By Spyridoula Pappa (PhD Student)
Often during my PhD research, I feel like a “bear dentist” and a “detective” at the same time. My project involves the analysis of teeth of the most remarkably diverse of the carnivores (at least in terms of diet), the bears (Family Ursidae), in order to answer questions concerning their life and diet. Teeth play a fundamental role during an animal’s life and come in many shapes and sizes for chewing food. A typical mammal tooth includes two parts: a crown and one or more roots. The crown is covered by a layer of dentine, overlain by enamel, while the root is coated with cementum.
In order to examine the changing nature of Pleistocene carnivore diet and palaeoecology, I use an innovative technique known as Dental Microwear Analysis. The technique allows me to examine the abundance, distribution, orientation, size and shape of micro-features on the chewing surface of enamel, which directly reflect the properties of food consumed. Enamel is the hardest and most mineralised tissue in the body and it is known, from studies on living mammals, that enamel micro-features relating to food consumption renew every few weeks in life. Thus, at the point of death, the teeth will illustrate the final weeks of diet of the animal.
We also know that (like humans) bears are mainly omnivores today, with large canine teeth for grabbing prey and big molars designed for grinding up vegetable matter. At the same time, great dietary diversity can be seen in living species. For example, polar bear (Ursus maritimus) is a hypercarnivore, preying almost exclusively on seals, whereas the giant panda (Ailuropoda melanoleuca) is a herbivore, existing on a diet of bamboo. The sloth bear (Ursus melursus) is an insectivore, feeding mainly on termites and ants, whereas the brown bear (Ursus arctos) is more omnivorous. Accordingly, all show different patterns of microwear on their teeth. In contrast, relatively little is currently known about the diets of extinct Pleistocene cave bears, and variation between species, or indeed whether the ubiquitous brown bears switched between more meat- or more plant-based diets depending on latitude and/or palaeoclimatic change. Microwear analysis is therefore a very promising approach for elucidating aspects of diet in extinct Ursidae.
My analysis begins with the study of well preserved bear teeth from different modern species inhabiting different geographical regions, in order to create a database of enamel micro-features for species with known diets. This information can then be used to compare against the micro-features in extinct Pleistocene bears for the purpose of palaeodietary reconstruction.
Over the last 12 months of my project, I have travelled around museums in the UK and mainland Europe, making hundreds of silicon moulds of extant and extinct bear teeth. The tooth selected for moulding is the first lower molar (m1, carnassial) for preference (photo 1.) This tooth is used by bears for both slicing and grinding their food and I am interested in exploring potential differentiation of micro-features between these two areas. The selected specimens are first cleaned with a cotton swab and acetone to remove any consolidants or varnish from the chewing surface. After that the surface is cleaned with a cotton swab and 96° alcohol (ethanol) to remove the acetone. This is done very carefully in order to avoid making any “fresh” scratches on the enamel.
For the moulding procedure, I use the same material as dentists utilise. Dental silicone (mixed with a hardener) is applied with a “gun”, directly on to the tooth. When the silicon is dry, a wall of lab putty is formed around the mould, onto which a specimen number is gently engraved. Once the putty is dry, the mould is carefully peeled off from around the tooth. Back in the lab at Royal Holloway, I fill the moulds with resin in order to cast the surface of the teeth.
At this stage, I can start my analysis of the cast under a stereomicroscope at 35x magnification to quantify the number of micro-features and later analyse them statistically.
From my preliminary results and for testing ratios meat:plant and fruit:plant matter of the living bear species, it is clear that the extant species can be separated into different groups related to their diet. Interestingly, differences on enamel micro-features are even evident even within living brown bears from different geographical regions. The next stage will be to plot the microwear features in the Pleistocene extinct species against the extant species. Thus, from tiny pits and scratches on the teeth, a whole array of dietary information can be generated for these exciting carnivores.