1. They were wiped out when an asteroid hit the earth.
   There was a significant increase in the earth's temperature, making it very difficult for most life forms to survive on earth.
2. There was a flu epidemic which wiped out the dinosaur population.

The prevailing theory is that they were wiped out when an asteroid hit the earth's surface around the area that is now Mexico.

1. Jurassic-Tertiary Mass Extinction event
   Cretaceous Mass Extinction event
2. Cretaceous-Tertiary Mass Extinction event

The mass extinction of dinosaurs is known as the Cretaceous-Tertiary Mass Extinction event, or the KT event for short. It wiped out 70 percent of life on the planet.

1. Tryannosaurus-rex
   pterosaurs
2. mosasaurs

Pterosaurs, the first vertebrae who learned to fly by flapping their wings, became extinct along with dinosaurs. So did a lot of aquatic life and algae.

1. reptiles
   amphibians
2. birds

A commonly held scientific theory is that surviving dinosaurs evolved into birds.

1. 12 percent
   68 percent
2. 84 percent

Scientists think that a few members of 84 percent of marine families survived the extinction, as did a few members of 82 percent of land vertebrates.

1. volcanoes
   disease
2. drought and famine

Some theorists claim that widespread volcanic eruptions also added to the unlivable conditions that caused the extinction of the dinosaur population.

1. Triassic
   Jurassic
2. Cretaceous

Dinosaurs lived during the Mesozoic era of the earth's history, which is divided into three periods: the Triassic, Jurassic and Cretaceous. They became extinct at the end of the Cretaceous period.

1. Precambrian Time
   Cenozoic era
2. Paleozoic era

The age of mammals, which followed the Cretaceous period, is called the Cenozoic era.

1. They preyed on dinosaur eggs.
   They contaminated the water sources.
2. They competed with the dinosaurs for food.

A past theory said that mammals consumed the dinosaur's eggs, thus causing them to become extinct.

1. two
   three
2. four

Monotremes were the first mammals, unusual because they laid eggs instead of giving birth to live young. Today, there are three monotreme species: the platypus and two types of echidnas.

1. Australia
   South Africa
2. New Zealand

The sphenodontians were prehistoric reptiles who lived at the same time as dinosaurs. Today, there is one remaining species of sphenodontian, the tuatara, whose home is in New Zealand.

1. crocodilian
   reptilian humanoid
2. amphibian

Alligators belong to the crocodilian species, which was around at the time of the dinosaurs.

1. three
   six
2. nine

Three main types of amphibians survived the extinction of the dinosaurs: caecilians, frogs and toads, and newts and salamanders.

1. cedar trees
   palm trees
2. ferns and conifers

Ferns and conifers existed during the Mesozoic era. In fact, there was a massive spike in their numbers just after the mass extinction.

1. tear drop shaped leaves
   fan shaped leaves
2. round leaves

Today's Gingko biloba plant, with it's fan-shaped leaves, is almost identical to its prehistoric ancestor.

1. angiosperm
   floralin
2. sow pomum

The scientific name for a flowering plant is angiosperm. They began to develop during the Cretaceous period, the dinosaur's final era, but survived the mass extinction.

1. monkeys
   birds
2. insects

Insects existed before the Mesozoic period. They probably developed in conjunction with flowering plants.

1. the Loch Ness monster
   dolphins
2. snakes

Ichthyosaurs, a marine animal that died in the mass extinction, looked like a modern day dolphin.

1. whales
   dolphins
2. sharks

Sharks, apparently, inhabited the earth's surface even before dinosaurs.

1. hagfish and lampreys
   shellfish
2. octopus

Hagfish and lampreys, sea creatures without jaws, bear a strong resemblance to the now extinct ostracoderms.