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DINOSAUR EXTINCTION
WHAT IS EXTINCTION?
K-T ASTEROID THEORY
OTHER K-T EXTINCTION THEORIES
STUDYING EXTINCTIONS

WHAT IS EXTINCTION?

Extinction is the process in which groups of organisms (species) die out. If the birth rate is less than the death rate over time, extinction results. Extinction is a natural result of evolution and natural selection. Species go extinct when they are unable to adapt to changes in the environment or compete effectively with other organisms. Well over 99 per cent of the species that have ever lived have gone extinct.

A graph of invertebrate extinctions over the last 600 million years.

The mass extinctions appear as periodic peaks rising above the background extinction levels. This data is from the work of D. M. Raup and J. J. Sepkoski.




BACKGROUND EXTINCTIONS

Most extinctions (perhaps up to 95 per cent of all extinctions) occur as background extinctions, occurring throughout time. These extinctions are not caused by major catastrophes or horrendous climactic changes, but by small changes in climate or habitat, depleted resources, competition, and other changes that require adaptation and flexibility.

Most dinosaur species perished in background extinctions that occurred throughout the Mesozoic Era. For example, Maiasaura, Styracosaurus, Protoceratops, Dilophosaurus, Cetiosaurus, Iguanodon, Allosaurus, Ouranosaurus, Deinocheirus, and Edmontosaurus were probably decimated in background extinctions. The flowering plants (angiosperms) appeared during the Cretaceous period, displacing most conifers and many other plants. This had major effects on dinosaurs. Some herbivorous dinosaurs, like Edmontosaurus, ate only conifers. As flowering plants came to dominate the landscape, Edmontosaurus died out, unable to find enough conifers to sustain itself.



MASS EXTINCTIONS

A mass extinction is a relatively sudden, global decrease in the diversity of life forms. Mass extinctions have occurred periodically throughout the existence of life on Earth. To be a mass extinction, the following must occur: The five largest mass extinctions in Earth's history occurred during: Currently, during the modern Holocene epoch, there are large number of extinctions occuring. Many minor extinctions have also occurred through Earth's history.


THE NEMESIS HYPOTHESIS

The nemesis hypothesis of Raup and Sepkoski theorizes that there is a periodicity of 26 million years to mass extinctions which is caused by collisions with comets from the Oort cloud as they are perturbed in their orbits by a dark star (a companion star to the sun). The search for the Oort cloud continues.

THE EXTINCTION OF THE DINOSAURS

Most dinosaur species perished in background extinctions that occurred throughout their Mesozoic Era. The other dinosaur species died out during the several mass extinctions that occurred in the Mesozoic: at the end of the Triassic (213 million years ago), during and at the end of the Jurassic (at 190, 160, 144 mya), and during and at the end of the Cretaceous (at 120, 82, and 65 mya).

Too big to fail?
Too big to fail T. rex
Don't worry, we're too big to fail.

Cope's Rule (named for the American paleontologist Edward Drinker Cope) states that organisms within a population evolve to become more massive over time. Although this increases each individual's fitness, it leaves the species more susceptible to extinction.

The Lilliput Effect (named by Adam Urbanek, 1993) notes the appearance of small body size in surviving animals after an extinction event. (The name Lilliput is from Jonathan Swift's novel Gulliver's Travels; in the novel, the Lilliputians were very tiny people.) Body size is determined by the amount of resources availabile to the species.




WHAT IS EXTINCTION?
CRETACEOUS ASTEROID THEORY
OTHER K-T EXTINCTION THEORIES
STUDYING EXTINCTIONS




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