That's Pretty Well Spot On Since Let's Face It-The Vary Fact Missingno Evolves Into Kangskhan Is PROF That Yes Cubone Is A Baby Kangaskhan After It's Mother Dies-You Just Never See Marowacks Evolve In The Anime Or Manga Since They Wont LET It Evolve In The Games (The Manga Is The Most Realistic Of The Three Since The Anime Fluffs Everything And The Games Have To Be Diffrent So They Are Easyer To Play (Like I Doubt You Can Just Walk Into A Random Person's House Like You Do In The Game) ). So Ya Spot On.^^
Vary Possible-The Skull Is Clearly Both A Tragic Way To Stay Close To It's Mother As Well As A Sign Of The Savage Pokemon It Is Growing Up To Be. And Of Corse It's A Factor On Rather A Curbone's Mother Dies When A Cubone Is BORN Or If It's Strictly Case By Case.
My theory is that when the baby Kangaskhan lost its mother and started wearing it's skull, it somehow triggered something that gave it an entirely different evolutionary line. Magic based evolution isn't unusual, such as Banette who used to be a doll who was abandoned by its owner and came to life to seek vengence.
belly and eyes are the same.. I just checked all my pokedexes.. oh my nintendo should have added this.. ._. so many we don't know.. even in the manga's they had a marowak and a baby kangaskhan together, the mother died.. and the marowak took care of the baby.. wait.. omg.. NOW IT EVEN MAKE MORE SENSE!!