SUPERCLASS GNATHOSTOMATA Gnathostomes Jawed Fishes Gnathostomes or

SUPERCLASS GNATHOSTOMATA

Gnathostomes: Jawed Fishes Gnathostomes or "jaw-mouths" are vertebrates that possess jaws. One of the most significant developments in early vertebrate evolution was the development of the jaw, which is a hinged structure attached to the cranium that allows an animal to grasp and tear its food. The evolution of jaws allowed early gnathostomes to exploit food resources that were unavailable to the jawless animals. In early evolutionary history, there were gnathostomes (jawed fishes) and agnathans (jawless fishes). Gnathostomes later evolved into all tetrapods (animals with four limbs) including amphibians, birds, and mammals. Early gnathostomes were jawed fishes that possessed two sets of paired fins, which increased their ability to maneuver accurately. These paired fins were pectoral fins, located on the anterior body, and pelvic fins, on the posterior. The evolution of the jaw combined with paired fins permitted gnathostomes to expand from the sedentary suspension feeding of jawless fishes and become mobile predators. The gnathostomes' ability to exploit new nutrient sources led to their evolutionary success during the Devonian period. Two early groups of gnathostomes were the acanthodians and placoderms , which arose in the late Silurian period and are now extinct. Most modern gnathostomes belong to the clades Chondrichthyes and Osteichthyes.

All members have the vertebrate characteristics All members have a jaw All have or have had paired appendages All have an endoskeleton of cartilage or bone

Classification

SUPERCLASS GNATHOSTOMATA Class Chondrichthyes Subclass Holocephali Order Chimaeriformes (chimaeras) Subclass Elasmobranchii 9 orders (sharks, rays, skates) Class Sarcopterygii Subclass Coelacanthimorpha Order Coelacanthiformes (coelacanths) Subclass Dipnoi Order Ceratodontiformes (lungfish) Order Lepidosireniformes (S. American, African lungfish) Class Actinopterygii - (rayfins, higher bony fishes) Subclass Chondrostei Order Polypteriformes (birchirs, reedfish) Order Acipenseriformes (sturgeons, paddlefishes) Subclass Neopterygii Order Semionotoformes (Lepisosteiformes) (gars) Order Amiiformes (bowfin) Division Teleostei 35 -38 orders (modern body fishes)

Chondrichthyes Cartilaginous fishes Great white shark Chondrichthyes (cartilage-fish) or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, a heart with its chambers in series, and skeletons made of cartilage rather than bone. The class is divided into two subclasses: Elasmobranchii (sharks, rays and skates) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class). Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates, the extant members of which all fall into Teleostomi.

Osteichthyes Bony fishes Rose fish Osteichthyes or bony fishes are a taxonomic group of fish that have bone, as opposed to cartilaginous skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of 45 orders, and over 435 families and 28, 000 species. It is the largest class of vertebrates in existence today. Osteichthyes is divided into the ray-finned fish (Actinopterygii) and lobefinned fish (Sarcopterygii). The oldest known fossils of bony fish are about 420 million years ago, which are also transitional fossils, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes.

Class Chondrichthyes Among the superclass Gnathostomata, class Chondrichthyes (Gr: chondrus=cartilage; ichthys=fish) is distinguished by (among other things) a cartilaginous skeleton. Sharks and rays (subclass Elasmobranchii) and a lesser known group called chimaeras, or ratfish, (subclass Holocephali) comprise the extant members of this class. Chondrichthyans share a distant ancestry with other jawed vertebrates, and retain some characteristics that may have been typical of early gnathostomes. The elasmobranchs are one of the more diverse groups within the fishes.

(B) Class Osteichthyes Subclass Sarcopterygii - fleshy-fin fishes (coelocanth) Lobe-fin fishes (coelacanth) Lung-fishes Subclass Actinopterygii- ray-fin fishes Superorder Chondrostei- sturgeons Superorder Holostei- gars and bowfins Superorder Teleostei- most bony fishes Extant members of the other gnathostome classes usually have bony skeletons, lungs or lung like structures, and other features that suggest they form a lineage that is separate from the sharks and rays. The class Osteichthyes the bony fishes, is a diverse assemblage of fish-like members of this line. It is usually divided into two groups: the ray fin fishes (subclass Actinopterygii), the fleshy-fin fishes (subclass Sarcopterygii).

Subclass Sarcopterygii Lobe-fin fishes - represented by only one extant form, the recently-discovered "living fossil", the lungless coelacanth from the Indian Ocean. Much like the extant lungfishes, many ancient lobe-fins lived in freshwater areas subject to stagnant conditions and drying up. Their functional lungs allowed them to breathe air, and their lobe -like fins allowed them to squirm over the ground. In the lobe-fins, the skeletal support for the paired fins extends out of the body wall, lending a lobe-like appearance to the fins. Lung-Fishes - six extant species of lungfish inhabit the Southern Hemisphere, usually living in stagnant, swampy areas gulping surface air. When water levels drop, they are capable of surviving burrowed in the mud in a state of torpor.

Subclass Actinopterygii- the rayfinned fishes The ray-fins have a long evolutionary history culminating in our most familiar fishes. There are three extant superorders of ray fin fishes: superorder Chondrostei (sturgeons and paddlefish), superorder Holostei (bowfins and gars), and superorder Teleostei (all other bony fishes). In the ray-fins, the skeletal support for the paired fins is inside the body wall, so that all you see of the fins externally are the raylike structures in the webbing of the fins themselves.

Jawless fish Conodonts Placodermi Chondrichthyes Gnathostomata Acanthodii Actinopterygii Osteichthyes (“Bony Fish”) Sarcopterygii

Answer the questions! 1. What characteristics can tell you about gnatostomatha? 2. Have gnatostomata a jaw? 3. How many types have gnatostomatha? 4. Which groups? 5. Which group consists of bony fish? 6. Chondrichtyes types are divided into 2 subclasses. Call it!

1. The class is divided into two subclasses: Elasmobranchii (sharks, rays and skates) and Holocephali 2). . . or bony fishes are a taxonomic group of fish that have bone, as opposed to cartilaginous skeletons a. Osteichthyes b. Chondrichthyes 3) The ray-fins have a long evolutionary history culminating in our most familiar fishes. There are three extant superorders of ray fin fishes: c. Actinopterygii 4) In some subgroup includes Ray-fin fishes: d. Indian Ocean 5)Lobe-fin fishes - represented by only one extant form, the recently-discovered "living fossil", the lungless coelacanth from the. . . e. Chondrostei, Holostei , Teleostei

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