Chondrichthyes
Sharks, skates and rays
Placoid scales
Ampullary organs
Placoid scales and drag

Chondrichthyes
No swim bladder for buoyancy
big liver
loss of weight
lift from tail, pectoral fins
Heterocercal vs. Homocercal tails
Heterocercal
Homocercal
Teeth in shark originate from modified
placoid scales
Enamel
Dentine
‘Denticles’

Denticles
Placoid scales
Teeth
Chondrichthyes
Septal gill design
Phylum Chordata
 Subphylum Urochordata (Tunicata)
 Subphylum Cephalochordata
Craniata group
 Subphylum 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 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
Sarcopterygii
Crossopterygii Several fossil forms with swim bladders
used as “lungs”
One living - Coelacanth
Crossopterygii
Homologies with Amphibia
Bones in fins correspond to bones in early
tetrapods
Labyrithodont teeth
Crossopterygian and
Labyrinthodont skulls
Crossopterygian fish
Early tetrapod
Fossil organisms showing a
fish/tetrapod transition
Acanthostega
Tiktaalik roseae
“Labyrinthodont” group
Actinopterygii - Ray-finned
Sacropterygii - fleshy-finned
Phylum Chordata
 Subphylum Urochordata (Tunicata)
 Subphylum Cephalochordata
Craniata group
 Subphylum Vertebrata
 Superclass Agnatha
 Superclass Gnathostomata
Class Placodermi
Class Chondrichthyes
Class Acanthodii
Class Osteichthyes
Class Amphibia
Class Reptilia
Tetrapods
Class Mammalia
Class Aves
From water to land:
From water to land:
“Problems”:
Support - Air is a thinner medium.
From water to land:
“Problems”:
Support - Air is a thinner medium.
Gas exchange - Oxygen in a different
state.
From water to land:
“Problems”:
Support - Air is a thinner medium.
Gas exchange - Oxygen in a different
state.
Temperature - Fluctuates more in air.
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?
Fossil amphibians
Amphibia - have aquatic larval stage



Toads and Frogs (Anura)
Salmanders (Urodela)
Caecilians (Gymnophiona)
Phylum Chordata
 Subphylum Urochordata (Tunicata)
 Subphylum Cephalochordata
Craniata group
 Subphylum Vertebrata
 Superclass Agnatha
 Superclass Gnathostomata
Class Placodermi
Class Chondrichthyes
Class Acanthodii
Class Osteichthyes
Class Amphibia
Class Reptilia
Tetrapods
Class Mammalia
Amniotes
Class Aves
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
Feathers
modification of skin
thermoregulation, flight
Microraptor gui
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
Distinguishing mammal from
reptile fossils
2. Lower jaw a single bone (dentary)
3. Jaw joint is articulation of dentary
and squamosal bone.
Major mammal groups:
Monotremes - oviparous
Therians - viviparous
Marsupials - partial internal - external
development
Therians - viviparous
Placentals (eutherians) - completely
internal development - Most diverse