Jawed Fishes

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Jawed Fishes

• Superclass Gnathostomata

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Whats the big deal about jaws?

• Allows grasping of objects
• Makes herbivory possible
• Can take bites and grind up food
• Perhaps the greatest of all advances in
  vertebrate history was the development of jaws
  and the consequent revolution in the mode of life
  of early fishes.
• Albert Sherwood Romer

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How did jaws evolve?

• Theory expansion of the third gill arch into a
  lower jaw
• Butno fossil intermediates between jawless and
  jawed fishes to say for sure

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Jawless fish
3rd Gill Arch
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3rd gill arch enlarges and swings forward
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Jawed Fish
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Why did jaws evolve?

• Old theory increased feeding efficiency
• New theory jaws provide suction, which means
  better gill ventilation. Better feeding
  efficiency was a side effect.

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Fish Systematics

• Cladists consider there to be 8 classes in the
  phylum Chordata
• 7 of these classes are fish!
• 1 class contains some very old fish AND all other
  vertebrates

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Traditional Systematics considers there to be 3
classes of fish

• Kingdom Animalia
• Phylum Chordata
• Subphylum Vertebrata
• Class Amphibia
• Class Reptilia
• Class Aves
• Class Mammalia
• Class Agnathajawless fish
• Superclass Gnathostomata
• Class Chondrichthyescartilaginous fish
• Class Osteichthyesbony fish

This is the system we will use for this class (to
keep it simple!)
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Superclass Gnathostomata

• Extinct
• Class Placodermi
• Class Acanthodii

• Living
• Class Chondricthyes
• Cartilaginous fishes
• Class Osteichthyes
• Bony fishes

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Superclass Gnathostomata

• Have jaws and paired fins
• More complex vertebrae than Agnatha
• Most numerous and diverse of vertebrate groups
• 24,600 species named (may actually be around
  28,500)
• Present in almost every imaginable aquatic habitat

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Class Placodermi (extinct)

• Covered in a
• thick bony shield
• Marine and freshwater species

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Class Acanthodii (extinct)

• Stout spines
• Up to 6 pairs of ventrolateral fins

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Class Chondrichthyes (living)Cartilaginous Fishes

• Sharks
• Rays
• Ratfish
• Much more later

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Class Osteichthyes (living)Bony Fishes

• All other fish

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• Class Osteichthyes
• Subclass Sarcopterygii (lobe-finned)
• Relict bony fishes
• Coelacanths, lungfish
• Subclass Actinopterygii (ray-finned)
• Infraclass Chondrostei
• Sturgeons, paddlefish
• Infraclass Neopterygii
• Gars, bowfin
• Modern bony fishes, the teleosts
• Remaining 22,000 or so species

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General Characteristics

• osteo bone
• ichthyes fish
• Bones in skeleton
• Respiration by gills, covered by operculum
• Mouth is usually terminal
• Have jaws

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Scale types of bony fishes

• Cosmoid
• Lungfishes and some fossil fishes only

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Scale types of bony fishes

• Ganoid
• Shaped like a rhombus
• Fit together with pegs and sockets
• Bowfin, gars, paddlefish, sturgeons

Peg
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Scale types of bony fishes
Cycloid

• Cycloid and ctenoid
• Most modern bony fish
• Overlapping
• Thin and flexible
• Can count growth rings, like in a
• tree stump

Ctenoid
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Scaleless Fish

• Less protection
• More flexibility
• Some catfishes and sculpins
• Other fishes have scaleless heads

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Subclass SarcopterygiiRelict Bony Fishes

• Thought to be closely related to terrestrial
  vertebrates because of structure of limbs
• Paired fins and lungs
• Enamel on teeth
• Lungfish (freshwater)
• Coelacanths (marine)

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Lungfishes

• Two orders
• Australia
• South America and Africa
• Long bodies
• Continuous rear fins
• Fins are fleshy
• Lungs are modified swim bladders

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Australian Lungfish

• One species
• Live in rivers that shrink to small pools in
  summer
• Has one lung that supplements oxygen
• Mainly breath through gills
• Thought to have remained unchanged for 100
  million years

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African and South American Lungfishes

• 2 species
• Have 2 lungs
• Live in swamps that
• dry up periodically
• Dig burrows, line them with mucus, and estivate
  until it rains
• During estivation, breath air through a small
  hole in burrow
• When rain enters burrow, water enters gills and
  they awaken by coughing

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Coelacanths

• Thought to be extinct until one found in
  1938very exciting!
• Life in the slow lane
• 1.3 m long
• Live up to 48 years, reproduce at 9 years
• Longest known gestation period of any animal--3
  years

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Groups hide (from sharks) in caves during the
day, travel up to 8km at night to forage. Do
headstands on the bottom.
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Subclass Actinopterygii (ray-finned fish)

• This subclass includes more old fish, and also
  all modern bony fish
• Fins are not fleshy like the lungfish, but have
  hard rays instead
• Infraclass Chondrostei
• Infraclass Neopterygii

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Infraclass Chondrostei

• Old fish
• Bottom-dwellers that eat invertebrates
• Thought to be a link between sharks and bony fish
• Skeleton more cartilaginous, like sharks
• Tail heterocercal, like sharks
• Ventral mouth (directed downward, under nose)
• BUT operculum and some bone, like bony fish

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Heterocercal Tail

Homocercal Tail

K.T. Shao
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Infraclass Chondrostei

• Order Polypteriformes
• All live in Africa
• Have multiple dorsal finlets
• Ganoid scales
• Fins are intermediate between ray fins and fleshy
  fins
• Can live in stagnant water with low O2

--the bichirs
J. Moreau
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Infraclass Chondrostei

• Order Acipensieriformes
• Family Acipenseridaesturgeons (23 species)
• Skeleton mostly cartilaginous
• Large bony plates on head
• 3-30 feet long, 1300 lbs
• Live up to 60 years
• Valued for caviar
• Eat worms, molluscs, crustaceans

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Sturgeons
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Infraclass Chondrostei

• Order Acipenseriformes
• Family PolyodontidaePaddlefish
• 2 species one in U.S., one in China
• 7 feet long, 250 lbs
• Long snout is covered with tastebuds
• Also valued for caviar
• Polydon spathula present in WV

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L. Lovshin
Paddlefish
L. Lovshin
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• Order Semionotiformes
• Family Lepisosteidae--Gars
• Diamond-shaped, non-overlapping ganoid scales
• Heterocercal tail
• To 9 feet, 220 lbs
• 7 species, 2 in WVlongnose gar and shortnose gar
• Predatory
• Sluggish except when catching prey
• Bony snout with lots of teeth

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• Amiiformes
• Family AmiidaeBowfin
• 1 species
• Present in WV
• Shallow, weedy waters
• Voracious predator
• Can breath by gulping air
• Thin layer of bone covers cartilaginous skull,
  otherwise skeleton is mostly cartilage

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Vocabulary

• Tetrapod
• Terminal mouth
• Estivation
• Heterocercal
• Homocercal
• Ventral
• Dorsal
• Lateral

• Proximal
• Distal