-oxic Alligator bone

In collaboration with Dr. James Hicks (UC, Irvine), Dr. Tomasz Owerkowicz (CSU, San Bernardino), and Dr. Bryan Rourke (CSU, Long Beach), we are studying the effects of different oxygen environments on the growth microstructure of alligator bones. During the last ca. 550 million years, atmospheric oxygen levels have varied when compared to the present atmospheric oxygen level of 21% (normoxia).

During the Permian, atmospheric oxygen is estimated to have been as high as 30-35% (hyperoxia) and in the Late Triassic as low as 12% (hypoxia). Vertebrate have been living and evolving in these variable conditions. Recent interest in the bone structure of fossil vertebrate has led to a great expansion comparative paleohistology. However, comparisons are restricted to animals that live in present-day, normoxic environments.

Estimates of atmospheric oxygen levels during the last ~550 million years before the present. Estimates have ranged from extremely hypoxic to extremely hyperoxic relative to present day (~21% O2). Data from Berner (2006 and 2009).

By raising alligators in different oxygen environments, first in eggs and then post-hatching, we will mimic a range of atmospheric conditions, from hypoxia to hyperoxia. These experiments will allow us to assess the effects of the prevailing environment on growth rates and microstructure of bone. We will also be able to provide a comparative context for future paleohistological studies.

The image above shows a representative cross-section of an alligator femur that has been injected with fluorochrome labels (red and yellow rings). The large dark areas are vascular canals, and the small dark dots are osteocytes.
Middleton Lab
Integrative Anatomy