It is because we determine things as more closely related if they share a more recent common ancestor. So orcas and moose shared a common ancestor more recently than orca and horse or moose and horse.
DNA supports Perissodactyla and Artiodactyla (or Cetartiodactyla) as two separate groups.
Within mammals, convergent evolution (traits that look similar but do not share a single origin), is pretty common. This makes determining relationships from morphology alone much more challenging!
If you are interested in cetacean evolution and how they came about from the artiodacyls you could look into transitional fossils for this group. It's actually really cool (to me anyway) to see the mix of traits as the cetaceans adapted back into life in the water!
PurplePeggysus t1_islp0iv wrote
Reply to Why are ungulates classified by toe parity? by randomizedsim
It is because we determine things as more closely related if they share a more recent common ancestor. So orcas and moose shared a common ancestor more recently than orca and horse or moose and horse. DNA supports Perissodactyla and Artiodactyla (or Cetartiodactyla) as two separate groups. Within mammals, convergent evolution (traits that look similar but do not share a single origin), is pretty common. This makes determining relationships from morphology alone much more challenging! If you are interested in cetacean evolution and how they came about from the artiodacyls you could look into transitional fossils for this group. It's actually really cool (to me anyway) to see the mix of traits as the cetaceans adapted back into life in the water!