1.8:
Phylogeny
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.
1.8:
Phylogeny
Phylogeny is concerned with the evolutionary diversification of organisms or groups of organisms. A group of organisms with a name is called a taxon (singular). Taxa (plural) can span different levels of the evolutionary hierarchy. For instance, the group containing all birds is a taxon (comprising the class Aves), and the group of all species of daisies (the genus Bellis) is a taxon. Phylogenies can likewise include just one genus (i.e., depict species relationships) or span an entire kingdom.
Typically, phylogeny is represented by a tree called a phylogenetic tree. It is a branching diagram that shows the evolutionary relationship between different organisms, with the most closely related species being grouped together. Each taxon of interest is depicted at the tip of the branch, and the branches represent the relationship between these taxa. Closely related taxa share a larger portion of their genome, resulting in morphological similarities. Sister taxa share an immediate common ancestor, represented by a shared node.
Nodes in the tree depict a morphological characteristic or molecular change that differentiates taxa. All taxa that directly connect to a specific node share a recent common ancestor. Hence, the root of the tree is the ancestor shared by all taxa in the tree. A lineage that evolved early from the root and remained unbranched is called a basal taxon. A tree without a root represents the relationship of taxa but does not provide information on the shared common ancestor.
The length of the branches of a tree may or may not have a meaning. In a scaled tree, the length of the branch may either represent time or the number of changes that occurred since the taxa evolved from a common ancestor.