Question

3. What is the relationship between diet/ecology and tooth crown size, shape, cusp height/sharpness, and enamel thickness? Describe the characteristics of the teeth associated with frugivory, insectivory, folivory, and ominivory. 15 pts

4. You are a paleoanthropologist working in a cave site in Europe dated to 30KYA. You have recovered the almost complete remains of a hominin – cranial and postcranial. Briefly detail key traits you would examine/use to attribute this specimen to H. neanderthalensis or H. sapiens. 15 pts

Answer 1

3.

Dietary ecology has been hypothesized to play an important role in determining the morphology of the skull. With advances in computer technologies, researchers now have the ability to test some of these hypotheses using previously unavailable methods: two such methods are dental topography and finite element analysis (FEA).

Dental topography is a method of quantifying and representing 2.5 or 3D whole tooth shape with a single metric. Originally developed using Geographic information systems (GIS) technology, it has since expanded to include non‐GIS specific technologies and metrics. Three of the most common metrics used are Dirichlet normal energy, a measure of curvature, relief index a measure of occlusal relief, and orientation patch count , a measure of the number of tools on the occlusal surface of a tooth. Teeth with higher DNE values are, on average, sharper, and it is hypothesized this makes them more efficient at fracturing food items. Teeth with higher RFI values have more tooth surface for the food item to come into contact with, and teeth with higher OPC values have more cusps and/or crests on the occlusal surface to breakdown food items.

In general, these dental topographic metrics have been successful at correlating mandibular tooth shape to dietary categories in extant mammals. While there are some differences in methodologies used in choosing what tooth/teeth to use and in obtaining tooth shape (e.g., differences in scanning techniques and cropping methods), the following pattern emerges in many studies: taxa with more fibrous diets (e.g., folivores) tend to have higher dental topographic values than taxa with less fibrous diets (e.g., frugivores, hypercarnivores) and hard object feeders. This implies that species with higher fiber diets tend to have relatively sharper teeth with more tools and higher occlusal relief. Disregarding hypercarnivores, it is hypothesized that teeth with higher topographic scores are more efficient at cutting fibers, and selection has acted for these teeth in taxa with higher fiber diets. Conversely, it has been hypothesized that teeth with lower topographic scores are more efficient at breaking open fruits/hard food items and/or resisting fracture, and selection has acted for these teeth in taxa with frugivorous and/or hard diets.

It was previously hypothesized under the Pointed Cusp Hypothesis that teeth with sharper cusps would be more efficient at brittle food item fracture, because they would reduce the contact area between the tooth and the food item, increasing the stresses in the food item and promoting food item failure. It was similarly hypothesized under the Blunt and Strong Cusp Hypotheses that blunt cusps would be more efficient at brittle food item fracture as they would reduce the energy necessary to fracture a brittle food item and reduce the stresses in the enamel, reducing the risk of enamel fracture. While the Pointed and Strong Cusp Hypotheses are true for single cusped teeth, they are not true for multicuspsed teeth. Instead, it was found that tooth asymmetry is more important in multicusped teeth, as symmetrical teeth distribute bite force equally between all cusps, creating an isostress condition in the food item. Conversely, asymmetrical teeth distribute the bite force unevenly between the cusps, which can produce the high stress concentrations in the food item while preventing high stresses from forming in the enamel, causing the food item to fail with less energy and a reduced risk of fracturing the enamel. Therefore, having a mix of sharp and dull cusps is more advantageous than having just sharp or just dull cusps when breaking down brittle food items.

Excluding the confounding effects of hypsodonty, DNE and RFI are measures of sharpness, while orientation patch count rotated (OPCR, a form of OPC) is a measure of the number of tools on the surface of the tooth. Given the lack of correlation between cusp sharpness in brittle food item breakdown efficiency, dental topographic measures of sharpness, such as DNE and RFI, may not be correlated to brittle food item breakdown efficiency. In addition, complex teeth with many tools on their surface, which would have high OPCR values, may not be efficient at brittle food item fracture, as the bite force is likely to be distributed between the many tools. Conversely, teeth with low OPCR values may be more efficient at brittle food item fracture as the bite force will be focused over a fewer number of tools, and create high stress concentrations in the food item. However, these relationships between dental topography and brittle food item breakdown efficiency have not yet been investigated.

Masticatory efficiency can be measured in terms of chewing or food item breakdown efficiency. Chewing efficiency is defined as “the ability to grind a certain portion of a test food during a given time is measured in terms of food item particle size reduction, and is frequently measured in vivo . In nonhuman subjects, it is measured by feeding individuals, collecting the masticated food particles either from the stomach or the feces, and sieving the masticated foods. Animals with higher chewing efficiencies will have a larger percentage of smaller food particles. This makes chewing efficiency a measure of overall masticatory efficiency representative of an entire feeding bout, which does not separate tooth performance from other masticatory and/or digestive variables (e.g., jaw kinematics, muscle forces, digestive enzymes). Food item breakdown efficiency is the proficiency with which a tooth or teeth cause a food item to fail. It is tooth, food item, and bite specific: that is to say, efficiency can change from bite to bite during a feeding bout. Unlike chewing efficiency, there are several ways to mechanically measure food item breakdown efficiency, such as reaction force, energy, stresses in the food, and stresses in the tooth. This is because different food items break down in different manners (e.g., nuts are fractured, leaves are sheared, and fruits are crushed/juiced, making different performance metrics important when breaking down different food items. Unlike chewing efficiency, food item breakdown efficiency isolates the interaction between the tooth and the food item. This makes tooth shape more likely to be correlated with food item breakdown efficiency than chewing efficiency. Therefore, masticatory efficiency is being defined as food item breakdown efficiency in this study.

A limiting factor in relating dental topography to food item breakdown efficiency is the difficulty of measuring breakdown efficiency in vivo . In lieu of in vivo data, in situ , in vitro , or in silico data can be used. One method that has become increasingly popular for gathering biomechanical data in silico is finite element analysis (FEA).

4. Homo sapiens living today have an average brain size of about 1350 cubic centimetres which makes up 2.2% of our body weight making the brains of this species absolutely smaller than those of Homo neanderthalensis. However, due to its gracile postcranial skeleton, the brain of Homo sapiens is larger relative to body size than that of Homo neanderthalensis. Early Homo sapiens, however, had slightly larger brains at nearly 1500 cubic centimetres. The skulls of modern Homo sapiens have a short base and a high braincase. Unlike other species of Homo, the skull is broadest at the top and the sides of the skull are nearly vertical. The fuller braincase also results in almost no post-orbital constriction or narrowing behind the eye sockets. The back of the skull is rounded and indicates a reduction in neck muscles. The face of Homo sapiens is reasonably small with a projecting nose bone. They also have a limited brow ridge and the forehead is tall with orbits that are square rather than round. The skull of Homo sapiensgenerally lacks evidence of being strongly built (e.g., it lacks the large brow ridges and bony prominences seen in Homo neanderthalensis).

So by taking into account all these facts, the paleoanthrapologist can find whether the hominin cranial belonhs to homo sapiens or homo neanderthalensis.