THE CAMBRIAN EXPLOSION
“Featured Scientists”

    James Valentine

 Simon Conway-Morris

      Paul Chien

    Jonathan Wells

   Richard Sternbe...
CHARLES DARWIN

     “Consequently, if my theory be true, it is
     indisputable that before the lowest Silurian
     str...
LOUIS AGASSIZ
DUANE T. GISH (1974)

“In the Cambrian geological strata there occurs a sudden, great
outburst of fossils of animals on a ...
PANDAS AND PEOPLE

      “[S]ome organisms appear with
      adaptational packages intact at the
      Cambrian boundary w...
The Cambrian
Explosion “presents a
 serious challenge to
Darwinian evolution”
“From nothing, we
   have almost
everything, almost
    overnight.”
Biola - “ID and the Future of Science” - 2004
Biola - “ID and the Future of Science” - 2004
Biola - “ID and the Future of Science” - 2004
Biola - “ID and the Future of Science” - 2004
Biola - “ID and the Future of Science” - 2004
Biola - “ID and the Future of Science” - 2004
Biola - “ID and the Future of Science” - 2004
Biola - “ID and the Future of Science” - 2004
Biola - “ID and the Future of Science” - 2004
CAMBRIAN (542 ± 0.3 TO 488.3 ± 1.7 MYBP)
TREPTICHNUS PEDUM
TRILOBITE
CAMBRIAN BOUNDARIES
• Noice-caps, deserted land
 masses

• Oxygen at 63% of modern,
 carbon dioxide at ~16 times
 pre-industrial levels

• Sur...
PRE-CAMBRIAN
CAMBRIAN
BECOMING
 A FOSSIL
MICHAEL DENTON



     “An irreducible gap in phenotypic space
     [i.e. morphology] cannot be taken to
     imply that t...
SOME KEY IDEAS



Cambrian Explosion – the geologically sudden appearance of many of
the Metazoan phyla.

Metazoan – multi...
PHYLUM


Morphological branch of the tree of life

Group of organisms sharing a “major body plan”

Number of extant phyla ...
ARTHROPODA
Protostomes and Deuterostomes are two superphyla within
the Bilateria differentiated by embryonic cleavage patterns.
Morphological   Molecular
FOUR QUESTIONS


1. Was there a Pre-Cambrian fauna?

2. What (if anything) happened in the Cambrian?

3. Is the “explosion...
WAS THERE A PRE-CAMBRIAN FAUNA?
RICHARD DAWKINS

      “Evolution makes the strong
      prediction that if a single fossil turned
      up in the wrong g...
Wassahpdug haldanei
STROMATOLITES (3,500 MY)
Lack of grazing predators
BANGIOMORPHA
(RED ALGAE - 1,200 MYBP)
Pre-Cambrian Trace Fossils




    Early Trace Fossils      Late Trace Fossils
EDIACARIAN FAUNA (575 MY)
Charniodiscusarboreus    Spriggina
      Cnidarian         Arthropod
SPRIGGINA
Arkarua    Kimberella
Echinoderm    Mollusc
Parvancorina
Precambrian trilobite ancestor
       (Arthropod)
“Small Shelly”
   Fauna
PRE-CAMBRIAN TIMELINE
                 SOFT-BODIED ORGANISMS

3,460 mybp - Stromatolites (microbial mats - “prokaryotes”)
...
WHAT (IF ANYTHING) HAPPENED IN THE CAMBRIAN?
Charles Walcott
Marella
Sidneyia
inexpectans
Waptia
Crustaceans
Ottoia
(priapulid)
Opabina (lobopod)
Hallucigenia
Hallucigenia
Modern onycophoran
Pikia
Chordates
Chordates
Yunnanozoon (hemichordate)
JONATHAN WELLS

    “Why don’t textbooks discuss the Cambrian
    explosion, in which all major animal groups
    appear t...
“Here we describe a recently discovered craniate-like
chordate, Haikouella lanceolata, … These findings indicate that
Haiko...
Is this an Ediacarian chordate?
“The Cambrian explosion gave rise to
most of the animal phyla alive today, as
well as some that are now extinct.” (p. 39)....
Placozoa

