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How many species of dinosaurs were living at the end of the Cretaceous period?

No one knows the exact number of dinosaur species living before the end of the Cretaceous period, as we do not have a complete dinosaur fossil record. The nature of fossilization or that not all animals were in the right place at the right time in order to become a fossil and the process of erosion have wiped away much of the evidence over time. Although scientists know there were probably many more dinosaurs, only a few species were still alive toward the end of the Cretaceous period, and most of them lived on the North American continent.

How many other organisms became extinct at the end of the Cretaceous period?

No one knows the exact number of other organisms land animals, marine animals, and plants that became extinct at the end of the Cretaceous period. But based on the fossil record, scientists believe that about 85 percent of all species on Earth went extinct at the end of the Cretaceous period, thought to be the second largest extinction (the Permian was first).

What were some other organisms besides dinosaurs that became extinct at the end of the Cretaceous period?

There are many other animals that became extinct at the end of the Cretaceous period. They include the flying pterosaurs and many types of ammonids, marine reptiles, redist bivalves, brachiopods, mollusks, and fish.

What animals didnt experience as many extinctions?

There were several animal groups that did not experience as many extinctions among species. They included most mammals, birds, turtles, crocodiles, lizards, snakes, and amphibians.

What plants became extinct at the end of the Cretaceous period?

Many species of plants became extinct at the end of the Cretaceous period, but few among the ferns and seed-producing plants. In North America alone, almost 60 percent of plant species became extinct.

Why did certain plants and animals survive through the end of the Cretaceous period?

Until a definite reason for the extinction is determined, it is difficult to answer such a question as why some animals and plants survived. Apparently, some species were not affected by the occurrence. In fact, nocturnal mammals probably through luck or inborn tolerance to harsh environmental conditions largely survived. They quickly exploited all the new places available to them, and soon dominated the planet. Eventually, over millions of years, humans evolved from those species.

Can scientists see the Cretaceous boundary in rock?

Yes, there are rock deposits all over the world that show the characteristic mineral signature that represents the Cretaceous boundary. Because they are found all over the globe, scientists know that no species was unaffected by whatever events occurred to create the mass extinction at the end of the Cretaceous period.

Why arent huge amounts of dinosaur bones found in late Cretaceous period rock layers?

This is another mystery surrounding the whole question of dinosaur extinction at the end of the Cretaceous. If indeed the dinosaurs were suddenly killed off by a catastrophe, there should be a thick layer of bones or a bone spike in the fossil record. However, no such bone spike has been found to date at the boundary between the Cretaceous and Tertiary periods. Equally puzzling, few dinosaur bones have been found within a foot or so below this boundary.

One possible theory to explain these missing dinosaur bones (if they truly are missing) involves acid rain. Models have shown that one consequence of a large asteroid impact would be highly acidic rainfall over the planet. This acidic water could have dissolved most of the dinosaur bones lying on the surface, and would have also penetrated below the surface into the upper soil zones. Combined with bacteria, the water would become even more acidic, dissolving any bones found there. Only already fossilized bones would have resisted the acidic water. Since the fossilization process takes a very long time, none of the more recent dinosaur bones would have been spared.

This theory and it is only a theory at present neatly explains why there are so few dinosaur bones found in rock below the boundary, and none at the boundary itself. Supporting evidence comes from the boundary layer: in many places around the world, a relatively thin layer of clay exists that could have formed from the erosion of rocks due to acid rain.

What bone spike was found in Late Cretaceous period rock layers?

A Late Cretaceous bone spike, the thick layer of bones found in the fossil record around the time of a catastrophic extinction, has not been found until recently. A large bed of fossil fish bones from this time has been discovered on Seymour Island, Antarctica, covering more than 31 square miles (50 square kilometers). Although there is a possibility that the fish were killed off by volcanic activity, climate change, or some other environmental cause, their bones lie immediately above the iridium rich layer that marks the end of the Cretaceous period. In other words, its highly likely that the fish were victims of the catastrophic extinction that also affected the dinosaurs.

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