Cannibalism in the Early Jurassic bony fish Pachycormus macropterus (Teleosteomorpha: Pachycormiformes) and its paleoecological significance

ABSTRACT

Cannibalism (conspecific predation) is a surprisingly common and widespread behavior in modern ecosystems; however, direct evidence for cannibalism is strongly lacking in the fossil record. Identifying cannibalism is important to help better understand recondite trophic interactions between extinct species, as well as to detect potential resource pressures and competition in their ecosystems. Here, I describe the first direct evidence for a cannibalistic diet in a pachycormiform fish, based on three exceptionally well-preserved specimens of Pachycormus macropterus (de Blainville, 1818) with conspecific gut contents from the Early Jurassic (Toarcian) of Normandy (France). The generalist diet of Pachycormus is proven to be more complex than previously considered, which has recently been shown to include vampyropod squids, belemnoteuthids, ammonites, and small teleosts. All of the prey fishes were ingested whole in a longitudinal orientation, revealing that Pachycormus actively hunted juveniles of its own kind and was an indiscriminate opportunistic predator. The cannibal individuals themselves are also juveniles, further supporting previous findings for a dietary shift in Pachycormus from piscivorous to teuthophagous over ontogeny. Despite a widespread European distribution of Pachycormus, only specimens from the Normandy area show evidence for cannibalism, suggesting that the more conventional prey resources were either scarce or restricted at the site, prompting Pachycormus juveniles to indiscriminately predate on one another.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author.

ACKNOWLEDGMENTS

E. Bernard is thanked for relocating specimens from the Tesson collection in the NHMUK and allowing me to examine materials under her care. Thanks to R. Brocke and the preparators at the SMF for assisting a collection visit to examine pachycormid gut contents. J. Kimmig and D. Grabow (SMNK), R. Hauff and F. Hauff (Urwelt Museum Hauff), and A. López-Arbarello (BSPG) are thanked for their hospitality and allowing me to examine specimens held in their institutions. J. Norton (University of Portsmouth) accompanied me to the NHMUK on the day that I studied the cannibalistic pachycormids. Paleoartist H. Bivittatus (Sky Jung) kindly gave permission for me to re-draw and modify some of his pachycormid reconstructions for Figures 4 and 5. E. Maxwell (SMNS) kindly provided helpful feedback on an earlier draft of the manuscript. Finally, many thanks to S. Giles (University of Birmingham), a second anonymous reviewer, and the editors for their insightful and constructive comments which greatly improved the scientific quality of the final manuscript.

Additional information

Funding

This research was partially supported by funding from the DFG grant MA 4693/7-1 (awarded to E. Maxwell, SMNS).