                          Mesozoa

                       Platyhelminthes

Extant Phyla without   Gnathostomulid...
Echinodermata

                    Cnidaria

                    Porifera

Pre-Cambrian        Mollusca

                 ...
Brachiopoda

           Onychophora
Cambrian
            Tardigrada
 6 of 34
            Priapulida
  18%
           Chaet...
Bryozoa

                 Ctenophora
Post-Cambrian     Nematoda

   7 of 34        Nemertini

    21%          Entoprocta
...
Extant Phyla with a Fossil Record




                                    Pre-Cambrian
                                   ...
Well’s version




                 Pre-Cambrian
                 Cambrian
                 Post-Cambrian
Extinct Phyla

Pre-Cambrian: 5

 Cambrian: 17

Post-Cambrian: 1
All Phyla with a Fossil Record




                                 Pre-Cambrian
                                 Cambrian...
WAS THE “EXPLOSION” REAL?
STEPHEN MEYER

“If you can preserve [a pre-Cambrian] embryo, you can preserve an
animal. If those animals were there, we s...
EXPERIMENTAL TAPHONOMY
                                               “Under conditions that prevent
                     ...
LAGERSTÄTTEN
LAGERSTÄTTEN
CONCLUSION FROM
         THE FOSSIL DATA
Metazoans certainly originated significantly earlier than 570my.
A date of 700my w...
WHAT ABOUT
GENETIC DATA?

    “The basal animal phyla (Porifera,
    Ctenophora and Cnidaria) diverged
    between about 1...
OTHER ESTIMATES

• Bromham   et al.(1998): 1,500 mybp

       Meyer gives this as 680 my

• Ayala, Rzhetsky
              ...
REVIEW IN 2005

“[M]olecular data analyzed over the past 3 decades have
found deeper divergences among animals (~800 to 1,...
THREE POINTS
        WORTH REMEMBERING
• Majorbranches on the Tree of Life (e.g. fungi, bacteria and
 other groups) actual...
POST-CAMBRIAN PLANTS
CHORDATE DIVERSIFICATION
POST-CAMBRIAN

•   Paleozoic (510 – 245my): Origin of plants, insects, bony fish,
    amphibians, reptiles, mammal-like rep...
Crown Group




       Stem Group
OUR FIVE QUESTIONS

Was there a Pre-Cambrian fauna?

      Yes – including multicellular ancestors of Cambrian forms.

Wha...
HOW DID IT HAPPEN?
HOW DID IT HAPPEN?
HOW DID IT HAPPEN?

       Environmental changes

       Opening of new niches

       Development of predator/prey system...
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The Cambrian Explosion

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  • BAD PEDAGOGY!!!!!
    No time scale
    No relationships between groups
    No names of groups
    Pre-cambrian record?















































