Any of a group of extinct jawless marine animals, known chiefly for their distinctive mineralized mouthparts, which are commonly found as fossils in rock strata dating from the early Cambrian to the end of the Triassic periods (about 525 to 200 mya). Specimens of complete animals are much rarer. The well-preserved Haikouella lanceolata, found in the Chengjiang fossil assemblage in China in 1999, is one of the earliest known chordates (see chordata). It had a soft, slender body, about 16–22 mm long, with eyes, a brain, a cartilaginous skeleton, and possibly a tail fin. The hardened cone-like dental elements incorporated calcium phosphate, like bone.