Eocene isopods on electric rays: tracking ancient biological interactions from a complex fossil record

Abstract

Isopod crustaceans have developed a variety of feeding strategies, which impact on their various life habits over time. Apart from morphological adaptations and the typical secondary deformations that some parasitic isopods inflict on their host's exoskeleton, traces of feeding behaviours involving isopods on their victim/food are seldom fossilized. Many of these rare occurrences consist of cases for which the degree of association between the isopods and their potential food source is unclear, or the interaction only very briefly explained (recently analysed cases excepted). There are two limiting problems in identifying the biological nature of fossilized associations: (1) direct associations of organisms preserved as ‘imprint’ (as opposed to inclusions in cherts or amber) are shaped by several taphonomic events difficult to identify (such as the time of death, burial and fossilization of the organism); (2) even in modern nature, differences within syn vivo interactions (like parasitism and micropredation) are poorly understood in marine systems. We report the occurrence of isopods associated with ancient chondrichthyans which also represent rare cases of the preservation of several fossil isopods on larger organisms. These organisms are adult electric rays of the genus †Titanonarke Carvalho from the late Ypresian (Eocene) of the Monte Postale site, Bolca Lagerstätte, Italy. By examining: (1) the involved lineages of rays and isopods; (2) the taphonomy of the association; (3) its environmental context; and (4) biological/adaptive features; we identify this association as a selective case, either of ancient scavenging or of micropredation on specific electric rays by isopods.

Diversity, palaeoecology and palaeoenvironmental significance of the Eocene chondrichthyan assemblages of the Bolca Lagerstätte, Italy

“…( 2018c ) revealed outstanding information about their palaeobiology, particularly about diet preferences, whereas the study of Robin et al . ( 2019 ) shed light on their biological interactions with isopod crustaceans. Rhinopristiform guitarfishes are represented by a single specimen of the rhinobatid Pseudorhinobatos dezignii (Marramà et al .…”

Geologicamente n. 02 - Luglio 2020

“…Nella porzione addominale di alcuni fossili di batoidi, inoltre, sono state osservate uova e embrioni perfettamente conservati (Marramà et al, 2018b). Infine, evidenze di parassitismo, commensalismo e micropredazione sembrano essere presenti in alcuni pesci provenienti sia dalla Pesciara sia dal Monte Postale (Petit, 2010;Petit et al, 2014;Robin et al, 2019).…”

“…Sala Manservigi, 1973), anellidi policheti erranti e irudinei (Alessandrello, 1990), brachiopodi terebratulidi, bivalvi e gasteropodi, cefalopodi coleoidi e nautiloidi, e numerosi crostacei isopodi, stomatopodi e decapodi (Fig. 6; Vonk, 2015;Robin et al, 2019;Pasini et al, 2019). Abbondanti resti di coralli coloniali sono stati rinvenuti presso il Monte Postale.…”

Description and ontogeny of a 40-million-year-old parasitic isopodan crustacean:Parvucymoides dvorakorumgen. et sp. nov.

“…Isopoda is an extremely species-rich and diverse group of organisms ( Wilson, 2009 ; Poore & Bruce, 2012 ). Among the marine forms of Isopoda, Cymothoida Wägele, 1989 is a morphologically and distributionally diverse group, with a variety of life strategies, ranging from scavengers and predators (see Holdich, 1981 ; Wilson, Sims & Grutter, 2011 ; Robin et al, 2019 ; Youssef et al, 2020 ) to highly specialised temporary and permanent parasitic individuals (see Hadfield, Smit & Avenant-Oldewage, 2009 ; Williams & Boyko, 2012 ; Alves-Júnior et al, 2019 ). Despite the large number of species and the morphological diversity within extant representatives of Cymothoida ( Boyko et al, 2019 ), the current fossil record does not reflect this diversity ( Hyžný, Bruce & Schlögl, 2013 ; Smit, Bruce & Hadfield, 2014 ).…”