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Zool 408: Evolution
Evolution & Dentition
| Question | Answer |
|---|---|
| When did mammals evolve? | 100 million period from late Paleozoic to early Mesozoic |
| Broad geological time divisions (era) | Paleozoic to Mesozoic to Cenozoic |
| Narrower geological time divisions (period) | Carboniferous (Paleozoic) to Triassic (Mesozoic) to Jurrasic (Mesozoic) to Cretaceous (Cenozoic) to Paleogene (Cenoozoic) to Neogene (Cenozoic) |
| Polyphyletic | derived from 2 or more ancestral lineages |
| Diphyletic | from 2 different ancestors |
| Mammalian origin | monophyly (single point of origin) |
| Cleidoic | shelled egg |
| Synapsids into terrestrial habitats when? | 320 million years ago |
| Therapsida | 'mammal-like reptiles' |
| Pelycosauria | more primitive than Therapsida |
| Pelycosaur | synapsid, small temporal opening, large angular bone |
| Therapsid | synapsid and top carnivores, large temporal opening, small post-dentary |
| Cynodontia | early synapsids to early mammals, more erect posture |
| 6 cynodont changes | zygomatic arch, double rooted cheek teeth, hearing, atlas + axis, calcaneous, hearing |
| Reptilian ear | 1 ear ossicle = stapes |
| Mammalian ear | 3 ear ossicles = stapes, incus, malleus |
| Decreased post-dentary jaw | increased hearing and efficiency of chewing (important for homeothermy) |
| Cynodont soft tissue changes | increased metabolism efficency for endothermy, better food gathering/processing, increased hearing (for hunting), maintaining homeostatis |
| Early prototherians | ancestral to monotremes |
| Early prototherian characteristics | incisors, canines, premolars, molars, body erect w/ legs under, flexion and extension of vertebrae (locomotion) |
| 55-25 million years ago | semi-aquatic mammals (beavers, otters) first appeared |
| Tribosphenic molars | 1st in early therians, molars with 3 main cusps in triangle pattern, diphyletic origin |
| Advantage of tribosphenic molars | food is crushed and sheared leading to more efficient food proccessing |
| Mammalian radiation | 65 million years ago in Cenozoic b/c of dinosaur extinction and Pangea breakup |
| Occipital condyle | 2 in mammals and aids in rotation and strength of skull |
| Secondary palate | simultaneous breathing + eating |
| Phalangeal formula | # of carpals and tarsals (2-3-3-3-3 in mammals) |
| Muscular diaphragm significance | allows more 02 to taken up, thus more energy |
| Skeletal changes | loss/fusion of bones (shoulder, pelvic girdle), dorso-ventral axial skeleton, determinate bone growth |
| Dire wolf | co-existed with gray wolf for 100,000 years |
| Dire wolf extinction | 10,000 years ago (Pleistocene extinction) |
| Mammalian shoulder | reduced coracoid, absent interclavicle, clavicle reduced in cursorial mammals |
| Repenomamus giganticus | large Mesozoic mammal which fed on young dinosaurs |
| Dendition adaptations for endothermy | increase food intake, increase diversity of food types, decrease foraging time |
| Cheek teeth adaptations | increased: surface area, # of cusps/shearing surfaces, overlap for grinding |
| Evolution of teeth | triconodont to symmetrodont (v-shape) to pantothere to tribosphenic to quadrate |
| Tooth is sealed in what? | alveolus |
| Narwhal tusks used for what? | display and sensing |
| Without teeth = | edendate (true anteaters, pangolins, monotremes) |
| Cranial asymmetry linked to what? | hearing |
| Cranial asymmetry lost in mystiectes because of? | shift to low-frequency hearing and bulk straining predation |
| 2 growth forms of teeth | open-rooted (ever-growing) and close-rooted (stop and wear) |
| Brachyodont | low crowned teeth, omnivores |
| Hypsodont | high crowned teeth, herbivores |
| Selenodont teeth | cusps form crescent shaped lophs (ridges) |
| Carnassial/sectoral teeth | carnivores, last upper premolar + 1st lower molar, used for slicing, chopping, sheering meat |
| Carnassial pair | P4 (inner surface)/M1 (outer surface) |
| Temporalis muscles | well developed in carnivores for shearing |
| Masseters | well developed in herbivores |
| Diastema | gap in tooth row which allows efficent food manipulation |
| Supernumerary dentition | extra teeth in position |
| Agenesis | absence or incomplete development of an organ or body part |
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