The article talks about the protective phenotypes hypothesis, which basically says that animals with physical or chemical traits that confer protection (e.g. armor, spines, shells, or venom) have slower aging and live longer (compared to other animals their size).

The thinking is that these protective mechanisms can reduce mortality rate (you're not getting eaten by others), so you're likely to live longer, which exerts pressure to age more slowly.

Biggest support for the protective phenotype hypothesis is in turtles.