Archaeopteryx represents a good example of what one would expect to find in a transitional organism. It is a mix of reptilian and bird characteristics. On the bird side: Fully formed flight feathers typical of a bird including assymetry. The clavicles have fused to form the furcula or wish-bone. The claws on the feet are adapted like those of a bird with the first digit extending backward. The knee and ankle joints are similar to birds and are on long, bird like legs. Some hollow bones like a bird. The pubis is pointed to the posterior. On the reptile side: Long bony tail. Teeth. Sternum lacks keel for attachment of flight muscles. Has stomach ribs, unlike birds. Maintains claws on wings. Some bones remain solid where birds have hollow wings. Vertebrae are shaped like those of reptiles and not birds. Carpals are unfused unlike birds who have fused carpals. Lack of fusion of bones in tail is different than birds. Birds have fused tarsals in ankle and Archaeopteryx has only the third tarsal fused. There are also some features that are unique to Archaeopteryx, that we will not go into here. Above should be enough to show the blend of features between reptile and bird. A true transitional even if it is unlikely to be on the direct lineage of birds. There is more if you are willing to do a quick search on "Archaeopteryx." For our creationist, I have two links for you. Here is a creationist site that says Archaeopteryx was a bird. http://www.answersingenesis.org/docs2/4254news3-24-2000.asp Here is a creationist site that says Archaeopteryx was a reptile. http://www.creationscience.com/onlinebook/FAQ19.html#wp1365100 We also have a number of specimens both which are more reptilian and which are more birdlike. If interested, look up information on some of the following animals: Sinosauropteryx, Confuciusornis, Caudipteryx, Protoarchaeopteryx, Hesperornis, Ichthyornis, and Oviraptor. Creationist hold that there are original "kinds" and that organisms cannot cross that boundary. Here is a creature that was a mix of reptiles and birds.