You and everyone else who missed out on all three animals despite constant effort have my heartfelt sympathy. I know exactly how that feels from the dog trio (59 failed attempts!). It's supremely frustrating and infuriating. I hope you have more luck with the next trio.
We got the skull trio so soon after the dogs that maybe we'll have trios a lot more often from now on than in the past. Breeding luck seems to circulate somewhat, so it should get better pretty soon when you miss out on a whole trio!