FIG. 44.1 A simple phylogenetic tree of animals. The tree shows increasing complexity from the closest protistan relatives of animals, the choanoflagellates, to bilaterian animals such as insects and mammals.
Photo sources: (top to bottom) Mark Dayel (http://www.dayel.com/choanoflagellates) and Nicole King (http://kinglab.berkeley.edu); James D. Watt/SeaPics.com; UMI NO KAZE/a.collectionRF/Getty Images; British Antarctic Survey/Science Source.