Extinct animals are gone for good, but living species can sometimes tell us about the food chains that existed long ago.
Hawthorns are members of the rose family with thorns up to five inches long. Like the thorns of other roses, these long thorns evolved as protection against animals.
The theory that thorns keep plants from being eaten makes sense, except that all the animals living today that might eat the hawthorn such as deer and wild goats are small enough to reach between the big thorns. A moose might be deterred by the large thorns, but moose and hawthorns don't live in the same habitats.
In fact the hawthorn's protection isn't really effective against anything that the hawthorn has to worry about.
Why Grow Heavy Thorns?
To understand why a plant would grow such heavy thorns, we need to look back ten or fifteen thousand years to a time when mastodons, mammoths, ground sloths, tapirs, and peccaries browsed from trees and bushes all over North America.
Unlike today's smaller herbivores, these animals would have had trouble getting through the big thorns. So the thorns helped create an ecological balance between the plants and a large group of voracious herbivores. Some of the other plants whose thorns evolved in response to ancient herbivores include wild plums, wild crab apples, honey locust and black locust.
Most of these large herbivores became extinct about ten thousand years ago but the thorns that we see on plants today are living reminders of a whole range of animals that we now know only in fossil form.