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General Biology: OrganismL Biology and Evolution - Set 1 > Vertebrate mammals > Flashcards

Vertebrate mammals Flashcards

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1
Q

When were mammals first found to be present in the fossil record?

A
  • Back to ~200 mya but were generally small and
    not abundant
  • With the extinction of dinosaurs &
    fragmentation of continents at close of
    Mesozoic, mammals undergo extensive adaptive
    radiation
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2
Q

When did the three living lineages of mammals emerge?

A
  • By the early Cretaceous, 140 mya
  • These three lineages were monotremes,
    marsupials, and eutherians
  • There were ~5,300 extant species of mammals
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3
Q

How many clades did mammals radiate into?

A

6 broad clades

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4
Q

What are the six main characters of mammals?

A
  • The presence of mammary glands
    • Milk, a balanced diet of fats, sugars, proteins,
      minerals & vitamins
  • Hair made of keratin
    • Hair & subcutaneous fat retain metabolic heat
  • Warm blooded (Endotherms)
    • Supports active metabolism, made possible by
      efficient respiration & circulation
    • Muscular diaphragm & four-chambered heart
  • Born, not hatched
    • Fertilization internal, embryo develops in
      uterus
    • In eutherian (placental) mammals &
      marsupials lining of uterus & extraembryonic
      membranes form placenta, which nourishes
      embryo
  • Generally have larger brains than vertebrates
    • many species capable of learning
    • Relatively long parental care extends time for
      learning important skills from parents
  • Feeding adaptations of jaws & teeth
    • Unlike uniform conical teeth of most reptiles,
      mammalian teeth have various shapes & sizes
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5
Q

What are monotremes

A

A small group of egg-laying mammals consisting of echidnas and the platypus
- No nipples
- Low body temp
- No teeth in adults
- Cloaca
- Reptile-like egg

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6
Q

What organisms are included in the marsupial family?

A

Opossums, kangaroos, and koalas

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7
Q

What are some of the main characteristics of marsupials?

A
  • Higher metabolic rates
  • Give birth to live young
  • Have nipples
  • The embryo develops within a placenta in the
    mother’s uterus
  • A marsupial is born very early in its development
  • It completes its embryonic development while nursing in a maternal pouch called a marsupium
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8
Q

What are some of the main characteristics that set eutherians apart from marsupials?

A

Compared with marsupials, eutherians have a
longer period of pregnancy
- Young eutherians complete their embryonic
development within a uterus, joined to the
mother by the placenta
- Blood supply provides oxygen and nutrients to
embryo
- Young are born helpless and nurtured by
mothers

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9
Q

What primates are included in the mammalian order?

A

Lemurs, tarsiers, monkeys and apes (Humans are members of the ape group)

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10
Q

What are the main derived characters of primates?

A
  • Most have hands & feet adapted for grasping
    • Opposable thumbs in monkeys & apes
  • Larger brains & shorter jaws than other
    mammals
  • Forward-looking eyes close together
  • Flat nails on their digits, rather than narrow
    claws
  • Relatively well-developed parental care &
    complex social behavior
    (Humans have distinctive bone structure at base of thumb which allows more precise manipulation)
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11
Q

What characteristics did our arboreal ancestors likely have?

A
  • Grasping hands & feet for hanging on branches
    • All modern primates, except Homo, have big
      toe widely separated from other toes
    • Thumb relatively mobile & separate from
      fingers
  • Forward looking eyes & binocular vision
    enhances depth perception, adaptation for
    brachiating
  • Excellent hand-eye coordination also important
    for arboreal maneuvering
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12
Q

What are the main differences between now world and old world monkeys?

A

New World
- Arboreal
- Prehensile tails
- Nostrils open to side
Old World
- Arboreal & ground-dwelling
- Lack prehensile tails
- Nostrils open downward

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13
Q

What are the 5 major ape genera?

A

Hylobates, pongo, gorilla, pan, and homo
- Modern apes confined exclusively to tropical
regions of Old World
- Evolved from Old World monkeys

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14
Q

What are the main derived characters of apes?

A
  • Modern apes larger than monkeys, with
    relatively long arms, short legs, and no tails
  • Sexual dimorphism in size, reflecting sexual
    selection, male competition
  • Increased social organization, varies among
    genera; gorilla & chimpanzees highly social
  • Apes have relatively larger brains than monkeys,
    behavior more flexible
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15
Q

Why are humans different than other mammals?

