Late Cretaceous

The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series. The Cretaceous is named after the white limestone known as chalk which occurs widely in northern France and is seen in the white cliffs of south-eastern England, and which dates from this time.

System/
Period
Series/
Epoch
Stage/
Age
Age (Ma)
Paleogene Paleocene Danian younger
Cretaceous Upper/
Late
Maastrichtian 66.0 72.1
Campanian 72.1 83.6
Santonian 83.6 86.3
Coniacian 86.3 89.8
Turonian 89.8 93.9
Cenomanian 93.9 100.5
Lower/
Early
Albian 100.5 ~113.0
Aptian ~113.0 ~125.0
Barremian ~125.0 ~129.4
Hauterivian ~129.4 ~132.9
Valanginian ~132.9 ~139.8
Berriasian ~139.8 ~145.0
Jurassic Upper/
Late
Tithonian older
Subdivision of the Cretaceous system
according to the ICS, as of 2017.[1]

Climate

During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident.[2] The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions.[2]

Geography

LateCretaceousMap
Map

Due to plate tectonics, the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia.[2] India maintained a northward course towards Asia.[2] In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America.[2] Europe was an island chain.[2] Populating some of these islands were endemic dwarf dinosaur species.[2]

Vertebrate fauna

Dinosaurs

In the Late Cretaceous, the hadrosaurs, ankylosaurs, and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated the large predator niche in North America.[2] They were also present in Asia, although were usually smaller and more primitive than the North American varieties.[2] Pachycephalosaurs were also present in both North America and Asia.[2] Dromaeosaurs shared the same geographical distribution, and are well documented in both Mongolia and Western North America.[2] Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America and Asia. Gondwana held a very different dinosaurian fauna, with most predators being abelisaurs and carcharodontosaurs; and titanosaurs being among the dominant herbivores.[2] Spinosaurids were also present during this time.

Birds

Birds became increasingly common and diverse, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes such as Vegavis co-existed with forms as bizarre as Yungavolucris and Avisaurus. Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in the open sea.

Pterosaurs

Though primarily represented by azhdarchids, other forms like pteranodontids, tapejarids (Caiuajara and Bakonydraco), nyctosaurids and uncertain forms (Piksi, Navajodactylus) are also present. Historically, it has been assumed that pterosaurs were in decline due to competition with birds, but it appears that neither group overlapped significantly ecologically, nor is it particularly evident that a true systematic decline was ever in place, especially with the discovery of smaller pterosaur species.[3]

Mammals

Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America.[4] In the northern hemisphere, cimolodont, multituberculates, metatherians and eutherians were the dominant mammals, with the former two groups being the most common mammals in North America. In the southern hemisphere there was instead a more complex fauna of dryolestoids, gondwanatheres and other multituberculates and basal eutherians; monotremes were presumably present, as was the last of the haramiyidans, Avashishta.

Mammals, though generally small, ranged into a variety of ecological niches, from carnivores (Deltatheroida), to mollusc-eater (Stagodontidae), to herbivores (multituberculates, Schowalteria, Zhelestidae and Mesungulatidae) to highly atypical cursorial forms (Zalambdalestidae, Brandoniidae).

True placentals only evolved at the very end of the epoch; the same can be said for true marsupials. Instead, nearly all known eutherian and metatherian fossils belong to other groups. [5]

Marine life

In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and giant-penguin-like polycotylid plesiosaurs (3 meters long) and huge long-necked elasmosaurs (13 meters long) also diversified. These predators fed on the numerous teleost fishes, which in turn evolved into new advanced and modern forms (Neoteleostei). Ichthyosaurs and pliosaurs, on the other hand, became extinct during the Cenomanian-Turonian anoxic event.

Flora

Near the end of the Cretaceous Period, flowering plants diversified. In temperate regions, familiar plants like magnolias, sassafras, roses, redwoods, and willows could be found in abundance.[2]

Cretaceous–Paleogene mass extinction

The Cretaceous–Paleogene extinction event was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 66 million years ago (Ma). It is widely known as the K–T extinction event and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the Cretaceous–Paleogene boundary (K–T boundary). K is the traditional abbreviation for the Cretaceous Period derived from the German name Kreidezeit, and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era.[6] "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy, the K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers.

