Temp Regulation In Animal Essay, Research Paper

Temperature Regulation in Animals

Animals differ widely in their physiologies according to

numerous factors. Two of the most widely divergent

characteristics are how they regulate their own body

temperatures. We typically separate animals into cold blooded

animals and warm blooded animals . Reptiles and fish are

representatives of the first category while mammals and birds

represent the second category. These broad categorizations have

nothing to do with the actual temperature of an animals blood,

however. As can be noted in Figure A

reptilian blood (graphed in green) can reach or exceed the

temperatures exhibited by some mammals (graphed in red). What

these categories describe are how an animal regulates its

temperature. While reptiles and fish are ectothermic, depending

on ambient conditions to control their internal temperatures,

mammals and birds control their temperatures through their own

internal regulation, they are endothermic.

Another interesting aspect of temperature regulation in

animals is the range of temperatures which can be found in any

one individual. While this range is narrow in birds and mammals

it is quite wide in reptiles and fish. Figure A depicts the

temperature in Cyclodus, for example as ranging from just over

zero degrees Celsius to just over thirty-five degrees Celsius.

In contrast the temperature in the rabbit ranges from just over

thirty-five degree Celsius to just under forty-five degrees

Celsius. The cold blooded animals are referred to as being

poikilothermic, having a body temperature which fluctuates

widely. The warm blooded animals are most often homeothermic,

having a narrowly constricted body temperature range.

Figure A. Body Temperature of Representative Animals in Response

to Ambient Temperature (reproduced from

http://rainbow.ldeo.columbia.edu/courses/v1001/21.html)

Bone histology reveals a considerable amount of information

about an animal s metabolic system (Freeman, 1994). Bones which

are highly vascularized and metabolically active, with few

osteons, are more representative of endothermic animals while

poorly vascularized bone which appears layered are most often

representative of ectothermic animals (Freeman, 1994). The first

histological structure is referred to as fibro-lamellar and the

second is lamellar-zonal (Freeman, 1994). In the more

vascularized bone type, the fibro-lamellar, there is a woven

appearance and it is typified by the presence of extensive

Haversian systems (Freeman, 1994). These observation are of

course generalities as many factors can affect an animal s bone

structure (Freeman, 1994). These factors include habitat and

size as well as numerous others (Freeman, 1994).

Figure B. Cross and longitudinal sections of the femur of an

unidentified gorgonopsid. (Reproduced from Freeman, 1998).

In the cross section and longitudinal section of the of the

gorgonopsid femur presented above the outer layer appears to be

of dense and compact but relatively thin bone (Freeman, 1994).

The vascular channels are obvious as are the primary osteons but

the secondary osteons are difficult to ascertain. This makes

this bone difficult to assess in terms of its metabolic status

(Freeman, 1994). The presence of the extensive Haversian canals

in these sections, however, and of the growth rings would

indicate that this specimen was ectothermic and, interestingly,

that their growth was affected by seasonality (Freeman, 1998).

The physiological differences in mammals and birds and

reptiles and fish are numerous. The first true mammals appear in

the fossil record approximately 220 million years ago (Crompton

and Jenkins, 1973; Crompton and Jenkins, 1979; Clemens, 1970).

The differences we find today between more advanced mammals and

reptiles or fish are quite dramatic. Many of these differences

had their origin during Mesozoic times. Exactly what stimuli

provoked the evolution of the mammals is a subject of much

speculation. One of the most popular opinions is that an

ecological niche opened up which could best be filled by small

nocturnal insect eaters, which could live in the presence of the

huge dinosaurs largely undetected. It is believed that the

endothermic nature of the mammals was a very positive

characteristic, as was their ability to find and process food.

Although mammals evolved from reptiles, and still share many

characteristics with them, their evolutionary paths have been

quite disparate. The evolution of mammals occurred quite rapidly

as the new species spread over more and more habitats and

utilized a wide variety of ecological niches. The morphological

and physiological differences in these animals became widely

different as well, both from their ancestors and from other

species of mammals. The ability to maintain a consistent range

in body temperature is believed to be one of the main reasons for

success of such a large diversity of these species.

Bibliography

Clemens, W. A. (1970). Mesozoic mammalian evolution: Annual

Review of Ecology and Systematics, v. 1, p. 357-390.

Columbia University. (1997). Lecture Notes: Dinosaurs.

http://rainbow.ldeo.columbia.edu/courses/v1001/21.html

Crompton, A. W., and Jenkins, F. A., (1979). Origin of Mammals,

in Lillegraven, J. A., Kielan-Jaworowska, Z., and Clemens,

W. A., eds., Mesozoic Mammals: Berkeley, Ca., University of

California Press.

Crompton, A. W., and Jenkins, F. A., Jr., (1973). Mammals from

reptiles: A review of mammalian origins: Annual Review of

Earth and Planetary Sciences, v. 1, p. 131-155.

Freeman, Alexandra. (1994). The Morphology and Behaviour of

Gorgonopsids, and a New Use for Computers in Paleontology.

http://163.1.139.1/student_pages/freeal/Fig8.htm

*PG is used to denote that a page number is not obtainable

since the source was an electronic version accessed off the

Internet.