Researchers studying modern-day low oxygen zones off the coast of California found several characteristics of the animal community living there. They tended to be smaller than members of closely related species, many ate trash or dead animals, a few were carnivores, and many also died young.

At some fossil sites, such as the one in Texas where these fossils were found, the fossilized collection of animals had similar characteristics to those above. Scientists concluded that they'd found the fossils in what was once a low-oxygen environment.

Some of those environments span large sections of rocks and millions of years. Scientists sampled the rocks from different levels of the preserved sequence, looking at the same environment at different points in time. When they checked the locality where the fossils in the photograph come from, they found that few groups of animals moved in or out of the community. While other ocean communities turned over more quickly, this community was stable for at least four million years.

Specimen Number: NPL 39288 References: Forcino, Frank L., Emily S. Stafford, Jared J. Warner, Amelinda E. Webb, Lindsey R. Leighton, Chris L. Schneider, Tova S. Michlin, Lauren M. Palazzolo, Jared R. Morrow, and Stephen A. Schellenberg. "Effects of data categorization on paleocommunity analysis: a case study from the Pennsylvanian Finish Shale of Texas." PALAIOS 25(2010):144-157. Kammer, Thomas W., Carlton E. Brett, Darwin R. Boardman, II, and Royal H. Mapes. "Ecologic stability of the dysaerobic biofacies during the Paleozoic." Lethaia 19(1986):109-121.