| 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 Late Cretaceous was the last epoch of the Cretaceous period and the Mesozoic era, spanning from the ending of the Albian age of the Early Cretaceous to the beginning of the Danian age of the Paleogene, 100.5 - 66 million years ago. It corresponds to the Upper Cretaceous series in stratigraphy. This epoch is characterized by the diversification of theropods, ornithischians, crocodylomorphs and lepidosaurs. The Late Cretaceous is significant for the asteroid impact that wiped out the pterosaurs, non-avian dinosaurs and other prehistoric creatures at the end of the era, known as the K-Pg extinction event.
Definition[]
The GSSP of the Upper Cretaceous and the Cenomanian stage was ratified in 2002. The lower boundary is fixed in Mount Risou, France, and related to the first appearance of the planktonic foraminifer Thalmanninella globotruncanoides.[2]
Subdivisions[]
The Upper Cretaceous divided into six stages, all of them correspond to the ages of the same names in geochronology. From youger to oldest:
- Maastrichtian (72.1 - 66 ma)
- Campanian (83.6 - 72.1 ma)
- Santonian (86.3 - 83.6 ma)
- Coniacian (89.8 - 86.3 ma)
- Turonian (93.9 - 89.8 ma)
- Cenomanian (100.5 - 93.9 ma)
Biostratigraphy[]
- Assemblage zone of Carnotaurus sastrei (Campanian)
Paleogeography[]
This epoch saw the highest sea levels in the last 300 million years. Central North America, northwestern South America, all of western Asia, almost all of Europe and coastal northern Africa were under water. The Atlantic Ocean expanded between Africa and South America. Hindustan was drifting to the north; at the end of the epoch, active volcanism occurred on its territory, which led to the formation of the Deccan Traps.
Late Cretaceous life[]
One of the most diverse faunas in Earth’s history existed in this epoch. The beginning of the Late Cretaceous, however, was marked by the extinction of some previously numerous groups of animals. Ichthyosaurs, many families of sauropterygians and tapejarid pterosaurs became completely extinct. Some later, rebbachisaurids disappeared. The likely cause of their extinction was sea level rise, which led to ocean desalination, and the evolution and spread of angiosperms on land.
Cephalopods probably reached the peak of their diversity during this epoch. The seas were inhabited by octopuses, giant squids, belemnites and ammonites, including Parapuzosia with a shell about 2 m in diameter.
Xiphactinus eating small mosasaur
Many new genera of sharks emerged, some of which fed on plankton or shellrd mollusks, while others like Cretoxyrhina resembled modern great white sharks in their lifestyle. Among bony fish, huge predators like Xiphactinus also appeared.
Mosasaurus hoffmanni was a famous animal that lived during the Late Cretaceous
After the extinction of the last large pliosaurids (such as Megacephalosaurus), two families remained among sauropterygians, the short-necked Polycotylidae and the long-necked Elasmosauridae. Some elasmosaurids have reached enormous sizes, more than 10 m in length. Large forms also appeared among turtles, especially close to the end of the epoch, when giant Archelon and Gigantatypus swam in the seas. It was a golden time for squamates, among which giant marine predatory mosasaurs such as Tylosaurus and Mosasaurus appeared. Already at the beginning of the Late Cretaceous, the first snakes appeared.
Futalognkosaurus, one of the largest land animals
This is the last epoch when dinosaurs were the dominant land group. The most massive land animals most likely existed during this time. Such sauropods as Argentinosaurus, Futalognkosaurus, Puertasaurus and poorly known Bruhathkayosaurus likely reached over 30 m length and over 60 t in body mass. Contrary to them, several other sauropods like Opisthocoelicaudia and Magyarosaurus have shrunk in size. Theropods of the late Cretaceous also varied greatly in size. Such animals as Giganotosaurus, Mapusaurus, Carcharodontosaurus, Tyrannosaurus and Tarbosaurus reached 12 m in length or more with mass estimation over 5 t. Spinosaurus, another huge theropod, reached 15 m in length but was likely less massive. Several large theropods like Deinocheirus, Therizinosaurus and Gigantoraptor were possibly omnivores, and their smaller relatives became common during this epoch.
