Apparentely evolution should lead to a graduation of living creatures rather than a rigid subdivision into species
From a distance it may look like a rigid subdivision into species, but it's certainly not. It may seem arbitrairy, but they're simply not random labels. Remember how there are a million ways of dividing groups of animals into 'species', which in the classic sense isn't much more than a group that allegedly belongs to the same family, having the same or a close common ancestor.
As we've already found out about a few times in the last decade, DNA is a much better method of determining family relationships of species.
The reason why we have a hard time to find the "inbetween"
creatures is simply, because the fossils are rather rare
That has little to do with how rare fossils are.. in my opinion they're not quite that rare. When it comes to 'missing links' though, creationists often simply do not acknowledge how evolution is a gradual process, meaning there won't be much fossils showing 'in between' forms, as entire generations of animals have been the 'in between' forms.
