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March 4, 2010

Evolution and Dinosaur Extinction

TECHNOLOGY - There are some bizarre myths (we might even call them scientific urban legends) about dinosaurs. The biggest of these is the idea that all the dinosaurs died off at the same time.

This is actually not true however. The dinosaurs died off in various stages, in a similar way cro-magnon man died off in different stages, replaced by a more superior biped.

The Cretaceous period included such beasties as the infamous T-Rex, pterosaurs and avian dinosaurs (early birds). The Cretaceous period didn't suddenly end either, it wound down slowly with creatures (both land and marine life) dying off slowly because of some kind of ecological crisis.

The chart below shows the extinction rates over millions of years of marine life (which dwarfs life on land and it should be noted most dinosaurs were either marine reptiles or amphibian). You will note the biggest stages of extinction were at the ends of the Cambrian, Ordovician, Permian, Triassic and Cretaceous periods.

Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Triassic
Jurassic
Cretaceous
Paleogene
Neogene


What we see in the chart is that extinctions tend to be periodic, with the rate of extinctions rising until they reach a pinnacle and then there is a sudden drop off (mass extinction). These cycles can easily be explained by evolutionary and ecological shifts.

1. Predators: If one group of predators becomes too efficient at killing off creatures the other species must either adapt or be eaten. A more efficient killing machine need not be big either, it could be smaller but hunt in packs, or it could be microscopic like an influenza virus. It doesn't have to be a single type of predator either, but the evolutionary change of many types of predators. When other predators gain dominance the ones that can't keep up die off pretty quickly. (This can be seen in modern demonstrations such as the re-introduction of wolves to Yellowstone National Park in 1995, causing foxes to vacate the area which allowed more food for bears and other wildlife. The wolves ultimately restored ecological balance to the park.)

2. Ecological Change: The Earth goes through periodic hot and cold cycles. This may / may not be brought on by comets, meteors, ice ages, increased/decreased solar radiation, earthquakes, flooding, climate change or any number of reasons which might destroy the local habitat.

A recent review by 41 scientists reasserted the idea that a giant asteroid may have killed off the dinosaurs at the end of Cretaceous period... but it should be noted that if you look at the chart they were already dying off anyway.

During such mass extinctions only the creatures with some kind of evolutionary advantage managed to stay alive. Examples:

Turtles : Hard shell for defense.

Komodo Dragon : Poisonous to the touch.

Alligators / Crocodiles : Semi-Aquatic, able to sneak up on prey easily.

Birds / Small Reptiles : Their size and ability to hide / fly gave them a distinct advantage.

So were some of the dinosaurs killed off by some kind of ecological event or asteroid? Probably. But evolution killed off most of them and it did it gradually over a period of 200 million years.

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