Full Title Name:  Biological Information: Reptile Biology and Physiology

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James M. Green Place of Publication:  Michigan State University College of Law Publish Year:  2005 Primary Citation:  Animal Legal & Historical Center

This overview describes the fundamental characteristics of reptile biology and physiology.


Reptiles Are Animals 

Reptiles are animals, as are amphibians. Physiologically, they are similar and are sometimes collectively called “herpetofauna.” All of the excepted scientific classification systems regard reptiles as such. Under the two most common classification systems, reptiles are either grouped as the Class Reptilia or the Class Diapsida under the Kingdom Animalia, meaning “animals”. Moreover, under most legal definitions, reptiles are considered to be animals as well. For example, Connecticut defines an animal as including “birds, quadrupeds, reptiles and amphibians.” Con. Gen. Stat. §26-1(1) (2004). Wisconsin is equally specific: "’Animal’ includes every living: (a) Warm-blooded creature, except a human being; (b) Reptile; or (c) Amphibian.” Wis. Stat. §951.01 (2004). Florida, albeit in an unflattering way, also defines “animal” to include reptiles as “the word ‘animal’ shall be held to include every living dumb creature.” Fla. Stat. §828.02 (2005). An unsettling discrepancy lies in the Federal Government’s Animal Welfare Act. 7 U.S.C. §§2131 et seq. There, the “term ‘animal’ means any live or dead dog, cat, monkey (nonhuman primate mammal), guinea pig, hamster, rabbit, or such other warm-blooded animal, as the Secretary may determine is being used, or is intended for use, for research, testing, experimentation, or exhibition purposes, or as a pet;” but excludes birds, mice, rats, horses and farm animals. 7 U.S.C. §2132(g). Conspicuously absent from the list are fish, amphibians and reptiles. Id. 

Unfortunately, many people, unaware of the backings from science and the law, do not consider reptiles to be animals. In his article entitled “Herpetofauna Keeping By Secondary School Students: Causes For Concern”, David Bride complied the results of some alarming graduate studies that currently remain unpublished. See http://www.psyeta.org/sa/sa6.1/bride.html . His compilation refers to a study by Martin and Nicholls (Martin, D. & Nicholls, M. (1993). The importance of children's provenance in the understanding of "animal" - a comparison of town and village primary school children in Kent. Christ Church College, Canterbury: Ecology Research Group) of 400 five- to eleven-year-olds found between 10-40% of those surveyed did not recognize either snakes or frogs as animals. Similarly, Tinkler (Tinkler, D. (1993) Zoo visitors' perceptions of animals - and the short-term effect of a zoo visit upon them. Unpublished M.S. dissertation. University of Kent at Canterbury, DICE) recorded 60% of 150 adult zoo visitors failed to classify a lizard as an animal. From his investigation into unpublished studies, Bride hypothesized that this may be due to a confusion of term "mammal" with "animal." He recently found that of 228 respondents to a questionnaire about wildlife, at least 25% appeared to confuse the two. Bride found this view, that "animal" equals "mammal," to be interesting as it gives an entirely new perspective to what many people's interpretations of such concepts as "animal protection," "animal welfare," and "animal rights" may entail. See http://www.psyeta.org/sa/sa6.1/bride.html. Knowledge of what a reptile actually is may go far in soliciting the sympathy of the public.  


A very common myth is that reptiles are “cold-blooded.” In addition to describing a general temperature of reptilian blood, the term also entails the negative connotations of evil and lifelessness. To be sure, in the Biblical story of Adam and Eve, it was a serpent that deceived mankind. However, reptiles are not “cold-blooded.” On occasion, they are quite the contrary and can even be “hot-blooded.” This gradation results in reptiles being “poikilothermic.” Poikilotherms have a body temperature that is variable with environmental conditions. If the ambient temperature is warm or even hot, that leads to a reptile having warm or hot blood. Another physiological term that accurately depicts reptiles is “ectothemy.” Ectotherms control the uptake of heat from the environment as a way to control internal body temperature. Reptiles are both poikilothermic and ectothemic, but are not cold-blooded. Moreover, some larger reptiles, such as large crocodilians, sea turtles and large monitor lizards approach a level of homeothermy. That is, their temperature does not fluctuate as much based upon the environment. This results from a physiology process known as gigantothermy, where a very large animal will maintain a constant body temperature with little input from the environment.  

Another popular assumption is that since reptiles are “cold-blooded,” they therefore feel little or no pain. In fact, they have little physiological control over their internal body temperature and are instead almost completely reliant on external heat sources to provide them with enough warmth for their natural activities and for metabolic processes to operate. This makes these animals extremely sensitive even to subtle changes in temperature and humidity in their captive environment. 

Added to the problems arising from their “cold-blooded” reputation, reptiles lack the repertoire of facial expressions and vocalizations that would alert keepers to their pain and distress. A sick, hurt, or chronically stressed reptile will typically suffer in silence. The suffering will often be far more prolonged than that experienced by mammals, due to reptiles' slow metabolic rate. Blood loss and the healing of injuries are both relatively slow, as are the consequent risk of infection and further complications. 

Most reptiles have a preferred optimum temperature zone, a zone of temperature that they try to maintain while performing daily activities. Their entire physiology, including their immune defense mechanism, is temperature dependent and operates optimally at this optimal zone. Reptiles in captivity often are maintained at suboptimal temperatures, which results in a compromised immune system. Such animals are subject to infection by a great variety of secondary invaders, including the gram-negative microorganisms commonly isolated from their oral cavity. A reptile that is kept at its preferred optimum temperature (with all other environmental conditions being ideal) and receives proper nutrition is often a healthy reptile. For a more complete discussion of reptile physiology, see 18 Carl Gans & David Crews, Biology of the Reptilia, Physiology E, (1991). The cumulative effect of these common misconceptions may play a large factor in the cruel treatment and neglect of reptiles in captivity. 

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