Dinosaurs

there where many resons

here are all the resons

Comet and cosmic rays killed the dinosaursThe theory: A massive comet travels close to Earth every 26 million years, bringing with it radioactive debris that collides with our planet, disrupting weather patterns and wiping out entire species, just as it did the dinosaurs some 65 million years ago. How likely? We have no concrete evidence of extraterrestrial events occurring at the point of dinosaur extinction. Furthermore, dinosaur remains show no evidence of radiation damage. An asteroid impact killed the dinosaursThe theory: A large asteroid struck Mexico, forming a 240 kilometre wide crater. Resulting debris created a deposit of white powder in the atmosphere. This 'nuclear winter' blocked out the sun, killed plants, then plant-eaters and, finally, meat-eaters. How likely? Those dismissing the theory claim that smaller reptiles like turtles, alligators and crocodiles would also have been harmed; others argue the crater simply wasn't large enough to have caused such devastation. Volcanos killed the dinosaursThe theory: Western India saw huge volcanic eruptions which unleashed enormous quantities of lava, blocking out the sun, causing widespread climatic change and wiping out the dinosaurs. How likely? Deadly iridium in the Earth's 'K-T boundary' could conceivably have been caused by lava eruptions. However, scientists have widely agreed that 65 million years ago there was a global fall in temperature; a volcanic eruption would have had the opposite effect. An ice age killed the dinosaursThe theory: Ice ages have occurred throughout Earth's history, with the last one ending about 10,000 years ago. A very severe ice age altered climates and froze waters to the extent that dinosaurs were unable to weather the conditions, and slowly died out. How likely? This theory has been largely discarded for one simple reason: scientists have not found a single scrap of evidence of an ice age occurring during the life of the dinosaurs. Hay fever killed the dinosaursThe theory: Flowering plants known as angiosperms arose around 65 million years ago, creating a mass allergic reaction among dinosaurs. How likely: Not very! Flowering plants were around for millions of years before the dinosaurs disappeared and we have no evidence whatsoever that their pollen was capable of killing the dinosaurs. Plus this wouldn't explain the massive marine extinction - there have never been any marine angiosperms. Obesity killed the dinosaursThe theory: The dinosaurs got too big and heavy, so much so they couldn't move about, defend themselves or withstand their own weight! How likely? There is absolutely no evidence to suggest the dinosaurs became so large and cumbersome that they couldn't move. Simply put, it is an evolutionary impossibility. Besides, most dinosaurs around by the end of the Cretaceous period were of medium or small size. Mammals killed the dinosaursThe theory: The ecosystems of Earth 65 million years ago were such that mammals were out-competing the dinosaurs for food and space. How likely? Evidence points to a simultaneous evolution in dinosaurs and mammals, and some believe mammals did eat dinosaur eggs. But it's unlikely that mammals and dinosaurs had similar diets, so competition wouldn't have occurred. And there were no marine mammals at the time, so they couldn't have wiped out marine reptiles. Disease killed the dinosaursThe theory: Towards the end of the Cretaceous period, land bridges opened up between places such as Asia and North America, allowing species to migrate. This led to a spread of disease to which other animals were not resistant. How likely? It could happen - Native Americans were nearly wiped out by smallpox, while the European invaders were resistant. But this argument fails to explain the disappearance of a multitude of species that lived in the sea. Climate change killed the dinosaursThe theory: Earth gradually changed in climate over a long time period and the dinosaurs were not able to adapt to the cooler, drier climate. How likely? Climate change could have come about because Earth somehow tilted over about 23.5 degrees around 65 million years ago. How likely? Tilting could have occurred but what could have caused it. Asteroid impact? Debris from a passing comet? Scientists have never been able to answer this question. Nothing killed the dinosaurs!The theory: Dinosaurs were not wiped out, they evolved into birds. There were certainly feathered dinosaurs and early birds resembled small meat-eating dinosaurs. Could it be that dinosaurs still walk - or fly - among us? Most scientists agree there is considerable evidence for many species of carnivorous theropod dinosaurs such as Velociraptor evolving into birds. But not all dinosaurs evolved into birds; Tyrannosaurus Rex died out with no evolutionary trace.

It's doubtful any dinosaurs could swim very well. The reason is that there legs are positioned to carry their weight efficiently against gravity, by being directly beneath their bodies. Swimming creatures which have four limbs tend to have them more off to the sides. It's possible, though, that some dinos whose diets consisted of mostly fish (like Baronyx) were able to negotiate short stretches of water.

The great swimming reptiles, like pliosaurs and icthyosaurs, were NOT dinosaurs.

Actually, there is evidence that at least two species of Hadrosaurs were fairly good swimmers - their fossils show carbon impressions indicating they had webbed feet.