The last two million years has seen several Ice Ages come and go.  The last ice age ended about 10,000 years ago.  Animals had to adapt to these colder conditions, or become extinct.  In turn, as the climate warmed, many animals could not survive the change.

Large mammals like mammoths and mastodons roamed the earth 15,000 years ago . Large cats, called sabre-toothed tigers, were also present.

As the climate warmed very rapidly, these animals slowly died out, although we can see some of their characteristics in modern day elephants and tigers.