Phylogeny describes the ancestral relationships between organisms. The connections often take the form of a tree called the Phylogenetic tree, with tips, branches, nodes —points where branches meet, and roots. The phylogenetic tree represents the pattern of descent and not physical characteristics. The tips of the tree generally represent extant or living taxa. The branches denote evolutionary changes between ancestors and descendants, such as a change in the DNA sequence or the evolution of a characteristic, like feathers. Species that share an immediate common ancestor —sister taxa, share nodes, like lizards and birds. These are each other's closest relatives. Rodents and humans can be another sister taxa. But, it would be wrong to assume that humans evolved from rodents or the other way around. The node, in this example, represents an extinct common ancestor that was not like a rodent or a human. A basal node corresponds to the most recent common ancestor of all organisms in the tree. The Metaspriggina in this case.