Mammals and Hominins
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| Mammals are amniotes that ___. | - have hair
- produce milk
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| Humans are mammals that ___. | - have a large brain
- bipedal locomotion
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| What are the major derived characters of mammals that distinguish them from the other amniotes (9)? | - mammary glands and milk
- hair
- fat layer under skin
- endothermic and high metabolic rate
- efficient respiratory and circulatory systems
- diaphragm
- larger brains
- long duration of prenatal care
- differentiated teeth
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| What does hair and a fat layer under the skin do for mammals? | helps the body retain heat, since mammals are endothermic
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| What does the production of milk in mammary glands do for mammals? | - provides nourishment to young
- milk consists of a balanced diet rich in fats, sugars, proteins, minerals, and vitamins
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| What does having larger brains do for mammals? | allows them to be capable learners
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| What does having longer durations of prenatal care do for mammals? | - social bonding
- protection
- extends the time for offspring to learn important survival skills by observing their parents
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| What does having a variety of teeth do for mammals? | allows them to eat many kinds of food
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| Mammals belong to a group of amniotes known as ___. | synapsids (one hole in skull behind eye socket)
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| Without going into details, by the early Cretaceous (145-100 million years ago), the three major lineages of mammals had emerged. What are these lineages? | - monotremes ("single opening" [cloaca])
- marsupials (from marsupium = "pouch")
- eutherians ("true beasts")
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| What are monotremes? What is characteristic about them? | egg-laying mammals, such as echidnas and platypuses
- like all mammals, they have hair and produce milk, but they lack nipples (secrete from glands on belly)
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| What are marsupials? What is characteristic about them? | - mammals (such as koalas, kangaroos, and opossums) whose young complete their embryonic development inside a maternal pouch (marsupium)
- have simple placentas
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| What are eutherians? What is characteristic about them? | - "placental mammal" = more complex placenta
- mammals whose young complete their embryonic development within the uterus, joined to the mother by the placenta
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| What are the main ways in which marsupials and eutherians differ from monotremes? | - have higher metabolic rates
- their nipples provide milk
- have placentas
- give birth to live young
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| Along with the endometrium, what do the extraembryonic membranes that arise from the embryo form in marsupials and eutherians? | a placenta (structure in which nutrients diffuse into the embryo from the parent’s blood)
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| How does the birth of marsupials differ from the birth of eutherians? | - marsupials: embryo develops inside the uterus with help from a placenta; offspring born early in development, finishes inside marsupium
- eutherians: embryo develops completely inside of the uterus with help from a complex placenta; pregnancy longer
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| The greatest diversity of marsupials is in ___, which has not been in contact with another continent for about 65 million years. | Australia
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| In Australia, ___ has resulted in a diversity of marsupials that resemble eutherians in similar ecological roles in other parts of the world. | convergent evolution
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| convergent evolution | the process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches
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| Describe the phylogenic relationship between eutherians, monotremes, and marsupials. | monotremes are basal to the group that leads to marsupials and eutherians (those 2 are sister taxa)
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| What are the major derived characters of primates? | - hands and feet adapted for grasping
- flat nails
- opposable thumbs
- large brain
- short jaws
- flat face
- forward-facing eyes that are close together (= depth perception)
- complex social behavior
- well-developed prenatal care
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| What are the three main groups of living primates? How do they fit in a phylogenic tree? | - lemurs, lorises, bush babies [basal]
- tarsiers
- anthropoids (humans part of this one)
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| anthropoids | - "human like"
- members of a primate group made up of the monkeys and the apes
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| What are the major differences between humans and non-human anthropoids? | - humans bipedal,
- brains larger and capable of language, symbolic thought, artistic expression, and manufacture/use of complex tools,
- have reduced jaw bones/muscles, and
- have a shorter digestive tract.
