- Superclass: Gnathostomata

“jaw-mouthed vertebrates”

~430 million years ago

Mandibular

arch Hyoid

arch

Gill

arches

• Two new characteristics:

• Jaw - Allows consumption of larger, more diverse prey.

• Paired fins - at least two sets of paired fins: pectoral and pelvic. Gives stability and lift, prevents roll.

pitch

yaw

roll

• Big evolutionary radiation after advent of first jawed fish...

– Acanthodians

– Placoderms

– Chondrichthyes

– Sarcopterygii

– Actinopterygii

• Phylum Chordata

– Subphylum Urochordata (Tunicata)

– Subphylum Cephalochordata

– Subphylum Craniata

-Vertebrata • Superclass Agnatha

• Superclass Gnathostomata – Class Placodermi

– Class Chondrichthyes

– Class Acanthodii

– Class Osteichthyes

– Class Amphibia

– Class Reptilia

– Class Mammalia

– Class Aves

Acanthodians -

• Body armor like ostracoderms, fins w/spines

• Skeleton had some bone

(p.63)

Placoderms - “plate-skinned” fish

• Bony plates are in smaller pieces compared to ostracoderms

• Mostly fed on bottom, some mid-level predators

(p.59)

placoderm skull

1 fossil shows live birth

Chondrichthyes

• Sharks, skates and rays

Placoid scales

Ampullary organs

• No swim bladder for buoyancy

– big liver

– loss of weight

– lift from tail, pectoral fins

Chondrichthyes • Heterocercal vs. Homocercal tails

Heterocercal

Homocercal

• Teeth in shark originate from modified placoid scales

‘Denticles’

Enamel

Dentine

Septal gill design

Chondrichthyes • Phylum Chordata

– Subphylum Urochordata (Tunicata)

– Subphylum Cephalochordata

– Subphylum Craniata

-Vertebrata • Superclass Agnatha

• Superclass Gnathostomata – Class Placodermi

– Class Chondrichthyes

– Class Acanthodii

– Class Osteichthyes

– Class Amphibia

– Class Reptilia

– Class Mammalia

– Class Aves

Osteichthyes

• “Bony fish”

• By far the most diverse class.

• Swim bladder (or gas bladder) present in most species

Swim bladder

• Opercular gills - bony covering overlying gill slits

Some major groupings in Osteichthyes

• Actinopterygii

– Teleostei

• Sarcopterygii

– Dipnoi

– Crossopterygii

2 major groups:

• Actinopterygians - ray-finned fish

– dominant form presently

– fins move via muscles in body wall

– fins w/ Lepidotrichia

Actinopterygii

• Teleosts - diverse group of Actinopterygians

– Recent radiation - 65 million years ago

– Has a derived swim bladder design (detached from gut)

• Sarcopterygians - fleshy-finned fish

– Thicker fins - muscles within fins

– Swim bladder connected to gut (ancestral)

– Internal nostril (choana) first arose in this group

fossil sarcopterygian w/choana

Early choanates

Sarcopterygii • Dipnoi - lungfish

– Paired lungs

– Survive in mud by breathing air.

– In warm waters - not as much dissolved oxygen

• Crossopterygii -

– Several fossil forms with swim bladders used as “lungs”

– One living - Coelacanth

Sarcopterygii • Crossopterygii

• Homologies with Amphibia

– Bones in fins correspond to bones in early tetrapods

– Labyrithodont teeth

Fossil organisms showing a fish/tetrapod transition

Tiktaalik roseae

Acanthostega

“Labyrinthodont” group

From water to land:

“Problems”:

Support - Air is a thinner medium.

Gas exchange - Oxygen in a different state.

Temperature - Fluctuates more in air.

Keeping moist - How to keep tissues, eggs, young moist?

Amphibia - have aquatic larval stage

• Toads and Frogs (Anura)

• Salmanders (Urodela)

• Caecilians (Gymnophiona)

• Phylum Chordata

– Subphylum Urochordata (Tunicata)

– Subphylum Cephalochordata

– Subphylum Craniata

-Vertebrata • Superclass Agnatha

• Superclass Gnathostomata – Class Placodermi

– Class Chondrichthyes

– Class Acanthodii

– Class Osteichthyes

– Class Amphibia

– Class Reptilia

– Class Mammalia

– Class Aves

Tetrapods Amniotes

Amniotes

• Amniotes - have embryos with extra-embryonic membranes

– amnion keeps water from leaving the egg or developing young.

Major living ‘reptile’ groups:

• Lizards and snakes (Squamata)

• Crocodiles and alligators (Crocodilia)

• Turtles (Testudinata)

Aves

• Most diverse class of tetrapods

• Feathers

– modification of skin

– thermoregulation, flight

Endothermy

• Puts particular requirements on some physiological systems:

• Circulatory, respiratory systems must be efficient and work at high rates

Mammalia Defining characteristics:

• Hair - for insulation, sensation.

• Mammary glands

• Other glands - sweat and sebaceous glands.

Distinguishing mammal from reptile fossils

• Via fossil evidence:

1. Three bones make up middle ear: malleus, incus, stapes

Theraspid

2. Lower jaw a single bone (dentary)

3. Jaw joint is articulation of dentary and squamosal bone.

Distinguishing mammal from reptile fossils

Major mammal groups:

• Monotremes - oviparous

Therians - viviparous

• Marsupials - partial internal - external development

Therians - viviparous

• Placentals (eutherians) - completely internal development - Most diverse