There are gaps between reptiles and mammals (Talk.Origins)
- Watchtower Bible and Tract Society, 1985. Life—How Did It Get Here? Brooklyn, NY, pp. 80-81.
It needs to be noted that Talk.Origins has chosen the worst possible source for this. Not only is it out of date but it is generally a poor quality source. A much better source would be Mammal-like reptiles: major trait reversals and discontinuities by John Woodmorappe.
(Talk.Origins quotes in blue)
1. The transition from reptile to mammal has an excellent record. The following fossils are just a sampling. In particular, these fossils document the transition of one type of jaw joint into another. Reptiles have one bone in the middle ear and several bones in the lower jaw. Mammals have three bones in the middle ear and only one bone in the lower jaw. These species show transitional jaw-ear arrangements. The sequence shows transitional stages in other features, too, such as skull, vertebrae, ribs, and toes.
[Specific examples snipped]
It needs to be noted that the main defining characteristic of mammals is the presence of mammary glands (milk producing organs) and they tend not to be fossilized. This makes a determination based on fossils potentially error-prone if the characteristics being used have not always been unique to reptiles or mammals. There are other differences, for example:
- Mammals have a four-chambered heart while reptiles have a three-chambered heart.
- Mammals are warm-blooded while reptiles are cold-blooded.
- Mammals have hair, while reptiles don't.
So the claim as worded is 100 percent correct if one looks at the right reptilian and mammalian features. This is largely a case of selecting traits that favor evolutionary theory as opposed to other traits that don't. Even in this list, Talk.Origins needs to use fossils that are not in the correct order according to evolutionary dating methods. However their more complete list shows even more out of order and contemporaneous fossils used.
Yes, there are some reptiles with a few mammal-like traits and some mammals with a few reptile-like traits, but from Biarmosuchia to Procynosuchus, there is a clear and sudden change in dominance from reptile to mammal traits. So rather than the smooth transition that Talk.Origins wants you to think is there, there is a sudden shift from reptile to mammal as creationists would expect.
- Mammal-like reptiles: major trait reversals and discontinuities
- Mammal-Like Reptiles
- Reappraising the "Crown Jewel"
- (Talk.Origins) Transition from synapsid reptiles to mammals