Milestones in Evolution, Video 7 - EART22101 - Palaeobiology and Evolution

00:08:22
https://www.youtube.com/watch?v=xjmp5NbXMyw

摘要

TLDRThe video concludes a series on evolutionary milestones, focusing particularly on the Cambrian Explosion that occurred over 540 million years ago. This event signifies a major shift in the fossil record, marking the end of the Proterozoic eon and the beginning of the Phanerozoic eon. During this time, a vast diversification of animal life occurred, leading to the establishment of complex food webs. The Cambrian Explosion is characterized by the emergence of hard-bodied animals and was determined through fossil evidence, particularly from sites like the Burgess Shale. Various theories exist regarding the factors that contributed to this event, including genetic, ecological, and environmental changes. The presenter encourages viewers to engage through Q&A sessions for further exploration of these topics.

心得

  • 🌍 The Cambrian Explosion started over 540 million years ago.
  • 🔍 It marks a significant diversification of animal life.
  • 🌊 The Burgess Shale is a key fossil site for studying this period.
  • 🧬 DNA studies suggest rapid evolutionary changes occurred during the Cambrian.
  • 🧫 Hard body parts emerged, improving preservation potential.
  • 📚 Join Zoom sessions for deeper discussions and Q&As.
  • 🔎 Discuss ongoing debates about the causes of the Cambrian Explosion.
  • 📈 Understanding morphological disparity is crucial to evolutionary biology.

时间轴

  • 00:00:00 - 00:08:22

    In this final video of the series, the presenter discusses the Cambrian explosion, a significant event that began over 540 million years ago, marking the end of the Proterozoic eon and the beginning of the Phanerozoic eon. The Cambrian explosion is known for the rapid appearance of diverse animal forms, characterized by the development of hard parts and the emergence of major animal groups in the fossil record. Key features of animals such as bilateral symmetry and development from a blastula are highlighted, with fossil evidence drawn from sites like the Burgess Shale showing exceptional preservation. The discussion also addresses ongoing debates about whether the explosion was a genuine evolutionary event or a result of changes in environmental conditions affecting fossil preservation. Modern genetic analysis, particularly through DNA studies, suggests that evolutionary rates may have increased during this period. The presenter concludes with a summary of various hypothesized causes for the Cambrian explosion, including developmental events, ecological changes, and abiotic factors, encouraging further exploration of the topic and inviting questions in upcoming Zoom sessions.

思维导图

视频问答

  • What was the Cambrian Explosion?

    The Cambrian Explosion was a significant event over 540 million years ago that led to the rapid emergence of diverse animal life and complex ecosystems.

  • What are some factors that may have caused the Cambrian Explosion?

    Possible causes include developmental or genetic changes, ecological factors like sea level rises, and abiotic changes such as increases in calcium and phosphate.

  • How do we know about the Cambrian Explosion?

    We know about the Cambrian Explosion from fossil records, especially from deposits like the Burgess Shale that showcase exceptional fossil preservation.

  • What is a blastula?

    A blastula is a hollow sphere of cells that forms during the early development of animals.

  • What is the significance of the Burgess Shale?

    The Burgess Shale is a famous fossil site that provides unique insights into early Cambrian life due to its exceptional preservation conditions.

  • What is meant by 'morphological disparity'?

    Morphological disparity refers to the range of different body forms and structures found in organisms.

  • What technological advances assist in studying evolutionary rates?

    Modern studies utilize DNA analysis, allowing scientists to examine evolutionary rates independent of the fossil record.

  • What will be discussed in Zoom sessions following the video series?

    Zoom sessions will cover course material, answer questions, and discuss topics related to the Cambrian Explosion and evolution.

  • How was the Cambrian period defined in the geological column?

    Periods in the geological column are often named after fossils; the Cambrian period is defined by significant changes and diversifications in the fossil record.

  • What are the metazoa and bilateria?

    Metazoa refers to all animals, while bilateria are animals with bilateral symmetry, which includes most animals, including humans.

