Authors:

Matthieu P. Weinberg

Date Created:

Not specified

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About Paper:

The Truckee Formation near Hazen, Nevada, presents a 10 million year old sequence of fossilized threespine stickleback fish (Gasterosteus doryssus). Fossil fish are preserved in diatomite, consisting of the salacious shells of ancient diatom remains that were continuously deposited on the Lake Truckee floor upon death. This depositional setting allows a high-resolution, near-continuous account of morphological evolution, stasis, and local extinction among stickleback populations. Within the formation, a series spanning about 21,000 years displays a replacement of low-armored stickleback fish to high-armored variants. Understanding the paleoecology of these fish can help inform the cause of this replacement event. Here, we present the taphonomy, or fossilization and depositional context, of this stickleback fish series. We photographed the approximately 4,000 unique fish from this series, including all available counterparts, and noted trends in disarticulation of various anatomical regions indicative of a taphonomic process. For instance, disarticulation of fin elements of an otherwise perfectly articulated fish is evidence of decay at low temperatures. The anatomy we noted included the skull, fins, ribs, vertebral column, and general skeleton, among others. We also noted trends in anoxia-induced muscle convulsions, or tetany. This takes form as expansions of the jaw and fins and extreme curvature of the spine. Any combination of these provides evidence of a low-oxygen environment. Tetany and disarticulation variables were each documented on scales of increasing magnitude, ranging from not present to extremely present. Other trends relevant to taphonomy were also noted, including excavation bias and fossil visibility. In collecting these variables, we reconstruct temperature, depth, and oxygen content throughout the time series. Given the Truckee Formation's temporal resolution, abundance of specimens, and expansive evolutionary phenomena, analyzing the taphonomy that underlies these patterns can further our understanding of evolutionary modes.

Source:

Loyola University Chicago

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Co-authors:

Matthieu P. Weinberg