COMPARATIVE VERTEBRATE ANATOMY

Comparative Vertebrate Anatomy

Comparative Vertebrate Anatomy

Question 1

Fish

The structure of a fish's jaw can reveal its feeding habits. Fishes can be divided into three feeding groups: top-, midwater- and bottom-feeders. Top-swimmers' jaws fish has a straight dorsal surface, and an upturned, scooplike jaw for gathering floating insects. Species that swim in midwater have jaws at the very tip of their snouts, and generally snatch their food as it falls through the water. A few have underslung jaws fringed with rasplike folds, enabling them to graze on algae. Bottom-dwellers' jaws fishes have underslung jaws with flattened ventral surfaces which can be brought into close contact with the riverbed where much of their food lies (Miller, 2007).

Jaw structure is also related to the feeding modes and habits offices. Jaw structure is highly variable, and this variability explains in part the evolutionary success of both teleosts and elasmobranches. More common among modern fishes are jaws modified for suction feeding. In suction-feeding fishes the jaw is shortened to limit the gape while the expansibility of the orobranchial (jaw and gill) cavity is maintained, resulting in increased water velocity through the smaller jaw when the cavity is expanded or contracted. Superior fish has an upturned, scoop-like jaw which is designed to feed on prey that swims above the fish, or perhaps on the surface of the ocean or lake, such as insects or plankton. Surface feeding fish usually have an undershot or upturned (superior) jaw for feeding on insects or floating prey (Hildebrand, 1995).

However a superior jaw doesn't automatically signify a surface swimming fish; fish with this jaw position feed on food that is above them and are either a predator or a strainer. Bottom feeding fish generally have an underslung or inferior jaws. Ventrally-oriented jaws or jaws located under the fishes head that are adapted for scavenging or grazing on algae, invertebrates or mollusks, and are usually seen in fish such as the catfish or flatfish like halibut or plaice. Fish with a terminal jaw position have a jaw in the middle, or center of their head. These fish either chase their food or feed on what is ahead of them. The terminal jaw position is considered the “normal” position, and most fish inhabiting the middle levels of the oceans or lakes possess terminal jaws (Miller, 2007).

Amphibians

Jaws develop by modification of the anterior (front) branchial arches. (Branchial arches are structures that ultimately gave rise to gills, as well as jaws.) In jawless amphibians, such as the Silurian genus Jaymoytius, each gill arch is supported by a single cartilaginous rod, all similar in structure. In amphibians with jaws, the cartilaginous rods are divided into four parts: pharyngo-branchials, epibranchials, ceratobranchials, and hypobranchials. The first visceral arch becomes enlarged, and the epibranchial forms the upper jaw (palatoquadrate cartilage). The ceratobranchial forms the lower jaw (mandibular cartilage, also known as Meckel's cartilage).

The second visceral arch, or hyoid arch, changes to support the tongue or the jaw articulation in lower amphibians. In higher amphibians it is modified further into an ...