What are Basal Vertebrates?
A “basal” vertebrate means a vertebrate at the base of the vertebrate family tree, either one of the vertebrates from which all others evolved or a close cousin of the same. Some basal vertebrates are stem group vertebrates, meaning they are older than the earliest common ancestor of all living vertebrate species. Vertebrates, like all other animal phyla, are extremely old. The first basal vertebrate fossil is likely Yunnanozoon lividum, which lived 530 million years ago in what is now China, although some researchers disagree, calling the species a hemichordate rather than a real chordate (vertebrate). Another basal vertebrate, Pikaia gracilens, resembles a modern lancelet. A third basal vertebrate, Myllokunmingia, is a primitive fish and one of the earliest vertebrates. Depending on the article, web page, or paper, each is sometimes referred to as the oldest vertebrate. It is a mystery as to how basal vertebrates initially evolved. There is a general consensus that a spinal column is