International Journal of Aquaculture, 2025, Vol.15, No.5, 255-265 http://www.aquapublisher.com/index.php/ija 258 The causes of differentiation between cartilage fish and bone fish may be related to niche differentiation and genetic development. Bonefish evolves the stubborn and true teeth of the endoskeleton, which gives them stronger support and bite ability; while cartilage fish retain cartilage bones, making the body lighter and more flexible, and develop shield scales and continuous growth and replacement teeth on the surface of the skin, which is conducive to swimming and predation. Most of the radial-finned fishes in early bone fish have smaller sizes, thin scales and light bones, and are active in nearshore or freshwater environments, and may feed on small invertebrates and plankton. Some special fish fossils discovered in the early days of the Silurian period in China provide an interesting perspective on this disagreement. For example, there is a fish called "Shenacanthus" in the newly reported Silurian Chongqing biota. It has the anatomy of a cartilage fish, but the front of the body is covered with a large bone deck - a feature that was previously only seen in squidfish (Zhu et al., 2022). 3.3 Multidisciplinary research methods for jaw structure and function evolution To gain an in-depth understanding of the origin and evolution of jaws, paleontologists and evolutionary biologists have adopted a multidisciplinary cross-cutting approach. In terms of morphology, the internal structure of ancient fish skulls and jaw bones can be studied in detail through three-dimensional reconstruction techniques such as high-precision CT scans. By scanning the fossil of the Silurian Chongqing biota fish with synchronous radiation CT, researchers have seen for the first time the details of the teeth, skulls and even fins of the earliest jawed fish (DeLaurier, 2018). In the field of biomechanics, by establishing a digital model of the jaw and using finite element analysis, the bite force and stress distribution of ancient fish can be simulated, thereby inferring their bite function. For example, for shield-skinned fish like Duns, simulation studies have shown that the jaw muscles and leverage systems can produce a great bite force enough to break shelled prey, which is consistent with the bitten invertebrate shells found in fossils. Developmental biology and molecular genetics also provide clues to the origin of the jaw. Embryoological studies of present animals show that the neural crest cells responsible for the formation of the gill arch in fish embryos partially evolve into upper and lower jaw structures in jawed species. Therefore, comparing the development of gill arches of jawless species (such as lampreys) with those of jawless species, we can find the differential genes. 4 Ray Fin Fish Diversification and Dominant Position 4.1 Characteristics of bones and fin structures of radial fin fish The radial fin fish (Actinopterygii) is the most numerous and widely distributed branch in the Bonefish. Their name "radial fins" are derived from their unique fin support structure: each fin is supported by multiple slender bone fin strips, which are arranged radially and are deployed or folded by muscles. This fin structure gives the radial-finned fish a highly flexible motility and fine control of water flow, which is in sharp contrast to the thick fleshy finned fish’s. The skeletal system of radial-finned fish is mainly composed of rigid bones, including axial bones centered on the spine, appendage bones and skulls. Early radial-finned fish body spindle-shaped, covered with rhombic hard scales. These rhombic scales are composed of hard scales and are gradually replaced by thin and flexible round scales or comb scales during the evolution process, making the body lighter and more flexible. A major feature of the skull of a radial-finned fish is that the maxilla is not completely fixed to the skull, but is connected by joints and ligaments, which allows the anterior part of the jaw to protrude to a certain extent, which is conducive to prey consumption (Datovo and Rizzato, 2018). This "retractable" jaw is very obvious in many modern radiant fin fish. For example, bass can instantly extend its mouth forward when preying to cause negative pressure to suck prey. The caudal fins of radial fin fish are generally symmetrical and crooked tails, which are different from the heterotails that are significantly up-breaked by cartilage fish, providing effective propulsion. It is the characteristics of these skeletons and fins that enable radial fin fish to show excellent maneuverability in the water and can adapt to the changing water environment. From high-speed swimming predators to maneuvering and flexible coral reef fish, all lifestyles have corresponding morphological adaptations.
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