Late Cretaceous

Last updated
Late/Upper Cretaceous
100.5 – 66.0 Ma
Chronology
Etymology
Chronostratigraphic nameUpper Cretaceous
Geochronological nameLate Cretaceous
Name formalityFormal
Usage information
Celestial body Earth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unit Epoch
Stratigraphic unit Series
Time span formalityFormal
Lower boundary definition FAD of the Planktonic Foraminifer Rotalipora globotruncanoides
Lower boundary GSSP Mont Risoux, Hautes-Alpes, France
44°23′33″N5°30′43″E / 44.3925°N 5.5119°E / 44.3925; 5.5119
Lower GSSP ratified2002 [2]
Upper boundary definition Iridium enriched layer associated with a major meteorite impact and subsequent K-Pg extinction event.
Upper boundary GSSPEl Kef Section, El Kef, Tunisia
36°09′13″N8°38′55″E / 36.1537°N 8.6486°E / 36.1537; 8.6486
Upper GSSP ratified1991

The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after creta, the Latin word for the white limestone known as chalk. The chalk of northern France and the white cliffs of south-eastern England date from the Cretaceous Period. [3]

Contents

Climate

During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident. [4] The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions. [4]

Geography

Late Cretaceous Map (Turonian) LateCretaceousMap.jpg
Late Cretaceous Map (Turonian)

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. [4] India maintained a northward course towards Asia. [4] In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. [4] Europe was an island chain. [4] Populating some of these islands were endemic dwarf dinosaur species. [4]

Vertebrate fauna

Non-avian 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. [4] They were also present in Asia, although were usually smaller and more primitive than the North American varieties. [4] Pachycephalosaurs were also present in both North America and Asia. [4] Dromaeosaurids shared the same geographical distribution, and are well documented in both Mongolia and Western North America. [4] 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 abelisaurids and carcharodontosaurids; and titanosaurs being among the dominant herbivores. [4] Spinosaurids were also present during this time. [5]

Birds

Birds became increasingly common, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes such as Vegavis [6] co-existed with forms as bizarre as Yungavolucris and Avisaurus . [7] Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in the open sea. [8]

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. [9]

Mammals

Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America. [10] 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).[ citation needed ]

True placentals evolved only 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. [11]

Marine life

In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and 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.[ citation needed ]

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. [4]

Cretaceous–Paleogene mass extinction discovery

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. [12] "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.

Asteroids of only a few kilometers wide can release the energy of millions of nuclear weapons when colliding with planets (artist's impression). Impact event.jpg
Asteroids of only a few kilometers wide can release the energy of millions of nuclear weapons when colliding with planets (artist's impression).

Non-avian dinosaur fossils are found only below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event. [13] 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. [14] [15] [16] 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. [17]

Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater, in combination with increased volcanic activity, such as that recorded in the Deccan Traps, both of which have been firmly dated to the time of the extinction event. In theory, these events reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology. A much smaller number of researchers believe the extinction was more gradual, resulting from slower changes in sea level or climate. [17]

See also

Related Research Articles

<span class="mw-page-title-main">Cretaceous</span> Third and last period of the Mesozoic Era, 145-66 million years ago

The Cretaceous is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.

<span class="mw-page-title-main">Cenozoic</span> Third era of the Phanerozoic Eon

The Cenozoic is Earth's current geological era, representing the last 66 million years of Earth's history. It is characterised by the dominance of mammals, birds, and angiosperms. It is the latest of three geological eras, preceded by the Mesozoic and Paleozoic. The Cenozoic started with the Cretaceous–Paleogene extinction event, when many species, including the non-avian dinosaurs, became extinct in an event attributed by most experts to the impact of a large asteroid or other celestial body, the Chicxulub impactor.

The Mesozoic Era is the second-to-last era of Earth's geological history, lasting from about 252 to 66 million years ago, comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of gymnosperms and of archosaurian reptiles, such as the dinosaurs; a hot greenhouse climate; and the tectonic break-up of Pangaea. The Mesozoic is the middle of the three eras since complex life evolved: the Paleozoic, the Mesozoic, and the Cenozoic.

<span class="mw-page-title-main">Paleogene</span> First period of the Cenozoic Era (66–23 million years ago)

The Paleogene Period is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago (Mya) to the beginning of the Neogene Period 23.03 Mya. It is the first part of the Cenozoic Era of the present Phanerozoic Eon. The earlier term Tertiary Period was used to define the span of time now covered by the Paleogene Period and subsequent Neogene Period; despite no longer being recognized as a formal stratigraphic term, "Tertiary" still sometimes remains in informal use. Paleogene is often abbreviated "Pg", although the United States Geological Survey uses the abbreviation "Pe" for the Paleogene on the Survey's geologic maps.

The Phanerozoic is the current and the latest of the four geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and plant life has proliferated, diversified and colonized various niches on the Earth's surface, beginning with the Cambrian period when animals first developed hard shells that can be clearly preserved in the fossil record. The time before the Phanerozoic, collectively called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.

<span class="mw-page-title-main">Multituberculata</span> Extinct order of mammals

Multituberculata is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, and reached a peak diversity during the Late Cretaceous and Paleocene. They eventually declined from the mid-Paleocene onwards, disappearing from the known fossil record in the late Eocene. They are the most diverse order of Mesozoic mammals with more than 200 species known, ranging from mouse-sized to beaver-sized. These species occupied a diversity of ecological niches, ranging from burrow-dwelling to squirrel-like arborealism to jerboa-like hoppers. Multituberculates are usually placed as crown mammals outside either of the two main groups of living mammals—Theria, including placentals and marsupials, and Monotremata—but usually as closer to Theria than to monotremes. They are considered to be closely related to Euharamiyida and Gondwanatheria as part of Allotheria.

