The giraffe is an even toed ungelate known for it's extremely long neck and inhabiting the savanas of Africa. It is an herbivore that evolved to have a long neck in order to forage from the leaves of trees decreasing the need to compete for food in an environment that it typically scarce of green folliage. The okapi is commonly known as the forest giraffe that resembles that of a horse and a giraffe. It to is an herbivore and is known for its odd appearance as it has a cobination of brown hair and black and white stripes.
The homologous structure that we will be analyzing in both these species is the necks of these maamals. The giraffe's neck has evoloved to have extremely large neck vertebrae that are adapted to support the weight of these towering heads. It has also adapted to use its head and neck as a means of fighting and defending itself. Okapis however have much smaller necks and exhibit a structure and diet much similar to that of horses. Therefore they have no need for enlarged vertebrae. However both the giraffe and okapi still have just seven vertebrae in their neck.Since these mamals are both apart of the family giraffidae their common ancestor was mostt likely a eventoed ungelate with some type of ossicone on it's head.The neck was mostlikely closer to the length of the okapi as it would seem that the girraffe was most likey the one to branch off.
The dolpin is an aquatic mammal that feed primarily off of small fish. There are about forty differnt types of dolphins that currently exist. However due to overfishing there numbers are in decline. Sharks are commonly known as viscious man eaters, which happens to be a false statement. There are approximately 440 different species of shark and while there diet varies from fish, to seals, to whale carcasses, they are don't exactly have a taste for humans.The analogous structures that we are analyzing is the pectoral fins of sharks and dolphins. Given there environment such strucures were developed in order to better glide and propel there bodies through the water. However while they may share a similar shape and size, structurally they are not the same as a dolphins pectoral fin is made of bones and sharks are made up of cartilage.
If we were to track down a common ancestor for these two animals we would have to go back closer to the start of evolution as the common ancestor was mostlikely one of the first nonvertebrates. However, we know that this trait is analagous as these animals are a part of two different classes and dolphins mostlikely evolved from an ancient land mammal that returned back to see.
Homology: Great opening description.
ReplyDeleteI appreciate the description of your traits, but I don't understand why the giraffe needs a long neck. You say that it is for fighting and defense, but then say the okape doesn't need it because of diet? So I don't see the connection. What drove the evolution of that long giraffe neck that didn't happen in the okapi?
Yes, we can be specific on the ancestor, but we can also just generalize a bit more. Both are mammals, so we know that the common ancestor would be an archaic mammal. We also know from the fossil record that early mammals possessed that generalized mammalian neck structure (7 cervical vertebrae) and passed that onto these two descendant species, with changes concurring over time due to differences in the environment (which needed to be explained). That is what we need to know to confirm common genetic origin and confirm homology.
Analogy: Good description.
Great discussion on the similarities of structure and function in your analogous traits.
Great discussion in the ancestry section, and you are correct that we know enough about dolphin ancestry to confirm analogy here. The common ancestor of the dolphin and sharks is an archaic fish, who did possess these fin structures and also passed that trait onto extant shark species. So the question is, did the dolphin also inherit it's fin from that common ancestor? Dolphins "fins" evolved after dolphins split off from terrestrial mammals, i.e., long after the split with ancient fish. This provides us with the evidence we need to confirm that this trait did evolve independently in at least one of these organisms, making these traits analogous.
Good images.