https://livingzoology.com/ by Matej Dolinay and Zuzana Dolinay
The North America was once an uninhabited wilderness where huge herds of big animals roamed. It was only about 15 thousand years ago when the Colombian mamooths, bisons, sabretooth cats and giant ground sloths lived here. After that, the climate change and human hunters caused the extinction of most of the big mammals. Only a few species survived in the harsh deserts of Southwestern USA and Northern Mexico until recent days. Today the deserts are not shaking under the hoofs of thousands of herbivores, but some animals which lived in that age are still present here. It is estimated that around 25 million years ago one particular group of vipers started to thrive in North America and they still dominate this continent. The rattlesnakes. After millions of years of evolution they attained body structures which allowed them to become the most successful venomous snakes in this part of the world.