FISH OUT OF WATER, A STABLE ISOTOPE PERSPECTIVE

Many Late Paleozoic fossil teeth have been analyzed with Laser Ablation Mass Spectrometry to evaluate the potential for aiding paleoecological research in the deep past. These teeth, from the red beds of Oklahoma, Texas and New Mexico range in age from 305 to 270 million years old (Kasimovian through Cisuralian) and include freshwater sharks, lungfish, Parareptilia, Lepospondyls, Temnospondyls, Synapsids (stem mammals) and Sauropsids. These outcrops, sediments, fossils, paleosols, oxbow lakes, etc., are among the best archives for the context and evolution of tetrapods, amniotes and their conquest of terrestrial environments.

Laser Ablation Mass Spectrometry is a tool that has been used to elucidate ecological information from Cenozoic mammal tooth enamel. Tooth enamel, as in humans, is composed of relatively large hydroxy apatite crystals where some crystal sites are occupied by carbon dioxide during formation. The carbon and oxygen isotope ratios of this carbon dioxide preserve aspects of the animal's respired carbon and body fluids and have implications for diet and environmental water during formation of the teeth.

Multiple hypotheses are being evaluated to understand these data. At worst, they could represent diagenetic alteration during hundreds of millions of years of exposure to ground waters. Compounding this issue, all Late Paleozoic teeth lack the thicker enamel of Cenozoic mammals and instead have a thin enameloid over dentin, sometimes folded together, both with smaller crystals than enamel. At best, these data could be important clues to ancient vertebrate food chains, water sources and terrestrial adaptations.

Results show increasing variability in both carbon and oxygen isotope ratios is observed from the younger teeth. Compared to a Cenozoic enamels, these results have a similar range of oxygen isotope ratios. The carbon isotope ratios are a few per mil heavier than the Cenozoic C3 cloud. However, associated organic carbon fossils are also a few per mil heavier than Cenozoic C3 organic samples. The Permian is thought to be a heavy carbon environment due to the light carbon preferentially stored as coal during the Carboniferous. So far, the exciting possibility of useful paleoecologic results has not been ruled out.