Actually, I believe, though I cannot back it up, that, besides shrinking in size, crocs are the least changed species in the fossil record.
However, if an animal or individual inside a species were to be able to live for a long time, that would imply that the current genetic make-up "works", so evolution would not "want" to cause change, and if a sudden change in enviornment came along, the individuals would die prematurly, so their extra longevity would not come into effect.
For example, humans' possible life-span has remained the same, but with advances in medication, more easily accesible nutrition, ect, more of us have been nearing that age (the cut-off seems to be around 120). This has not stopped us from evolving, however, because those unsuited died long before reaching the cutoff. Therefore, a long lifespan, or lack of one, is not a tool of evolution, because those who die do so long before the age limit.