Animal Diversity

Besides their names, what do horses, and seahorses, have in common? Although they look vastly different, they are both animals. Generally, we define animals as multicellular organisms that are motile, meaning capable of independent motion, consume organic matter for energy, and are capable of sexual reproduction. Species have evolved their different traits with specific functions to maximize their fitness in their habitats like lungs and gills for example. A good rule of thumb is that form follows function, meaning that the function of a feature can be predicted by its structure and appearance. For example, different finch species in the Galapagos Islands have evolved different beaks for specific diets like thin beaks to consume nectar and thick beaks to crack open large seeds. Thus, we can predict the diets of a species by observing structures involved with feeding.

Certain features mark branching points on the evolutionary tree and this is true all the way up throughout the whole tree of animal life. If we look at the basic structure of the evolutionary tree of animals, we can see that it is split into many different phyla with each phylum defined by major shared characteristics.