These included brachiopods, which lived in shells resembling those of clams or cockles, and animals with jointed, external skeletons known as arthropods—the ancestors of insects, spiders ...

Bryozoans and brachiopods, nearly equal in abundance, form about 60% of the allochems in local limestone. Crinoids form about 20% and trilobitesnearly 10% of the allochems. According to detailed ...

A. Apatite (calcium triphosphate): This mineral makes up the bones and teeth of vertebrates and the shells of inarticulate brachiopods. Calcium phosphate looks chalky when new, but can darken to black ...