Carbon Isotope Paleoecology

This sloth is eating from a C3 photosynthetic plant.

       Coprolites are not the only way to study what dead animals ate.    Carbon isotope studies of teeth and bone can be used to identify whether an animal was herbivorous or carnivorous, what plants it may have eaten, or whether an animal was marine or terrestrial (Barrick, 1998.)  Quade et al., 1992; Cerling et al., 1993; MacFadden et al., 1994, 1996 have used stable carbon isotope studies to show the spread of grasslands in the Miocene (Barrick, 1998)

     The two main photosynthetic pathways, the C3 (Calvin cycle), and C4 (Hatch-Slack cycle)  leave different isotopic signatures in the enamel and bones of the animals that eat them (Barrick, 1998). C3 plants, which include trees, shrubs, and cool weather grasses typically produce a more negative carbon isotope value than C4 plants, which are the warm weather grasses (Barrick, 1998.) 

Corn uses the C4 photosynthetic system

     Carbon isotope analysis can be used in conjunction with traditional morphological studies to do a detailed reconstruction of past ecosystems (Barrick, 1998).  MacFadden (1998) used carbon and oxygen isotopes to explore the ecology of two extinct species of Neogene rhinoceros, Aphelops and Teleoceras  These two species were very common in the past, and coexisted in North America (MacFadden, 1998)

Fossil Teleoceras preserved in volcanic ash.                   Photo from Dott and Prothero, (1994)

Previous morphological research on these species had labelled Teleoceras an aquatic grazer, much like the modern hippo, while Aphelops  was classified as a terrestrial browser (MacFadden, 1998). Carbon isotope values from the teeth of each species show that both species fed on C3 vegetation previous to 7 Ma (MacFadden, 1998).  MacFadden's (1998) carbon isotope data from 4.5 Ma shows that Teleoceras began ingesting C4 grass, which would make it a grazer not a browser.

The modern Hippopotamus spend much of its time in water.

Teeth are often used in isotopic studies

Further oxygen isotope studies show that Teleoceras was not likely an aquatic animal (MacFadden, 1998).  According to Bocherns et al., (1996) oxygen isotope values can be used to differentiate terrestrial animals from aquatic animals (MacFadden, 1998).  Oxygen isotope values from teeth should be more negative for an aquatic animal, an example is the hippopotamus, Hippopotamus amphibius  (MacFadden, 1998).  MacFadden's data (1998) does not support this.  With carbon isotopes paleoecologists now have a precise quantitative method for niche determination, and paleodiet reconstructions.

These values can be used to describe very specific ecological interactions.  Sillen and Lee-Thorp (1994) use Carbon isotopes in conjunction with  Sr/Ca trace element ratios to define predator/prey relationships (Barrick, 1998). 

Pleistocene predation
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