THE ECOLOGY OF LATE ORDOVICIAN CEPHALOPODS, AND THEIR ROLE IN FOOD WEB STRUCTURE

The Cephalopoda experienced a mass radiation at multiple taxonomic levels during the Great Ordovician Biodiversification Event (GOBE). During the Ordovician, thanks to the increasing availability of energy in pelagic food chains, cephalopods were able to occupy multiple trophic levels in increasingly complex ecosystems from large apex predators to small benthic scavengers. While predators influence community structure and dynamics in many modern ecosystems, little is known regarding the importance of cephalopods in the structure and functioning of Ordovician food webs. Here we examine the role of cephalopods in shallow marine food webs resulting from the GOBE across a biotic invasion during the Late Ordovician (Katian) in the Cincinnati Arch (USA). The studied time interval also includes the Richmondian Invasion, which may also have led to changes in cephalopod paleoecology and their role in local food webs.

To identify the role of cephalopods in Ordovician food web structure, cephalopods were assigned into trophic guilds based on their ecology, feeding habits, morphology, and body size. Taxonomic lists of cephalopods from the Maysvillian and Richmondian stages were assembled using museum collections, the PDBD and a comprehensive literature search. Body size data were measured for 33 species from specimens in the Karl E. Limper Museum, online collections and the literature. We identified siphuncular structure as a key characteristic in differentiating trophic guilds, as it relates to buoyancy control, metabolic efficiency, and feeding behavior. Cephalopods were divided into 4 ecotypes including benthic scavengers, both shallow and deep water pelagic ambushers, and suspension feeders. Preliminary data indicates an increase in mean cephalopod length, potentially resulting from changes in energetics that occurred across the invasion. In addition, of the 15 species present after the invasion, only 3 of which were present prior to the invasion, suggesting a complete reorganization of the local marine food web.

Morphological and structural differences in the Cephalopoda during the Late Ordovician allow us to reconstruct paleo-food webs and accurately assign cephalopod guilds using data that suggest more energy efficient feeding strategies as time progressed.