Final answer:
The fossil record of mammalian origins includes transitional forms like morganucodonts, with features indicating evolution from therapsids. It supports the notion that mammals diversified during the Mesozoic era and that mammals and dinosaurs coexisted. The fossil record shows gradual evolutionary changes, including the specialization of teeth.
Step-by-step explanation:
The fossil record of mammalian origins suggests that mammals evolved from therapsids in the late Triassic period, with the earliest known mammal fossils dating back to the early Jurassic period, around 205 million years ago. One notable transitional form is the morganucodonts, which exhibited transitional features in their jaws, combining reptilian and mammalian characteristics. The fossil record provides evidence for the evolution of differentiated teeth and homeothermy in mammals. Throughout the Mesozoic era, mammals began to diversify, with evidence of small gliding mammals appearing during this time. The fossil record also demonstrates that mammals and dinosaurs overlapped in geologic time, contradicting the statement that they did not.
Detailed records of the fossil record, such as those for horses and whales, show a progression of evolution. The record for horses, for example, includes transition fossils that show intermediate anatomy between earlier and later forms, indicating gradual adaptation to changing environments over millions of years. This narrative is consistent with the patterns observed in the fossil record of mammalian evolution, where transitional forms with progressively specialized teeth are present.