How Are Birds & Reptiles Alike?

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Birds and reptiles are more similar than you may think! (Photo: Sharon Kennedy/iStock/Getty Images)

The relationship and similarities between reptiles and birds has fascinated scientists and animal lovers alike since the notion of evolution became accepted, and the results of their inquiries has been fruitful in producing evidence that birds and reptiles evolved from a prehistoric reptile. In addition to sharing a common ancestry that predates the age of dinosaurs, birds and reptiles feature several similar attributes and physical characteristics.

Reptiles and birds are oviparous, meaning they reproduce by laying eggs. (Photo: Jupiterimages/Photos.com/Getty Images)

They Lay Eggs

Birds and reptiles are oviparous, a word that literally means "egg bearing" and refers to animals that reproduce by laying eggs that develop outside the body. The structure of the amniotic shelled eggs reptiles and birds lay are quite similar, as are the cloaca orifices, where the eggs are laid from, that both of these species have. There is also evidence that suggests reptiles often show the same care and attention a mother hen will provide her young chicks, and birds and reptiles will protect their nests with a vigor few predators may test twice.

The skin of birds and reptiles are covered in various forms of scales. (Photo: Mike Watson Images/moodboard/Getty Images)

They Have Scales

The bodies of birds and reptiles are covered entirely with different versions of scales that have developed over hundreds of thousands of years. Reptiles feature the familiar scales we think of: the hide of a crocodile or the bumpy texture of a lizard's skin. Birds, on the other hand, only have scales like these on their legs and feet, but in reality their beaks, feathers and claws are all modified scales. These scales, like those found on reptiles, are made up of a tough structural protein called beta-keratin, which is harder and stronger than the alpha-keratin of found in the hair and nails of mammals.

Some birds can rotate their neck 270 degrees. (Photo: Nick Free/iStock/Getty Images)

Skeletal Similarities

Birds and reptiles also share several skeletal and internal characteristics. Both have five fused bones in their jaws, a single middle ear bone and an almost identical nucleated red blood cell structure. Reptiles and birds also have a single occipital condyle; this bony knob located at the back of the skull attaches the head to the neck. This single occipital condyle allows a wider range of motion than mammals and humans that have double occipitals, with some birds being able to rotate their necks more than 270 degrees.

Many think reptiles and birds are descended from theropods. (Photo: Aneese/iStock/Getty Images)

Ancient Ancestry

The leading theory in the evolution of modern reptiles and birds proposes that they descended from a common group of dinosaurs called theropods, which were carnivorous, bipedal (two-legged) dinosaurs that lived during the Triassic and Cretaceous periods. It is a widely accepted notion that birds and reptiles share an ancestry, but there is still no general consensus among paleontologists over the dinosaur lines they evolved from.

The idea of a close relationship between birds and dinosaurs was first proposed in the 19th century after the discovery of the primitive bird Archaeopteryx in Germany by Thomas Huxley, an admirer and follower of Darwin's works on evolution.

Birds and reptiles have one single line carrying the urinary, intestinal and reproductive tracts through their bodies. (Photo: Digital Vision./Photodisc/Getty Images)

A Cloaca

Unlike mammals, reptiles and birds have a cloaca that serves as their body's only means of waste, reproductive and intestinal tract evacuations. From the Latin word for "sewer," a cloaca serves as the only opening for the single line carrying the urinary, intestinal and reproductive tracts throughout the bodies of birds and reptiles.

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