Felidae Oligocene, about 25 million years ago, with the appearance of "Proailurus" and "Pseudaelurus". The latter species complex was ancestral to two main lines of felids, the cats in the extant subfamilies and a third major group of extinct cats, which are assigned to the subfamily Machairodontinae. The machairodonts included the saber-toothed cats such as the "Smilodon". The "false sabre toothed cats", the Barbourofelidae and Nimravidae, are not true cats, but are closely related and together with Felidae and other cat-like carnivores (hyaenas, viverrids and mongooses) make up the feliform carnivores. Results of mitochondrial analysis indicates that all the Felidae descended
People for the Ethical Treatment of Animals They promote alternatives, including embryonic stem cell research and in vitro cell research. PETA employees have themselves volunteered for human testing of vaccines; Scott Van Valkenburg, the group's Director of Major Gifts, said in 1999 that he had volunteered for human testing of HIV vaccines. PETA opposes the use of animals for producing clothing made with fur, leather, wool, or silk. It also opposes the use of down from birds and the use of silk from silkworms or spiders. The group notes on its website: "Every year, millions of animals are killed for the clothing industry—all in the name of