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  • 00:00:00
    hello and welcome to video number seven
  • 00:00:03
    of our tour through the evolutionary
  • 00:00:05
    milestones in the first 3000 million
  • 00:00:07
    years of life this is in fact our last
  • 00:00:09
    video
  • 00:00:10
    very well done for making it this far i
  • 00:00:12
    hope you found it interesting and
  • 00:00:14
    obviously you will have the opportunity
  • 00:00:15
    to ask questions
  • 00:00:17
    in a zoom session associated with this
  • 00:00:19
    series of videos
  • 00:00:20
    i want to finish by highlighting an
  • 00:00:23
    event called the cambrian explosion that
  • 00:00:25
    happened just over
  • 00:00:26
    540 million years ago or at least
  • 00:00:29
    started
  • 00:00:30
    just over 540 million years ago since
  • 00:00:33
    periods of time in the geological uh
  • 00:00:36
    column tend to be named after the
  • 00:00:38
    fossils that appear in the rocks and
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    this marks a distinct change in those
  • 00:00:41
    fossils
  • 00:00:42
    this event also marks the end of the
  • 00:00:45
    proterozoic eon
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    and the start of the phanerozoic
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    it's an event in which a group of
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    organisms
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    that is the animals appears animals are
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    creatures that generally respond
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    oxygen they get their energy by
  • 00:01:01
    consuming organic material
  • 00:01:03
    and they can move furthermore
  • 00:01:07
    they have a number of interesting
  • 00:01:09
    features in their mbo
  • 00:01:11
    envionic development that they hold in
  • 00:01:13
    common
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    so all animals grow from a hollow sphere
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    of cells called the blastula
  • 00:01:18
    during the development of their envios a
  • 00:01:21
    large subset
  • 00:01:22
    of animals are also bilaterally
  • 00:01:24
    symmetrical so animals
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    as a whole are called the metazoa that
  • 00:01:28
    group of bilaterian animals those that
  • 00:01:30
    have this line of symmetry down the
  • 00:01:32
    middle including us
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    are called the bilateria so between 541
  • 00:01:36
    and 515
  • 00:01:38
    million years ago there was this unique
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    period
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    it's marked first by the appearance of
  • 00:01:44
    hard parts
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    in the fossil record and then over a
  • 00:01:48
    relatively short period of time
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    the vast majority of major groups of
  • 00:01:52
    animals that
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    is animals that are members of monfila
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    which are still around today
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    appear in the fossil record this is
  • 00:02:00
    alongside a number of
  • 00:02:02
    relatively unusual seemingly unique body
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    plans
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    for creatures that were around at this
  • 00:02:07
    time and this is what we call the
  • 00:02:08
    cambrian explosion
  • 00:02:14
    examples of fossils are shown on this
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    slide these are all creepy crawlies so
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    arthropods creatures with segmented legs
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    but a wide range of other creatures of
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    phyla appear
  • 00:02:27
    during this time period and we know
  • 00:02:29
    about this event
  • 00:02:30
    from deposits like the burger shale a
  • 00:02:32
    very very famous
  • 00:02:34
    site of exceptional fossil preservation
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    in canada
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    this and other sites from around this
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    time have an unusual preservational
  • 00:02:42
    mechanism
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    where they represent a deep seabed
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    that's been rapidly buried by
  • 00:02:47
    fine sediment this is so common in fact
  • 00:02:50
    that it's called
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    burgess shale type reservation and is
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    fairly widespread
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    during the time period when this event
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    was happening
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    when these sediments were starved of
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    oxygen oxygen preservation of
  • 00:03:02
    carbon films including the soft parts of
  • 00:03:05
    all of
  • 00:03:05
    the animals that were around during this
  • 00:03:07
    period occurred
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    providing unique insights into the early
  • 00:03:12
    animals
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    i don't have a great deal of time to
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    provide details of the
  • 00:03:18
    ins and the outs of what we do and we
  • 00:03:20
    don't know about the cambrian explosion
  • 00:03:22
    but i wanted to highlight that debate
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    has raged for a long time
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    about the very nature of this event was
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    this a genuine event
  • 00:03:29
    in which evolution did something a bit
  • 00:03:31
    different and it was faster
  • 00:03:33
    and these animals actually appear or
  • 00:03:36
    is it a change in say sea water
  • 00:03:38
    chemistry or preservational
  • 00:03:41
    style which means that organisms that
  • 00:03:43
    had been around for a lot longer
  • 00:03:45
    while actually just being preserved in
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    the fossil record for the first time
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    or could it represent the evolution of
  • 00:03:53
    say hard parts and thus an increased
  • 00:03:55
    preservation potential
