Differences and Similarities between Reptiles and Birds

The people who study evolution claim that birds evolved from reptiles. However, there are very many structural differences which demonstrate that these two classes are very different from each other, casting doubt that that kind of evolution could have occurred between them.  Though they may have some similarities the differences outdo them (Anatomy of Animals, 2009).

Differences between birds and reptiles
Anatomical differences

     The bone structure of the species of these two classes is very different. People who study evolution claim that dinosaurs were the ancestors of birds, but they had a very thick and solid bone due to their massive structure. The bones of all living and extinct birds is hollow making it to be very light. They are also filled with extensions of air sacs that allow increased respiration efficiency. The skeletal system of a bird plays a very major role in the process of flight. It is extremely light and strong enough so that it can withstand the stress of taking off and landing. The other difference is the presence of feathers in birds and its absence in reptiles (Scientific Memoirs III, 1870). Reptiles have whole of their bodies covered with scales. Birds have highly shortened tails as compared to dinosaurs which had a very long and bony tail. Birds do not have a true jaw or teeth. Their stoma cavity is covered by a horny beak that is extremely light in weight. Reptiles on the other hand have two jaws and they are covered by teeth. Birds are the only animals that have a fused collar bone. Their neck vertebrate is also more cervical than that of reptiles (Feuerbacher, 2009).

Biological differences
The digestive systems of birds and reptiles show very remarkable differences. Reptiles have a very slow metabolic rate while the birds have a very fast metabolic rate. As a result of metabolism, birds can produce their own body heat while reptiles due to theirs low metabolism rate cannot produce their own body heat. Reptiles depend on the solar heat in order to warm their bodies. Reptiles consume a very small amount of energy in nature whereas birds are the highest energy consuming animals. In case of an infection, reptiles tend to lower their body temperatures as bacteria cannot thrive at low temperatures whereas the temperature of birds increases in case of an infection (Anatomy of Animals, 2009).

 Respiratory system
According to Wissman (2006), respiratory system of birds and reptiles are very different. In reptiles, air taken in enters the lungs through the trachea and then through the same trachea, air is breathed out. The process of breathing in birds is very different from that of reptiles. Air follows a one way journey all the way to the lungs and after entering the lungs, it follows the lungs channels and leaves the lungs from the other side. Birds therefore have a much modified type of respiratory system than all other living creatures. Birds do not have a diaphragm which is present in reptiles. This system helps them to effectively fly even to high altitudes where oxygen levels are very minimal. Reptiles on the other hand have a well developed lungs enclosed in a ribcage (Pat Shipman, 1997).

Excretory system differences
Birds do not have a bladder, and they excrete their waste materials in form of uric acid rather than urine so as to conserve water as uric acid can be produced in concentrated form due to its low toxicity level. Reptiles on the other hand have got a bladder, except snakes and some lizards.  Reptiles excrete their nitrogenous waste is in the form of ammonia, urea, uric acid or a combination of these (Anatomy of Animals, 2009).

Circulatory system differences
The heart of birds is separated in to four chambers that completely separate the oxygenated blood from the deoxygenated blood. The heart of reptiles is always separated into right and left atrium but the separation of the ventricle varies with animals. The chambers are however, connected and this allows for the mixing of oxygenated and the deoxygenated blood.

Reproduction differences
The courtship behavior in birds is much elaborated for mating purposes. These behaviors include, building of nests, dancing, singing and colorful displays. Birds have two reproduction types. Some birds like chicken incubate for a very long time, bearing chicks with feathers while some incubate for a very short time bearing chicks without feathers. Reptiles do not have distinctive courtship behaviors like birds. Reptiles leave their young ones to feed for themselves whereas birds take care of their young until they reach the age they are capable of taking care of themselves.

Anatomical structures

     According to anatomy of Animals (2009), birds have feathers which are said to be modified scales. Birds have scales on their feet. They show some skeletal similarity for example both reptiles and birds have occipital condyles. These enable the skull to articulate with the vertebral column. They both have a single middle ear bone called the oscicles. The jaws of both reptiles and birds are composed of fused bones which are five in number.

The mode of fertilization in both reptiles and birds is internal. Both reptiles and birds lay eggs. The structure of a birds egg is similar to that of a reptile. The egg has got embryonic membranes which provide the developing embryo with oxygen, food and water. The membrane also removes nitrogenous wastes from the embryo. The eggs are covered by a hard shell that protects the embryo from any form of physical injury and also from drying. The hatchlings of both reptiles and birds have an egg tooth for breaking trough the egg shell when the time of hatching comes.

Birds and reptiles have similar endocrine glands and they secrete similar hormones which play a very essential role in controlling development, growth and reproduction.
They both have nucleated red blood cells.

Birds and reptiles are very distinctively different creatures. If the theory of evolution was to be followed, these two have evolved differently despite the few structural similarities that they share. No fossil of bird like reptile has been found yet.