Polyplacophoran Feeding Traces on Mediterranean Pliocene Sirenian Bones: Insights on the Role of Grazing Bioeroders in Shallow-Marine Vertebrate Falls

Abstract

Chitons (Polyplacophora) include some of the most conspicuous bioeroders of the present-day shallow seas. Abundant palaeontological evidence for the feeding activity of ancient chitons is preserved in the form of radular traces that are usually found on invertebrate shells and hardgrounds. We report on widespread grazing traces occurring on partial skeletons of the extinct sirenian Metaxytherium subapenninum from the Lower Pliocene (Zanclean) of Arcille (Grosseto Province, Tuscany, Italy). These distinctive ichnofossils are described under the ichnotaxonomic name Osteocallis leonardii isp. nov. and interpreted as reflecting substrate scraping by polyplacophorans. A scrutiny of palaeontological literature reveals that similar traces occur on fossil vertebrates as old as the Upper Cretaceous, suggesting that bone has served as a substrate for chiton feeding for more than 66 million years. Whether these bone modifications reflect algal grazing, carrion scavenging or bone consumption remains unsure, but the first hypothesis appears to be the most parsimonious, as well as the most likely in light of the available actualistic data. As the role of bioerosion in controlling fossilization can hardly be overestimated, further research investigating how grazing organisms contribute to the biostratinomic processes affecting bone promises to disclose new information on how some marine vertebrates manage to become fossils.

Bioerosion traces on the Campanian turtle remains: New data from the lagoonal deposits of the Quseir Formation, Kharga Oasis, Egypt

“…Campanian of the Qarn Ganah, Kharga Oasis (this study). Radulichnus inopinatus was previously recorded from the Middle Devonian of Germany (Bohatý, 2011), Maastrichtian of Netherlands and Belgium (Jagt, 2003;Mulder et al, 2005; Janssen et al, 2013), Pliocene of France and Italy (Gibert et al, 2007;Collareta et al, 2023b), and Pleistocene of Southern Brazil (Lopes and Pereira, 2019).…”

“…Producer. Invertebrate (chiefly molluscan) shells and polyplacophorans (chitons) (Voigt, 1977;Jagt, 2003;Gibert et al, 2007;Lopes and Pereira, 2019;Collareta et al, 2023b).…”