  • HALDANE





























































  • 1. Precambrian forms
    2. Disparity and Diversity rise together









































  • The Cambrian Explosion

    1. 1. THE CAMBRIAN EXPLOSION
    2. 2. “Featured Scientists” James Valentine Simon Conway-Morris Paul Chien Jonathan Wells Richard Sternberg Douglas Axe Paul Nelson Stephen Meyer
    3. 3. CHARLES DARWIN “Consequently, if my theory be true, it is indisputable that before the lowest Silurian stratum was deposited, long periods elapsed, as long as, or probably far longer than, the whole interval from the Silurian age to the present day; and that during these vast, yet quite unknown periods of time, the world swarmed with living creatures. To the question why we do not find records of these vast primordial periods, I can give no satisfactory answer.”
    4. 4. LOUIS AGASSIZ
    5. 5. DUANE T. GISH (1974) “In the Cambrian geological strata there occurs a sudden, great outburst of fossils of animals on a highly developed level of complexity. In the Cambrian rocks are found billions of fossils of animals so complex that the evolutionists estimate they would have required one and a half billion years to evolve. Trilobites, brachiopods, sponges, corals, jellyfish, in fact every one of the major invertebrate forms of life are found in the Cambrian. What is found in rocks supposedly older than the Cambrian, that is in the so-called pre- Cambrian rocks? Not a single indisputable fossil! Certainly it can be said without fear of contradiction, the evolutionary predecessors of the Cambrian fauna have never been found.”
    6. 6. PANDAS AND PEOPLE “[S]ome organisms appear with adaptational packages intact at the Cambrian boundary where multicellular life first ‘flowers,’ with no evidence whatsoever of fossil ancestors… only an intelligent designer has the ability to coordinate the design requirements of multifunctional adaptational packages.” (71-72)
    7. 7. The Cambrian Explosion “presents a serious challenge to Darwinian evolution”
    8. 8. “From nothing, we have almost everything, almost overnight.”
    9. 9. Biola - “ID and the Future of Science” - 2004
    10. 10. Biola - “ID and the Future of Science” - 2004
    11. 11. Biola - “ID and the Future of Science” - 2004
    12. 12. Biola - “ID and the Future of Science” - 2004
    13. 13. Biola - “ID and the Future of Science” - 2004
    14. 14. Biola - “ID and the Future of Science” - 2004
    15. 15. Biola - “ID and the Future of Science” - 2004
    16. 16. Biola - “ID and the Future of Science” - 2004
    17. 17. Biola - “ID and the Future of Science” - 2004
    18. 18. CAMBRIAN (542 ± 0.3 TO 488.3 ± 1.7 MYBP)
    19. 19. TREPTICHNUS PEDUM
    20. 20. TRILOBITE
    21. 21. CAMBRIAN BOUNDARIES
    22. 22. • Noice-caps, deserted land masses • Oxygen at 63% of modern, carbon dioxide at ~16 times pre-industrial levels • Surface temperature at 7 degrees C above present • Sealevel at 30 - 90m above present • Warm shallow seas at continental edges • Presence of lagerstätten
    23. 23. PRE-CAMBRIAN
    24. 24. CAMBRIAN
    25. 25. BECOMING A FOSSIL
    26. 26. MICHAEL DENTON “An irreducible gap in phenotypic space [i.e. morphology] cannot be taken to imply that there is a similar gap in genotypic space [i.e. genetics].”
    27. 27. SOME KEY IDEAS Cambrian Explosion – the geologically sudden appearance of many of the Metazoan phyla. Metazoan – multicellular organisms
    28. 28. PHYLUM Morphological branch of the tree of life Group of organisms sharing a “major body plan” Number of extant phyla differ depending on source, but generally taken to be in the low to mid thirties. Therefore, we should be careful of “essentializing” them.
    29. 29. ARTHROPODA
    30. 30. Protostomes and Deuterostomes are two superphyla within the Bilateria differentiated by embryonic cleavage patterns.
    31. 31. Morphological Molecular
    32. 32. FOUR QUESTIONS 1. Was there a Pre-Cambrian fauna? 2. What (if anything) happened in the Cambrian? 3. Is the “explosion” a real event or an artifact of preservation? 4. How did it happen?
