The Vah'Dhir are the ancestral cat people. The Kerra left on Norrath evolved in a slightly different direction, apparently. There are some tomes that describe the history of the Kerra that go into this.
The Vah Shir, Kerrans, and Kejekens all originated and lived on Odus, before the Erudites came along. The Vah Shir and a large chunk of Odus itself were teleported up to Luclin when the Erudites were testing out teleportation magic (which would eventually become stabilized as the Quellithulian spire network in EQ2). When the gods withdrew their influence from Norrath following the Plane of Time event, teleportation up to Luclin was cut off. The Vah Shir adventurers who were stuck on Norrath decided to integrate into the Kerran societies on Odus, and eventually passed on their genetics across multiple generations to turn the Kerrans into the now more muscular versions that they now are.