part iv: the history of life the cambrian explosion and beyond
TRANSCRIPT
![Page 1: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/1.jpg)
Part IV: The History of Life
The Cambrian Explosion and beyond...
![Page 2: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/2.jpg)
The earliest animal remains
These date to 580-600 million years ago (Ma) [later Precambrian]
Often very abundant, these are thought to represent burrows and tubes of worm-like creatures
[if remains of worms, these ancient animals must have been Bilateria]
Trace fossils
![Page 3: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/3.jpg)
The Ediacaran Period
• 560-580 Ma
• named for Ediacaran hills in SE Australia, where the first deposits were found
• flattened, non-mobile, non-predatory animals with uncertain affinities to modern forms
![Page 4: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/4.jpg)
Dickensonia, a common fossil of unknown affinity
Ediacaran fossils
probably an ancestor of sea pens (Pennatulacea)
Kimberella, the only known bilaterally symmetrical Precambrian animal
![Page 5: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/5.jpg)
Ediacaran animals
• disappeared by 560 Ma
• ancestors of Cambrian animals, or…
• a failed experiment in animal evolution?
![Page 6: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/6.jpg)
tick marks are 12 my
Paleozoic:
From start
of Cambrian
through
major (end-
Permian)
extinction
![Page 7: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/7.jpg)
tick marks are 12 my
Paleozoic
Cambrian explosion!
540-525 Ma
![Page 8: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/8.jpg)
The Burgess Shale
• 520-515 my old Cambrian deposits
• in Yoho Provincial Park, British Columbia
![Page 9: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/9.jpg)
The Burgess Shale• perhaps the most spectacular fossils ever
found
• exquisitely preserved remains of invertebrates from most phyla (and several chordates)
• many predatory and highly complex
![Page 10: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/10.jpg)
The Burgess Shale “Problematica”
HallucigeniaAnomalocaris
Opabinia Wiwaxia
![Page 11: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/11.jpg)
From Smithsonian Inst., NMNH
From AAAS
Opabinia regalis was probably an arthropod
the “nozzle” was a claw
![Page 12: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/12.jpg)
Most Burgess Shale animals are clearly from modern phyla
Olenoides, a trilobite
a priapulid worm (with muscles
showing)
Pikia, a cephalochordate
Vauxia, a sponge
dinner, 520 my ago
![Page 13: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/13.jpg)
Molecular phylogenies of the animal phyla allow us to “order” major events in animal evolution that occurred in the Cambrian.
Cambrian: a revolution in animal evolution
![Page 14: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/14.jpg)
Chordate synapomorphies
Origin of bilateral symmetry (?)
Protostomes
Major patterns of embryonic development (e.g. gastrulation)
![Page 15: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/15.jpg)
Precambrian diversification of bilateral animals (~600 my)
Cambrian explosion of fossilizable forms (~20 my)
Some studies of protein evolution push origins of phyla back to 1000-1200 mya
![Page 16: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/16.jpg)
tick marks are 12 my
Paleozoic
Cambrian explosion!
540-525 Ma
480 Ma
440 Ma
425 Ma
365 Ma
360 Ma
![Page 17: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/17.jpg)
tick marks are 7.5 my
Mesozoic190 Ma
150 Ma
110 Ma
![Page 18: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/18.jpg)
Cenozoictick marks are 2.7 my 30 Ma
5-6 Ma??
![Page 19: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/19.jpg)
Macroevolution, according to...
Darwin (1859)Eldredge and Gould (1972)
![Page 20: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/20.jpg)
Gradual morphological change occurs continuously
Morphological evolution is not associated with speciation
Phyletic gradualism
Darwin (1859)
![Page 21: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/21.jpg)
Morphological change occurs in bursts
Most change occurs at speciation
“Stasis” otherwise
Punctuated equilibrium
Eldredge and Gould (1972)
![Page 22: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/22.jpg)
Tests for punctuated equilibrium vs gradualism• must avoid “circular reasoning”
(species are recognized by breaks in morphology)
• valid tests require– a good phylogeny– coexistence of species after
speciation
![Page 23: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/23.jpg)
Punctuated equilibrium in fossil Bryozoa
![Page 24: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/24.jpg)
Jackson and Cheetham 1994
![Page 25: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/25.jpg)
From Futuyma 2005
![Page 26: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/26.jpg)
From Futuyma 2005
![Page 27: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/27.jpg)
From Futuyma 2005
![Page 28: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/28.jpg)
Why stasis…a lack of genetic variation?
No.
Morphologically conservative horseshoe crabs show as much (or more) genetic divergence as between king crabs and hermit crabs.
from Avise et al. (1994)
![Page 29: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/29.jpg)
Stasis may occur due to “zigzag” evolution
24 different shell characters in 3 Pliocene bivalve lineages change, but fluctuate around a mean value...
from Stanley and Yang (1987)
![Page 30: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/30.jpg)
Extinction
![Page 31: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/31.jpg)
The marine fossil record shows that diversity has increased, more or less steadily, to the present.
This has been punctuated by 5 major “mass extinctions.”
from Primack, 3rd ed., Sinauer
![Page 32: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/32.jpg)
The end-Permian extinction eliminated ~ 95% of the species, and >50% of the families on Earth
Mass Extinction (% of Families): The Big Five
![Page 33: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/33.jpg)
Based on Stanley (1979), from Freeman and Herron (1998)
Lyellian curves are used to estimate extinction rates
![Page 34: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/34.jpg)
• find the X-value (in My) at which 50% of the species are extinct
• double this value
– this yields the time (in My) for 100% turnover
– this is also the average duration of a single species in the fossil record (its “survivorship”)
![Page 35: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/35.jpg)
• the “lifespan” of mammal species (~1.5 My) is much less than that of Pacific bivalve molluscs (~15 My)
• this suggests great variation in extinction rates (and speciation rates?) across lineages
![Page 36: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/36.jpg)
• still, species durations in most groups range from 1-10 My
From Freeman and Herron (1998)
![Page 37: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/37.jpg)
Other analyses of Lyellian curves confirm that extinction rates are highly variable
For example, Tertiary extinction rates for tetrapods are much greater than those of insects or bivalves
![Page 38: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/38.jpg)
Survivorship of species with range >2500 km is 10 times that of species with range <1000 km. From Jablonski (1986)
![Page 39: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/39.jpg)
Marine species extinction rates depend on larval dispersal
Fossils of species with plankton-feeding larvae (planktotrophs) persist 3 times as long as nonplanktotrophs. From Jablonski (1986)
![Page 40: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/40.jpg)
Extinction rates depend on larval
dispersal powers
Why? Planktotrophs have longer periods of development, allowing greater dispersal and broader geographic range. This “buffers” against extinction.
![Page 41: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/41.jpg)
Recent bird and mammal extinction rates
• the best data on recent extinction rates• a dramatic rise in extinction rate after 1850• this is followed by a drop 1950-2000
![Page 42: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/42.jpg)
Predicting future extinctions: The Species Report Card (NHDC and The Nature Conservancy 1997)
![Page 43: Part IV: The History of Life The Cambrian Explosion and beyond](https://reader035.vdocuments.site/reader035/viewer/2022070400/56649f155503460f94c2ad27/html5/thumbnails/43.jpg)
Aquatic inverts, FW fishes, flowering plants are most vulnerable to future extinctions