Fish and Amphibians
Geology 331
Paleontology
Phylum Chordata: Subphyla Urochordata, Cephalochordata, and:
Subphylum Vertebrata
Class Agnatha: jawless fish, includes the hagfish, conodonts,
and ostracoderms (armored jawless fish)
Gnathostomates: jawed fish
Class Chondrichthyes: cartilaginous fish
Class Placoderms: armored fish
Class Osteichthyes: bony fish
Subclass Actinopterygians: ray-finned fish
Subclass Sarcopterygians: lobe-finned fish
Order Dipnoans: lung fish
Order Crossopterygians: coelocanths and rhipidistians
Class Amphibia
lampreys,
Urochordates: Sea Squirts. Adults have a pharynx with
gill slits. Larval forms are free-swimming and have a
notochord. Chordates are thought to have evolved from
the larval form by precocious sexual maturation.
Chordate evolution
Cephalochordate: Branchiostoma,
the lancelet
Pikaia, a cephalochordate from the Burgess Shale
Yunnanozoon, a cephalochordate from the Lower
Cambrian of China
Haikouichthys,
agnathan, Lower
Cambrian of
China Chengjiang fauna,
scale is 5 mm
A living jawless fish, the lamprey,
Class Agnatha
Jawless fish do
have teeth!
A fossil jawless fish, Class Agnatha,
Ostracoderm, Hemicyclaspis, Silurian
Agnathan,
Ostracoderm,
Athenaegis,
Silurian of Canada
Agnathan,
Ostracoderm,
Pteraspis,
Devonian of
the U.K.
Agnathan,
Ostracoderm,
Liliaspis,
Devonian of
Russia
Jaws evolved by
modification of
the gill arch
bones.
The placoderms
were the armored
fish of the Paleozoic
Placoderm, Dunkleosteus, Devonian of Ohio
Asterolepis,
Placoderms,
Devonian of
Latvia
Placoderm, Devonian of Australia
Chondrichthyes: A freshwater shark of the
Carboniferous
Fossil tooth of a
Great White shark
Chondrichthyes, Great White Shark
Chondrichthyes, Carcharhinus
Sphyrna - hammerhead shark
Himantura - a ray
Manta Ray
Fish Anatomy: Ray-finned fish
Osteichthyes: ray-finned fish:
clownfish
Osteichthyes: ray-finned fish, deep water
species
Lophius, an Eocene
fish showing the ray
fins. This is an
anglerfish.
Osteichthyes, ray-finned fish, Jurassic
Leptolepis, ray-finned, Jurassic of
Australia
Osteichthyes, ray-finned fish, Eocene, Wyoming
Fish Anatomy: Lobe-finned fish
Osteichthyes, lobe-finned fish,
Devonian of Scotland
Coelocanth, a
living lobefinned fish:
Osteichthyes,
Sarcopterygian
A Coelocanth
Evolution of the tetrapod walking leg from
the lobe fin
Sauripterus,
rhipidistian, Late
Devonian,
Pennsylvania
Late Devonian digits from a lobe-finned fish,
Pennsylvania
Hindlimb of Ichthyostega, Devonian of Greenland
Ichthyostega: Photographs of part and
counterpart superimposed to show seven digits
Skull roof of
the Late
Devonian
tetrapod
Ichthyostega
Tetrapods: Acanthostega and
Ichthyostega, Devonian of Greenland.
Fish or Amphibians?
Evolution of
Tetrapods
South American lungfish in its burrow. The
lung evolved in early Devonian bony fish and
became the swim bladder of ray-finned fish.
Mudskippers,
ray-finned fish
acting like
amphibians.
They gulp air
into their swim
bladder.
The
evolutionary
step from fish to
amphibian was
not difficult.
Looking for water in the Devonian
Permian amphibian, Seymouria, with 5 digits