Phylogeny describes the ancestral relationships between organisms. The connections often take the form of a tree, with tips, branches, nodes, and roots, called the phylogenetic tree.
Specifically, the tips of the tree represent extant—or living—taxa, and the branches denote evolutionary changes between ancestors and descendants, such as the change in the DNA sequence or the evolution of a characteristic like feathers.
Species that share an immediate common ancestor, sister taxa, are their closest relatives and share nodes—points where branches meet, like lizards and birds, and rodents and humans. A basal node, the root, corresponds to the most recent common ancestor of all organisms in the tree, the Metaspriggina in this case.