Originally posted by john6:63
Evidence is the key word here. There are still no bona fide transitional fossils, not one, which has stood the test of time.
I believe enough evidence has been presented to demonstrate that Archaeopteryx is a fine example of a transitional creature. It possesed a wonderful mix of avian and reptilian features. So we have proven that this one has "stood the test of time."
I have also given a short list of some of the other transitional fossils. Some of the easiest to see transitionals come from those animals at the border between aquatic life and terrestrial life.
Utatsusaurus is an early ichthyosaur who is basically a lizard with paddles. The skeleton is very much like a land dwelling reptile except for the adaptations that allow it to live in the water. Its bones even indicate that it still swam similar to the way that other reptiles swim whan they get into the water unlike later ichthyosaurs who adopted a more efficient means of locomotion.
Acanthostega is a walking fish. OK, that is not really true. It did not have a skelton that could have done a very good job of moving it about on land. But it is a "fish" with four legs and eight digits on each foot. It would have been well adapted for scurrying around on the bottom of shallow, murky waters. And even limited ability to get around on land may be useful if none of your predators can get out of the water. A fish with legs.
Ambulocetus and Basilosaurus are different stages between the land dwelling artiodactyls and the water dwelling whales. Ambulocetus most likely spent time both in the water and on the land. It would have been something like the mammal version of a crocodile. Basilosaurus was a fully aquatic animal in which the legs had shrunk to something no longer useful on the land.
Cynognathus is an interesting transitional between reptiles and mammals and it contains both the mammalian and the reptilian jaws at the same time.
Here is my short list again. Acanthostega, Adelobasileus, Ambulocetus, Australopithecus, Basilosaurus, Cantius, Caudipteryx,Confuciusornis, Cynodesmus, Dimetrodon, Eusthenopteron, Homo erectus, Homo habilis, Hovasaurus, Hylonomus, Ichthyostega, Kenyapithecus, Microraptor, Oreochima, Osteolepis, Pachycynodon,Pakicetus, Panderichthys, Parapithecus, Parasemionotus, Peramus, Proailurus, Probainognathus, Proconsul, Procynosuchus, Proganochelys, Proterogyrinus, Protoclepsydrops, Rodhocetus, Sinoconodon, sinornithosaurus, Spathobatis, Thrinaxodon, Triadobatrachus, Tristychius, Ursavus, Ursus, Utatsusaurus