Crawling before sitting?

I am wondering if this will be the case with Jackson. He sits only for a few seconds unassisted (being a big boy-he has more to hold up), yet in his crib he will raise himself up on all 4s and rock back and forth on his hands and knees. Anthony did this just before the crawling began. It will be interesting to see what happens next. Yet no matter what milestone he hits first, he is a happy, happy boy-what could be better?