological niches of their older relatives. In the absence of pterosaurs, avian dinosaurs became the top predators in the air. Berruornis resembled modern great owls and probably also hunted at dusk. Odontopterygiforms like Dasornis were large flying birds with pseudoteeth in their beaks. Anseriforms (Presbyornis) and gruiforms (Gradiornis, Walbeckornis) lived along the banks of rivers and lakes. Fissuravis, a relative of modern ostriches and rheas, was capable to fly. Probably the largest bird of the time was Gastornis that lived in forests of Europe. With the height of around 2 m, it has a huge and strong beak probably used for crushing large nuts and seeds.

Ocepeia skull

Plesiadapis

At this time, the active evolution of mammals was underway. Although primitive eutherian forms like Bustylus still existed, more and more specialized mammalian groups appeared. Bizarre jumping leptictids like Prodiacodon and Dyaphiodectes hunted small invertebrates on the forest floor. They were probably similar to jumping shrews (Adapisorex, Prolouisina, Berrulestes) , which also had proboscis that helped them search for food. Large ungulates had not yet appeared, but their close ancestors already existed. Lived near the sea coast, Ocepeia, Hadrogeneios and Abdounodus were at the origins of a large group that includes embrithopods, proboscideans, hyracoids and sirenians. Hyopsodontids like Paratricuspiodon were small omnivores that had claws and probably lived in trees, but their more recent relatives are perissodactyls (the odd-toed ungulates). Primate-like plesiadapiforms (Plesiadapis, Saxonella) lived in trees and had many primitive features, such as a long snout and large teeth. By this time, predatory hyaenodonts (Lahimia, Boualitomus) appeared. Other carnivorous group was Arctocyonidae, including the Mentoclaenodon, one of the first saber-toothed synapsids in many millions of years.

External links

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