Biology » Vertebrates » Reptiles

Summarizing Reptiles

Summary

The amniotes are distinguished from amphibians by the presence of a terrestrially adapted egg protected by amniotic membranes. The amniotes include reptiles, birds, and mammals. The early amniotes diverged into two main lines soon after the first amniotes arose. The initial split was into synapsids (mammals) and sauropsids. Sauropsids can be further divided into anapsids (turtles) and diapsids (birds and reptiles). Reptiles are tetrapods either having four limbs or descending from such. Limbless reptiles (snakes) are classified as tetrapods, as they are descended from four-limbed organisms. One of the key adaptations that permitted reptiles to live on land was the development of scaly skin containing the protein keratin, which prevented water loss from the skin. Reptilia includes four living clades: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles).

Glossary

amniote

animal that produces a terrestrially adapted egg protected by amniotic membranes

allantois

membrane of the egg that stores nitrogenous wastes produced by the embryo; also facilitates respiration

amnion

membrane of the egg that protects the embryo from mechanical shock and prevents dehydration

anapsid

animal having no temporal fenestrae in the cranium

archosaur

modern crocodilian or bird, or an extinct pterosaur or dinosaur

brumation

period of much reduced metabolism and torpor that occurs in any ectotherm in cold weather

Casineria

one of the oldest known amniotes; had both amphibian and reptilian characteristics

chorion

membrane of the egg that surrounds the embryo and yolk sac

Crocodilia

crocodiles and alligators

diapsid

animal having two temporal fenestrae in the cranium

Hylonomus

one of the earliest reptiles

lepidosaur

modern lizards, snakes, and tuataras

sauropsid

reptile or bird

Sphenodontia

clade of tuataras

Squamata

clade of lizards and snakes

synapsid

mammal having one temporal fenestra

temporal fenestra

non-orbital opening in the skull that may allow muscles to expand and lengthen

Testudines

order of turtles

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