The tongues of many reptiles help detect odors by gathering scent particles and transferring them to a chemoreceptor organ.

     
  "Many snakes and reptiles combine the senses of smell and taste. When a snake flicks its forked tongue in and out of its mouth, it is sampling the air. The snake does not even need to open its mouth to do this. The tongue is flicked out through a small hole in the snake's lips, so its two slender forks can collect scent particles from the air or from an object such as a stone. Back inside the mouth, the tongue's forks are pressed into a pair of domed pits in the roof of the mouth, which have a moist lining that is sensitive to the chemicals it has picked up. The olfactory particles are transferred to the pits, which are well supplied with nerve endings, and are collectively known as Jacobson's organ. Although most often found in snakes, this organ is also common in other reptiles, especially terrestrial lizards." (Shuker 2001:31)
  Learn more about this functional adaptation.

   

 

 

 

Reptilia, presented as a Class in our classification, includes turtles (Testudines), snakes and lizards (Lepidosauria), crocodiles and their relatives (Crocodilia), and birds (Aves), as well as a number of extinct groups. Reptiles (including birds!) are amniotes; that is, their eggs are protected from dessication and other environmental problems by an extra membrane, the amnion, not found in the first terrestrial vertebrates (amphibians). Mammals (Mammalia) are also amniotes, but they differ from reptiles in the structure of their skulls (especially the regions associated with chewing and hearing). Mammals also have hair and feed their young with milk produced by modified skin glands (mammary glands).

 

In addition to being amniotes, all reptiles have (or did have, in their evolutionary history) horny epidermal scales made of a particular kind of protein, paired limbs with 5 toes, skulls with a single occipital condyle, lungs instead of gills for respiration, and a 3 or 4 chambered heart. Their eggs are covered with a leathery or calcium-based shell (partially or completely lost in some species that give birth to live young), and fertilization occurs inside the female, rather than outside, as it does in most amphibians. Members of Reptilia generally share many additional traits, for example in their nervous and excretory systems, locomotion, and reproduction.

 

Why are birds included within Reptilia, and how are they and other members of this group related to each other? Both the fossil record and comparative analyses of living species (especially those based on molecular evidence) convincingly establish that, among living reptiles, birds and crocodiles are more closely related to each other than they are to lepidosaurs (snakes and lizards). The position of turtles is more controversial; in the past they were thought to represent an early branch of Reptilia. Recent evidence suggests they may have a special relationship with crocodiles and birds. Because birds clearly arise from within the groups we traditionally consider to be reptiles, not separately from them, most systematists now formally consider birds (Aves) to be a subgroup within Reptilia.

 

 

 

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References:

 

 

 
• Hickman, C. P. Jr., L. S. Roberts, and A. Larson. 2003. Animal Diversity, 3rd edition. McGraw Hill, Boston.
 
• Laurin, M. and J. A. Gauthier. 2001. Amniota. http://tolweb.org/tree?group=Amniota&contgroup=Terrestrial_Vertebrates
 

 

 

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Related Sites:

 

 
•     Savannah River Ecology Lab's Herpetology Homepage 
 

 

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Last updated 24 February 2004.