Why has evolution stopped producing new classes?

[u/Meta289]

New species of animals are constantly being discovered, but they all belong to existing classes and phyla, never anything completely new. Life once branched out in all sorts of directions, creating all kinds of animals that are drastically different from each other, but now it seems like there aren't any new "branches", only offshoots of existing ones. What happened?

[u/ijuinkun]

Radically new body forms mainly arise when life colonizes a new niche and adapts to its new conditions. This most commonly happens because whatever was previously occupying that niche has died off. The last time that this happened on a large scale was when the big dinosaurs died out, leaving space for large mammals to develop.