Weird thing to read after discussing the origins of pizza. Why? Because one of pizza's ancestors was a flat bread/cake called placenta. The mammal placenta got this name because the ancients thought that it looked like the flat bread.
...it isn't the first time that we integrate genetic material from other species. The eukaryotes are basically archaea plus, and yet our mitochondria were originally a bacterium; and there's also the possibility that our flagella+cilia are from another bacterium. Humans apparently have up to 8% of their DNA coming originally from viruses, and probably other mammals are like this too, so it isn't that surprising that some virus genetic material became useful later on.