Dermestes maculatus and periplaneta Americana: bone modification criteria and establishing their potential as climatic indicators

[摘要] Various insect taxa are known to modify bone with their mandibles, including membersof the orders of Dermestidae, Tenebrionidae, Calliphoridae, Tineidae and Termitidae.Despite bone modification being a known behavioural trait of many of these taxa, littlework has been done to record the distinctive ways in which they modify the bonesurface, and a lack of concise descriptions of modification suites inhibits decisiveidentification and interpretation. The most widely inferred causal agents inpalaeontological literature are either termites or dermestid beetles, whilst cockroachesas potential bone modifying agents have not yet been considered. The primary aims ofthis investigation were to establish whether or not cockroaches and dermestids modifybone, and if so in what ways, develop an interpretative framework to aid futureresearchers in the identification and differentiation between the variously reportedagents of bone modifications, test whether or not the agents will modify bone of varyingdensities (thin cortical, thick cortical, compact and cancellous bone) or in a particularstate of preservation/condition (fresh, dry, weathered or fossilised), and investigatewhether or not the occurrence of insect modifications on bone can be used as a proxy toestablish a broad climatic signature based on their known thermal physiological limits. Asingle experimental trial of 18 bone specimens were exposed to the African cockroachPeriplaneta americana for a period of six months and a further four experimental trials(totalling 80 bone specimens) were exposed to the Coleopteran Dermestes maculatusfor periods of four months each under the absence or presence of substrate andvariable feeding conditions. Experiments were conducted within an insectary at 28° C,40 % humidity and 12 hour light/ 12 of darkness. Subsequently, all specimens wereviewed using an Olympus SZX 16 Multifocus microscope fitted with a digital camera atmagnifications between 7 and 115x. Three modification types were identified for P.Americana, namely discolouration, destruction of bone and gnawing. A total of fivemodification types were established for D. maculatus including the occurrence ofsurface tunnels, destruction of bone, bore holes, surface pits (Classes 1–3) and gnawing.Three distinctive surface pits morphologies were identified; Class 1 pits are highlyvariable but most often semi-circular to elliptical shallow depressions with a U-shapeprofile with striations radiating around the outer circumference of the depression. Class2 surface pits are semi-circular shallow depressions with randomly orientated striationsoccurring over the entire feature. Class 3 surface pits are irregular shaped depressionswith complex profiles not associated to gnawing striations. Broad climatic signatures forboth of these agents were developed based on their known physiological thermal limits.The indistinct modification signature of P. americana in combination with limitedoccurrence and frequency patterns may prove difficult to identify from anarchaeological or palaeontological context. Periplaneta americana and D. maculatus dosignificant damage to aves bones, which could result in their under representation in thearchaeological and palaeontological records. The highly distinctive signature as well asoccurrence and frequency patterns of modifications produced by D. maculatus hasenabled the reinterpretation of existing palaeontological analyses, suggesting thatdermestids are in fact not responsible for reported instances in which they aresuggested as the causal agent during the Mesozoic and Cenozoic.

[发布机构] University of the Witwatersrand