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Skull structure of all Mammals
- Synapsid skull
- the mammal clade is defined as snyapsid for the skull.
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Characteristics of synapsid skull
- One pair of temporal openings
- 1st amniote lineage to radiate extensively into terrestrial environment
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Importance of pelycosaurs
- Most basal synapsids
- diverse-both carnivores and herbivores
- extinct by the end of Paleozoic (Permian)
- paraphyletic - therapsid lineage emerged from within pelycosaur lineage (from carnivores)
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Importance of therapsids
- persisted into Mesozoic (Triassic)
- radiated into many carnivores and herbivorous forms
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Importance of cynodonts
heterodonty - differntiation of tooth types
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Importance of cynodonts
- changes in jaw musculoskeletal structure: enlargement of dentary and reduction of posterior jaw bones
- paraphyletic group: mammals not included
- turbinate bones-suggests endothermy
- more upright posture & greater agility
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What group did early mammals arise from?
within the cynodont lineage 200 million years ago
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Dentary characteristics of early mammals
- diphyodont dentition - teeth replaced one time in life
- new jaw joint between squamosal & dentary-quadrate & articular incorporated into middle ear
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Characteristics of early mammals
- had hair and probably endothermic
- had a secondary palate (shared with cynodonts) that separated feeding and breathing pathways that permitted suckling by young
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How long did mammals and dinosaurs coexist for?
140 million years ago
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Significance of dinosaur extinction
- dinosaurs extinct in early Cenozoic, about 65 million years ago
- mammals diversified into many lineages and many achieved large body size
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Characteristics of hair
- unique structure of mammals
- made of dead cells impregnated with keratin
- epidermal structure (hair follicles extend into dermis but is lined with epidermal cells)
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Significants of glands
- mammals have greatest variety of glands among vertebrates (humans have all major types)
- sweat glands: evaporative cooling
- scent glands: communication
- sebaceous glands: expel sebum
- mammary glands: homologous to sweat glands
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How many species are there of extant monotremata?
3 species (3 in echidnia, and 1 in platypus)
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Characteristics of extant metatheria (Marsupials)
- oviparous -lay yolky eggs and incubate them
- young fed with maternal milk secretions
- viviparous with altrical young (early development stage)
- ~270 species
- independently and convergently evolved most ecologiical types seen in placental mammals, except powered flight and marine habit
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Repruduction in Metatherians (marsupials)
- females-vagina with two lateral canals and one medial canal (3 passages0
- males-forked penises fit lateral vaginal canals
- sperm travel up bifrucated vaginal canals and young pass through medial vaginal canal
- young born at atrical stage, and hae extended development while nursing
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Characteristics of Eutheria (Placentals)
- viviparous with young born relatively precocial (later stage in development)
- tremendous variety of forms in almost every habitat
- worldwide distribution with ~4500 species
- almost 1/2 are rodents and 1/4 are bats
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Reproduction in Eutherians
- uterus/uteri join single vaginal canal
- connections between fertlized egg and maternal uterine tissue form placenta (homology). site of gas/nutrient exchange
- long period of in utero development (compared to metatherians)
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Describe first primate apperance
- first primates had apperance of tree shrews with long snouts, good olfaction, poor diurnal vision
- appeared ~65 million years ago (Paleocene)
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When did primates first adapt to arboreal habitat
- ~55 million years ago (Eocene)
- improved diurnal vision (including color vision-reversal)
- larger brain
- stereoscopic vision
- increased capacity for grasping motions
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Where did the linage leading to modern humans arise?
Africa
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When did the hominid ancestor appear?
- ~14 million years ago (miocene)
- clade comprising Grade Apes (including humans)-extant and extinct forms
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Evoltuion of human traits
"Uniquely" human traits evolved through the modification of traits that existed in ancestral forms
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characteristics of extinct lineages sharing a more recent common ancestor with humans than with extant non-human Great Apes
- enlargement of cranium (larger brain)
- more reliance on vision and reduced olfactory capacity
- paedomorphic characteristics
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What is the earlist known hominin fossil?
dated to 7.6 to 6.0 million years ago
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Examples of other hominin fossils spanning the next several million years
- Ardipithecus (2 speceis) - 5.6 to 4.3 million years ago
- Australopithecus (4 species) - 4.1 to 3.0 million years ago
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When did Homo appear?
~2.3 million years ago
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Apperance of other homo species
- H. habilis - 2.3 to 1.4 mya (tools)
- H. erectus - 1.8 to 0.1 mya (possibly more recent, first Homo to leave Africa to SE Asia
- H. sapiens (modern humans) appeared ~200k years ago
- H. neanderthalensis - Near East/Europe to ~30k years ago (replaced by H. sapiens)
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