Million of years ago the earth was once filled with gigantic creatures e.g. dinosaurs.?

Question

Why does evolution bring the giants into smaller size creatures?

Answer 1

It didnt actually happen this way. It isnt so much a question of evolution as it is a question os succession.
In the Cretaceous era, a large meteorite impacted the earth off the coast of Mexico (Yuccatan penninsula) This massive bolide impact would have caused devastating tsunamis and would have sent the entire globe into what is known as a nuclear winter (dust blocks the sun). The impact was so massive that it caused volcanoes to errupt in India, so you can only imagine the impact. The volcanoes that errupted in India would have increased the duration of the nuclear winters.
This phenomena would have killed off any of the large organisms on earth, in this case the dinosaurs. Because dinosaurs reigned supreme at this time, the mammals and small reptiles were not able to establish a foothold, simply because they were out competed and eaten by larger terrestrial predators i.e. Dinosaurs.
After many of the giant dinosaurs were wiped out by starvation and extreme fluctuations in temperature, mammals began coming out of the woodwork, small things like shrew-like mammals began to appear and establish. This sudden opening up of niches left behind by the dinosaurs created this evolutionary whirlwind, where there was great amounts of diversification and speciation among mammal and remaining reptile lineages (crocs, snakes, lizards etc)
The fossil record proves that this happened, looking back through the fossil record shows that all of a suddent here was a drastic hault to the age of dinosaurs soemthing happened within a very short time whihc put an end to them. Then as you go higher in the rock profile, mammals begin to appear, then more and more begin turning up.... This proves that once the mighty dinosaurs had fallen, the tiny mammals were right there to userp their title as dominant creatures on the planet.

I hope this answers your question.

Answer 2

Whatever killed the dinosaurs apparently left primarily small animals however in few million years these small animals grew into giants and moved into the niche of the dinosaurs. There was a "megafauna that occupied much of Eurasia and Americas that included mammoths and giant ground sloths. There are even some giants walking the earth today such as elephants.

Answer 3

The dinosaurs were wiped out rather quickly, there are a number of reasons to explain why, but the most common is that the earth was hit by an asteroid causing lots of dust in the atmosphere, this blocks out the light and reduces the plants that many of the dinasaurs fed on and also cooled the planet, and since Dinosaurs were reptile, they need a warm climate to survive.

Therefore, in this cooler climate, animals that can keep themselves warm (mammals) thrived, and eventually lead to humans.

For more info on exactly how evolution works see http://www.scienceaid.co.uk/biology/ecology/evolution.html

Answer 4

It is my understanding that an asteroid blasted into Earth, killing many at once, but the worst was that the ash cloud created a few years of overcast daylight that cooled the Earth's climate to the point that most plants died, including plants in the oceans. Even algae needs sunlight.

All the animals that ate those plants starved. All the animals that ate those animals starved. Most of the species on the Earth died. Especially the ones that needed lots of food... the giants.

The smaller ones, especially the ones who could live on roots and seeds, survived and by constant sexual selection, and the occasional mutation, have breed themselves into the animals that we see today.

Have you seen pictures of the African Pygmies? [1] Of the Tallest man? [2] Of the Sumo Wrestlers? [3] Of the Miao people in China? [4] Of UNHCR Goodwill Ambassador Angelina Jolie? [5]

;-D This is all accomplished by breeding.

Answer 5

The animals that survived were already small. The mass extinction presumably happened too fast to allow animals to adapt much.

At other times, the disadvantage of being big was more modest and did allow the large anomals to adapt. There are many examples of species that have become smaller after they colonized small islands where the food resources are limited.

Answer 6

When the environment is harsh, there isn't enough resource to support large bodies. Therefore, larger animals becomes extinct.

That's why there is so many supports on drastic change of the environment that leads to the massive extinction of dinosaurs.

Answer 7

Well first off to start, I don't believe in the theory of Evolution, but the way the proccess of Evolution is supposed to work is by making smaller creatures(let's say a lizard)grow into size by the pass of time and Ancestry.

In biology, evolution is the change in the heritable traits of a population over successive generations, as determined by shifts in the allele frequencies of genes. Through the course of time, this process results in the origin of new species from existing ones (speciation). All contemporary organisms are related to each other through common descent, the products of cumulative evolutionary changes over billions of years. Evolution is the source of the vast diversity of extant and extinct life on Earth.

The modern understanding of evolution is based on the theory of natural selection, which was first set out in a joint 1858 paper by Charles Darwin and Alfred Russel Wallace and popularized in Darwin's 1859 book The Origin of Species. In the 1930s, Darwinian natural selection was combined with the theory of Mendelian heredity to form the modern evolutionary synthesis, also known as "Neo-Darwinism". The modern synthesis describes evolution as a change in the allele frequency within a population from one generation to the next.

Did that help?

Answer 8

Because as they're environment changed they had to evolve into smaller animals to survive.

Answer 9

smaller creatures can adapt more quickly to changing environments

Answer 10

Conspiracy nailed it.