Question

what was the earliest ancestor of birds, reptiles and mammals?

Answer 1

The ancestry of birds remain a topic of heated, often acrimonious debate. There are scientists who insist that birds descended from a dinosaur. This theory is based on a comparison of the skeletons of the theropod dinosaur Deninonychus and first known bird Archaeopteryx, 2 fossil animals of different ages. There are similarities between them, prompting John Ostrom of Yale University to propose that birds evolved from a dinosaur in the 1970's. The problem with this theory is that Deinonychus lived some 40 million years after Archaeopteryx, therefore making it unsuitable as the ancestor of birds. As we look back in time to the theropods that are about the same age or older than Archaeopteryx, they don't look anything like Deinonychus at all. The most logical explanation for the available fact is therefore Deinonychus and Archaeopteryx each evolved their similarity independently from different immediate ancestors, and that their similarities are only the result of convergent evolution. Indeed, if you look more closely at their similarities, that is exactly what we find. For example, even though Archaeopteryx and Deinonychus both have 3 fingers, they are different fingers. Embryological evidence suggests that birds have fingers 2-3-4. They are missing their thumb and little fingers. Fossil evidence suggests that theropod dinsosaurs have fingers 1-2-3. That means they are missing their ring and little fingers. Scientists such as Louis Dollo, a paleontologist, have learned that evolution is irreversible. That means once a feature has been lost, it cannot be regained. A theropod dinosaur therefore cannot regain the ring finger it has lost in order to evolve into a bird. Because a suitable dinosaurian ancestor of birds has yet to be found, the belief that is held by the supporters of the dinosaurian origin of birds is stronger than the available evidence. They are absolutely certain of their belief despite a dearth of evidence. That is why the opponents of the dinosaurian origin of birds call the supporters of the theory "dogmatic." A dogmatic person is someone who insists on being right even in the face of opposing evidence.

Looking at the evidence, Longisquama is the most likely ancestor of birds. It lived some 75 million years before the first bird, and it has feathers. But because it is not a dinosaur, but a small, lizard-like animal that lived in the trees, the supporters of the dinosaurian origin of birds deny that it has feathers, and they deny that it can even be considered a bird ancestor.

Th situation is a lot better concerning the ancestor of mammals. There is no dispute as to the reptilian ancestor of mammals. Because of the unique mammalian middle ear, which is formed by several bones that are found in the reptilian jaw, there is an entire series of fossils that show this change over time. Scientists agree that therapsid reptiles, specifically a group that is called the cynodonts (which means "dog-toothed") , contain the immediate ancestor of the mammals. The earliest mammal is Morganucodon, which shows evidence of Harderian glands. The secretions of these glands are used to groom fur. Therefore Morganucodon probably had a full body covering of fur if it had Harderian glands. The immediate ancestor of mammals has not been identified, despite the overwhelming evidence that it was a cynodont therapsid reptile.

Answer 2

So much information! (ી(΄◞ิ౪◟ิ‵)ʃ)♥

Answer 3

wow ummmmmm thanks?

Answer 4

Psst, you should give Cherry-Ann a medal. (❀¬‿¬)

Answer 5

Your welcome!;)