The ancient and, in other more recent cultures, way of classifying animals was by locomotion. Thus bats were naturally in with birds. Whales were naturally in with fish.
We may disagree with this method of classification, but that does not make it wrong. It was right for what it was intended to do. We need to recognize that.
As far as rabbits chewing the cud, it depends on how you define cud. If it is ONLY the product of undigested food which is passed back up through a first stomach, then rabbits do not chew the cud. If, however, it is simply undigested food which is reingested by whatever means, then rabbits DO chew the cud! http://www.nixonandmarshall.co.uk/rabbi ... tract.html