Answer:
C) mammals evolved from a reptilian ancestor
Step-by-step explanation:
Mammals, amphibians, and reptiles are tetrapods. Reptiles and mammals are shown to be originated from a common ancestor, the early tetrapods which in turn diversified into two lineages. One of the lineages evolved into synapsids and the other gave rise to reptiles and birds. Synapsids diversified into two lineages one of which later formed mammals.
According to the given information, fossil records of Thrinaxodon have a reptile-like skeleton and were oviparous like reptiles. However, the presence of furs and the possibility of being warm-blooded make it like a mammal.
Reptiles are cold-blooded egg-laying tetrapods while mammals are warm-blooded viviparous tetrapods. The presence of some of the features from both the groups in Thrinaxodon provides proof that mammals evolved from a reptilian ancestor.