Turtle barnacles have been turtle riders for more than 30 million years

Abstract

In contrast to other kinds of biological interactions, symbiosis is a scarcely investigated aspect of the fossil record. This is largely due to taphonomic biases that often frustrate any attempt to make a strong case that two organisms shared an intimate association in life. Among extant marine vertebrates, the sea turtles (Cheloniidae and Dermochelyidae) bear a broad and diverse spectrum of epibiotic symbionts, including specialists such as the turtle barnacles (Chelonibiidae and Platyleapadidae). Here, we reappraise an early Oligocene (Rupelian) fossil cheloniid skeleton, featuring the remains of cirripedes on the exterior of its entoplastron, from the Rauenberg fossil-lagerstätte, southwestern Germany. The barnacle specimens are assigned to Protochelonibia melleni, an extinct protochelonibiine species and the geologically oldest known member of Chelonibiidae. In the light of taphonomic and palaeoenvironmental considerations, and given that the extant chelonibiids are mostly known as epizoic symbionts of sea turtles, we conclude that this unique fossil association resulted from the epizoic growth of the barnacles on the external surface of the plastron of the turtle during its lifetime. This remarkable fossil association provides evidence that chelonibiids, including the extinct protochelonibiines, have been chelonophilic epizoans for more than 30 Myr. A survey of the trace and body fossil records shows that platylepadids are also likely as old as the Rupelian as is their symbiotic association with cheloniid hosts. This early emergence of the modern-looking, turtle-dwelling barnacle lineages corresponds to a climate-driven phase of major radiation and taxonomic turnover among sea turtles at the Eocene–Oligocene transition.

Ghosts of the Holobiont: Borings on a Miocene Turtle Carapace from the Pisco Formation (Peru) as Witnesses of Ancient Symbiosis

“…The fragmentary fossil record of turtle barnacles mostly comprises isolated shells and disarticulated wall plates. Occurrences of barnacle remains associated with those of the putative host organism(s) are exceedingly rare [25,[126][127][128]. Although morphofunctional considerations can provide some hints of what sort of host the extinct turtle barnacles might have been on [129][130][131], body fossils alone cannot disclose much information on the ancient basibionts of chelonibiids and platylepadids, nor on the nature of the intercurrent symbiotic association.…”

“…They interpreted this scar, depicted in their figure 5E, as possibly caused by a sea turtle barnacle, which appears as reasonable (as well as consistent with the aforementioned divergence time estimates). Evidence that other lineages of turtle barnacles (i.e., archaic chelonibiids) inhabited the sea turtle shell as early as in early Oligocene times is provided by an exceptional cheloniid fossil, featuring Protochelonibia on its plastron-bottom, from the Rauenberg Fossil-Lagerstätte of southwestern Germany [25].…”

“…In spite of the widespread occurrence of chelonibiid and platylepadid genera such as Chelonibia, Cylindrolepas and Playtlepas on extant marine turtles [24], and although the association between the coronuloids and their chelonian hosts has existed for more than 30 million years [25], only a few studies have investigated this symbiotic relationship on palaeontological grounds [22,26,27]. The present paper adds to this short list by describing probable platylepadid borings on a Miocene fragmentary turtle carapace from the celebrated Pisco Lagerstätte of Peru based on the recently published nomenclatural frameworks provided by Zonneveld et al [23,28,29].…”

Symbiont-Bearing Colonial Corals and Gastropods: An Odd Couple of the Shallow Seas

“…In order to overcome the limitations associated with a sessile lifestyle, some symbiont-bearing colonial corals have developed a simple solution: colonizing a "moving" substrate. The effectiveness of such an approach is evidenced by the many invertebrate lineages that have convergently adopted similar life habits: for instance, acorn barnacles of the superfamily Coronuloidea have become able to "ride" different motile substrates-whales, turtles, and crabs, to name just a few [15][16][17]. Choosing the right kind of living substrate can provide a sessile organism with most of the beneficial traits of a motile lifestyle, including the capability to escape unfavorable conditions, avoid predation, and survive burial.…”

Learning from Caretta caretta (Linnaeus, 1758) epibionts: a study from the Adriatic Sea

“…The so called "turtle barnacles" indicate barnacle species that exclusively or preferentially live on carapace, plastron or skin of chelonians (Ross and Newman, 1967;Ross and Frick, 2011;Hayashi et al, 2013). It has been demonstrated that chelonibiids have been turtle-dwelling species for more than 30 million years (Collareta et al, 2023).…”