Structure and composition of the incisor enamel of extant and fossil mammals with tooth pigmentation

The inclusion of iron compounds in teeth, which impart a red to orange colour to them, is a phenomenon shown by several groups of vertebrates in different periods of their evolution. Incisors from fossil and extant shrews and from extant rodents were sectioned and studied with the techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) to compare their structure and the distribution of Fe. The enamel in white- and red-toothed soricids has three layers; two of them are divided into two zones in the red-toothed species. However, the most external layer varies among taxa; it is well defined in Sorex but difficult to identify in the Early Pleistocene genera Beremendia or Dolinasorex. In the arvicoline rodent Terricola, only two layers can be defined, the outer of which is divided into two zones depending on the presence or absence of Fe. The Fe proportions in the larger soricids reach up to 45%, but in rodents only up to 10% (weight % with respect to Fe + Ca + P). The STEM study shows that in a fossil soricid the Fe phases form clusters of nanometric particles of very poor crystalline oxides or hydroxides surrounding the apatite crystals that form the enamel

Bite club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxa

We provide the first predictions of bite force (B(S)) in a wide sample of living and fossil mammalian predators. To compare between taxa, we calculated an estimated bite force quotient (BFQ) as the residual of B(S) regressed on body mass. Estimated B(S) adjusted for body mass was higher for marsupials than placentals and the Tasmanian devil (Sarcophilus harrisii) had the highest relative B(S) among extant taxa. The highest overall B(S) was in two extinct marsupial lions. BFQ in hyaenas were similar to those of related, non-osteophagous taxa challenging the common assumption that osteophagy necessitates extreme jaw muscle forces. High BFQ in living carnivores was associated with greater maximal prey size and hypercarnivory. For fossil taxa anatomically similar to living relatives, BFQ can be directly compared, and high values in the dire wolf (Canis dirus) and thylacine (Thylacinus cynocephalus) suggest that they took relatively large prey. Direct inference may not be appropriate where morphologies depart widely from biomechanical models evident in living predators and must be considered together with evidence from other morphological indicators. Relatively low BFQ values in two extinct carnivores with morphologies not represented among extant species, the sabrecat, Smilodon fatalis, and marsupial sabretooth, Thylacosmilus atrox, support arguments that their killing techniques also differed from extant species and are consistent with ‘canine-shear bite’ and ‘stabbing’ models, respectively. Extremely high BFQ in the marsupial lion, Thylacoleo carnifex, indicates that it filled a large-prey hunting niche