The other groups mentioned are, like dinosaurs and pterosaurs, members of Sauropsida the reptile and bird cladewith the exception of Dimetrodon which is a synapsid. Definition Triceratops skeleton, Natural History Museum of Los Angeles County Under phylogenetic nomenclaturedinosaurs are usually defined as the group consisting of the most recent common ancestor MRCA of Triceratops and Neornithesand all its descendants.
Extinction of Dinosaurs Extinction of Dinosaurs Two-hundred and thirty million years ago the first dinosaur-like creature roamed the earth. Dinosaurs were a very successful and diverse group, dominating the terrestrial environments of the earth for million years.
The apparently sudden mass extinction of dinosaurs marks the boundary between the Cretaceous and Tertiary periods. The theories that explain their extinction at the end of the Cretaceous period are the asteroid, the volcanoes, and the major climatic changes.
The most popular "disaster theory" for the extinction of the dinosaurs is that the Earth was hit by an asteroid or a comet 65 million years ago. An asteroid called Chicxulub hit the earth creating a mile wide crater near the Yucatan Peninsula in Mexico.
The asteroid is thought to have weighed 4 million tons. When it hit the Earth it would have formed a crater 60 to 90 miles to km wide. The asteroid would have exploded deep down in the crater and shot out up to trillion tons of rock and dust.
The dust would have blocked the light from the sun. The asteroid might also have heated the air and produced acid rain.
The effects of this kind of impact would have killed off many forms of life. However, no crater of the right size and age has been found. The best evidence for the asteroid is found in the sedimentary rocks at the very end of the Craterous.
In several places around the world, at exactly 65 million years age, geologists have found large amounts of the metal iridium in clay bands. Iridium is a rare metal that comes only from space.
We normally find only very small amounts, which come from the tiny meteorites that land on earth all the time. But there are very large amounts of iridium at the time the dinosaurs died out. Many scientists believe this is good evidence for an asteroid, but the case is not proved.
The Deccan Traps was a massive volcanic eruption that took place just about the time the dinosaurs died. So much lava was spewed in this eruption that the Himalayan Mountains were formed.
Also, enough ash could have been thrown up into the atmosphere in this eruption, that the sun would have been blocked out, killing the dinosaurs, some plants and other animals.
Over a time span of several million years, the volcanic activity could have possibly created enough dust and dirt to prevent sunlight exposure which produced drastic climatic changes.Dinosaur Extinction for Kids How Did Dinosaurs Become Extinct?
Want to know more information about dinosaur extinction? We ask "How did dinosaurs become extinct?".
Mar 24, · Watch video · The Cretaceous-Tertiary extinction event, or the K-T event, is the name given to the die-off of the dinosaurs and other species that took place some million years ago.
The extinction wiped out the dinosaurs while most mammals, turtles, crocodiles, salamanders, and frogs survived. Birds escaped. So did snails, bivalves, sea stars (starfish), and sea urchins. 2. Investigating the different “kill mechanisms” in place, such as the type of material released into the atmosphere, that may have caused the extinction of the dinosaurs.
3. This is an artist’s representation of what may have killed the dinosaurs – although he took some license in representing species that were not all alive at the same time. That has made the identity of the dinosaurs’ true killer — an impact, volcanism or both — less clear, says Paul Renne. He is a geoscientist at the Berkeley Geochronology Center in California.
He is a geoscientist at the Berkeley Geochronology Center in California.