A

They have larger brains and bipedal locomotion

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16
Q

What are the main derived characteristics of humans?

A
  • Humans stand upright and walk on two legs
    (bipedal)
  • Humans have a much larger brain than apes and
    are capable of language and complex tool use
  • Humans have reduced jawbone and jaw muscles
    and a shorter digestive tract
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17
Q

What is paleoanthropology?

A

The study of human origins and evolution
- Focuses on a tiny fraction of geologic time
during which humans & chimpanzees diverged
from a common ancestor

18
Q

Hominoid

A

The family containing apes and humans collectively

19
Q

Hominin

A

Humans and their extinct close relatives eg. Australopiths (Homo spp)

20
Q

What are some common myths about how Humans evolved?

A
  • Our ancestors are neither chimps nor a modern
    ape
    • Chimps & humans had a common ancestor
  • Evolution not a ladder to Homo sapiens
    • Many dead ends, coexisting species, multi-
      branched
  • Mosaic, not uniform evolution of human traits
    such as upright posture & enlarged brain
    • Our pedigree includes ancestors who walked
      upright but had brains much less developed
      than ours
21
Q

What are some common trends in hominin evolution?

A
  • Brain size: Brain tripled in 6 MY
    • From ~400-450 cm^3 in hominoids (and
      chimps) to ~1,300 cm^3 in modern humans
  • Jaw shape: Ancestral projecting jaws
    • Changes in dentition
    • Trend to flatter face, more pronounced chin
  • Bipedal posture: Ancestors probably walked on
    all four limbs on ground, like apes
    • Early hominid fossils have key skeletal
      modifications, such as the knee joint of
      Australopithecus afarensis
    • Confirmed striking by 3.6 MY Laetoli
      footprints discovered by Mary Leakey
  • Reduced sexual size dimorphism
    • Male gorillas & orangutans 2X as heavy as
      females; male chimps & bonobos 1.35X
      heavier than females
    • Male humans ~1.2X weight of females
  • Changes in Family structure
    • Monogamy, with long-term pair-bonding,
      prevails in human cultures, unlike most ape
      species
      - Testes size, human testes small by hominoid
      standard (chimps 10x larger) - supports idea
      of monogamy
      - Parental care, human newborns
      exceptionally dependent on mothers,
      duration of parental investment much longer
      than in other hominoids

Over time our skulls developed less jaw protrusion and flatter faces

22
Q

Who is Lucy?

A

In 1974, Donald Johanson discovers a new 3.2 MYA fossil, about 40% complete, in the Afar region of Ethiopia nicknamed “Lucy”
- Had small and slender bones
- Brain the size of chimps, projecting jaw, longer
arms (some brachiating), sexual size
dimorphism
- Pelvis, skull, knee bones & tracks show A.
afarensis walks bipedally

23
Q

What is the environmental context of human evolution?

A
  • Divergence of hominids 6-8 mya coincided with a
    global cooling trend
  • Coincidental with climatic cooling is aridification
    and concomitant changes in vegetation toward
    an open savannah grassland
  • Theory that adaptation to savannah was critical
    step in human evolution
    - Needed large brains to compete with top
    carnivores
    - Upright stance was and advantage for
    hunting
  • Climatic fluctuations and a hominid’s ability to
    exploit varied and varying habitats might have
    been a selective pressure
24
Q

What does the skull of the Ardipithecus look like?`

A
  • Small brain - similar size to female chimp
  • Ridge above eye socket is different
  • Lower face does not project forward so much,
    indicating less aggression
  • Lacks large cheeks
25
Q

What was different about the teeth of the Ardipithecus?

A
  • Reduced canines
  • Males and females have similar detention
  • Enamel thicker, indicative of switch away from
    fruit towards more abrasive terrestrial foods
26
Q

What was different about the hand bones of Ardipithecus?

A
  • It did not knuckle walk and lacked all of the
    specializations needed to avoid injuries in
    arboreal life
  • Wrist and finger joints were more flexible than
    those of apes
  • Midcarpal joint in wrist was very flexible
  • Suggests that hand form has changed more
    dramatically in ape lineage
27
Q

What was different about the pelvis of Ardipithecus?

A

They had a mosaic pelvis
- Changes in upper pelvis indicated that walked
upright on ground
- Gluteal muscles repositioned so could walk
without moving from side-to-side
- Lower pelvis was ape-like and so probably
maintained capacity to climb

28
Q

What was different about the feet bones of Ardipithecus?

