A specimen of the trilobite Palaeolenus lantenoisi from the Guanshan Biota in southern Yunnan Province, China. Rarely are internal organs preserved in fossils, but this specimen shows the digestive system preserved as reddish iron oxides. The digestive system is comprised of a crop (inflated region at top of specimen), lateral glands, and a central canal that runs along the length of the body; the iron oxides that extend beyond the fossil are the remains of gut contents that were extruded during preservation. Credit: © F. Chen
Phys.org has a story about some interesting details of trilobite digestion. A paper, published in 2017 in the journal PLOS ONE, revealed that trilobites had a stomach structure about 20 million years earlier than what had been known. The exceptionally preserved specimens of Palaeolenus lantenoisi used in the study lived about 514 million years ago during the Cambrian. They are shown to have both a crop and digestive glands. This study backs up some earlier research from Sweden. Trilobites are known to have have two body plans of their digestive system. One is a tube down the length of the body with lateral digestive glands. The other consists of an expanded stomach, called a "crop", leading into a tube with no lateral glands.
"Trilobites are one of the first types of animals to show up in large numbers in the fossil record," said lead author Melanie Hopkins, an assistant curator in the Division of Paleontology at the American Museum of Natural History. "Their exoskeletons were heavy in minerals, and so they preserved really well. But like all fossils, it's very rare to see the preservation of soft tissues like organs or appendages in trilobites, and because of this, our knowledge of the trilobite digestive system comes from a small number of specimens. The new material in this study really expands our understanding."
Trilobites are a group of extinct marine arthropods—distantly related to the horseshoe crab—that lived for almost 300 million years. They were extremely diverse, with about 20,000 species, and their fossil exoskeletons can be found all around the world. Most of the 270 specimens analyzed in the new study were collected from a quarry in southern Kunming, China, during an excavation led by Hopkins' co-author, Zhifei Zhang, from Northwest University in Xi'an.
