Stable isotopes in early Eocene mammals as indicators of forest canopy structure and resource partitioning

• Published in: Paleobiology 2008-03, Vol.34 (2), p.282-300
• Main Authors: Secord, Ross, Wing, Scott L, Chew, Amy
• Format: Article
• Language: English
• Subjects: atmosphere; Atmospheric circulation; Bighorn Basin; C-13/C-12; Canopies; carbon; Carbon isotopes; Cenozoic; Chordata; Diet; enamel; Eocene; Fauna; Forest canopy; Forest habitats; Forests; Fossils; Geochemistry; habitat; Habitats; herbivorous taxa; isotope ratios; Isotopes; lower Eocene; Mammalia; Mammals; Mass spectrometry; Microhabitats; O-18/O-16; oxygen; Oxygen isotopes; Paleoecology; paleoenvironment; Paleogene; Paleontology; Plants; Resource partitioning; s; Stable isotopes; statistical analysis; teeth; Terrestrial ecosystems; terrestrial environment; Tertiary; Tetrapoda; Understory; United States; Vegetation; Vertebrata; vertebrate; Water availability; Willwood Formation; Woodlands; Wyoming
• ISSN: 0094-8373; 1938-5331
• DOI: 10.1666/0094-8373(2008)034[0282:SIIEEM]2.0.CO;2

The three dimensional structure of vegetation is an important component of ecosystems, yet it is difficult to reconstruct from the fossil record. Forests or woodlands prevailed at mid-latitudes in North America during the early Eocene but tree spacing and canopy structure are uncertain. Here we use stable carbon isotope values (δ13C ) in early Eocene mammalian faunas to infer canopy structure. We compare δ13C values in two diverse fossil assemblages from the central Bighorn Basin to values predicted for mammals in a variety of open and closed habitats, based on modern floras and faunas. We conclude that these early Eocene faunas occupied an open canopy forest. We also use carbon and oxygen isotopes to infer diet and microhabitat. Three higher level taxa have significantly different mean δ13C values, and values are negatively correlated with body mass. The pattern suggests diets high in leaves for larger mammals, and fruit or other non-foliar plant organs for small ones. A preference in the larger mammals for wetter habitats with high water availability to plants may also have contributed to the pattern.