25.2 Part II. The Cladogram of Animals

The Cladogram of animals The features of animal body plans provide information for building a cladogram of animals The animal cladogram presents our current understanding of relationships among the animal phyla Animals are defined by the adult body plans and patterns of embryological development

The blue boxes represent important traits that have evolved over time

Difference Between Phyla The animal cladogram represents the sequence in which important body plan features evolved Every phylum has a unique combination of ancient traits inherited from its ancestors and new traits found only in that particular phylum Remember just because an animal has a more complicated body system does not mean it can function better than an animal with a more simple body system Any system found in living animals are able to function well enough to enable those animals to survive and reproduce Example: Monkey brains are much more complicated than a fish brain, but fish brains work well enough to enable fish to survive

Changes within Phyla: Themes and Variations Within each phylum different groups represent different variations on the basic body plan themes that have evolved over time For example: Both wings and arms evolved through changes in the standard vertebrate forelimb Many land vertebrates typically have four limbs In birds the front limbs have evolved into wings In primates the front limbs have evolved into arms

Evolutionary Experiments Each phylum’s body plan can be viewed as an evolutionary experiment in which a particular set of body structures perform essential functions Fossil records of each phylum marks the beginning of the experiment The very first versions of most major body plans were developed hundreds of millions of years ago Ever since a phylum’s body plan was first developed each phylum’s evolutionary history has shown variations in its body plan to adapt to changing environments If the variation in body plan allowed the phylum to reproduce and survive than the phylum still exists If the variation in body plan hasn’t functioned well enough over time then the phylum or particular groups within the phylum become EXTINCT