#acantod

• Acanthodian — A fossil representative of the extinct class Acanthodii, a group of ancient jawed vertebrates (gnathostomes), considered among the earliest to possess jaws, which inhabited global waters from the Silurian to the Permian periods. Popularly termed 'spiny sharks', these small primitive fish were characterized by a partially cartilaginous skeleton and, definitively, by the presence of stout, rigid bony spines located at the leading edge of all their fins, serving for structural support and predator defense.
• Fringe-toed lizard — A small to medium-sized lizard belonging to the genus Acanthodactylus, Lacertidae family, native to the arid, desert, and semi-desert zones of North Africa, Southern Europe, and the Middle East. Anatomically, it is individualized by the presence of scaly fringes or spine-like lateral protrusions along the digits of its hind limbs, a remarkable ecological adaptation that increases the surface area and prevents sinking into fine sand during rapid movement.
• Acanthodii — An extinct class of early bony fishes (Acanthodii) from the Paleozoic era, recognized as the earliest jawed vertebrates in the fossil record. The organisms were individualized by their generally small size, a streamlined body protected by tough rhombic scales, and the characteristic presence of long, rigid bony spines located at the base of both paired and unpaired fins. Due to their intermediate traits, which blend anatomical features of sharks and modern bony fishes, they are commonly termed 'spiny sharks' in literature.
• Acanthodont — A scholarly morphological term used as an adjective to describe an organism, tooth, or dental structure that features a sharp, conical, and prickly shape resembling a thorn or spine. In comparative anatomy and the study of extinct fauna, it details the configuration of teeth fused directly onto the jaw margins in certain fossil reptiles or fishes, where the teeth lack deep roots and project as rigid spikes adapted for prey retention.