They were plants that preferred a warm temperature and couldn't survive in a cold one.
They discovered these plant fossils in Svalbard, Norway, which was once home to a forest. They were thought to have originated in a tropical jungle that was close to the equator. However, these fossils were discovered in the north, where the environment prevented their growth. This demonstrated that these trees were transported by continental drift to the northern, colder region that is now Norway.
