Differences Between Reptiles & Birds
Scientists teach that birds evolved from reptiles. The first birds began evolving sometime during the Mesozoic era, from 144 million years to 66 million years ago, according to the PBS science television program Nature. Although birds and reptiles appear very different on the outside, both species lay eggs. Reptiles are a diverse species in that various reptiles do not closely resemble each other. Reptiles include alligators, crocodiles, lizards, snakes and turtles. However, despite evolving from reptiles, birds and reptiles have many differences.
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Metabolism
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One of the key differences between reptiles and birds is metabolism. While reptiles are cold blooded, or ectothermic, birds are warm blooded or endothermic. That means the main source of body heat for a reptile is absorbing external heat, which is why you often see reptiles basking in sunlight. It is their way of raising and regulating their body temperature. On the other hand, birds have the ability to keep their body warm through metabolism, which is the process of converting food into energy in the body.
Skeleton and Wings
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Some key differences between reptiles and birds involve their skeletal structure and the fact that birds have wings. Reptiles have solid bones that are dense and they travel on land or in the water. Birds have hollow or pneumatic bones filled with air that are lighter and allow them to fly, according to Texas A&M University Department of Biological and Health Sciences. In addition, birds have a lightweight beak instead of teeth, or a heavy jaw.
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Skin
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Reptiles have dry, glandless skin with scales, according to the Oklahoma School of Science and Mathematics Biology Department. Feathers cover birds. However, biologists say there are similarities between the early development of reptile scales and bird feathers. In addition, bird feather is "made primarily of beta keratin, as is reptile scale," according to Texas A&M University. The feathers that cover the wings and bodies of birds are not only lightweight, which helps with flight, but the feathers also insulate birds, which helps them to maintain a high body temperature.
Heart
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Most reptiles have a three-chamber heart, with the exception of crocodiles, which have a four-chamber heart, according to the Oklahoma School of Science and Mathematics. However, all birds have four-chambered hearts, according to Texas A&M University.
Eggs
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Although both reptiles and birds reproduce through eggs, there are differences in the eggs of the two species. Most reptiles, like birds, lay eggs. The exceptions include some snakes that are viviparous, meaning the "embryo develops in a placenta-like structure inside of the mother's uterus," according to the Oklahoma School of Science and Mathematics. Moreover, there are a few snakes that are ovoviviparous and the eggs hatch inside the snake. However, the majority of reptiles, like birds, are oviparous and lay fertilized eggs in shells from which live offspring hatch. Nevertheless, there are differences in the shells of the eggs laid by reptiles and birds. The shells of reptile eggs are flexible, or leathery, while the shells of birds are inflexible, or hard.
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References
- Oklahoma School of Science and Mathematics: Vertebrate Zoology Lecture Notes
- Texas A&M University, Kingsville, Department of Biological and Health Sciences: Chapter 17 - Aves, Feathers and Flight
- Back Yard Nature.net: Birds as Little Dinosaurs, by Jim Conrad M.Sc. in Botany, B.Sc. in Biology & Geology
- PBS, Nature: American Eagle Bald Eagles' Evolutionary Ancestors
- Photo Credit turtle and duck image by JASON WINTER from Fotolia.com
