| 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. | ||||
Maastrichtian landscape
The Maastrichtian (pronunciation: /mɑːˈstrɪktiən/) is a sixth and upper stage of the Upper Cretaceous series, Cretaceous system and the whole Mesozoic erathem. Its geochronological equivalent is the Maastrichtian age, a last age of the Late Cretaceous epoch, Cretaceous period and Mesozoic era. It lasted from approximately 72.1 Ma to around 66.0 Ma (million years ago). It is preceded by the Campanian age of the Late Cretaceous and is followed by the Danian age of the Paleocene epoch. The earliest species of the various bony fish orders, such as Anabantiformes, Scombriformes, Kurtiformes and Cyprinodontiformes, are known from this stage.
At the end of the Maastrichtian, there was a mass extinction known as the Cretaceous–Paleogene extinction event, (formerly known as the Cretaceous–Tertiary extinction event). At this extinction event, many commonly recognized groups such as non-avian dinosaurs, plesiosaurs and mosasaurs, as well as many other lesser-known groups, died out. The cause of the extinction is most commonly linked to an asteroid about 10 kilometres (6.2 mi) wide colliding with Earth at the end of the Cretaceous.
Definition[]
The GSSP of the Maastrichtian stage was ratified in 2001. The lower boundary is fixed in the geological site at Tercis les Bains, Landes, France, and related to 12 biostratigraphic markers including first appearance of ammonite Pachydiscus neubergicus and belemnite Belemnella lanceolata.[2]
Maastrichtian life[]
Due to high sea levels, bivalves were able to spread over large areas. Malletia, Clisocolus, Pholadomya, Tellinimera, Inoceramus and many other genera lived on the bottom of the Western Interior Seaway that covered the central part of modern North America. All seas contained a variety of cephalopods, including octopods (Enchoteuthis) and shelled nautiloids (Eutrephoceras). Ammonites (Diplomoceras, Pseudophyllites, Kitchinites, Grossouvrites) also had shells, but their closest living relatives are considered to be octopuses, not nautiluses. Cartilaginous fishes remained numerous, although some of their families had become extinct by this time. Various lamniforms (Lamna, Serratolamna, Squalicorax, Paranomotodon), orectolobiforms (Cretorectolobus, Plicatoscyllium), rajiforms (Ischyrhiza, Protoplatyrhina, Myledaphus, Protoplatyrhina) and myliobatiforms (Brachyrhizodus, Rhombodus) are known from the Maastrichtian strata. marine bony fishes of the time include amiiforms (Cyclurus), aspidorhynchiforms (Belonostomus), aulopiforms (Enchodus) and ichthyodectiforms (Xiphactinus). Noticeable evolutionary processes among bony fishes took place in coastal and fresh waters, where the oldest kurtiforms (Serranidarum, Apogonidarum) and scombriforms (Sphyraenodus) lived. The earlist indeterminate anabantiforms and kyprinodontiforms were also discovered in the Maastrichtian sediments.
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Amphibians of that time differed little from modern ones. Lisserpeton, a close relative of modern mole salamanders, is known from the Upper Maastrichtian of North Dakota, USA. Beelzebufo, one of the largest anuran amphibians, lived in swamps in the territory of modern Madagascar.
Dolichorhynchops skeleton
The diversity of aquatic reptiles was already low. Among the sauropterygians by this time, only long-necked elasmosaurids (Aristonectes, Chubutinectes, Marambionectes) and long-snouted polycotylids (Dolichorhynchops, Sulcusuchus) remained. Numerous turtles (Taphrosphys, Adocus, Erymnochelys, Sokatra) lived in seas, rivers and lakes. The largest marine predators were mosasaurs (Mosasaurus, Tylosaurus, Moanasaurus, Kaikaifilu), relatives of lizards, some of which reached a length of 13 m and more. Their close relatives, snakes (Eomadtsoia, Indophis, Kelyophis, Adinophis), lived in water and on land. Champsosaurus, a choristodere, resembled modern crocodiles and probably led a similar lifestyle to them.
Mahajangasuchus head
Sauropsids remained the dominant group on the continents. Crocodylomorphs occupied various ecological niches. Shamosuchus, Borealosuchus, Hyposaurus and Thoracosaurus were ambush semiaquatic predators, while Mahajangasuchus hunted on the land, and Simosuchus was a herbivore. Similar diversity among pseudosuchians was observed only in the Triassic period.
Titanosaurus looking at tsunami
Among dinosaurs, herbivorous Hadrosaurids (Hadrosaurus, Edmontosaurus, Amurosaurus, Barsboldia) reached the greatest numbers. Some of them, such as Shantungosaurus, reached gigantic sizes, over 14 m in length. The number of ceratopsias by this time began to decline. Pachyrhinosaurus and Arrhinoceratops are known from the Lower Maastrichtian, while Triceratops, Torosaurus and small Leptoceratops lived at the very end of the age. All of them lived in North America and defended themselves from predators with the help of frills and horns. Pachycephalosaurids like Pachycephalosaurus and Sphaerotholus probably defended themselves by striking their attackers with their heads, which had a bony thickening at the top. The armoured ankylosaurs were the best protected from attack. Edmontonia had sharp side spines, and Ankylosaurus could also deliver strong blows with a bony thickening on its tail. Few sauropods are known from the Maastrichtian, but among them are such giants as Dreadnoughtus and Alamosaurus with a length of up to 30 m. Titanosaurus, a type genus of titanosaurs, also existed in this age.
Among theropods, abelisaurids (Majungasaurus, Carnotaurus, Rajasaurus, Indosuchus) and noasaurids (Masiakasaurus, Laevisuchus) widespread on the southern continents, while tyrannosaurids (Tyrannosaurus, Albertosaurus, Tarbosaurus, Dryptosaurus), ornithomimosaurs (Deinocheirus, Ornithomimus, Struthiomimus) and therizinosaurs (Nanshiungosaurus, Therizinosaurus) lived in more northern areas of land. Oviraptorosaurs like Anzu were omnivores, and their characteristic feature is the crests on their heads, reminiscent of the crests of cassowaries. Dromaeosaurids (Adasaurus, Rahonavis) and birds (Vorona, Canadaga, Vegavis, Gargantuavis) have spread throughout the world. Some modern groups of birds, such as the Anseriformes, already existed at this time.
Quetzalcoatlus feeding on ground
Pterosaurs were represented mainly by the three families: azhdarchids, among which there were medium-sized (Phosphatodraco) and large (Quetzalcoatlus, Hatzegopteryx) members with a wingspan of more than 10 m, nyctosaurids (Barbaridactylus) and pteranodontids (Tethydraco). Azhdarchids probably ate carrion, as evidenced by their long necks and beaks, while nyctosaurids and geese pteranodontids hunted for fish in the seas.
Numerous mammals already lived on all continents, some of which reached the size of a domestic cat. Maastrichtian mammals include multituberculates (Meniscoessus, Essonodon, Cimolodon), dryolestoids (Coloniatherium, Reigitherium) and stagodontids (Didelphodon, Ectoconodon).
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.