Oxygen Isotope 

Can chickens help paleontologists study dinosaurs?

     In an interesting study by Folinsbee et al., published in 1970, they determined that the oxygen isotope signature of modern chicken egg shells could be altered by giving them drinking water of varied isotopic composition.  The experiment was done as the result of a failed attempt to determine whether dinosaurs were warm or cold blooded (Folinsbee et al., 1970).  The fact that ingested water changes the isotopic composition of biogenic calcite is important for today's isotope paleobiologist to know.

     Reese Barrick works on that same question and has made many advances toward answering it.  His studies have included work on Hypacrosaurus, Tyrannosaurus rex, and modern studies of deer, pheasants, and alligators (Barrick and Showers, 1994,1996; Barrick, 1998).   In his work he uses inter-, and intra-bone oxygen analysis techniques to determine the thermoregulatory mechanisms of extinct organisms. 

These huge creatures may have had a thermoregulatory style all of their own.

     Inter-bone analysis compares one bone to another, and is most effective in elucidating thermoregulatory physiology when a bone from the body core is compared with a bone from the extremities.  (Barrick, 1998)  Endotherms must maintain a constant core temperature in order for metabolic processes to work.  In a cold environment, body temperature will be preferentially maintained in the body core at the expense of the extremities, a process called regional heterothermy (Barrick, 1998).  If bone is deposited in a cold period the isotopic ratios will vary between core and limb bones (Barrick, 1998.)  The deposition of bone, under variable temperatures, may seem unlikely to you if you think of a cold period in terms of the time spent running from your home to your car in a Canadian winter.  Animals that spend their winters outdoors deposit bone in under varying seasonal temperatures.

Oxygen isotope analysis gives paleontologists a quantitative methods to study dinosaurs.

The bones of this whitetail deer may display regional heterothermy if it lives in a cold winter climate.

     Intra-bone analysis looks at one bone in detail.   Is it isotopically homogeneous or heterogeneous?  It measures the maximum variability of the isotopic signature within the bone.  Ectotherm intra-bone ratios should have larger variations than intra-bone ratios for endotherms.  This is due to the fact that ectotherms are more susceptible to seasonal temperature changes than endotherms (Barrick et al., 1996; Barrick, 1997; Barrick 1998)  Again, the bone selected is important. Whereas core bones in endotherms will have low variability, limb bones may show more variability; however, in ectotherms, both core and limb bones should show variability.

     Unfortunately for paleoclimatologists, regional heterothermy negates the usefulness of oxygen isotopes in paleotemperature studies.  Intra-bone isotopic signatures will not show paleotemperatures if regional heterothermy is at play.  Isotopic signatures could be misleading and direct a scientist to false paleoclimatic conclusions (Barrick, 1998).  Ectotherms, on the other hand, do not preferentially maintain a certain temperature in their cores, and therefore oxygen isotope signatures should be more indicative of paleoclimates.

This elephant is less likely to show regional heterothermy because it lives in a warm climate.

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