Amniotes

Amniotes =

Reptiles + birds + mammals

Amniotes completed the first transition from …

water to land. Adapted to terrestriality.

Most important feature of amniotes.

Amniote egg

• tough shell - prevents water loss

• Amnion encloses sac of water (amniotic cavity)

What are the four extra embryonic membranes in amniote eggs?

• Amnion

• Chorion

• Allantois

• Yolk sac

Amniotes evolved from a lineage of ….

amphibians related to anthracosaurs in the Carboniferous (350 mya)

Amniote groups include

Synapsids - one hole

Diapsids - two holes

Anapsids - no holes.

Skull fenestrae

Traditional class of Amniotes

Class Reptilia

Class Aves

Class Mammalia

Orders in Class Reptilia

Order Squamata (snakes and lizards)

Order Sphenodonta (tuatara)

Order Testudines (turtles)

Order Crocodilia (crocodilians)

Amniote Characters

• Amniote egg

• Keratinized epidermis

• Aspiration breathing

• Greater separation of pulmonary and systemic circuits > high pressure blood flow.

  • Uricotelism (most reptiles) or ureotelism (mammals and some turtles)

Order Testudines

Turtles - amniotes.

Terrestrial, freshwater, and marrine.

• bony shell consisting of dorsal carapace and ventral plastron

• Temperature-dependent sex determination

Order Squamata

Snakes and lizards

Terrestrial, burrowing, freshwater, marine

• Snakes , dervided limbless lizards - amniotes

• Entire clade has a modified diapsid skull

  • lower temporal bar lost

  • enables internally moveable (kinetic) skull

• males with hemipenes

Suborder Sauria

Amniotes - Lizards

• oviparous or viviparous

• chameleons - tongue projection

Suborder Serpentes

• highly modified skulls - swallow large prey

• Venom

• infared sense in pit vipers like rattlesnakes

• Use tongue and vomeronasal organ to smell

• constriction to suffocate prey

Four modes of movement in snakes

• Lateral undulation

• Concertina

• Rectilinear

• Sidewinding

Order Sphenodonta

Tuatara - Amniotes

• lizard-like. Offshore islands in New Zealand.

• Complete diapsid skull retained

• Well-developed parietal eye

• Highly threatened by rats

Order Crocodilia

Alligators and Crocodiles - Amniotes

• 23 spp.

• Survivors of archosaur radiation

• diapsid skull

• thecodont dentition

• amphibious - saltwater and freshwater

• Well-dev parental care

Dinosaur Groups

• Saurischians

• Ornithischians

Extinct Reptile Groups that aren’t dinos

• Pterosaurs

• Icthyosaurs

• Plesiosaurs

• Pelycosaurs

Saurischians

• Theropods

• Sauropods

Ornisthischians

• Ceratopsians

• Stegosaurs

• Ornithopods

• Ankylosaurs

End-Cretaceous Extinction

65 mya, all non-avian dinos went extinct.

2 hypotheses:

• Asteroid impact

• Volcanism