Frogs (amphibians) and alligators (reptiles) are both
animals that posses homologous traits. Homologous traits are traits that are
shared between two different species but they share a comment ancestor. Both
frogs and alligators have similar bones in similar positions like their bones
in their hands and they both breathe out of water but can hold there breaths
for long periods of time under water. There arm bones and back bones are
positioned differently probably because the different paths they took in
evolution. Alligators are big and arms are positioned to be able to push there
weight along. Frogs are small and their arms are positioned to jump freely out
of harms way. This is just my hypothesis on why there arms might have evolved differently
from each other. Frogs backbones are also shaped to enhance their ability to
jump where as alligators are positioned straight so they can swim fast through
water. The common ancestor frogs and alligators shared was the tetra-pods, “Fish
out of water” (http://dinosaurs.about.com/od/otherprehistoriclife/a/tetrapods.htm)
In prehistoric times tetra pods were the first fishes’ to crawl out of water
and make their way on land to start breathing air. Then they evolved from there
into amphibians and reptiles.
Fun fact I read online amphibians 300 million years ago grew
up to 15 feet long
(about.com).An example of analogous traits would be in hummingbird wings and butterfly wings. They both use there wings for flying but there structures are completely different. Hummingbird wings are made of forelimbs while butterfly wings are not, because butterflies are bugs. Hummingbirds evolved from reptiles while butterflies evolved from other bugs or arthropods.
Good description of your homologous traits. Frog front legs are small because the emphasis on locomotion is from the rear legs. Front legs are primarily for support, not movement. I'm not sure how much action is involved for alligators/crocs during swimming. I believe a lot of the power actually comes from the tail with the legs primarily for terrestrial locomotion, but you are correct that these difference reflect differences in environmental selection pressures.
ReplyDeleteSo the fact that the common ancestor was a tetrapod means it had forelimbs and passed that trait onto both frogs and alligators, confirming the genetic relationship of these traits? This is needed to provide evidence that these are homologs, not analogs.
Okay on your analogous traits. Agreed that these two species are distantly related but that doesn't automatically mean that they didn't inherit their traits from a common ancestor... for example, our tiny ear bones are homologous with the gill arches of fish. So how do we know that the bird wing developed independently from the butterfly wing? What do we know about bird evolution that can help us figure this out?
Judy,
ReplyDeleteI like your comparison of frogs and alligators. You're correct about the similarities shown between them.
A would have gone a little more in depth in your analogous traits, but you chose two good examples.