Concept 34.3: Gnathostomes are vertebrates that have jaws

Flashcards from Concept 34.3 of Pearson's Campbell Biology, Twelfth Edition.

Gnathostomes

Jawed vertebrates with teeth to grip and slice food; these outnumber jawless vertebrates and include:

• Sharks and their relatives

• Ray-finned fishes

• Lobe-finned fishes

• Amphibians

• Reptiles (including birds)

• Mammals

Jaws

Hinged structures in gnathostomes with teeth used to grip and slice food

• May have evolved by modification of the skeletal rods supporting the pharyngeal (gill) slits

Gnathostome characteristics

Includes:

• Jaws

• Genome duplication, including four sets of Hox genes

• Enlarged forebrain

• Enhanced senses of smell and vision

• Lateral line system, or rows of organs sensitive to vibrations along body sides

Lateral line system

Rows of organs in aquatic gnathostomes sensitive to vibrations located along body sides

440 mya

Time where gnathostomes first appeared in the fossil records, exhibiting adaptations like paired fins, a tail, and a more efficient gas exchange system in the gills for efficiency and control

Placoderms

Early gnathostomes; these are extinct armored vertebrates ranging in size from less than a meter to more than 10 m

Gnathostome lineages

Includes:

• Chondrichthyans (sharks, rays, and their relatives)

• Ray-finned fishes

• Lobe-fins

Chondrichthyans

One of the three lineages of gnathostomes including the 1,000 species of sharks, rays, and their relatives; these have skeletons composed primarily of cartilage and some calcium

• Traces of bone are found in scales, at the base of teeth, and coating vertebrae in some sharks

• Bone likely evolved in these before diverging

Shark

One example of a chondrichthyan, with a streamlined body for swift but less maneuverable swimming

• Dorsal fins function as stabilizers, and paired pectoral and pelvic fins are used for maneuvering

• Oil is stored in the liver for buoyancy

• Continual swimming is necessary to avoid sinking, also keeping water flowing for gas exchange

  • During rests, muscles of the jaw and pharynx are used to pump water over gills

• Eggs are fertilized internally, but can undergo oviparous, ovoviviparous, or viviparous development

Oviparous development

Development of the embryo where eggs hatch outside the shark mother’s body after internal fertilization

Ovoviviparous development

Development of the embryo where eggs are retained within the oviduct and young are born after hatching within the uterus

Viviparous development

Development of the embryo within the uterus, nourished by:

• A yolk sac placenta,

• Absorption of nutrient-rich fluid, or

• Eating other eggs

Cloaca

A common chamber with a single opening to the outside of the body, with the reproductive tract, excretory system, and digestive tract all emptying into this

Osteichthyans

The vast majority of vertebrates, with a majority having bony endoskeletons

• Includes bony fishes and tetrapods; aquatic species of these are informally called fishes

Operculum

A bony flap protecting the gills of fishes, helping draw water into the mouth and over the gills via muscle contractions

Swim bladder

An air sac in fishes filled to maintain buoyancy

Ray-finned fishes

A group of gnathostomes including over 27,000 species, including most familiar osteichthyans

• Have modifications in body form and fin structure affecting maneuvering, defense, and other functions

Lobe-fins

A group of gnathostomes with rod-shaped bones surrounded by a thick layer of muscle

• Used to maneuver across the substrate of aquatic habitats

Lungfishes

Types of lobe fins initially arising in the ocean, but today living in stagnant ponds and swamps with gas exchange in water using gills or gulping air into lungs attached to the pharynx