The 4km pursuit is one of the longest typical individual TT distance on the track, but most track racing is actually a lot longer than 12 laps on a 333 velodrome. If you want to track race more than a couple events a year you'll end up doing a lot more mass start track events like scratch races (basically crits on the track), points races, miss and outs, win and outs, Tempo races, snowball races, chariot races, handicap races, Australian pursuits, etc. There are a ton of creative and interesting events on the track and the typical weeknight track racing session spends a lot more time doing mass start events than doing solo events, two up pursuits or even match sprints.
Bottom line, the fitness starts in the same place as on the road with building core aerobic fitness as you'll see in the presentation Swampy pointed you to. From there you can specialize a lot towards things like the kilo, pursuit or match sprinting or you can leverage your road fitness for events like points races, handicap races, miss and outs, scratch races, etc.
For the mass start events a good sprint is very useful but perhaps more important is high power for up to eight minutes of a typical shorter track race (points races and madisons can go for an hour or more) and the ability to repeatedly do big bursts and slightly sub maximal sprints for events like miss and outs and points races. Micro-intervals would be useful there with an emphasis on short near maximal sprints as opposed to longer L6 style bursts. Get out to your local track, take advantage of any sort of intro to track program they have (most do) and you'll learn quickly what sort of events they run, which play to your strengths and what sort of training you'll want to do to transfer your road fitness to the track.
Track racing is really fun and a great way to tune up your crit and fast road race skills. Race a few miss and outs and you'll get really good at knowing where you are in the field, who's around you, who's attacking and where you should be to avoid getting trapped with nowhere to go in a sprint. That and after a season on the track most crits will feel like they're ridden in slow motion, they may still hurt plenty but the speeds will seem tame after some track racing.
Good luck,
-Dave