The author concludes that Thrinaxodon was probably warm-blooded. As support, the author says that its skull suggests that it had whiskers. The author then provides the following conditional premise: If Thrinaxodon had whiskers→ Thrinaxodon had hair elsewhere on its body. The author claims that this hair elsewhere on its body would have regulated its body temperature. The evidence cited by the author affirms the sufficient condition (that Thrinaxodon probably had whiskers), so we can say that it probably had hair elsewhere. Since cold-blooded animals would have little use for insulation, the author concludes that Thrinaxodon was probably warm blooded.

The statement in the question stem provides support for the claim that Thrinaxodon was warm-blooded, because a cold-blooded animal would have little use for such insulation.