Phylogenies

Regarding the carnivorans, the character #6, tail, has two character states. In this phylogenetic analysis, an elongated tail is the ancestral character state (scored with a 0) and a short tail is the derived character state (scored with a 1). In phylogeny A, a short tail is hypothesized to have evolved after the split between otters and the group of bears, sea lions, walrus, and seals. This proposes that a short tail is the synapomorphy for the monophyletic group of bears, sea lions, walrus, and seals. In phylogeny B, a short tail is hypothesized to have evolved twice. This is an example of homoplasy. For example, a short tail here is a derived trait for the seals, but it is also a shared derived trait for bears, sea lions, and walrus. However, there are a few separate divergences between seals and this group, and the common ancestor is hypothesized to have an elongated tail. In phylogeny C, a short tail is hypothesized to have evolved twice as well, but then lost in one lineage branch. For example, a short tail is a derived trait for the bears, but it also initially evolved as a shared derived trait for the sea lions, walrus, seals, civets, hyenas, and cats taxa. Cats, hyenas, and civets then lost this short tail trait. This is an example of an evolutionary reversal. In phylogeny D, a short tail evolved once in the lineage to include its monophyletic group branching from seals to dogs, but then this trait was lost later in the phylogeny in otters, raccoons, and dogs. This is another example of an evolutionary reversal. Based on this trait and the parsimony principle, phylogeny A is the most likely. The parsimony principle guides us to the evolutionary tree with the fewest character-state changes, and this is the one usually regarded as the best. In phylogeny A, the tail trait only evolved once in the lineage and was not lost at any point.