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    for creatures that had previously just
  • 00:03:58
    been squishy and thus not likely
  • 00:04:00
    to survive in the fossil record well we
  • 00:04:04
    don't know for sure
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    but use in modern studies we can use dna
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    as a source of data that's independent
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    of the fossil record
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    largely we can get into that if you're
  • 00:04:15
    interested in
  • 00:04:16
    asking questions about it in our zoom
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    chat and rob will cover
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    cover some of the topics um that are
  • 00:04:21
    required for
  • 00:04:22
    understanding these analyses called
  • 00:04:24
    molecular clocks in his lectures for
  • 00:04:26
    this course
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    but suffice it to say that dna can be
  • 00:04:30
    used to analyze
  • 00:04:31
    evolutionary rates deep into the history
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    of life and i've included an example
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    of a tree from a paper by lee attel that
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    was published in 2013
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    which uses modern uh animals dna
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    to to analyze evolutionary rates and
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    suggests
  • 00:04:52
    that evolution was genuinely
  • 00:04:56
    occurring at a faster rate during this
  • 00:04:58
    campaign explosion
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    than it was on the time periods either
  • 00:05:01
    side of it
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    so much discussion is ongoing
  • 00:05:07
    about the exact details of how that may
  • 00:05:10
    have happened
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    and in fact the the rate at which this
  • 00:05:13
    occurred but some things are fairly
  • 00:05:14
    generally agreed
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    we can all agree that the cambrian
  • 00:05:17
    represents the main diversification
  • 00:05:20
    within the animals a substantial
  • 00:05:22
    increase
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    in the morphological disparity so that's
  • 00:05:25
    the range of different body forms
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    that are found in the organisms that
  • 00:05:29
    were alive compared to what had come
  • 00:05:31
    before this time period
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    and it represents the first emergence of
  • 00:05:36
    really complex food webs
  • 00:05:38
    which occurred in the early campaign so
  • 00:05:41
    that's what we
  • 00:05:41
    do know and some elements of where
  • 00:05:44
    debate remains regarding
  • 00:05:46
    the cambrian explosion
  • 00:05:50
    there are a multitude of suggested cause
  • 00:05:52
    possible causes
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    and this diagram which i've borrowed
  • 00:05:55
    from smith and harper paper in 2013
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    provide just a few of these there are
  • 00:06:00
    too many to discuss in detail here but i
  • 00:06:02
    recommend you check out smith and harper
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    if you want some more details recent
  • 00:06:07
    hypotheses generally fall into three
  • 00:06:09
    categories one that this could have been
  • 00:06:11
    a developmental or genetic
  • 00:06:14
    event where the evolvability of
  • 00:06:16
    bilateral animals and the tendency to
  • 00:06:19
    induce escalatory arm races led to
  • 00:06:22
    rapid evolution it could have been
  • 00:06:26
    number two an ecological event uh there
  • 00:06:30
    was a long period
  • 00:06:31
    of erosion in the end of the proteomic
  • 00:06:33
    eon
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    this led to low relief continental
  • 00:06:38
    interiors
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    major sea level rises at the start of
  • 00:06:41
    the campaign then led to the flooding of
  • 00:06:43
    these
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    and then that in turn led to an increase
  • 00:06:46
    in the habitable area that could have
  • 00:06:47
    driven
  • 00:06:48
    this event camp number three of possible
  • 00:06:51
    causes
  • 00:06:52
    are those which are abiotic
  • 00:06:54
    environmental or geochemical hypotheses
  • 00:06:57
    such as continental flooding which led
  • 00:06:59
    to increases in calcium
  • 00:07:00
    and phosphate facilitating the origins
  • 00:07:03
    of biomineralization
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    and it could of course be that a
  • 00:07:07
    combination of these different
  • 00:07:09
    types of potential causes led to the
  • 00:07:12
    events that we do see
  • 00:07:13
    in the cambium explosion if you're
  • 00:07:16
    interested
  • 00:07:17
    in the caribbean explosion please do
  • 00:07:19
    check out the reading that i provided
  • 00:07:22
    on this topic for the course
  • 00:07:28
    now if it feels like i have skipped over
  • 00:07:32
    a lot of details while looking at these
  • 00:07:33
    evolutionary milestones
  • 00:07:35
    that's because i have i could have
  • 00:07:37
    written an entire lecture course on the
  • 00:07:38
    contents
  • 00:07:39
    of the videos that you've just watched
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    so in order to support your learning
  • 00:07:44
    i provided some reading online i would
  • 00:07:46
    also strongly encourage you to come to
  • 00:07:48
    the zoom sessions
  • 00:07:49
    where we can discuss some of the topics
  • 00:07:52
    that we
  • 00:07:53
    have identified in these videos i can
  • 00:07:55
    answer any questions you have
  • 00:07:57
    and where i'll be able to give you out
  • 00:08:00
    the coursework
  • 00:08:01
    assignment for this unit and answer any
  • 00:08:03
    questions that you have
  • 00:08:05
    about that in the meantime though thank
  • 00:08:07
    you very much for making it this far to
  • 00:08:09
    the end of video number seven
  • 00:08:11
    thank you for your attention and i look
  • 00:08:13
    forward to talking about these topics
  • 00:08:15
    with you
  • 00:08:16
    sometime in the near future thank you
  • 00:08:18
    very much
标签
  • Cambrian Explosion
  • Evolution
  • Fossil Record
  • Animal Diversification
  • Burgess Shale
  • Metazoa
  • Bilateria
  • Molecular Clocks
  • Morphological Disparity
  • Geological Column