There are some of us that already know this particular fact, as it is logical. However, for those that don't know, it may come as a surprise that Dimetrodon is an ancestor of humans. Of course, it eventually became all other mammals as well, but it's still interesting that we are descended from the bloodthirsty, sail-backed pelycosaur. So what proves this, and why is it so important in human evolution? Well, that is what I am about to tell you.
It begins with the ancestor of all pelycosaurs, the Ophiacodon. Unlike most other pelycosaurs, this one had only one kind of tooth, sharp, for predatory creatures. But that would change when Edaphosaurus came along. This pelycosaur had evolved to be a strict plant eater, and its sharp teeth became more blunt for chewing plants. Then came Dimetrodon. This name means "two measures of teeth". Where did that name come from? Even when Dimetrodon evolved to be carnivorous once again, it gained the teeth necessary for shearing flesh while also retaining the vestigial teeth of the Edaphosaurus it evolved from.
Despite this adaptation, Dimetrodon was no plant eater, so it died rather quickly. However, its descendants would live on as the mammal-like reptiles, and eventually the mammals, which didn't make the mistake Dimetrodon made and put both of their types of teeth to good use, making them omnivores, and even devoloping a third type of tooth eventually, the incisor. So who knows? If it weren't for Dimetrodon, we might still be grinding plant stems right now. It was, without doubt, a very important step in the path that would lead to us.