Analogy and Homology

 Analogous

Two species that have an analogous trait are the  North American porcupine and the purple sea urchin. The North American porcupine can be found most numerous in the northwestern U.S and all of Canada. They are one of the largest rodents weighing in at 20 pounds. They have short brown or black fur, round bodies and a small head. Their most defining trait are quills that are lightly attached to the body and used for defense. Porcupines are not aggressive unless provoked and spend most of their time in the trees to find food since they are herbivores. They are solitary and nocturnal creatures that live in hollow trees or caves and are also very good swimmers. Sea urchins can be found globally across the oceans and reside from intertidal to about 5,000 meters below sea level. They are invertebrates most closely related to sea cucumbers and sea stars and feed off of algae. They are small, rounded creatures about 3 inches across that use a tube foot with the help of spines to get around. Their mouth is on the underside of the body consisting of a set of teeth and they use spines for defense as well.

The analogous traits of the two species are their quills and spines. Both animals use their respective features for defense. The spines on a sea urchin are mainly made up of calcite and are microscopically barbed. The quills on a porcupine are made up of hardened keratin that expand due to body heat once inside of their victim and are also barbed. Both quills and spines are lightly attached to the creature's body and can puncture an attacking enemy and are used as a deterrent rather than a killing mechanism. Porcupines and sea urchins could not have a more different environment. Both creatures are herbivores, meaning they do not need to kill anything they just need to make it unfavorable for their predators. They are both very slow, so they developed armor to stop other creatures from praying upon them. For some reason this defense from creatures took the form of spines and quills protruding out from the main body. Porcupine quills develop as specialized hair and the spines develop as amorphous calcium carbonate from the exoskeleton  and crystallize into calcite. 

The porcupine and the sea urchin are most closely related by the superphylum Deuterostomia which they first form the anus in embryonic development. There hasn’t been a common ancestor found since their respective clades Chordate and Ambulacraria split in the precambrian era. Going this far back it is impossible to tell the traits of their common ancestor and considering that other earlier members of the rodent family do not have quills it is safe to assume that the common ancestor between sea urchins and porcupines would not as well.

Homologous

The two different species that share a homologous trait are toucans and the red-naped sapsucker. Toucans can be found from Southern Mexico to Northern Argentina. They can range from 5 oz to 1.5 pounds and are 12 to 30 inches in size. They are omnivores but mostly eat fruit with the occasional insect. They are social creatures and spar with other toucans using their beaks. The red-naped sapsucker is about 8 inches long and weighs 1.5 ounces. Their habitat is in the Rocky Mountains and Great Basin areas of North America. They drill hundreds of holes into a tree and use their tongue to sip the sap of that tree and also feed on insects. They drill holes into trees in order to make their nests.

They both have very strange beaks. The beak of the toucan is used for picking fruits from the rainforest trees, sparing with other toucans and helping the toucan regulate body temperature. The sapsucker uses its beak in order to puncture trees and obtain sap. It seems like their beak shapes have evolved to obtain the available food in their respective habitats. The beak of the toucan is mostly hollow with sponge-like bone structures connecting the outer and inner layers of the beak which is great at impact absorption. The sapsucker has a very long and chiseled beak used to drill into trees, the density of the tip of the beak is greater than the base which allows for more force to be absorbed by the beak and not the head of the sapsucker.

The toucan and sapsucker both belong to the same order of birds Piciformes, which have zygodactyl feet, arboreal and have no down feathers when young. Considering that all living birds, Aves, have a beak there must have been a common ancestor to have a beak. The common ancestor had a beak but different environmental pressures, mainly food, gave shape to the two different beaks of today.