She focused on one bivalve, Leptodesma (Leiopteria), and two brachiopods, Floweria and Schizophoria (Schizophoria), as well as a predatory crustacean, Archaeostraca.
These small, shelled marine animals were some of the most common inhabitants of the Late Devonian oceans, which had the most extensive reef system in Earth's history.
The seas teemed with huge predatory fish such as Dunkleosteus, and smaller life forms such as trilobites and crinoids (sea lilies).
The first forests and terrestrial ecosystems appeared during this time; amphibians began to walk on land.
As sea levels rose and the continents closed in to form connected land masses, however, some species gained access to environments they hadn't inhabited before.
The hardiest of these invasive species that could thrive on a variety of food sources and in new climates became dominant, wiping out more locally adapted species.
The invasive species were so prolific at this time that it became difficult for many new species to arise.
"The main mode of speciation that occurs in the geological record is shut down during the Devonian," said Stigall. "It just stops in its tracks."
Of the species Stigall studied, most lost substantial diversity during the Late Devonian, and one, Floweria, became extinct.
The entire marine ecosystem suffered a major collapse. Reef-forming corals were decimated and reefs did not appear on Earth again for 100 million years.
The giant fishes, trilobites, sponges and brachiopods also declined dramatically, while organisms on land had much higher survival rates.
The study is relevant for the current biodiversity crisis, Stigall said, as human activity has introduced a high number of invasive species int
|Contact: Cheryl Dybas|
National Science Foundation