>>42954793This chart represents all of the different possibilities for mixing fossil heads and tails. Question marks denote the gen eight fossil halves not revealed and Xs denote the four extant gen eight fossils combos. Line down the middle are full fossils and do not count.
Imo most "heads" are the entire head and forelegs with exception for Omastar who'd have either the shell or tentacles/face and Cradily who'd be bisected in the middle of the second yellow line on the 'neck'. This way you have no Pokemon with zero limbs.