- differ in expression of regulatory genes
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| What two species are representative of the earliest hominins? | - Sahelanthropus tchadensis (Sahel=region of Chad, Africa; anthropus=human)
and then
- Ardipithecus ramidus (Ardi=ground/floor; pithecus=ape; ramid=root)
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| hominins | - members of the human branch of the evolutionary tree; human lineage
- include homo sapiens and our ancestors (those more closely related to us than chimps or bonobos)
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| What characteristics made early hominins such as Sahalanthropus tchadensis and Ardipithicus ramidus more human-like than chimpanzee-like? | - reduced canine teeth
- relatively flatter faces
- more upright/bipedal (foramen magnum more central)
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| What were some of the more “primitive” characteristics of the early hominins such as Sahalanthropus tchadensis and Ardipithicus ramidus? | - small brain size
- small overall body size
- large teeth
- jaw fairly prominent
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| Chimpanzees/bonobos represent the tip of a separate branch of evolution, and they acquired derived characters of their own after they diverged from ___ with humans. | their common ancestor
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| At times, several hominin species ___. Those species often differed in skull shape, body size, and diet. Ultimately, all but one lineage--the one that gave rise to Homo sapiens--ended in ___. | - coexisted
- extinction
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| What two major trends developed during the evolution of Australopiths? | - complete bipedalism
- complex tool use
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| Approximately ___ years ago, the first members of the genus Homo appeared: Homo habilis and Homo rudolfensis. | 2.4 million
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| Homo habilis and Homo rudolfensis had ___ and ___ that more closely resembled those of modern humans. They also appear to have made abundant use of ___. | - brain volumes larger than the Australopiths
- other morphological characters, such as shorter jaws
- tools
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| Homo ergaster appeared in ___, and Homo erectus appeared in ___ then ___, ___, and ___ around 2 million years ago. | - Africa
- Africa; Europe, Asia, South Pacific
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| Relative to earlier hominins, Homo erectus was ___. In addition to fashioning and using stone tools, by 600-400k years ago, Homo erectus was ___. | - taller with longer legs and considerably larger brains
- making use of fire to cook food and keep warm
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| Homo erectus was so successful, ecologically, that it was able to spread from Africa throughout ___. | Europe, Asia, and the South Pacific
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| What was the first species of hominin to migrate out of Africa? | Homo erectus
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| What does the out-of-Africa hypothesis suggest about hominins? | - they left Africa and colonized the rest of the Old World in two major waves:
- first as Homo erectus in an initial wave out of Africa about 2 million years ago
- then a second time as Homo sapiens about 120,000 years ago
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| The out-of-Africa hypothesis suggests that ___ emerged in Africa, and then in a second wave of colonization out of Africa they replaced the premodern hominins (e.g., Homo erectus, Homo heidelbergensis, and Homo neanderthalensis) of Europe and Asia. | modern Homo sapiens
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| As part of the out-of-Africa hypothesis, it is now believed that there was another migration and colonization involving ___ about 600,000 years ago. | Homo heidelbergensis
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| Homo heidelbergensis appears to have evolved from populations of ___, about 800,000 years ago. Then, some populations migrated to ___ and beyond while other populations remained in ___. | - African Homo erectus/Homo ergaster
- Europe
- Africa
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| The out-of-Africa hypothesis predicts that premodern hominin populations in Europe and Asia died out without contributing to the modern human gene pool, and that all modern humans are descended from ___ alone. | premodern humans (H. erectus/H. ergaster) in Africa
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| What evidence supports the out-of-Africa hypothesis? | - fossil evidence shows gradual divergence of the premodern Homo species in Africa, Europe, and Asia, with H. sapiens arising in Africa 195k years ago
- after, there is rapid replacement of the other Homo forms by H. sapiens sometime after 120k years ago
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| ___ migrated out of Africa approximately 2 million years ago. It was contemporaneous with ___, a species that evolved in Africa from populations of African Homo erectus/Homo ergaster about 800,000 years ago. | - Homo erectus
- Homo heidelbergensis
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| Some populations of ___ migrated to Europe and Asia approximately 600,000 years ago while other populations remained in Africa. | Homo heidelbergensis
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| was present in Europe and central Asia from around 350,000 years ago until around 28,000 years ago. It is believed to have evolved from European populations of ___. | - Homo neanderthalensis
- Homo heidelbergensis
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| ___ were heavier, stronger, stockier, and had a more pronounced brow ridge, but they shared many social and cultural characteristics with modern humans. | Neanderthals
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| ___ appeared in Africa roughly 195,000 years ago. It is believed that Homo sapiens evolved from African populations of ___. | - Homo sapiens
- Homo heidelbergensis
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| Within the last 120k years, some ___ populations (others stayed) migrated out of Africa and throughout Europe and Asia, which at the time were inhabited by other Homo species (H. erectus, H. heidelbergensis, H. neanderthalensis, others). | Homo sapiens
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| Homo sapiens and ___ coexisted for thousands of years in some areas. | other Homo species, like H. erectus, H. heidelbergensis, H. neanderthalensis, and others
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| Around ___ years ago, Homo sapiens developed a suite of new behavioral and cultural traits, and it is possible that language became fully developed at this stage. At this point, Homo sapiens became physiologically and culturally fully modern. | 50,000
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| Around ___ years ago, Homo sapiens started to rapidly replace other Homo species around the globe. With the possible exception of Homo floresiensis, these other Homo species were gone by about years ago. | - 50,000
- 28,000
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| Homo floresiensis, discovered in 2004 on the Indonesian island of Flores, appears to have been present as recently as ___ years ago. | 18,000
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