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Pomona College Professor Uncovers Bizarre Lifestyle of Trilobites

Elrathia kingii, the world’s most familiar trilobite fossil, found in rock shops and museum and university collections worldwide, lived a bizarre lifestyle as possibly the first among Earth’s few lifeforms to flourish without benefit from the sun, or photosynthesis, according to new research by Pomona College Visiting Professor of Geology Robert Gaines.

“We propose that Elrathia kingii, the ‘world’s most famous trilobite,’ represents the oldest known example of an animal-microbial symbiosis, a finding that has important ramifications for the nature and development of the earliest animal ecosystems on the planet,” said Gaines.

Gaines and co-author Mary L. Droser of the University of California, Riverside, reported their findings in an article titled “Paleoecology of the familiar trilobite Elrathia kingii: An early exaerobic zone inhabitant,” published in November by Geology, the journal of the Geological Society of America.

Trilobites are hard-shelled, segmented creatures that originated more than 500-million years ago in the Earth's ancient seas, long before life existed on land. They appeared in the Cambrian period, during the dawn of animal life, became extinct before dinosaurs came into existence and are one of the key signature fossils of the Paleozoic Era, the first era to exhibit a proliferation of the complex lifeforms that established the foundation of life as it is today. Trilobites were arthropods, and their relatives include crabs and insects.

E. kingii, one of more than 15,000 species of trilobites presently known, lived in dark, oxygen-depleted ocean waters in what is now western Utah. It was the only animal among its contemporaries that could survive in these harsh conditions, and due to this unique adaptation, it was able to tap into an abundant food source: sulfur oxidizing bacteria. These bacteria, which do not need sunlight to survive, served as the base of a very short food chain.

A similar, but much, much younger, example of an ecosystem that thrives without photosynthesis are the hydrothermal vent and seep communities of the deep sea, seemingly hostile environments that nonetheless support hundreds of species. Scientists first discovered the deep-sea vents and seeps in 1977, and they became the first ecosystems on Earth known to prosper without the sun’s rays. Before that, most biologists believed that only sunlight, through photosynthesis, could support life on Earth.

Now, the discovery of E. kingii’s alternative lifestyle pushes the minimum age for the establishment of such unusually-rooted ecosystems back considerably – placing the origin of non-photosynthesis-based communities close in time to the dawn of animal life.