Dental microwear texture analysis (DMTA) is a key proxy used to reconstruct the diets of extant and extinct animals. Causal agents of dental wear have been debated for decades, but the recent controversial suggestion that exogenous abrasives (or 'grit' particles) from the environment exert a greater influence on microwear formation than food items has led to renewed interest in this field of research. Feeding trials using large mammals suggest that DMTA can distinguish dietary differences despite variable grit loads. However, the effect of exogenous abrasives on the dental microwear of small, non-herbivorous mammals with quantified grit loads remains untested. Here, we examine dental microwear textures from the European mole (Talpa europaea), which provides an ideal test for the role of grit given moles' subterranean habitat and diet dominated by earthworms that contain, and are coated by, exogenous abrasives. We quantify the environmental abrasive load (by measuring silicate content of soils) and dietary abrasive load (by measuring silicate content of stomach contents) for moles from sites across Norfolk, UK to evaluate the effect of variation in grit loads on microwear textures. No significant relationships are found between microwear texture parameters and any metric of exogenous abrasive load, or between texture parameters and physical soil grit characteristics. Comparing mole microwear textures with those of bats, which have negligible environmental abrasive loads, reveals that moles are indistinguishable in multivariate texture-dietary space from bats that consume 'soft' prey, supporting suggestions that microwear textures preserve accurate dietary signatures and are not overwritten by wear from exogenous abrasives. Drawing upon examples from Jurassic mammaliaforms, we demonstrate the implications of these results for reconstructing the diets and habits of fossil mammals.
Pyrite-permineralized fruits and seeds from the London Clay Formation (Ypresian; England) in the NHMUK are stored in silicone oil to retard decay processes. X-ray micro-computed tomography (micro-CT) has revealed internal morphology for multiple holotypes (including severely cracked and encrusted specimens) scanned in the protective fluid. Silicone oil alone has a similar X-ray attenuation to parts of the specimens, causing minor uncertainty for digitally rendered surfaces, but key systematic characters are readily visualized. Further work is needed to optimize visualization of fine-scale cellular detail. Labelling and segmentation to visualize important structures is achievable with these micro-CT datasets. However, manual labelling of individual slices is required, and defining boundaries between features can be difficult due to differential pyritization and silicone oil permeation. Digital sections through specimens can be made in any orientation and digital locule casts can be produced for studies in virtual taphonomy. These achievements have been accomplished with minimal risk to specimens, which remained in silicone oil and were studied within the museum. The datasets provide a potentially permanent record of at-risk specimens, can be made widely available to researchers unable to visit the collections and to other interested parties, and they enable monitoring for future conservation.
ABSTRACT Although fossil assemblages from the late Early Pleistocene are very rare in Britain, the site of Westbury Cave in Somerset, England, has the potential to address this gap. The mammal fossils recovered previously from the Siliceous Member in Westbury Cave, though few in number, have hinted at an age for the deposits that is as yet unparalleled in Britain. Here, we describe the first bona fide occurrence of Hippopotamus in the British Early Pleistocene, discovered during recent reinvestigation of the Siliceous Member. The hippo fossil indicates a refined biochronological age of ca. 1.5–1.07 Ma for the Siliceous Member and a palaeoclimate that was warm and humid, which accords well with previous palaeoenvironmental inferences. A synthesis of late Early Pleistocene hippo occurrences suggests that the Siliceous Member hippo may have been part of an early colonization of north‐west Europe by these megaherbivores, possibly during MIS (Marine Oxygen Isotope Stage) 31. Alternatively, it evidences a currently cryptic northward migration during an even earlier temperate phase. In either case, the Siliceous Member is likely to represent a warm period that has not been recognized previously in the British Quaternary record.
Pyrite-permineralized fruits and seeds from the London Clay Formation (Ypresian, England) in the NHMUK are stored in silicone oil to retard decay processes. X-ray micro-computed tomography (micro-CT) has revealed internal morphology for multiple holotypes (including severely cracked and encrusted specimens) scanned in the protective fluid. Silicone oil alone has a similar X-ray attenuation to parts of the specimens, causing minor uncertainty for digitally rendered surfaces, but key systematic characters are readily visualised. Further work is needed to optimise visualization of fine-scale cellular detail. Labelling and segmentation to visualise important structures is achievable with these micro-CT datasets. However, manual labelling of individual slices is required and defining boundaries between features can be difficult due to differential pyritization and silicone oil permeation. Digital sections through specimens can be made in any orientation and digital locule casts can be produced for studies in virtual taphonomy. These achievements have been accomplished with minimal risk to specimens, which remained in silicone oil and were studied within the museum. The datasets provide a potentially permanent record of at-risk specimens, can be made widely available to researchers unable to visit the collections and to other interested parties, and they enable monitoring for future conservation.
Amino acid geochronology can provide effective relative dating frameworks for the Pleistocene and has enabled correlation of terrestrial deposits to the global climatic fluctuations described by the marine oxygen isotope record. Using methods developed for the analysis of intra-crystalline amino acids in tooth enamel, we aimed to construct an enamel-based amino acid geochronology for the terrace deposits in the valley of the River Thames in southern Britain using different mammalian taxonomic groups: elephant, horse and bison. To achieve this, chiral amino acid analysis was applied to 58 elephantid, 21 horse and 15 bison teeth from 10 horizons in the Upper Thames Valley, three in the Lower Thames Valley and one from a Thames tributary in the Lea Valley. We evaluate differences in the rates of amino acid breakdown between the taxa and establish which species are similar enough to enable comparison for relative dating purposes. The relative dating of the river terrace deposits is in good agreement with the terrace stratigraphy, biostratigraphy, and other independent estimates of age for all three taxonomic groups. These frameworks demonstrate the potential of enamel-based amino acid geochronologies for relative dating of Middle–Late Pleistocene deposits in the UK, and establish an aminostratigraphic framework from which the dating of other tooth material can be refined. Enamel offers an opportunity to evaluate the age of sites where shell material is absent or poorly preserved. It can also, crucially, provide direct relative dating of mammalian fossils, which are often the focus of study in terms of their evolution, distributional changes or extinction. Direct dating negates the risk that the mammal fossils themselves might be reworked, or of different ages to shell, sediments or other dated material in the same deposits; it also enables archived samples with insecure provenance (e.g. from early 17th-19th century collections) to be directly dated.
Multituberculate mammals thrived during the Mesozoic, but their diversity declined from the mid-late Paleocene onwards, becoming extinct in the late Eocene. The radiation of superficially similar, eutherian rodents has been linked to multituberculate extinction through competitive exclusion. However, characteristics providing rodents with a supposed competitive advantage are currently unknown and comparative functional tests between the two groups are lacking. Here, a multifaceted approach to craniomandibular biomechanics was taken to test the hypothesis that superior skull function made rodents more effective competitors. Digital models of the skulls of four extant rodents and the Upper Cretaceous multituberculate Kryptobaatar were constructed and used (i) in finite-element analysis to study feeding-induced stresses, (ii) to calculate metrics of bite force production and (iii) to determine mechanical resistances to bending and torsional forces. Rodents exhibit higher craniomandibular stresses and lower resistances to bending and torsion than the multituberculate, apparently refuting the competitive exclusion hypothesis. However, rodents optimize bite force production at the expense of higher skull stress and we argue that this is likely to have been more functionally and selectively important. Our results therefore provide the first functional lines of evidence for potential reasons behind the decline of multituberculates in the changing environments of the Paleogene.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
