Homologous and Analogous Traits

Homologous Traits (Examples of Divergent Evolution)

The Irrawaddy dolphin has a tail, a trait that is shared by many mammals and all cetaceans, the effect of having a common ancestor. Muscles in the dolphin's back move its tail to propel the animal through the water. Dolphins can also use their tales to express their emotion. Certain other animals, like the Micromys minutus, have a prehensile tail which they can use to climb. This trait of a tail has been adapted to serve very disparate purposes.

The Irrawaddy dolphin's flippers are adapted from the hands that many mammals also share. The Irrawaddy dolphin uses its flippers to direct its movement. The same bone structure is shared by bats, flying mammals in the order Chiroptera. While the trait for them was inherited from a common ancestor, the bones that form flippers in dolphins form a  bat's wings. Here is a bat's wing compared to the flipper of a porpoise, a marine mammal similar to the Irrawaddy Dolphin. 


Analogous Traits (Examples of Convergent Evolution)

The Irrawaddy dolphin, like other marine mammals, has a layer of fat, called blubber, which is essential in retaining its body heat and maintaining its internal environment while in the water. Other mammal's fur serves a very similar purpose.  An example of this is the fur of the Macaca fuscata, a monkey with a kind of coat that is well adapted to cold so that the monkey can live in environments that are below 0° F. This species is also a mammal but is a primate.

Irrawaddy dolphins may stun their prey by hitting them or by emitting a loud sound (See "More Information'). Other animals have traits that allow them to debilitate their prey as well. Scorpions, predatory arachnids of the order Scorpiones, have a venomous stinger that injects venom into prey. This either kills they prey or paralyzes it. This is a Heterometrus laoticus, in the phylum Arthropoda.

File:Asian forest scorpion in Khao Yai National Park.JPG