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DINOSAUR CONNECTIONS

AFTERMATH OF EXTINCTION

What is the Cretaceous/Tertiary boundary and what does it indicate about the extinction at the end of the Cretaceous period?

The mass extinction at the end of the Cretaceous period is evident in the Cretaceous/Tertiary (K/T) boundary, a thin layer of rock found in various areas around the world all dominated by a large amount of iridium, a chemical element found in abundance in comets and asteroids but rare on Earth. It was this K/T boundary that first clued scientists in to the fact that there was a mass extinction about 65 million years ago. According to this layer and other evidence in the fossil record, mass extinctions of animals and plants in both oceans and on land occurred around the same time.

What groups survived the extinction at the end of the Cretaceous period?

The survivors include most land plants and land animals insects, snails, frogs, salamanders, crocodiles, lizards, snakes, turtles, and certain mammals. Most marine invertebrates also survived, including starfishes, sea urchins, mollusks, arthropods, and most fishes.

What was a common characteristic of the surviving land animals?

The land animals that survived were all small in stature, such as mammals, frogs, and snakes. The larger animals, such as the dinosaurs, did not survive this extinction. In fact, some scientists estimate that no animal heavier than 55 pounds (25 kilograms) survived on land.

What groups did not survive the extinction at the end of the Cretaceous period?

The groups that did not survive the massive extinction include the dinosaurs, pterosaurs, and some families of birds and marsupial mammals on land. In the oceans, mosasaurs, plesiosaurs, some families of teleost fishes, ammonites, belemnites, rudist, trigoniid, and inoceramid bivalves became extinct, as well as over half the oceans various plankton groups. Some groups appear to have vanished completely at the end of the Cretaceous period, whereas others were already gradually diminishing in diversity in the last 10 million years of the Cretaceous period.

How did the end of the Cretaceous period rank among Earths extinctions?

The mass extinction at the end of the Cretaceous period was the second largest in geologic history; around 76 percent of all species disappeared. The largest mass extinction was at the end of the Permian period, about 250 million years ago, in which about 90 to 97 percent of all species disappeared.

What types of plants did not disappear at the end of the Cretaceous period?

Although many species of plants disappeared at the end of the Cretaceous period, many ferns and seed-producing plants continued to survive into modern time.

What percentage of marine animals went extinct at the end of the Cretaceous period?

The marine biota was hit very hard by the Cretaceous extinctions. About 15 percent of all marine families died out, as well as perhaps 80 to 90 percent of all species. Here are some examples of the approximate percentage of certain groups that went extinct:

Ammonites 100%

Marine reptiles 93%

Planktonic foraminifera 83%

Sponges 69%

Corals 65%

Sea urchins 54%

Ostracodes 50%

All of the flying pterosaur species, like this Quetzalcoatlus, became extinct at the end of the Cretaceous (Big Stock Photo).

What percentage of land animals went extinct at the end of the Cretaceous period?

At the end of the Cretaceous period, many land animals became extinct. For example, about 25 percent of all land animal families disappeared. About 56 percent of the reptiles in general died out, and 100 percent of all non-avian (bird) dinosaurs and pterosaurs became extinct.

 
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