Velociraptor hunting
Baptornis, an aquatic avian dinosaur of the Late Cretaceous
Dromaeosaurids were numerous, genera of the Late Cretaceous include Buitreraptor, Saurornitholestes, Dromaeosaurus, Velociraptor and Adasaurus. Their close relatives, birds, have already achieved great diversity. They spread across all continents, and hesperornithiforms like Baptornis and Hesperornis even adapted to life in the sea. Many avian and non-avian dinosaurs went extinct, but, at the end of this epoch, some modern orders of birds, for example, Anseriformes, already appeared. Alvarezsaurids, unusual theropods with only one finger on their front limbs, existed in the Late Cretaceous. These were small animals, their fossils are known from South America (Alvarezsaurus) and Asia (Mononykus). Abelisaurids, the last members of the Ceratosauria group, reached large numbers on the southern continents. Late Cretaceous genera include Abelisaurus, Majungasaurus, Rajasaurus and Carnotaurus.
The most common species at this time were ornithischian dinosaurs. Ornithopods, from small Thescelosaurus to large hadrosaurids like Edmontosaurus, spread across all continents. Some hadrosaurids like Corythosaurus and Parasaurolophus developed unusual crests on their heads that helped them recognize their relatives and, probably, produce certain sound ranges. It is assumed that such animals lived mainly in swamps and near reservoirs, where they fed on soft, lush vegetation. Some hadrosaurids grew to gigantic sizes, surpassing even some of the sauropods of that time. Magnapaulia and Saurolophus could grow to approximately 12 m in length, and Shantungosaurus was even larger, up to 17 m.
Thyreophoran group was likely presented only by ankylosaurs during this epoch. Some ankylosaurs like Nodosaurus, Edmontonia or Panoplosaurus defeated themselves from predators with armor and spikes. Other, like Ankylosaurus, Pinacosaurus and Euoplocephalus, also had bony protuberances on their tails that could be used to deliver powerful blows. Some of these dinosaurs reached impressive sizes. The largest was probably Saichania with the length of about 7 m.
During the Late Cretaceous, marginocephalians reached the peak of evolution. Pachycephalosaurs like Stegoceras and Pachycephalosaurus had bony thickenings on their skulls, with the help of which these herbivorous animals probably fought with each other. Ceratopsoidea, the last successful ornithischian group, also existed in this epoch. From early and small forms like Turanoceratops to the large late Triceratops, they had beaks with which they cut vegetation, elongated cheekbones and bony frills at the back of the skulls. The purpose of these cheekbones and frills remains a matter of debate, but they were probably used to attract mating partners and to deter predators. Many ceratopsoids also had horns, sometimes of unusual shape. Styracosaurus has a single long horn located at the front end of the snout. Centrosaurus and Coronosaurus had an additional pair of small horns located above the eyes. Xenoceratops had two long horns located above the eyes and two more on the frill. Einiosaurus had a single, forward-curved horn located in the front of the snout. Some ceratopsoids like Pachyrhinosaurus and Achelousaurus had bone spurs of unknown purpose on their snouts and above their eyes. All marginocephalians have been found in modern Asian and North America.
Among pterosaurs, predominantly large and toothless forms remained. Some of them like Pteranodon lived on sea coasts and, in their feeding habits, were probably reminiscent of modern pelicans. Azhdarchids probably adapted to scavenging, judging by their long necks and beaks. Among azhdarchids, there were the largest flying animals of all time, Quetzalcoatlus and Hatzegopteryx, with a wingspan of 10 m or more.
Among mammals, modern groups of monotremes, marsupials and placentals had already appeared, although their members remained small species. Steropodon from the Cenomanian stage of Australia was a relative of modern platypus while Zalambdalestes from the Campanian stage of Mongolia was a basal eutherian mammal.
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.