Cretaceous (100.5–66 Ma) is the younger of two epochs into
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.
3 Vertebrate fauna
3.4 Marine life
Paleogene mass extinction
6 See also
During the Late Cretaceous, the climate was warmer than present,
although throughout the period a cooling trend is evident. The
tropics became restricted to equatorial regions and northern latitudes
experienced markedly more seasonal climatic conditions.
Due to plate tectonics, the Americas were gradually moving westward,
causing the Atlantic Ocean to expand. The Western Interior Seaway
North America into eastern and western halves; Appalachia and
Laramidia. India maintained a northward course towards Asia. In
the Southern Hemisphere, Australia and Antarctica seem to have
remained connected and began to drift away from Africa and South
America. Europe was an island chain. Populating some of these
islands were endemic dwarf dinosaur species.
In the Late Cretaceous, the hadrosaurs, ankylosaurs, and ceratopsians
experienced success in
North America and eastern
Asia). Tyrannosaurs dominated the large predator niche in North
America. They were also present in Asia, although were usually
smaller and more primitive than the North American varieties.
Pachycephalosaurs were also present in both
North America and Asia.
Dromaeosaurs shared the same geographical distribution, and are well
documented in both Mongolia and Western North America. 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. Spinosaurids
were also present during this time.
Birds became increasingly common and diverse, diversifying in a
variety of enantiornithe and ornithurine forms. Early
Vegavis co-existed with forms as bizarre as
Avisaurus. Though mostly small, marine
relatively large and flightless, adapted to life in the open sea.
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.
Several old mammal groups began to disappear, with the last
eutriconodonts occurring in the
Campanian of North America. 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).
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. 
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
Turonian anoxic event.
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.
Paleogene mass extinction
Main article: Cretaceous–
Paleogene extinction event
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
Neogene periods). The
event marks the end of the
Mesozoic Era and the beginning of the
Cenozoic Era. "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
Paleogene boundary and became extinct immediately before
or during the event. 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. 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.
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.
Flora and fauna of the
^ a b c d e f g h i j k l m "Dinosaurs Ruled the World: Late
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Carpenter, Kenneth & Forster, Catherine A. & Gillette, David
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Geologic history of Earth
Quaternary (present–2.588 Mya)
Holocene (present–11.784 kya)
Pleistocene (11.784 kya–2.588 Mya)
Neogene (2.588–23.03 Mya)
Pliocene (2.588–5.333 Mya)
Miocene (5.333–23.03 Mya)
Paleogene (23.03–66.0 Mya)
Oligocene (23.03–33.9 Mya)
Eocene (33.9–56.0 Mya)
Paleocene (56.0–66.0 Mya)
Cretaceous (66.0–145.0 Mya)
Late (66.0–100.5 Mya)
Early (100.5–145.0 Mya)
Jurassic (145.0–201.3 Mya)
Late (145.0–163.5 Mya)
Middle (163.5–174.1 Mya)
Early (174.1–201.3 Mya)
Triassic (201.3–251.902 Mya)
Late (201.3–237 Mya)
Middle (237–247.2 Mya)
Early (247.2–251.902 Mya)
Permian (251.902–298.9 Mya)
Lopingian (251.902–259.8 Mya)
Guadalupian (259.8–272.3 Mya)
Cisuralian (272.3–298.9 Mya)
Carboniferous (298.9–358.9 Mya)
Pennsylvanian (298.9–323.2 Mya)
Mississippian (323.2–358.9 Mya)
Devonian (358.9–419.2 Mya)
Late (358.9–382.7 Mya)
Middle (382.7–393.3 Mya)
Early (393.3–419.2 Mya)
Silurian (419.2–443.8 Mya)
Pridoli (419.2–423.0 Mya)
Ludlow (423.0–427.4 Mya)
Wenlock (427.4–433.4 Mya)
Llandovery (433.4–443.8 Mya)
Ordovician (443.8–485.4 Mya)
Late (443.8–458.4 Mya)
Middle (458.4–470.0 Mya)
Early (470.0–485.4 Mya)
Cambrian (485.4–541.0 Mya)
Furongian (485.4–497 Mya)
Series 3 (497–509 Mya)
Series 2 (509–521 Mya)
Terreneuvian (521–541.0 Mya)
(541.0 Mya–2.5 Gya)
Neoproterozoic era (541.0 Mya–1 Gya)
Ediacaran (541.0-~635 Mya)
Cryogenian (~635-~720 Mya)
Tonian (~720 Mya-1 Gya)
Mesoproterozoic era (1–1.6 Gya)
Stenian (1-1.2 Gya)
Ectasian (1.2-1.4 Gya)
Calymmian (1.4-1.6 Gya)
Paleoproterozoic era (1.6–2.5 Gya)
Statherian (1.6-1.8 Gya)
Orosirian (1.8-2.05 Gya)
Rhyacian (2.05-2.3 Gya)
Siderian (2.3-2.5 Gya)
Archean eon² (2.5–4 Gya)
Neoarchean (2.5–2.8 Gya)
Mesoarchean (2.8–3.2 Gya)
Paleoarchean (3.2–3.6 Gya)
Eoarchean (3.6–4 Gya)
Hadean eon² (4–4.6 Gya)
kya = thousands years ago. Mya = millions years ago.
Gya = billions
years ago.¹ =
Phanerozoic eon. ² =
Source: (2017/02). International Commission on Stratigraphy. Retrieved
13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic
and Geochronologic Units USGS Retrie