Friday, September 29, 2023

[Paleontology • 2023] Uniquely preserved Gut Contents illuminate Trilobite Palaeophysiology

Bohemolichas incola  

in Kraft, Vaškaninová, Mergl, Budil, Fatka et Ahlberg, 2023.

Artwork: Jiri Svoboda.

Trilobites are among the most iconic of fossils and formed a prominent component of marine ecosystems during most of their 270-million-year-long history from the early Cambrian period to the end Permian period1. More than 20,000 species have been described to date, with presumed lifestyles ranging from infaunal burrowing to a planktonic life in the water column2. Inferred trophic roles range from detritivores to predators, but all are based on indirect evidence such as body and gut morphology, modes of preservation and attributed feeding traces; no trilobite specimen with internal gut contents has been described3,4. Here we present the complete and fully itemized gut contents of an Ordovician trilobite, Bohemolichas incola, preserved three-dimensionally in a siliceous nodule and visualized by synchrotron microtomography. The tightly packed, almost continuous gut fill comprises partly fragmented calcareous shells indicating high feeding intensity. The lack of dissolution of the shells implies a neutral or alkaline environment along the entire length of the intestine supporting digestive enzymes comparable to those in modern crustaceans or chelicerates. Scavengers burrowing into the trilobite carcase targeted soft tissues below the glabella but avoided the gut, suggesting noxious conditions and possibly ongoing enzymatic activity.
a, Internal mould of specimen (inventory no. 8) in the nodule (coated with ammonium chloride). b–d, Scan model of the same specimen in dorsal (b), ventral (c) and left lateral (d) view. Exoskeleton in cream, hypostome in gold, digestive tract contents in shades of red and blue. The red dotted line indicates an anomalous position of segments five and six. Voxel size, 11.35 µm (applies for all figures and extended data). Scale bar, 10 mm.

a, In ventral view. b,c, Left lateral view of scan model of exoskeleton with hypostome reconstructed in life position (b) and reconstruction of the digestive tract (c). Locomotory (including spines) and respiratory appendages suppressed for clarity. Hypostome in a and c is transparent; exoskeleton in c is transparent.

Bohemolichas feeding on the sea floor, moments before it is engulfed, buried and preserved by an underwater mud flow.
Artwork: Jiri Svoboda.

The described specimen of Bohemolichas provides by far the most detailed source of information to date concerning the diet and the feeding mode of trilobites. This information includes indirect but robust evidence for a high-pH gut environment, aligning Bohemolichas with extant crustaceans and xiphosurans, and suggesting that such a digestive physiology may be primitive for the euarthropod crown group. It appears to have been an indiscriminate feeder on small, shelly, benthic invertebrates, most likely by scavenging rather than active hunting. Bohemolichas gives a unique glimpse of the role of lichid trilobites in an Ordovician marine ecosystem and provides evidence for the great antiquity of pH-neutral digestive physiology in arthropods.

Petr Kraft, Valéria Vaškaninová, Michal Mergl, Petr Budil, Oldřich Fatka and Per E. Ahlberg. 2023. Uniquely preserved Gut Contents illuminate Trilobite Palaeophysiology.  Nature.  DOI: 10.1038/s41586-023-06567-7