Boundless (2016) Boundless Biology. Available at: https://www.boundless.com/biology/textbooks/boundless-biology-textbook/vertebrates-29/reptiles-174/characteristics-of-reptiles-672-11894/ .
Boundless (2016). Boundless Biology. Retrieved from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/vertebrates-29/mammals-176/characteristics-of-mammals-677-11899/
Boundless (2016). Boundless Biology. Retrieved from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/vertebrates-29/amphibians-173/characteristics-and-evolution-of-amphibians-668-11889/
Amphibians, Reptiles and Fish - National Wildlife Federation. (n.d.). Retrieved May 25, 2016, from https://www.nwf.org/Wildlife/Wildlife-Library/Amphibians-Reptiles-and-Fish.aspx
Boundless (2016). Boundless Biology. Retrieved from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/vertebrates-29/birds-175/characteristics-of-birds-675-11897/
Boundless (2016). Boundless Biology. Retrieved from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/vertebrates-29/mammals-176/characteristics-of-mammals-677-11899/
Boundless (2016). Boundless Biology. Retrieved from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/vertebrates-29/amphibians-173/characteristics-and-evolution-of-amphibians-668-11889/
Amphibians, Reptiles and Fish - National Wildlife Federation. (n.d.). Retrieved May 25, 2016, from https://www.nwf.org/Wildlife/Wildlife-Library/Amphibians-Reptiles-and-Fish.aspx
Boundless (2016). Boundless Biology. Retrieved from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/vertebrates-29/birds-175/characteristics-of-birds-675-11897/