Extinction of the Dinosaurs

The last of the non-avian dinosaurs, primitive birds, pterosaurs, all marine reptiles except turtles, and ammonites became extinct about 65.5 million years ago, at a point in time that geologists call the K-T extinction. The name of the extinction signifies a division in time between the Cretaceous (kreta in Latin) and Tertiary, or Neogene, Periods. The K-T event was a mass extinction, wiping out at least 50 percent of all animal life alive at the time. Even those groups of organisms that survived, including plants, insects, other invertebrates, fishes, frogs, salamanders, turtles, lizards, crocodiles, birds, and mammals, lost great numbers of species. Extinction is a natural occurrence: the irreversible elimination of an entire species of organism. Once it occurs, there is no turning back. It is happening all of the time. More than 99.9 percent of all the species of organisms that have ever lived are now extinct.

Chief among the causes of extinction are environmental changes that affect the food supply or body chemistry of organisms, disease, and natural disasters (such as volcanic eruptions, earthquakes, and the changing surface of the Earth).

Evidence has been mounting that the great K-T extinction was caused by the collision of a large asteroid with the Earth. Debris thrown into the atmosphere from such a collision could have blackened the skies and poisoned the air for many months, maybe even years. If the poisoning affected oceanic ecosystems, it might have led to the demise of the mosasaurs and other remaining marine reptiles. Plankton forms the base of most oceanic food chains, and

The extinction of the dinosaurs possibly was capped by the collision of Earth with a giant asteroid.

we know that much of it was wiped-out by the K-T extinction event. Many of the creatures that predatory marine reptiles would have fed upon were probably plankton eaters. So, the demise of plankton would have led to demise of plankton eaters, and eventually marine reptiles would have nothing left to eat but themselves.

The K-T extinction brought an end to the great era of reptiles and ushered in a new age during which mammals would soon rise to dominate environments all over the Earth. The great clades of marine reptiles arose and diminished during different times of the Mesozoic. Several of them, such as ichthyosaurs, had already come and gone by the end of the Cretaceous Period.

The Rise of Mammals will explore the rapid diversification and radiation of the mammals following the extinction of the non-avian dinosaurs.

Dinosaurs Human

Invertebrates Fishes Land Plants Amphibians Reptiles Mammals & Birds Ancestors

0 65.5 100 150 200 250 300 350 400 450 500 542

NEOGENE

CENOZOIC

PALEOGENE

p

M E

CRETACEOUS

H

S

A N

z o

JURASSIC

I

E

c

TRIASSIC

R

p

PERMIAN

O

A

CARBON

Z

L

IFEROUS

E O

O

DEVONIAN

I

Z

SILURIAN

C

O

ORDOVICIAN

I

C

CAMBRIAN

Proterozoic

Precambrian

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