Early Crops

A P. lantenoisi specimen with its digestive system—comprised of a crop (inflated region at top of specimen, left side of image), lateral glands, and a central canal that runs along the length of the body—preserved as reddish iron oxides.

Feiyang Chen

Trilobites, an ancient marine arthropod, once proliferated throughout Earth’s oceans for almost 300 million years. Nearly 20,000 trilobite species have been identified from their fossilized exoskeletons, but only 42 such species have been preserved with even a trace of their digestive systems. A new discovery of trilobites with remarkably preserved internal structures sheds new light on their digestive architecture. 

A team of researchers led by paleobiologist Melanie Hopkins at the American Museum of Natural History extracted and analyzed 270 fossilized trilobite specimens of two species, Redlichia mansuyi and Palaeolenus lantenoisi, from an early Cambrian formation in the Yunnan Province of China. Eight R. mansuyi specimens and 19 P. lantenoisi specimens were found to contain traces of the digestive system, preserved as iron oxides. 

Previous specimens have led to two proposed digestive systems in trilobites: a single tube with a series of glands, or a single tube leading from a stomach, or crop. Because crops had never been found in the oldest trilobite fossils, researchers believed that the crop evolved later, as a type of digestive system distinct from glands. Hopkins and her colleagues, however, found evidence of a crop in their R. mansuyi specimens that date to about 514 million years ago, indicating that the crop was present in trilobites roughly 20 million years earlier than previously thought.

Furthermore, one P. lantenoisi specimen examined by the researchers appeared to have not only a crop but also digestive glands. One possibility is that trilobites had a third type of digestive system featuring both a crop and glands. Another possibility, said Hopkins, is that these findings represent not a new digestive system, but a more complete look at systems that have been previously observed only in part, due to incomplete preservation of internal body tissue. These recently analyzed, well-preserved trilobite specimens are cause for rethinking how these ancient creatures digested their food. (PLOS ONE)