- Superclass: Gnathostomata
“jaw-mouthed vertebrates”
~430 million years ago
• 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.
roll
Mandibular
arch
Hyoid
arch
Gill
arches
pitch
yaw
• 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
–
–
–
–
–
–
–
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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
placoderm skull
• Bony plates are in smaller pieces compared
to ostracoderms
• Mostly fed on bottom, some mid-level
predators
Chondrichthyes
• Sharks, skates and rays
Placoid scales
Ampullary organs
(p.59)
1 fossil shows live birth
Chondrichthyes
• Heterocercal vs. Homocercal tails
• No swim bladder for buoyancy
Heterocercal
– big liver
– loss of weight
– lift from tail, pectoral fins
Homocercal
• Teeth in shark originate from modified
placoid scales
Enamel
Dentine
‘Denticles’
Chondrichthyes
Septal gill design
• 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
Swim bladder
• “Bony fish”
• By far the most diverse class.
• Swim bladder (or gas bladder) present in
most species
• 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
• 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
Actinopterygii
• Teleosts - diverse group of Actinopterygians
– Recent radiation - 65 million years ago
– Has a derived swim bladder design (detached
from gut)
Sarcopterygii
• Dipnoi - lungfish
– Paired lungs
– Survive in mud by breathing air.
– In warm waters - not as much dissolved oxygen
Sarcopterygii
• Crossopterygii – Several fossil forms with swim bladders used as
“lungs”
– One living - Coelacanth
Fossil organisms showing a
fish/tetrapod transition
Acanthostega
Tiktaalik roseae
“Labyrinthodont” group
• Crossopterygii
• Homologies with Amphibia
– Bones in fins correspond to bones in early
tetrapods
– Labyrithodont teeth
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 extraembryonic 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
Endothermy
• Feathers
• Puts particular requirements on some
physiological systems:
– modification of skin
– thermoregulation, flight
Mammalia
Defining characteristics:
• Hair - for insulation, sensation.
• Circulatory, respiratory systems must be
efficient and work at high rates
Distinguishing mammal from reptile fossils
• Via fossil evidence:
1. Three bones make up middle ear:
malleus, incus, stapes
• Mammary glands
• Other glands - sweat and sebaceous glands.
Theraspid
Distinguishing mammal from reptile
fossils
2. Lower jaw a single bone (dentary)
Major mammal groups:
• Monotremes - oviparous
3. Jaw joint is articulation of dentary and
squamosal bone.
Therians - viviparous
• Marsupials - partial internal - external
development
Therians - viviparous
• Placentals (eutherians) - completely
internal development - Most diverse