Zonneveld et al.—Bored turtle shell
cortex layers and an internal cancellous layer (Achrai and Wagner, 2013; Fig. 5). The bone consists of both organic (collagen helices) and inorganic (hydroxyapatite nanocrystals) components (Weiner and Wagner, 1998; Achrai and Wagner, 2013). This differs significantly from borings in gastropod or bivalve shells wherein the borer had to penetrate through a thin periostracum layer and one or more layers of calcite or aragonite (CaCO3). There is considerable precedence in distinguishing ichno-
genera by the substrate in which they occur (Bertling et al., 2006). Borings in wood, rock, and unconsolidated sediment form distinct ichnotaxonomic groups. Clavate borings emplaced in rock are typically referred to the ichnogenus Gastrochaenolites, those emplaced in wood are referred to Teredolites, and those excavated in firm, unconsolidated sediment are referred to Amphorichnus. It has been suggested that bone be considered ‘lithic’ in ichnological analyses (Bertling et al., 2006; Pirrone et al., 2014). We disagree. These authors specifically considered dead, predated, or scavenged bone in their analyses. Evidence of bone healing at the site of many borings as well as the location on the carapace and plastron of many other borings indicates that many, if not all, of the turtle bone borings discussed herein were emplaced while the host animals were alive. The borers had to penetrate through the epidermal scute to penetrate into or through the dermal bone. In addition to the keratin of the epidermal layer and the hydroxyapatite (3Ca3(PO4)2-Ca(OH)2) in the bone, blood vessels, cartilage, and collagen would have formed part of the substrate. Bone, particularly living bone, is clearly not a typical lithic substrate and should be considered differently.
Karethraichnus lakkos new ichnospecies
Diagnosis.—Shallow (non-penetrating) Karethraichnus having a simple hemispherical profile with a rounded to flattened, hemispherical terminus.
Description.—The holotype (Fig. 6.1) and associated material (Figs. 6, 7) of Karethraichnus lakkos occur in the carapaces and plastrons of the geoemydid turtle cf. Echmatemys sp. (Fig. 3). In the material analyzed, trace diameter ranges from 0.6 to 9.0mm and depth ranges from 0.3mm to 5.5mm. The width-to-depth ratio of specimens ofK. lakkos ranges from>2 to approximately 1 (i.e., specimens range from half spheres to pits that aremuchwider than deep). Specimens commonly form imperfect circles with circularities typically less than 1 and greater than 0.75 (Fig. 4). The bases are typically rounded although flattened bases were also observed (Fig. 6.1–6.8, 6.12, 6.16–6.21).
Etymology.—From the greek ‘lakkos’ (romanization of λάκκος) meaning pit referring to the shape of the traces.
Holotype.—The holotype (UA-TF140-1) consists of a small pit on the ventral surface of a peripheral (Fig. 6.1). Paratypes are herein identified as other shallow pits on this, and other, peripheral carapace bones (UA-TF140; Fig. 6.1–6.7). The type locality consists of a low relief badland hill consisting of interstratified pedogenically altered siltstone and mudstone, and sheet-like to channelized sandstone and conglomerate of the
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Cathedral Bluffs Tongue of the Wasatch Formation at Bush Rim, South Pass, Wyoming (Fig. 1.2).
Occurrence.—Early Eocene (Ypresian-Lutetian/Wasatchian- Bridgerian) of southwestern Wyoming, USA.
Remarks.—Karethraichnus lakkos are the most common bone boring ichnotaxon encountered in the study area. They occur on the dorsal surface of the carapace, the ventral surface of the plastron or on the internal lip of the epiplastra, xiphiplastra, nuchal, and foremost peripherals. Numerous examples were noted in lines on or adjacent to epidermal sulci (Figs. 6.12 and 7.3). Karethraichnus lakkos range in abundance on individual turtle specimens from single borings to over 100 occurrences. The size range of this ichnospecies, even on individual turtle fossils, is highly variable (Figs. 6 and 7). This may indicate that the size range of the infesting parasite was highly variable or that infection/colonization by the parasites was ongoing throughout the turtle’s lifespan. The shallow penetration of this ichnotaxon means that these traces penetrate through the external cortical layer of the bone, but seldom penetrate deeply into the cancel- lous bone layer.
Karethraichnus kulindros new ichnospecies
Diagnosis.—Deep, non-penetrative Karethraichnus having a cylindrical profile, axis approximately perpendicular to the substrate surface, with rounded to flattened, hemispherical terminus.
Description.—The holotype (Fig. 6.13–6.15) and associated material of Karethraichnus kulindros (Fig. 6.9–6.11) occur in the carapaces and plastrons of the geoemydid turtle cf. Echmatemys sp. In the material analyzed, trace diameter ranges from 0.6 to 5.5mm and depth ranges from 0.5 to 6mm. Karethraichnus kulindros commonly co-occurs with K. lakkos and K. fiale on individual turtle fossils.
Etymology.—From the greek ‘kulindros’ (romanization of
κύλινδρος) meaning cylinder, referring to the shape of the traces.
Holotype.—The holotype (UA-TF140-8) consists of a subvertical cylindrical pit on the dorsal surface of costal bone (Fig. 6.13–6.15).The type locality consists of a lowrelief badland hill consisting of interstratified pedogenically altered siltstone and mudstone, and sheet-like to channelized sandstone and conglomerate of the Cathedral Bluffs Tongue of the Wasatch Formation at Bush Rim, South Pass,Wyoming (Fig. 1.2).
Occurrence.—Early Eocene, Cathedral Bluffs Tongue, Wasatch Formation, South Pass, Wyoming.
Remarks.—The depth of Karethraichnus kulindros means that these traces invariably penetrate through the external cortex, and typically terminate deeply within the cancellous layer, commonly bottoming out at or near the inner surface of the internal cortex. Note that this trace does not penetrate fully through the bone. Karethraichnus kulindros differs from
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