Presentation on theme: "EVOLUTION OF THE HORSE: A LOOK AT TEETH"— Presentation transcript:
1EVOLUTION OF THE HORSE: A LOOK AT TEETH Kaelin Creange
2The Question at HandHow have horses’ teeth adapted to their more evolutionarily recent niche of grazers versus browsers?
3The Modern Equine Skull Long face to accommodate large crown reserves of grinding teeth, and set of cropping teeth in the frontDeep mandible, allowing for large masseter muscles that enable grinding type mastication.
4“crown” is described as the enamel covered area above the gum line Tooth StructureHorse teeth have evolved hypsodonty, which means they have a high crown.This allows them more tooth to wear down, thus being able to utilize a tougher food sourcePresence of cementum increases the hardness of the tooth.Also creates ridges on the occlusal surface of the tooth, which aids in more effective grindingBorn with full set of fully developed adult teethMilk teeth precede the eruption of the adult teeth, which will continuously erupt throughout their lifetime.“crown” is described as the enamel covered area above the gum line
5The Mouth INCISORS Center Lateral Corner WOLF TOOTH (premolar 1) MOLARS(3)PREMOLARSCANINES(premolars and molars are virtually the same size and shape)
6Mastication Grinding, circular motion Aids in eating grasses, which are an abrasive, fibrous food sourceCondemns the teeth to a great deal of wear (avg 2-3mm/yr)
7Looking at the Evolution Early horses (Eohippus, Orohippus, Mesohippus)Short crownedNo cement on the outside of toothPremolars smaller than molars (4 premolars, 3 molars)Later horses (Merychippus, Pliohippus, Equus)High crowned (hypsodonty)Teeth covered in cementPremolars resemble molars (except pm1; very small)
8A. Example of a brachydont (human) B. Examle of a hypsodont (horse)
9Caroline A. E. StrombergExamined the hypothesis that hypsodonty in equids evolved as an adaptation to the emergence of grass-dominated habitatsCompared the timing of the emergence of the taxa first displaying hypsodonty (along with sister taxa having mesodont and brachydont teeth) with the emergence of grass-dominated habitats in the Great Plains of North America.
11Which phylogenic tree? Black bar = trait of hypsodonty Grey bar = appearance of the demand for feeding on grass
12Stromberg’s ResultsHypsodonty fully present in members of Equinae (~18mya)Equinae emerged at least 4my after the earliest open, grass-dominated habitats.With this 4 million year gap, does this result support hypsodonty as an adaptation to increasing dominance of open grasslands??
13Stromberg’s Results cnt. Parahippus possible intermediate taxa between brachydont and hypsodont taxa?Were mixed feeders (grazed and browsed)Increased crown height (mesodonts)Emerged almost same time as open-grasslandsSpecies within taxa showed a thicker, and (modestly) modified radial enamel that are similar to some characteristics of the hypsodont horses of EquinaeThis suggests that small changes were made over much longer time periods than initially thoughtsupports ?
15Future ResearchHow genetically similar are Parahippus and Equinae taxa?This could shed light on if parahippus is in fact very closely related to equinae, or if there is another intermediate taxa between them.
16REFERENCESCerling, T.E., Harris, J.M., MacFadden, B.J., and Prado, J Ancient latitudinal gradients of C3/C4 grasses interpreted from stable isotopes of new world pleistocene horse (Equus) teeth. Global Ecology and Biogeography 8:Dacre, I.T Physiology of mastication. American Association of Equine Practitioners (reproduced in the IVIS website).Kainer, R.A., McCracken, T.O Horse anatomy, a coloring atlas. Loveland, CO: Alpine Publications, Inc.Matthew, W.D The evolution of the horse: a record and its interpretation. The Quarterly Review of Biology 1:McKenna, M.C Review: the horse tree. Science 260:Strömberg, C.A.E Evolution of hypsodonty in equids: testing a hypothesis of adaptation. Paleobiology 32: