Nonbony

Nonbony is an adjective used in biology and medicine to describe tissues, structures, or organisms that do not contain bone tissue (osseous tissue). It is a relative term, used to contrast with bony or osseous components, and it does not imply a complete absence of a skeleton or framework in all cases.

In vertebrate anatomy, nonbony structures include cartilage, tendons, ligaments, muscles, and other connective tissues. When applied to skeletons, the term often refers to a cartilaginous endoskeleton, as seen in cartilaginous fishes (Chondrichthyes) such as sharks and rays, whose skeletons are made primarily of cartilage rather than bone.

Invertebrates typically have nonbony support systems, such as exoskeletons or internal frameworks composed of materials like chitin, calcium carbonate, or other substances, and they do not possess true bones as vertebrates do.

In paleontology and comparative anatomy, nonbony can describe fossils or anatomical features where bone is absent, poorly preserved, or replaced by other materials. The term highlights structural differences in skeletal composition across taxa and over evolutionary time.

Limitations of the term include its dependence on context and its variability within lineages that may have both cartilaginous and osseous tissue at different life stages. It is most informative when contrasted with osseous tissues to describe composition, development, or evolutionary relationships.

See also: bone, cartilage, endoskeleton, exoskeleton, osteology.