Journal of Paleontology, 89(5), 2015, p. 802–820 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2015.61
Borings in early Eocene turtle shell from the Wasatch Formation, South Pass, Wyoming
John-Paul Zonneveld,1 William S. Bartels,2 Gregg F. Gunnell,3 and Luke P. McHugh4
1University of Alberta, Edmonton, Alberta T2G 2E3, Canada 〈
zonneveld@ualberta.ca〉 2Department of Geological Sciences, Albion College, Albion, Michigan 49224, USA 〈
wbartels@albion.edu〉 3Division of Fossil Primates, Duke Lemur Center, Durham, North Carolina, 27705, USA 〈
gregg.gunnell@
duke.edu〉 4Canadian Natural Resources Limited, Calgary, Alberta T2P 2Z2, Canada
Abstract.—Borings in fossil turtle shells collected from the lowermost beds of the early Eocene Cathedral Bluffs Tongue of the Wasatch Formation in the northwestern part of the Green River Basin near South Pass, Wyoming, are herein described. Individual turtle shells in the study area are characterized by as few as one or two and as many as >100 borings. The borings include both non-penetrative forms (those which do not pass fully though the shell) as well as penetrative forms (those which pass fully from the exterior to the interior surface of the shell). All non-penetrative forms occur on external surfaces of the carapace and plastron (i.e. those that would have been accessible while the host taxon was alive). Two new ichnogenera and four new ichnospecies are established to describe these borings. Karethraichnus (new ichnogenus) includes three ichnospecies: K. lakkos (new ichnospecies), K. kulindros (new ichnospecies), and K. fiale (new ichnospecies). Karethraichnus lakkos are shallow (non-penetrating), hemispherical pits with rounded, to flattened bases. Karethraichnus kulindros are deep, non-penetrative traces with a cylindrical profile, an axis approximately perpendicular to the substrate surface and with rounded to flattened, hemispherical termini. Karethraichnus fiale are penetrative traces with a cylindrical to bi-convex or flask-shaped profile, and an axis approximately perpendicular to the substrate surface. Thatchtelithichnus (new ichnogenus) Thatchtelithichnus holmani (new ichnospecies) consist of non-penetrative borings into a bone substrate. They consist of a ring-shaped trace, with a central pedestal or platform. The position of the borings on the shells, and evidence of syn-emplacement healing of the borings in several of the turtles, indicates that these borings were emplacement by ectoparasites/mesoparasites while the animals were living. Similar traces in modern emydid turtles are attributed to ticks, leeches, or spirorchid liver flukes.
Introduction
Bioerosional structures on fossil bone are common in the rock record. Scratch marks, tooth marks, and other evidence of predation and scavenging occur on fossil bone material from a variety of successions (e.g., Behrensmeyer, 1978; Fiorillo, 1987, 1990; Tappan, 1994; Hasiotis, 2004; Tapanila et al., 2004). In the past couple of decades, the influence that inverte- brate borings have on bone preservation and modification has become evident (e.g., Rogers, 1992; Paik, 2000; Kaiser, 2000; Britt et al., 2006; Cabral et al., 2011). In marine settings, a variety of organisms have been shown
to be involved in bone boring activities including amoebae (Ascenzi and Silvestrini, 1984), annelid worms (Kiel et al., 2010; Higgs et al., 2011), and bivalves (Tapanila et al., 2004; Belaústegui et al., 2012). Some organisms such as the annelid worm Osedax have recently been shown to be significant bio- degraders of whale bones in marine settings (Kiel et al., 2010; Higgs et al., 2011). In continental settings, microbial bioerosion, via fungi,
bacteria, and cyanobacteria is a primary means of bone degradation (Jans, 2008). Bone macroborings in continental settings are generally attributed to the activity of insects and
their larvae. Silphid beetles, dermestid beetles, and termites have all been shown to bore into the bones of a variety of vertebrates (Tappan, 1994; Kaiser, 2000; Britt et al., 2006; Roberts et al., 2007; Cabral et al., 2011; Pirrone et al., 2014). In all of these studies, however, the borings were emplaced in the bones of dead organisms. The borings occurred to the animals after necrosis and were not demonstrably involved in the death of the organisms involved. For most parasites, and for most host taxa, boring is only likely to occur after death. Elaterid beetles prey upon, and kill, living land snails but have not been known to bore into vertebrate material (Baalbergen et al., 2014). Herein we describe a suite of borings emplaced in the
plastron and carapace of fossil geoemydid turtles. The turtles were collected from the lowermost beds of the early Eocene Cathedral Bluffs Tongue of the Wasatch Formation in the northeastern part of the Green River Basin near South Pass, Wyoming (Figs. 1 and 2). Individual turtle shells are characterized by as few as one or two borings but may have over 100 borings. The position of the borings on the shells, and evidence of syn-emplacement healing of the borings in several of the specimens, indicates that these borings were usually if not always emplaced by ectoparasites/mesoparasites while the animals were living.
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