Differentiation of Lower Jaw Toothrow Length among Feeding TypesINTRODUCTIONNo matter how you compare animals, whether it is among different habitats, different phyla, different feeding types, different species, and even within a species, there is variation in every aspect of an animal’s size. But why? Scientists continue to research animals and why each and every one of us is sodifferent. One specific difference animals have is the size and shape of our skulls. Animals are divided into one of three groups: Carnivores, meaning it eats only other animals, Herbivores, meaning it eats only plants, and Omnivores, meaning it eats both animals and plants. Based on our observation from week one, the carnivore skulls seemed to have more prominent incisors and canides and larger jaws, while the herbivores seemed to have more prominent molars and smaller jaws. We thought the difference could possibly be related to what the animals ate. Skulls evolve so that they are not greatly over- or underbuilt relative to the forced they must sustain (G. J. Slater, E. R. Dumont, & B. Van Valkenburgh, 2009). Even though it is unclear what exactly the drive behind the evolution of skullsdue to such a wide range of diversity in cranial shape (G. J. Slater, E. R. Dumont, & B. Van Valkenburgh, 2009), we thought there could possibly be a relationship between the size of the jaw and toothrow and what the animal eats.We hypothesized that if carnivores need a larger mouth to eat other animals, then they will havea longer mandible length and toothrow length. Our null hypothesis was that carnivores will not have a longer mandible length and toothrow than herbivores. We predict that carnivores will have a longer mandible length and toothrow due to the force they must sustain while feeding. METHODSIn our experiment we used a total of 24 skulls. We measured four different carnivore species: coyote, fox, mink, and bobcat. We measured four different herbivore species: deer, beaver, muskrat, and rabbit. We measured three different skulls of each species to account for variations among individual animals among the same species. We measured both the mandible length and toothrow or each skull testing to see if the skull length to mandible/toothrow ratio was greater in carnivores and herbivores. Our independent variable was the skull length of each individual skull. The dependent variables were themandible and toothrow lengths. All skulls were measured in centimeters using a ruler. All measurements were then divided by the skull length to standardize for variations in sizes among the same species (see table 1). In order to accept our hypothesis the P-value must be less than 0.05 for both categories with the carnivore averagesbeing greater than those of the herbivore averages.RESULTSTable 1 shows the ratio of each individual skull’s mandible and toothrow length in comparison to its skull length. The mean mandible length/ skull length for carnivores was 0.68 and 0.76 for herbivores. The mean toothrow length/ skull length for carnivores was 0.43 and 0.53 for herbivores. You can also seethe standard deviations and standard errors in Table 1. Figure 1 and 2 compare the average values of mandible length and toothrow between carnivores and herbivores. As you can see, the average values were greater in both categories among herbivores.DISCUSSIONOur experiment resulted in a p-value of 0.00723 when comparing carnivore and herbivore mandible length. We also calculated a p-value of 0.0292 when comparing carnivore and herbivore toothrow length. However, because it was the herbivore averages that were higher than the carnivore averages, we rejected our alternative hypothesis and failed to reject the null hypothesis that carnivores will not have a longer mandible and toothrow length than herbivores. Though our results did not back up our hypothesis, there was a significant difference in data. Therefore, we could build off of the experiment and develop a hypothesis backing up why the herbivore had larger mouths. Possibly, carnivores need a more condensed center of gravity due to more movementin the mouth when eating so that nothing breaks.If we could re-do the experiment, we would have many more replicates and possibly more precise measuring tools. With the measuring, we would have the same person measuring all of the subjects to control for different measuring techniques.Table 1Mandible and toothrow length compared to skull lengthMand.Length/ SkullLengthTooth.Length/ SkullLength Replicate CarnivoresCoyote 1 0.64 0.362 0.62 0.383 0.62 0.38Fox 1 0.75 0.542 0.77 0.503 0.81 0.56Mink 1 0.58 0.332 0.62 0.313 0.6 0.32Bobcat 1 0.7 0.502 0.73 0.493 0.74 0.51Mean 0.68 0.43St. Dev 0.0769691 0.091820295St. Error 0.022219065 0.026506236HerbivoresDeer 1 0.85 0.652 0.83 0.673 0.74 0.57Beaver 1 0.86 0.552 0.83 0.553 0.78 0.52Muscrat1 0.67 0.502 0.62 0.463 0.70 0.52Rabbit 1 0.74 0.472 0.75 0.453 0.74 0.42Mean 0.76 0.53St. Dev 0.075302716 0.077155375St. Error 0.021738022 0.022272838T-Test 0.0072261 0.0292482Carnivores Herbivores0.640.660.680.700.720.740.760.78Mandible LengthMandible Length/Skull LengthFigure 1- Average mandible length comparison between carnivores and herbivoresCarnivores Herbivores0.000.100.200.300.400.500.60Toothrow LengthToothrow Length/Skull LengthFigure 2- Average toothrow length comparison between carnivores and herbivoresREFERENCESG. J. Slater, E. R. Dumont, & B. Van Valkenburgh (2009). Implications of predatory specialization for cranial form and function in canids. Journal of Zoology, 278,