    33. 33. WAS THERE A PRE-CAMBRIAN FAUNA?
    34. 34. RICHARD DAWKINS “Evolution makes the strong prediction that if a single fossil turned up in the wrong geological stratum, the theory would be blown out of the water. When challenged by a zealous Popperian to say how evolution could ever be falsified, J.B.S. Haldane famously growled: 'Fossil rabbits in the Precambrian.’ No such anachronistic fossils have ever been authentically found...”
    35. 35. Wassahpdug haldanei
    36. 36. STROMATOLITES (3,500 MY)
    37. 37. Lack of grazing predators
    38. 38. BANGIOMORPHA (RED ALGAE - 1,200 MYBP)
    39. 39. Pre-Cambrian Trace Fossils Early Trace Fossils Late Trace Fossils
    40. 40. EDIACARIAN FAUNA (575 MY)
    41. 41. Charniodiscusarboreus Spriggina Cnidarian Arthropod
    42. 42. SPRIGGINA
    43. 43. Arkarua Kimberella Echinoderm Mollusc
    44. 44. Parvancorina Precambrian trilobite ancestor (Arthropod)
    45. 45. “Small Shelly” Fauna
    46. 46. PRE-CAMBRIAN TIMELINE SOFT-BODIED ORGANISMS 3,460 mybp - Stromatolites (microbial mats - “prokaryotes”) 2,700 mybp - Oxygen-generating photosynthesis 2,200 mybp - Single-celled eukaryotes 1,200 mbyp - Multicellular eukaryotes (red algae) 1,100 mybp – Trace fossils (burrowing & movement) 600 mybp – Early bilaterans 575 mybp – Edicarian Fauna – Unknown affinities (?) 570 mybp – Possible Metazoan embryos (see later) 545 mybp – “Small shelly” fauna
    47. 47. WHAT (IF ANYTHING) HAPPENED IN THE CAMBRIAN?
    48. 48. Charles Walcott
    49. 49. Marella
    50. 50. Sidneyia inexpectans
    51. 51. Waptia
    52. 52. Crustaceans
    53. 53. Ottoia (priapulid)
    54. 54. Opabina (lobopod)
    55. 55. Hallucigenia
    56. 56. Hallucigenia
    57. 57. Modern onycophoran
    58. 58. Pikia
    59. 59. Chordates
    60. 60. Chordates
    61. 61. Yunnanozoon (hemichordate)
    62. 62. JONATHAN WELLS “Why don’t textbooks discuss the Cambrian explosion, in which all major animal groups appear together in the fossil record fully formed instead of branching from a common ancestor – thus contradicting the evolutionary tree of life?” Reply: Fish, amphibians, reptiles, birds, and mammals all are post-Cambrian - aren’t these “major groups”? Wells: “Fish DID make their first appearance in the Cambrian explosion.”
    63. 63. “Here we describe a recently discovered craniate-like chordate, Haikouella lanceolata, … These findings indicate that Haikouella probably represents a very early craniate-like chordate that lived near the beginning of the Cambrian period” Jun-Yuan Chen, Di-Ying Huang and Chia-Wei Li, “An early Cambrian craniate- like chordate,” Nature 402 (1999), 518-522.
    64. 64. Is this an Ediacarian chordate?
    65. 65. “The Cambrian explosion gave rise to most of the animal phyla alive today, as well as some that are now extinct.” (p. 39). Chart gives 18 “major living animal phyla” “One phylum (the sponges) and possibly two others appeared just before the Cambria; two worm phyla appeared much later, in the Carboniferous … and one [phylum] in the Ordovician.” Therefore, claim is that 12 of 18 (66%) phyla appeared in the Cambrian
    66. 66. Placozoa Mesozoa Platyhelminthes Extant Phyla without Gnathostomulida a fossil record Gastrotricha Acantochephala 12 of 34 Loricifera Kinorhyncha 35% Pogonophora Sipuncula Phoronida Urochordata
    67. 67. Echinodermata Cnidaria Porifera Pre-Cambrian Mollusca Arthropoda 5 + 4 of 34 15 to 26% Chordata (?) Annelida (?) Platyhelminthes (?) Echiura (?)
    68. 68. Brachiopoda Onychophora Cambrian Tardigrada 6 of 34 Priapulida 18% Chaetognatha Hemichordata
    69. 69. Bryozoa Ctenophora Post-Cambrian Nematoda 7 of 34 Nemertini 21% Entoprocta Rotifera Nematomorpha
    70. 70. Extant Phyla with a Fossil Record Pre-Cambrian Cambrian Post-Cambrian
    71. 71. Well’s version Pre-Cambrian Cambrian Post-Cambrian
    72. 72. Extinct Phyla Pre-Cambrian: 5 Cambrian: 17 Post-Cambrian: 1
    73. 73. All Phyla with a Fossil Record Pre-Cambrian Cambrian Post-Cambrian
