Irregular echinoids appeared for the first time and rapidly specialized for deposit feeding, possibly triggered by ever rising levels of ocean productivity. Echinoids generally become a major constituent of the shallow-water benthos from this time onwards. Whereas cassiduloids dominated the Jurassic and Cretaceous shallow-water clastic settings atelostomates diversified in more offshore settings. In the Cretaceous heart urchins make their first appearance and thrived in the deeper water settings provided by chalk seas. The end Cretaceous extinction 65 million years ago had a major influence on the structure of echinoid communities and the Tertiary saw the rise to dominance of clypeasteroids over cassiduloids, spatangoids over holasteroids and camarodonts over stirodonts.
Sea urchins are more diverse today than they have ever been.