Gnathostomes-jawed fish

Innovation: the jaw

Biting devices derived from anterior pharyngeal arches. Redundant elements

Importance of metamerism

New ecological niche that leads to adaptive radiation

Biting to capture prey and pulverize it. Tend toward larger prey and larger size. Vertebrates are big animals relative to most invertebrates and this is part of the reason-jaws.

Class Placodermi-axis of tail tilts up, head and thoracic armor shields separate and joined by a hinge, notochord persists, had claspers like chondrichthyes. Paired fins.

Placodermi likely lacked a swimbladder and may have suffered heavy predation pressure based on head and thoracic armor shields.

Innovation: paired fins

Pectoral and Pelvic

Precisely controlled roll

How do fish behave in water-

Roll (rotation around long sagittal axis) pectoral and/or pelvic fins, sometimes dorsal fin

Pitch (rotation around transverse axis) tail fin

Yaw (rotation around vertical axis, side-to-side movement) myomeres and/or pelvic fins

A structure that adds stability for one may increase instability for another.

For example having extreme lateral compression of the body tends to make a fish taller. This tends to decrease roll, but increase yaw instability.

Heteroceral tails increase lift

Hypoceral tails decrease lift

Better control, means you can chase down more active prey, larger prey. Better sensory system, better muscle coordination, bigger brain, evolutionary arms race between prey and predator with sensory and locomotor control.

These fish can take bait trolled at 28 km/hr and can swim for short distances at twice that speed.

Pointed pectoral fins

High aspect ratio (the span/chord)

Laterally compressed

Short and long dorsal fins.

Fusiform tapered body.

Trout can accelerate at 40 m/sec/sec

Impediments to movement

Frictional drag

SHOW OVERHEAD HILDEBRAND page 530

Laminar flow at slow speeds, little drag.

Class Chondrichthyes-males have claspers, skeleton cartilaginous, small and abrasive scales, external series of gill slits

Both Placodermi and sharks had claspers suggesting internal fertilization.

Class Acanthodii-bony opercular, blunted snout, scales are small and thick, axis of tail tilts upward, eyes large and lateral, armor shields absent, multiple paired fins with spines and webbing between spines.

Class Osteichthyes-well ossified skeleton, gills of each side of the body in a common chamber covered by a movable bony operculum, lung or gas bladder present. Vast majority of moder fishes are Osteichthyes.

Buoyancy released constraints of tail shape for providing lift-instead more homoceral.

Swim bladder-modifies buoyancy at will. Becomes a pre-adaptation for lungs since it is an air-filled sac. Changes the relative importance of pectoral fins and the caudal fin in maintaining elevation and/or pitch…consequence-mostly homoceral tail.

Subclass Actinopterygii-ray-finned fishes-most fish you think of.

Fins lack fleshy stalks (95% of all fish)

Significance of rays through a fin--increase control.

The fin can be retracted, extended, or undulated.

Subclass Sarcopterygii-fleshy fins includes lungfish, internal nares,

poorly ossified (secondarily), degenerate scales.

Subclass Crossopterygii-functional lungs, internal nares (open into

mouth), advanced circulatory system, conical teeth, gave rise to

amphibians

Pre-adaptations:

swim bladder,

lobed heavily muscularized fins,

fish that walked on the bottom (pre-locomotor adaptation), poorly oxygenated water where multiple sources of air may be required. Vascularized skin.

Importance of bones.

Pelvic and/or pectoral girdle in close proximity to vertebrae

Why do we have four limbs-mostly because the crossopterigian fish from which tetrapods were derived had pectoral and pelvic girdles

Class Amphibia-legs! (except caecilians) vertebral column attaches to pelvic girdle attaches with single pair of sacral ribs and one sacral vertebra, vascularized thin and moist skin evolved from. Evolved from crossopterigians.

Labyrinthodonts

Lepospondyls

Lissamphibians (modern amphibians)…

Based on vertebrae structure. Not likely to be accurate anymore.

Recent fish ancestors of amphibians is one thing that is unlikely to change regarding our concepts of evolutionary relationships among vertebrates.

Even fossil amphibians show evidence of a lateral line system among juveniles of many extinct species….this is a purely aquatic sensory organ.

The earliest known amphibians also possessed fin rays and a large notochord extending into the braincase.

A notochord functions well in aquatic environments because of its flexibility, but because the effects of gravity aren't kind.

Perhaps one of the more surprising findings that changed the way we think about our own evolutionary history, were the number of digits they found on different amphibian fossils. Sometimes five..but sometimes six or even seven..sometimes different numbers in the front and back.

We will be talking about this in one of our discussion sessions later..so I won't dwell on it now..but it seems to suggest the reason for our having five digits was a product of serendipity rather than any real adaptive value of having 5 digits over 4 or 6, or even seven.

Class Reptilia-pelvic girdle attaches to the vertebral column by at least two sacral vertebrate. Horny scales cover skin. Cleidoic egg, amnion surrounds embryo, stored yolk. Calcareous shell secreted by the oviduct

Class Aves-endothermic (4 times higher metabolic rate than reptiles), produced mostly by visceral organs, feathers, subcutaneous fat, pectoral appendages modified as wings, horny bill, keeled sternum

Class Mammalia-hair, mammary glands, independent evolution of endothermy,

Show overhead of figure page 53 Hilderbrand-synapomorphies

No scales

Single median nasal opening

Most had headshields

Most had a prominent rostrum

Mostly external skeleton

Hypoceral tail

Paired nostrils

No paired appendages

gill pouches

Fusiform bodies sometimes occur.

Often dorsoventrally flattened bodies

Lobed heads

No paired appendages

includes lampreys

Secondarily cartilaginous skeleton

Pelvic claspers

Internal fertilization

Large livers with oil

Varied reproduction methods

bony opercula (placoderm/osteichthyes)

non-overlapping scales (chondrichthyan)

subterminal mouth (chondrichthyan)

partially ossified skeleton (osteichthyes)

axis of tail tilts upward (chondrichtyans)

eyes large, lateral, anterior (?)

paired spiny webbed fins (?)

common chamber

• Movable bony operculum
• lung or gas bladder present.
• Usually overlapping scales
• Fins possess rays

Have lobed appendages

Heavily ossified skeltons

Muscularized fin lobes

(used for pivoting or manuevering in soft bottoms)

Includes lungfishes and coelacanths.

Swim bladder present

Lobed heavily muscularized fins

Fish that walked on the bottom

Live in poorly oxygenated water, ephemeral pools

Vascularized skin

Well ossified skeleton

Legs (except caecilians)

Vertebral column attaches to pelvic

Vascularized thin skin

Mucous glands

Papilla amphibiorum-unique auditory

Aquatic larval forms common

Scales

Ectothermic

Respiration primarily through lungs

Flight

Endothermy

Sebaceous and sweat glands

Mammary glands

Blood cells that lose nuclei when mature

openings separated by postorbital and

squamosal

opening bordered below by postorbital

and squamosal