The Late Cretaceous (100.5–66
Ma) is the younger of two
epochs into which the
Cretaceous
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 ...
Period is divided in the
geologic time scale
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochr ...
.
Rock strata from this epoch form the Upper Cretaceous
Series. The Cretaceous is named after
''creta'', the Latin word for the white
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...
known as
chalk
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. C ...
. The chalk of northern France and the
white cliffs of south-eastern England date from the Cretaceous Period.
Climate
During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident.
The
tropics
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also refer ...
became restricted to equatorial regions and northern
latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...
s experienced markedly more seasonal climatic conditions.
Geography
Due to
plate tectonics
Plate tectonics (from the la, label= Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of larg ...
, 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.
India maintained a northward course towards Asia.
In the Southern Hemisphere, Australia and
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
seem to have remained connected and began to drift away from Africa and South America.
["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. .] Europe was an island chain.
Populating some of these islands were endemic
dwarf
Dwarf or dwarves may refer to:
Common uses
*Dwarf (folklore), a being from Germanic mythology and folklore
* Dwarf, a person or animal with dwarfism
Arts, entertainment, and media Fictional entities
* Dwarf (''Dungeons & Dragons''), a humanoid ...
dinosaur species.
Vertebrate fauna
Non-avian dinosaurs
In the Late Cretaceous, the
hadrosaurs,
ankylosaurs
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...
, and
ceratopsians experienced success in
Asiamerica
Asiamerica was a supercontinent formed from the Laurasian landmass and separated by shallow continental seas from Eurasia to the West and eastern North America to the East. This region incorporated what is now politically China, Mongolia, western ...
(Western North America and eastern Asia).
Tyrannosaur
Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontin ...
s 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
titanosaur
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
s being among the dominant herbivores.
Spinosaurids
The Spinosauridae (or spinosaurids) are a clade or family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. They came into prominence during the Cretaceous period. Spinosaurid fossils have been recovered worldwide, includi ...
were also present during this time.
Birds
Birds became increasingly common, diversifying in a variety of
enantiornithe and
ornithurine forms. Early
Neornithes such as ''
Vegavis''
[Supporting information]
/ref> co-existed with forms as bizarre as ''Yungavolucris
''Yungavolucris'' is a genus of enantiornithean birds. It contains the single species ''Yungavolucris brevipedalis'', which lived in the Late Cretaceous ( Maastrichtian, c.70.6 – 66 mya). The fossil bones were found in the Lecho Formation ...
'' 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
Azhdarchidae (from the Persian word , , a dragon-like creature in Persian mythology) is a family of pterosaurs known primarily from the Late Cretaceous Period, though an isolated vertebra apparently from an azhdarchid is known from the Early Cret ...
, other forms like pteranodontids
The Pteranodontidae are a family of large pterosaurs of the Cretaceous Period of North America and Africa. The family was named in 1876 by Othniel Charles Marsh. Pteranodontids had a distinctive, elongated crest jutting from the rear of the head ...
, tapejarids (''Caiuajara
''Caiuajara'' is an extinct genus of tapejarid pterosaur from the Late Cretaceous period (Santonian stage) of Brazil. It is known from a single type species, ''Caiuajara dobruskii''.
Discovery and naming
In 1971, the labourers Alexandre D ...
'' and ''Bakonydraco
''Bakonydraco'' is a genus of pterodactyloid pterosaur from the Late Cretaceous period ( Santonian stage) of what is now the Csehbánya Formation of the Bakony Mountains, Iharkút, Veszprém, western Hungary.
Etymology
''Bakonydraco'' was n ...
''), nyctosaurids
Nyctosauridae (meaning "night lizards" or "bat lizards") is a family of specialized soaring pterosaurs of the late Cretaceous Period of North America, Africa, and possibly Europe. It was named in 1889 by Henry Alleyne Nicholson and Richard Lyde ...
and uncertain forms (''Piksi
''Piksi'' is a potential pterosaurLongrich, N.R., Martill, D.M., and Andres, B. (2018). Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary. PLoS Biology, 16(3): e2001663. genu ...
