The number of species of terrestrial vertebrates reached its maximum in the middle
Miocene, 12-14 million years ago, and had declined since.
Major Groups of Vertebrates
Two major groups are Amniotes and non-Amniotes.
Generally, amniotes are terrestrial and non-amniotes are aquatic, but there are a few
o Are animals that have an amnion which surrounds the embryo. This is one of three
fetal membranes derived from the embryo.
Secondarily aquatic animals such as sea turtles and whales are exceptions to the
terrestrial Amniote pattern.
o Ancestral characters of this group includes scaled-covered skins without an
insulating layer of hair of feathers, a simple kidney, simple lungs, and a heart
without a septum dividing the ventricle.
o During the Late Devonian Period Amniotes broke into Sauropsides (reptiles and
birds) and Synapsids (mammals).
o Sauropsid Amniotes
Contains turtles, scaly reptiles, crocodilians, and birds.
Extinct sauropsids include dinosaurs, pterosaurs (flying reptiles), ichthyosaurs,
Turtles (Testudinia) ~209 species
Only vertebrates with pectoral girdle and pelvic girdle inside the ribs.
Tuatara, Lizards, and Snakes (Lepidosauria)
Tuatara (2 species) only remnants of sphenodontida lineage.
Lizards (5000 species) and snakes (3015) species are at the peak of their
Alligators, and Crocodiles (Crocodilia) ~23 species
From same lineages as dinosaurs and birds (Archosauria).
Crocodilians range between less than a meter to 7 meters long.
Skin contains bones (Osteoderms) that act as armor.
Birds (Aves) ~9670 species
Lineage of dinosaurs that evolved for flight during the Mesozoic.
Feathers characteristic of extant species.
Dinosaur fossils with feather show they came before flight.
o Synapsid Amniotes ~4800 species Living mammals can be traced back to an origin in the late Paleozoic Era.
Most mammals are placental.
Contains 3 kinds of extant mammals:
1. Monotremes (Prototheria; Platypus and echidna)- hatchyoung from eggs.
2. Marsupials (Metatherians)- have a placenta, but have a shorter gestation
period and must care for immature young.
3. Placentals (Eutherians)
Extincit Synapsids include pelycosaurs, therapsids, an multituberculates.
o Embryos enclosed by membrances produced by the reproductive tract of the female
o Hagfishes and Lampreys (Myxinoidea and Petromyzontoida)
Elongate, limbless, scaleless, slimy and have no internal bony tissue.
Scavengers and parasites
Lack jaws and were therefore traditionally grouped as agnathans or cyclostomes.
Hagfishes are marine and live on the seabed. They have a skull, but no vertebral
Lampreys are mostly migratory (live in oceans and spawn in rivers). They have a
o Sharks, Rays, and Ratfishes (Chondrichthyes)
"Cartilage- fish" -Cartilaginous skeletons
Extant sharks and rays form a group called Neoselachii
Sharks range 15cm to 10 meters.
Rays are dorsoventrally flattened and are frequently bottom dwellers
that swim with the undulations of their pectoral fins.
Ratfishes or chimaeras consist of 33 species in the group Holocephalii ("whole
head") which refers to the single gill cover that extends over all four gill
They live on the sea floor and eat crustaceans and mollusks.
o Bony Fishes (Osteichthyes)
"Osteo"=Bone and "ichthyes"= fish
Ray finned fishes (actinopterygians) consist of 27000+ species discovered
1. Chondrostei (bichins, sturgeons, and paddles fishes)
i.Gars (Lepisosteiformes, 7 species)
ii.Bowfin ( one species, Arnia calva)
iii.Teleostei (27000+ species including trout and bass)
Lobe-finned fishes / fleshy finned (Sarcopterygians)- 8 species
6 Species of lungfishes (Diproi)