    74. 74. WAS THE “EXPLOSION” REAL?
    75. 75. STEPHEN MEYER “If you can preserve [a pre-Cambrian] embryo, you can preserve an animal. If those animals were there, we should have found them. And they’re not there.” But: • Special conditions required for preservation • We haven’t found pre-Cambrian adult sponges but they must have existed • Pre-Cambrian specimens create a problem for the “explosion”!
    76. 76. EXPERIMENTAL TAPHONOMY “Under conditions that prevent autolysis, embryos within the fertilization envelope can be preserved with good morphology for sufficiently long periods for mineralization to occur. ... Although embryos within the fertilization envelope have high preservation potential, primary larvae have negligible preservation potential. Thus the paleo- embryological record may have strong biases on developmental stages preserved.” Raff EC, Villinski JT, Turner FR, Donoghu PCJ, Raff RA (2006) Proc Nat Acad Sci USA 103(15):5846-5851.
    77. 77. LAGERSTÄTTEN
    78. 78. LAGERSTÄTTEN
    79. 79. CONCLUSION FROM THE FOSSIL DATA Metazoans certainly originated significantly earlier than 570my. A date of 700my would not conflict with the evidence currently to hand. We thus see an approximately 170 million year period for the evolution of the Cambrian fauna. A exponential increase in diversity occurs in the Cambrian (Valentine et al, 1999, Development 126: 851)
    80. 80. WHAT ABOUT GENETIC DATA? “The basal animal phyla (Porifera, Ctenophora and Cnidaria) diverged between about 1200 – 1500 MYA. This suggests that at least six animal phyla originated deep in the Precambrian, more than 400 million years earlier than their first appearance in the fossil record.”
    81. 81. OTHER ESTIMATES • Bromham et al.(1998): 1,500 mybp Meyer gives this as 680 my • Ayala, Rzhetsky & Ayala (1998): 670 mybp for Protostome / Deuterostome split Still 130my before the start of the Cambrian
    82. 82. REVIEW IN 2005 “[M]olecular data analyzed over the past 3 decades have found deeper divergences among animals (~800 to 1,200 MYA), with and without the assumption of a global molecular clock. Recently, two studies have instead reported time estimates apparently consistent with the fossil record. Here, we demonstrate that methodological problems in these studies cast doubt on the accuracy and interpretations of the results obtained. ... With these results aside, molecular clocks continue to support a long period of animal evolution before the Cambrian explosion of fossils.”
    83. 83. THREE POINTS WORTH REMEMBERING • Majorbranches on the Tree of Life (e.g. fungi, bacteria and other groups) actually pre-date the Cambrian. • All plants post-date the Cambrian, and flowering plants, by far the dominant form of land life today, only appeared about 140 mya • None of the animal groups that people think of as major taxonomic groups, such as mammals, reptiles, birds, or insects, appeared in the Cambrian.
    84. 84. POST-CAMBRIAN PLANTS
    85. 85. CHORDATE DIVERSIFICATION
    86. 86. POST-CAMBRIAN • Paleozoic (510 – 245my): Origin of plants, insects, bony fish, amphibians, reptiles, mammal-like reptiles, • Permian (marine) extinction • Mesozoic (245 – 65 my): Radiation of dinosaurs, early mammals & birds. Appearance of flowering plants • Cretaceous extinction • Cenozoic (65 my – present): Major radiation of mammals, birds & insects. Origin of primates and humans
    87. 87. Crown Group Stem Group
    88. 88. OUR FIVE QUESTIONS Was there a Pre-Cambrian fauna? Yes – including multicellular ancestors of Cambrian forms. What happened in the Cambrian? A geologically rapid morphological diversification Is the explosion real? Yes, but it was phenotypic rather than genotypic. How did it happen?
    89. 89. HOW DID IT HAPPEN?
    90. 90. HOW DID IT HAPPEN?
    91. 91. HOW DID IT HAPPEN? Environmental changes Opening of new niches Development of predator/prey systems Development of visual systems Ecological feedback Activation of genetic pathways (see next week)

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