Fossil isopods associated with a fish skeleton from the Lower Cretaceous of Queensland, Australia – direct evidence of a scavenging lifestyle in Mesozoic Cymothoida

Abstract

A dense assemblage of fossil isopod crustaceans (Brunnaega tomhurleyi Wilson, sp. nov.) from the Lower Cretaceous (Albian) Toolebuc Formation of Queensland, Australia, has been found within the carcass of a large actinopterygian fish, Pachyrhizodus marathonensis (Etheridge). Preservation of fine anatomical details supports referral to the genus Brunnaega Polz, which is herein reassigned to the family Cirolanidae. Furthermore, placement of this taxon within the cirolanid subfamily Conilerinae Kensley and Schotte is significant because the group includes modern species that are well known as voracious scavengers. This isopod-fish association represents the oldest unequivocal evidence of scavenging by Mesozoic cymothoidean isopods on a large vertebrate carcass.

150 million years old isopods on fishes: a possible case of palaeo-parasitism

“…In cases of scavenging we should expect quite higher numbers of isopods (examples and comparably discussions in Frickhinger 1999, Polz 2004, Wilson et al 2011.…”

“…Representatives of Cymothoidae and Gnathiidae prefer fishes as hosts, while species of Bopyridea and Cryptoniscoidea are generally found on decapod crustaceans. Species of Gnathiidae only parasitise fishes as larvae, whereas those of Cymothoidae and Aegidae infest fishes in larval and adult stages (Romestand et al 1982, Lester 2005, McKiernan et al 2005, Ravichandran et al 2009, Wilson et al 2011, Roche et al 2013. Representatives of Cymothoidae are obligate parasites of both marine and freshwater fishes and are more or less permanently attached to their host fish, while representatives of Aegidae visit a host only for a short blood meal (e.g.…”

“…Parasitic isopods represent an important factor in fisheries and aquaculture, because they reduce host fitness by influencing physiological, behavioural and morphological aspects (Yesmin & Khanum 2011, Roche et al 2013. For understanding the evolution of specific groups, including the evolution towards a parasitic lifestyle, fossils are an important source of information (e.g.…”

“…There are different criteria for identifying a parasite in the fossil record; some are less direct than others (for a longer discussion see Nagler & Haug 2015). Identification can be made possible by: 1) Pathological deformations as reactions of the host's body to the parasite (Conway Morris 1981, Wilson et al 2011) such as pearls in molluscs (e.g. De Baets et al 2011), galls (e.g.…”

A remarkably well-preserved terrestrial isopod (Peracarida: Isopoda: Armadillidiidae) from the upper Oligocene of Hungary, with remarks on the oniscidean taphonomy

“…A direct consequence of this is that there are only a few occurrences in which the morphology of mouthparts or appendages, which are important for isopod systematics and taxonomy, are preserved (e.g., Guinot et al, 2005;Vega et al, 2005;Feldmann, 2009;Wilson et al, 2011;Nagler et al, 2016), including specimens preserved in amber (e.g., Spahr, 1993;Dunlop, 2010;Perkovsky et al, 2010). In view of the fact that oniscidean isopods live in terrestrial habitats, their fossils are scarce and are dominated by amber inclusions (Broly et al, 2013(Broly et al, , 2015.…”