<span class="mw-page-title-main">Placentalia</span> Infraclass of mammals in the clade Eutheria

Placental mammals are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished from monotremes and marsupials in that the fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less developed young which are then nurtured for a period inside the mother's pouch. Placentalia represents the only living group within Eutheria, which contains all mammals more closely related to placentals than to marsupials.

<i>Meniscoessus</i> Extinct genus of multituberculates

Meniscoessus is a genus of extinct multituberculates from the Upper Cretaceous Period that lived in North America.

<span class="mw-page-title-main">Maastrichtian</span> Sixth and last age of the Late Cretaceous

The Maastrichtian is, in the ICS geologic timescale, the latest age 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.

The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian is at the Cretaceous–Paleogene extinction event 66 Ma. The age ended 61.6 Ma, being followed by the Selandian.

<i>Protungulatum</i> Extinct genus of mammals

Protungulatum is an extinct genus of eutherian mammals within extinct family Protungulatidae, and is possibly one of the earliest known placental mammals in the fossil record, that lived in North America from the Late Cretaceous to early Paleocene.

The Paleocene, or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek παλαιός palaiós meaning "old" and the Eocene Epoch, translating to "the old part of the Eocene".

The Lopez de Bertodano Formation is a geological formation in the James Ross archipelago of the Antarctic Peninsula. The strata date from the end of the Late Cretaceous to the Danian stage of the lower Paleocene, from about 70 to 65.5 million years ago, straddling the Cretaceous-Paleogene boundary.

<span class="mw-page-title-main">Nacimiento Formation</span> A geologic formation in New Mexico

The Nacimiento Formation is a sedimentary rock formation found in the San Juan Basin of western New Mexico. It has an age of 61 to 65.7 million years, corresponding to the early and middle Paleocene. The formation has yielded an abundance of fossils from shortly after the Cretaceous-Paleogene extinction event that provide clues to the recovery and diversification of mammals following the extinction event.

<span class="mw-page-title-main">Ojo Alamo Formation</span> Geologic formation in New Mexico

The Ojo Alamo Formation is a geologic formation in New Mexico spanning the Mesozoic/Cenozoic boundary. Non-avian dinosaur fossils have controversially been identified in beds of this formation dating from after the Cretaceous–Paleogene extinction event, but these have been explained as either misidentification of the beds in question or as reworked fossils, fossils eroded from older beds and redeposited in the younger beds.

The following outline is provided as an overview of and topical guide to dinosaurs:

The climate across the Cretaceous–Paleogene boundary is very important to geologic time as it marks a catastrophic global extinction event. Numerous theories have been proposed as to why this extinction event happened including an asteroid known as the Chicxulub asteroid, volcanism, or sea level changes. While the mass extinction is well documented, there is much debate about the immediate and long-term climatic and environmental changes caused by the event. The terrestrial climates at this time are poorly known, which limits the understanding of environmentally driven changes in biodiversity that occurred before the Chicxulub crater impact. Oxygen isotopes across the K–T boundary suggest that oceanic temperatures fluctuated in the Late Cretaceous and through the boundary itself. Carbon isotope measurements of benthic foraminifera at the K–T boundary suggest rapid, repeated fluctuations in oceanic productivity in the 3 million years before the final extinction, and that productivity and ocean circulation ended abruptly for at least tens of thousands of years just after the boundary, indicating devastation of terrestrial and marine ecosystems. Some researchers suggest that climate change is the main connection between the impact and the extinction. The impact perturbed the climate system with long-term effects that were much worse than the immediate, direct consequences of the impact.

<i>Acheroraptor</i> Dromaeosaurid dinosaur genus from the Late Cretaceous

Acheroraptor is an extinct genus of dromaeosaurid theropod dinosaur known from the latest Maastrichtian Hell Creek Formation of Montana, United States. It contains a single species, Acheroraptor temertyorum. A. temertyorum is one of the two geologically youngest known species of dromaeosaurids, the other being Dakotaraptor, which is also known from Hell Creek. A basal cousin of Velociraptor, Acheroraptor is known from upper and lower jaw material.

<span class="mw-page-title-main">Cretaceous–Paleogene extinction event</span> Mass extinction event about 66 million years ago

The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary(K–T)extinction, was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs. Most other tetrapods weighing more than 25 kilograms also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians. It marked the end of the Cretaceous period, and with it the Mesozoic era, while heralding the beginning of the Cenozoic era, which continues to this day.

<span class="mw-page-title-main">Insular India</span> Isolated land mass which became the Indian subcontinent

Insular India was an isolated landmass which became the Indian subcontinent. Across the latter stages of the Cretaceous and most of the Paleocene, following the breakup of Gondwana, the Indian subcontinent remained an isolated landmass as the Indian Plate drifted across the Tethys Ocean, forming the Indian Ocean. The process of India's separation from Madagascar first began 88 million years ago, but complete isolation only occurred towards the end of the Maastrichtian, a process that has been suggested to be the creation of the Deccan Traps. Soon after, the land mass moved northward rather quickly, until contact with Asia was established 55 million years ago. Even then, both landmasses did not become fully united until around 35 million years ago, and periods of isolation occurred as recently as 24 million years ago.

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