Non-avian dinosaur fossils are only found below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event.[7] A very small number of dinosaur fossils have been found above the Cretaceous–Paleogene boundary, but they have been explained as reworked fossils, that is, fossils that have been eroded from their original locations then preserved in later sedimentary layers.[8][9][10] Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through the boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms.[11]

Scientists have hypothesized that the Cretaceous–Paleogene extinctions were caused by one or more catastrophic events such as massive asteroid impacts or increased volcanic activity. Several impact craters and massive volcanic activity in the Deccan Traps have been dated to the approximate time of the extinction event. These geological events may have reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology. Other researchers believe the extinction was more gradual, resulting from slower changes in sea level or climate.[11]

See also

References

  1. ^ http://www.stratigraphy.org/index.php/ics-chart-timescale
  2. ^ a b c d e f g h i j k l m "Dinosaurs Ruled the World: Late Cretaceous Period." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. Pp. 103-104. ISBN 0-7853-0443-6.
  3. ^ Prondvai E., Bodor E. R., Ösi A. (2014). "Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity". Paleobiology. 40: 288–321.
  4. ^ Fox Richard C (1969). "Studies of Late Cretaceous vertebrates. III. A triconodont mammal from Alberta". Canadian Journal of Zoology. 47: 1253–1256. doi:10.1139/z69-196.
  5. ^ Halliday Thomas J. D. (2015). "Resolving the relationships of Paleocene placental mammals". Biological Reviews. doi:10.1111/brv.12242.
  6. ^ Fortey R (1999). Life: A Natural History of the First Four Billion Years of Life on Earth. Vintage. pp. 238–260. ISBN 978-0375702617.
  7. ^ Fastovsky DE, Sheehan PM (2005). "The extinction of the dinosaurs in North America". GSA Today. 15 (3): 4–10. doi:10.1130/1052-5173(2005)015<4:TEOTDI>2.0.CO;2. Archived from the original on 2011-12-09. Retrieved 2007-05-18.
  8. ^ Sloan RE; Rigby K; Van Valen LM; Gabriel Diane (1986). "Gradual dinosaur extinction and simultaneous ungulate radiation in the Hell Creek formation". Science. 232 (4750): 629–633. Bibcode:1986Sci...232..629S. doi:10.1126/science.232.4750.629. PMID 17781415. Retrieved 2007-05-18.
  9. ^ Fassett JE, Lucas SG, Zielinski RA, Budahn JR (2001). "Compelling new evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone San Juan Basin, New Mexico and Colorado, USA" (PDF). International Conference on Catastrophic Events and Mass Extinctions: Impacts and Beyond, 9–12 July 2000, Vienna, Austria. 1053: 45–46. Retrieved 2007-05-18.
  10. ^ Sullivan RM (2003). "No Paleocene dinosaurs in the San Juan Basin, New Mexico". Geological Society of America Abstracts with Programs. 35 (5): 15. Retrieved 2007-07-02.
  11. ^ a b MacLeod N, Rawson PF, Forey PL, Banner FT, Boudagher-Fadel MK, Bown PR, Burnett JA, Chambers, P, Culver S, Evans SE, Jeffery C, Kaminski MA, Lord AR, Milner AC, Milner AR, Morris N, Owen E, Rosen BR, Smith AB, Taylor PD, Urquhart E, Young JR (1997). "The Cretaceous–Tertiary biotic transition". Journal of the Geological Society. 154 (2): 265–292. Bibcode:1997JGSoc.154..265M. doi:10.1144/gsjgs.154.2.0265. Archived from the original on 2013-05-25.
Arecales

Arecales is an order of flowering plants. The order has been widely recognised only for the past few decades; until then, the accepted name for the order including these plants was Principes.

Arkharavia

Arkharavia is a dubious genus of somphospondylan sauropod, but at least some of the remains probably belong to a hadrosaurid. It lived in what is now Russia, during the Late Cretaceous. It was described in 2010 by Alifanov and Bolotsky. The type species is A. heterocoelica.

Aurorachelys

Aurorachelys is an extinct genus of turtle which existed in Canada (Nunavut) during the late Cretaceous period, containing a single species, A. gaffneyi.

Bonatitan

Bonatitan is a genus of titanosaurian dinosaur from the Late Cretaceous Allen Formation of Argentina.

Borealosaurus

Borealosaurus is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous of northern China.

Borealosuchus

Borealosuchus (meaning "boreal crocodile") is an extinct genus of crocodylians that lived from the Late Cretaceous to the Eocene in North America. It was named by Chris Brochu in 1997 for several species that had been assigned to Leidyosuchus. The species assigned to it are:

B. sternbergii, the type species, from the Maastrichtian (Late Cretaceous) of Colorado, Montana, North Dakota, South Dakota, and Wyoming; B. acutidentatus, from the Paleocene of Saskatchewan; B. formidabilis, from the Paleocene of North Dakota; B. griffithi, from the Paleocene of Alberta; and B. wilsoni, from the Eocene of Wyoming. B. formidabilis is particularly well-known, represented by the remains of many individuals from the Wannagan Creek site in North Dakota.Borealosuchus was a mid-sized crocodylian; B. acutidentatus reached up to 2.8 metres (9.2 ft) in length with a 36 centimetres (14 in) skull.

Campylodoniscus

Campylodoniscus is a genus of sauropod dinosaur from the Late Cretaceous Period of what is now Argentina.

