Ferns are hardy and adaptable, far more ancient than dinosaurs, flowering plants, or true trees. There are about 12,000 species, in a primordial, spore-producing (similar to fungi) plant division: Pteridophyta, which is separate from all other plants with "normal" seeds and fruit.
They have a distinct two-stage life story. A fern's spore first develops into a small, flat, moss-like plant called a gametophyte, which reproduces sexually with neighbouring gametophytes.
That union "gives birth" to a second, physically separate plant: the adult phase with the fronds that we all know and love, known as the sporophyte.
The adult fern does not reproduce sexually: it makes spores by itself, which waft off through the air to land, and grow into a new gametophyte.
The oldest fern fossil is from the mid-Devonian period, some 383-393 million years ago (Carboniferous Period), so the first ferns must be even older than that! The specific ferns that were familiar to dinosaurs are extinct, but their diverse descendants are found almost everywhere on Earth.
Victorian era women were so effective at getting their husbands to build enchanting fern grottos for their gardens that the word Pteridomania, "Fern Fever", was coined by Charles Kingsley, author of The Water Babies, in his 1855 tome Glaucus.
Pteridomania came hot on the heels of Orchidelirium, and art historians can trace those trends in depictions of ferns and orchids on all manner of objects made throughout the 1800's. The original 1908 Custard Cream biscuit design used a fern pattern, harking back to that era.
Fearn is the old English word for fern, and may be connected to feather. The Latin word for fern is filix, and the old word for the study of ferns specifically was Filicology: these days the standard umbrella term is Pteridology, which includes all related fern-like plants such as Horsetail.