- Cynognathus is an extinct genus of therapsids (mammal-like reptiles) from the early Triassic period, and it is considered an intermediate form between Reptiles (Reptilia) and Mammals (Mammalia). Cynognathus exhibited features that are characteristic of both reptiles and mammals, making it a critical species in understanding the evolution of mammals.
Thus, the correct answer is Option D, as Cynognathus forms an intermediate link between Reptilia and Mammalia.