'', ''Navajodactylus
''Navajodactylus'' (meaning "Navajo finger") is an extinct genus of pterodactyloid pterosaur from Late Cretaceous (late Campanian stage) deposits of the San Juan Basin in New Mexico, United States.
Discovery
The holotype specimen of ''Navajodac ...
'') 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.
Mammals
Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
. In the northern hemisphere, cimolodont
Cimolodonta is a taxon of extinct mammals that lived from the Cretaceous to the Eocene. They were some of the more derived members of the extinct order Multituberculata. They probably lived something of a rodent-like existence until their ecolo ...
, multituberculates, metatheria
Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as w ...
ns 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
''Schowalteria'' is a genus of extinct mammal from the Cretaceous of Canada. It is the earliest known representative of Taeniodonta, a specialised lineage of non-placental eutherian mammals otherwise found in Paleocene and Eocene deposits. It is ...
'', Zhelestidae and Mesungulatidae
Mesungulatidae is an extinct clade of meridiolestidan dryolestoid mammals from the Late Cretaceous of South America and possibly other Gondwannan landmasses. They are particularly notable for their ecological speciation and large size.
Characte ...
) to highly atypical cursorial forms ( Zalambdalestidae, Brandoniidae).
True placentals evolved only at the very end of the epoch; the same can be said for true marsupial
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in ...
s. Instead, nearly all known eutherian and metatherian fossils belong to other groups.
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
The Cenomanian-Turonian boundary event, also known as the Cenomanian-Turonian extinction, Cenomanian-Turonian oceanic anoxic event ( OAE 2), and referred to also as the Bonarelli event, was one of two anoxic extinction events in the Cretaceous p ...
.
Flora
Near the end of the Cretaceous Period, flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants t ...
s diversified. In temperate regions, familiar plants like magnolia
''Magnolia'' is a large genus of about 210 to 340The number of species in the genus ''Magnolia'' depends on the taxonomic view that one takes up. Recent molecular and morphological research shows that former genera ''Talauma'', ''Dugandiodendr ...
s, sassafras, rose
A rose is either a woody perennial flowering plant of the genus ''Rosa'' (), in the family Rosaceae (), or the flower it bears. There are over three hundred species and tens of thousands of cultivars. They form a group of plants that can be ...
s, redwoods, and willows could be found in abundance.
Cretaceous–Paleogene mass extinction discovery
The Cretaceous–Paleogene extinction event was a large-scale mass extinction
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...
of animal and plant species in a geologically short period of time, approximately (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
Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago.
The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...
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
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
Era and the beginning of the Cenozoic
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...
Era. "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy
The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...
, the K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers.
Non-avian
Avian may refer to:
* Birds or Aves, winged animals
*Avian (given name) (russian: Авиа́н, link=no), a male forename
Aviation
*Avro Avian, a series of light aircraft made by Avro in the 1920s and 1930s
*Avian Limited, a hang glider manufactur ...
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
fossils are found only below the Cretaceous–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
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
layers. Mosasaurs, plesiosaurs, pterosaur
Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...
s and many species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
of plants and invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
s also became extinct. Mammalian
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...
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.
Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater
The Chicxulub crater () is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore near the community of Chicxulub, after which it is named. It was formed slightly over 66 million years ago when a large a ...
, 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
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
, leading to a massive disruption in Earth's ecology
Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...
. A much smaller number of researchers believe the extinction was more gradual, resulting from slower changes in sea level
Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardis ...
or climate
Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...
.
See also
* Flora and fauna of the Maastrichtian stage
This is an incomplete list that briefly describes vertebrates that were extant during the Maastrichtian, a stage of the Late Cretaceous Period which extended from 72.1 to 66 million years before present. This was the last time period in which ...
* Hațeg Island
References
{{Geological history, p, m
Late
Geological epochs