Cretaceous-Tertiary extinction event

The Cretaceous-Tertiary (K-T or KT) extinction event, also known as the KT boundary, was a period of massive extinction of species, about 65.5 million years ago. It corresponds to the end of the Cretaceous Period and the beginning of the Tertiary Period. (K is the traditional abbreviation for the Cretaceous period. Cretaceous comes from the Latin for chalk, creta. The K comes from the German word for chalk kreide, or possible Greek kreta. The K is used so as to avoid confusion with the Carboniferous period which uses the letter C.)

Casualties of the extinction

A wide range of organisms became extinct at the end of the Cretaceous period. The most conspicuous, of course, were the dinosaurs. While there is evidence that dinosaur diversity declined in the Late Cretaceous of North America, many species are known from the Hell Creek and Lance Formations of the Late Cretaceous. These include six or seven families of theropods and a similar number of ornithischians. Among the Dinosauria, the only survivors were the birds, but birds suffered heavy losses. A number of diverse groups became extinct, including the Enantiornithes and Hesperornithiformes; the last of the pterosaurs also went extinct. A number of mammal groups also became extinct. In the sea, many species of phytoplankton were wiped out. The great sea reptiles of the Cretaceous, the mosasaurs and plesiosaurs, also fell victim to extinction. Among molluscs, the ammonites, a diverse group of coiled cephalopods, were exterminated, as were the specialized rudist and inoceramid clams. Freshwater mussels and snails also suffered heavy losses in North America. Much less is known about how the K-T event affected the rest of the world. It should be emphasized that the survival of a group does not mean that the group was unaffected: a species might have been 99% annihilated by the asteroid strike, yet still manage to survive.

Related Topics:
Theropods - Ornithischians - Bird - Enantiornithes - Hesperornithiformes - Mosasaurs - Plesiosaurs - Mollusc

~ ~ ~ ~ ~ ~ ~ ~ ~ ~