The holdfasts of giant kelp (Macrocystis pyrifera) have been found preserved in sedimentary rocks from the Eocene epoch, approximately 55 million years ago. This indicates that giant kelp, a large brown algae, existed far before any of the terrestrial animals commonly associated with forests were present. The fossil record indicates that kelp existed before mammals, flowering plants, birds, and even certain insect species that play significant roles in forest dynamics. Giant kelp forests formed underwater ecosystems and served as habitats for marine organisms long before the emergence of modern forests on land. They persisted alongside changes in sea level, shifts in global temperatures, and various fluctuations in Earth's ecosystems throughout history.