306: Evolution of Cartilage

Pharyngula::Invertebrate cartilages:

The data on invertebrate cartilaginous endoskeletons presented here offer unique insights into the evolution of vertebrate skeletal tissues. The ability to form cellular connective tissues structurally similar to cartilage without type II collagen is a feature that appeared before the evolution of vertebrates, supporting the notion that cartilage is not simply an embryonic adaptation (as per Romer), but was present in vertebrates before calcification evolved.

Something like cartilage is ubiquitous in the Metazoa.