The type species was first named and described by Friedrich von Huene in 1929 as Campylodon ameghinoi, the genus name meaning 'bent tooth', from Greek καμπυλος, 'bent' or 'curved' (as of a bow) and ὀδών meaning 'tooth'. The specific name honours Florentino Ameghino. In 1961 Oskar Kuhn noted that the name was pre-occupied by a fish and renamed the genus into Campylodoniscus, the diminutive.The fossil remains of Campylodoniscus were found in the Sierra de San Bernardo and consist of a single jaw bone, the maxilla, holding seven teeth.

The age of Campylodoniscus could be from the Cenomanian, about 95 million years ago, or the Campanian-Maastrichtian, about 70 million years old. It is sometimes estimated as being around twenty meters in length.

Campylodoniscus is probably a member of the Titanosauria. Some researchers consider it a nomen dubium.

Cenomanian

The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding age. Both age and stage bear the same name.

As a unit of geologic time measure, the Cenomanian age spans the time between 100.5 ± 0.9 Ma and 93.9 ± 0.8 Ma (million years ago). In the geologic timescale it is preceded by the Albian and is followed by the Turonian. The Upper Cenomanian starts approximately at 95 M.a.

The Cenomanian is coeval with the Woodbinian of the regional timescale of the Gulf of Mexico and the early part of the Eaglefordian of the regional timescale of the East Coast of the United States.

At the end of the Cenomanian an anoxic event took place, called the Cenomanian-Turonian boundary event or the "Bonarelli Event", that is associated with a minor extinction event for marine species.

Coniacian

The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by the Turonian and followed by the Santonian.

Cretaceous

The Cretaceous ( , kri-TAY-shəs) is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation Kreide (chalk, creta in Latin).

The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.

Isurus

Isurus is a genus of mackerel sharks in the family Lamnidae, commonly known as the mako sharks.

Maastrichtian

The Maastrichtian ( ) is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned the interval from 72.1 to 66 million years ago. The Maastrichtian was preceded by the Campanian and succeeded by the Danian (part of the Paleogene and Paleocene).At the end of this period, 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 to 15 kilometres (6.2 to 9.3 mi) wide colliding with Earth at the end of the Cretaceous.

Perciformes

Perciformes, also called the Percomorpha or Acanthopteri, is an order or superorder of ray-finned fish. If considered a single order, they are the most numerous order of vertebrates, containing about 41% of all bony fish. Perciformes means "perch-like". This group comprises over 10,000 species found in almost all aquatic ecosystems.

The order contains about 160 families, which is the most of any order within the vertebrates. It is also the most variably sized order of vertebrates, ranging from the 7-mm (1/4-in) Schindleria brevipinguis to the 5-m (16.4 ft) marlin in the genus Makaira. They first appeared and diversified in the Late Cretaceous.

Among the well-known members of this group are perch and darters (Percidae), sea bass and groupers (Serranidae), mackerel and tuna (Scombridae), billfish (Xiphiidae and Istiophoridae), and icefish (Nototheniidae).

Qingxiusaurus

Qingxiusaurus is a genus of titanosaur sauropod dinosaur from the Late Cretaceous of Guangxi, China. The type species, described by Mo et al. in 2008, is Q. youjiangensis. Like other sauropods, Qingxiusaurus would have been a large quadrupedal herbivore. It is known from only limited remains: Two humeri, two sternal plates, and the neural spine of a single vertebra.

Santonian

The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. The Santonian is preceded by the Coniacian and is followed by the Campanian.

Sphaerium beckmani

Sphaerium beckmani is an extinct species of fossil freshwater pea clams from the Late Cretaceous deposits of North America. This species was first described by the American paleontologist Loris Shano Russell in 1976. The specimens were collected by the American paleontologist Karl M. Waage from 1961 to 1962 from the Hell Creek Formation of eastern Montana. The locality is dated to the late Maastrichtian Age (around 66.0 to 72.1 million years ago).

Turonian

The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by the Cenomanian stage and underlies the Coniacian stage.At the beginning of the Turonian an anoxic event took place which is called the Cenomanian-Turonian boundary event or the "Bonarelli Event".

Varanoidea

Varanoidea is a superfamily of lizards, including the well-known family Varanidae (the monitors or goanna). Also included in the Varanoidea are the Lanthanotidae (earless monitor lizards), and the extinct Palaeovaranidae.

Throughout their long evolutionary history, varanoids have exhibited great diversity, both in habitat and form. This superfamily includes the largest-known terrestrial lizard, Megalania (5–6 meters), and the largest extant lizard, the Komodo dragon (Varanus komodoensis, 3+ meters).

Western Interior Seaway

The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that existed during the mid- to late Cretaceous period as well as the very early Paleogene, splitting the continent of North America into two landmasses, Laramidia to the west and Appalachia to the east. The ancient sea stretched from the Gulf of Mexico and through the middle of the modern-day countries of the United States and Canada, meeting with the Arctic Ocean to the north. At its largest, it was 2,500 feet (760 m) deep, 600 miles (970 km) wide and over 2,000 miles (3,200 km) long.

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