[Solved] An organ made primarily of nerve tissue is the ____________________, and the nerve cells are called ____________________. Rhyniophyta: An extinct group of early vascular plants from the Silurian and Devonian periods. Megafossils: Larger fossilized remains of organisms, such as bones or plant stems, that are easily visible to the naked eye and provide significant evidence of life from the past. Dichotomously Branched: A branching pattern where each branch divides into two parts at a certain point. Megaphylls: Leaves with a highly branched vascular system, characteristic of the majority of vascular plants, offering increased efficiency in photosynthesis.