Hi, I'm preparing for an exam and was wondering about which groups are more closely related evolutionarily. The actinopterygii (ray-finned fish) and Dipnoi (lungfish) or testudinia (turtles) and aves (birds). I initially thought it would be the ray-finned fish and lungfish would be more closely related because they are both bony fish (osteichthyes) but apparently I'm wrong. Is there anyway you can explain why birds are more closely related? Thanks so much!
Firstly, ray-finned fish, and lungfish don't even have the same skin...rayfish have scales, the lung fish have a smooth skin, much like catfish. Secondly, lung fish can breathe for a considerable amount of time out of water. Such is not the case with any rayfinned fish. Those two differences are HUGE. There are significant differences in how the heads are put together, indicating a significant amount of generations going back to their common ancestor. And if someone has mapped both of the genomes of these two, the differences would be greater, in contrast to the differences between a turtle and birds despite what looks to be even bigger differences with these two.
Birds are descended from dinosaurs, as are turtles....(And I'm guessing the generations between the first two--- rayfins and lung fish--- would be greater. i.e., more, than the number of generations separating turtles and birds to their common ancestor.)
Interestingly, even tho crocs are "cold blooded", they have a four chambered heart, as do all mammals. I am guessing that turtles as well, have a four chambered heart, as do all birds. Not knowing if the genomes of either of these two have been mapped, I cannot compare them at the cellular level, which is the true, and best way to find just how closely two animals are related.
But since you learned that the first two are less closely related, you then must find things about the second two that make them closer, kin-wise.
1. Both turtles and birds, breathe with only lungs...fully developed lungs.
2. Both have the exact pattern that all animals with an internal skeleton have.... a head, four distinct and fully developed limbs, a body and a tail. However the fin arrangements in finray fish, and lung fish are drastically different. Perhaps one being cold blooded threw you off? Coldbloodedness is an adaptation of survival.... being able to shut down the heart rate to one or two beats per minute during hibernation is a huge advantage, since food for turtles in winter is at times scarce. Birds either survive the cold, remaining active, or migrate. Migration isn't an option for turtles.
The two within each group are on the surface hugely and vastly different. Yet take away some of the 'superficial' physical differences and they are closer than would first appear. But the superficial differences aren't what make animals closer or farther apart on an evolutionary tree... it is in the DNA and a mapped genome, which we don't have.
So, and until that is available, we go with physical likenesses. And it would appear that a shell on a turtle, and feather on a bird would eliminate them as close relatives, until we remember that each has as an ancestor the dinosaur and as well, those items listed above for skeletal animals..head, body, four fully developed limbs and a tail.
You might find more things by googling each of these and comparing and contrasting each set.
Hope this helps?