A
  • Modern apes have a highly flexible midfoot for
    grasping and vertical climbing
  • Ardipithecus still has opposable big toe for
    grasping
  • Ardipithecus possesses a foot bone (os
    peroneum) that keeps the foot rigid
29
Q

What does the Troglodytian model say about Humans last common ancestor?

A

It suggests that our last common ancestor was ape-like, had short back, arms for swing, and pelvis and limbs for knuckle-walking
- Chimps and apes kept these features while our
ancestors lost these traits
- Scientists surprised that Ardipithecus was
strikingly different to our primate relatives
- Ardipithecus represents a new type of hominin
that is neither ape or human like
- Suggests that our common ancestor never
knuckle-walked
- Suggests that it might be apes that have evolved
most from the last common ancestor

30
Q

What were Homo erectus

A

Also known as the Upright Man, they were the first hominin to migrate out of Africa, colonizing Europe and Asia (Java man)
- Lived from ~1.9 to 0.1 MYA
- Had human-like body proportions:
- Larger brain
- Same sexual size dimorphism as modern
humans
- Bipedal bone structure

31
Q

What are the origins of anatomically modern humans?

A
  • All homo sapiens evolved from a second major
    migration out of Africa ~100 MYA
    • Migrants completely replaced all regional
      populations derived from first H. erectus
      migrations (1-2 mya)
      Evidence
    • High genetic similar between ethnic groups
      suggests recent origin and small founding
      population
32
Q

What are Homo neanderthalensis?

A
  • Neanderthals present in Europe from 600,000 to 40,000 YA
  • Coexisted with Homo sapiens 30-40,000 YA
  • Neanderthals had brains as large as ours,
    though somewhat different in shape
  • They buried their dead
  • Neanderthals were generally more heavily built
    than modern humans
33
Q

What is paleogenomics?

A

Sequence analysis of ancient DNA samples and their comparison with those of extant species
- Ancient DNA is highly fragmented
- Microbial contamination
- Recent innovations in sequencing technology
perform well with such short fragments

34
Q

What is so different about Neanderthal and human DNA?

A

Neanderthal mtDNA falls outside the variation of extant human mtDNA variation
- Mean divergence time between Neanderthal and
extant human mtDNAs of 660,000 years
- Chimps and hominins diverged 6-8 MYA

35
Q

Did Humans and Neanderthals interbreed?

A

Yes,
- Europeans and Asians share 1-4% of their
nuclear DNA with Neanderthals
- Strikingly, 50% of our human leukocyte antigen
(HLA) genes, come from Neanderthals, have an
important role in our immune response
- Africans do not share DNA with Neanderthals

36
Q

What have Pääbo’s discoveries provided us with?

A
  • Important information on how the world was
    populated at the time when Homo sapiens
    migrated out of Africa and spread to the rest of
    the world
  • Neanderthals lived in the west and Denisovans
    in the east on the Eurasian continent
  • Interbreeding occurred when Homo sapiens
    spread across the continent, leaving traces that
    remain in our DNA
37
Q

What is molecular anthropology?

A

The use of molecular tools (protein and DNA sequences) to determine the evolutionary links between ancient and modern hominids
- The protein evolution hypothesis proposes that
changes in the coding region of genes resulted in
important modifications
- Gene regulatory evolution hypothesis proposes
that differences between chimps and humans
due to patterns of turning on and off of genes
- The less-is-more hypothesis proposes that man
has lost many ape-like traits (body hair, muscle
mass) through loss-of-function mutations

38
Q

What is the FOXP2 gene?

A

The ‘language’ gene
- FOXP2 (Forkhead box P2) is thought to play a role in human language
- Mutations in gene linked to speech
impediments
- Mutations linked to reduced activity in Broca’s
area of brain
- Gene sequence is very well conserved across
mammals but 2 amino-acid substitutions in
humans
- FOXP2 is a transcription factor and so fits the
gene regulatory evolution theory
- Mice carry ‘humanized’ FOXP2 gene solve mazes
better

39
Q

What is the gene copy number?

A

DUF1220 (unknown function) is expressed at high levels in the brain regions associated with higher cognitive function (neocortex)

40
Q

What are regulatory changes in humans?

A

Searched for differences in gene expression between brains of humans, chimps, orangutan, and monkeys
- Found that transcription factors are more
abundant in human liver, consistent with the
theory of gene regulatory evolution

General Biology: OrganismL Biology and Evolution - Set 1 (23 decks)

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