the life and times of the earliest horseshoe crabs david rudkin.pdf · no complex land life . no...
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Peter Van Roy
The Life and Times of the Earliest Horseshoe Crabs
Dave RudkinDepartment of Natural History (Palaeobiology)
Royal Ontario MuseumToronto, Canada
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The Life and Times of the Earliest Horseshoe Crabs• Geological Time: the Ordovician Period in context
• The Great Ordovician Biodiversification Event: “GOBE”
• The Ordovician World: Geography, Climate & Life
• The Earliest Horseshoe Crabs
• End-Ordovician Mass Extinctions
• Post-Ordovician Record
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Geological Time – 4.6 Billion Years of Earth History
65 million years 291 million years186 million years 4 BILLION years!
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http://pubs.usgs.gov/gip/2008/58/geotimespiral_text.pdf
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Setting the Stage - The Cambrian Explosion• advent of widespread biomineralization - establishment of eumetazoan body plans - marine substrate “revolution” - ecological “escalation” - by close of Cambrian Period (~488 MYA) all
major animal phyla were present in the seas of the Earth
542 MYA
488 MYA
(after Xiao & Laflamme, Peterson et al & Dunn et al.)
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The Great Ordovician Biodiversification Event
GOBE marks abrupt rise of both “Paleozoic” & “Modern” Evolutionary Faunas - mostly at lower taxonomic levels & in “shelly” biotas
“The Great Ordovician Biodiversification Event” (GOBE) was
arguably the most important and sustained increase of
marine biodiversity in Earth’s history.”
[Servais, et al., 2009 GSA Today, v. 19, no. 4/5]
ORDOVICIANORDOVICIAN
[Webby 2003]
488.3
443.7
460.9
471.8
455.8
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488 MYA
443 MYA
251 MYA
0
The Great Ordovician Biodiversification Event• fossil record of family-level diversity through the Phanerozoic
[Servais, et al., 2009]
25 MY
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The Great Ordovician Biodiversification Event• a Cambrian hold-over & important new elements of the Paleozoic Fauna
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The Ordovician World• a dynamic global paleogeographic picture for the GOBE
600 MYA Ediacaran 560 MYA
Late Cambrian - 500 MYAEarly Cambrian - 540 MYA Late Ordovician - 450 MYA• rapid seafloor spreading - maximum dispersal of continental land masses, island arcs & rifted “terranes” - exceptionally high sea levels - maximum extent of tropical shelf areas
[http://cpgeosystems.com/mollglobe.html - Ron Blakey, Colorado Plateau Geosystems, Inc.]
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The Ordovician World•global environmental context for the GOBE
[Vandenbroucke, et al. 2010]
• “greenhouse” climate for much of the Early & Middle Ordovician & a terminal ice age!
[Trotter, et al. 2008]
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The Ordovician World• global environmental context continued …
• global mean surface temperature approximately 2oC higher than present day, with equatorial Sea Surface Temperatures as high as 40oC
• mean atmospheric CO2 content approximately 15 times higher than PAL (Pre-industrial Atmospheric Level)
• mean atmospheric O2 volume approximately 68% of modern value
• global sea levels up to 220 metres higher than today – possibly the highest of the entire Phanerozoic!
• prolific volcanic activity related to rapid sea-floor spreading, break-up of Rodinia,maximal dispersal of tectonic plates … increased erosion & inorganic nutrient influx
• lower (2.7% average) solar luminosity, shorter days (~21 hours = 417 days/year due to faster rotation), closer Moon (approx. 160,000 km) & stronger tides
• possible correlation (470 MYA) with major asteroid break-up event (L-chondriteparent body) & high influx of meteorites (incl. km-size impacters)
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Ordovician Life• extraordinary diversity in the seas – no comparable macroeukaryotic life on land!
Reconstruction image courtesy of The Manitoba Museum
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Liopleurodon93 at en.wikipedia Apokryltaros at en.wikipedia© 1997 Philippe Janvier
• more appropriately … a sea without gnathostome (jaw-bearing vertebrate) predators
• conodonts & agnathan(“jawless”) craniate “fishes”
… small size & mostlymicrophagous
G. Nowlan
M. Purnell
Ordovician Life
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Ordovician Life – the oldest horseshoe crab fossils
20072008
Lunataspis aurora
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488.3
443.7
460.9
471.8
455.8
Ordovician Life – the oldest horseshoe crab fossils
*
Lunataspis aurora
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Ordovician Life – fossils found with Lunataspis
0.5 mm
10 mm
10 mm
10 mm
•shallow, near-shore, restricted
marine setting
•eurypterids•medusans•chlorophytes•polychaetes•pycnogonids….. + + + + !
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Ordovician Life – new Lunataspis material
10 mm
NEW juvenile specimensreveal proportional growth
changes
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Ordovician Life – the NEWEST oldest horseshoe crab fossils!
Van Roy, et al. 2008
P. Van Roy
2010
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488.3
443.7
460.9
471.8
455.8
Ordovician Life – the NEWEST oldest horseshoe crab fossils!
Van Roy & Briggs 2011
Courtesy P. Van Roy
* 10 mm
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Ordovician Life – other Fezouata fossils
•anomalocaridids•trilobites •chlorophytes•polychaetes•diverse echinoderms•graptolites….. + + + + !
•deep, open water, fully marine, low-energy
setting
All images courtesy P. Van Roy
Model of Laggania by E. Horn
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Early horseshoe crab fossils – the changing picture
?
• re-interpreting the telson of Lunataspis
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Terminal Ordovician Extinctions• global cooling, southern glaciation, sea-level drop & loss of tropical shelf habitat
[Trotter, et al. 2008]http://commons.wikimedia.org/wiki/File:Phanerozoic_Climate_Change.png
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488 MYA
443 MYA
251 MYA
0
Terminal Ordovician Extinctions• second-most severe of the “Big 5” Phanerozoic Mass Extinctions
[Servais, et al., 2009]
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MAJOR CASUALTIES IN MARINE ECOSYSTEMS …
Terminal Ordovician Extinctions• second-most severe of the “Big 5” Phanerozoic Mass Extinctions
BUT HORSESHOE CRABS SURVIVED!
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The Post-Ordovician Record
NO Silurian-Devonian horseshoe crabs … so far!
Earliest fossil record in Ordovician
? Probable, but as yet undetected, Cambrian origin
Reappearance & peak diversity
Survival & recovery
Modest late Mesozoic presence
Very poor Tertiary record
4 extant species … but for how much longer?
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Summary• the horseshoe crab fossil record is now traceable back to the Early Ordovician, but may eventually be extended into the Cambrian Period
• the earliest known horseshoe crabs were established in open marine habitats during the Great Ordovician Biodiversification Event
• environmental parameters during the GOBE were VERY different from those prevailing today …
much higher atmospheric CO2 & lower O2extreme global “greenhouse” conditionsexceptionally high sea levelsno complex land life no vertebrate predatorschanging planktic trophic systems & benthic substrate utilizationmeteor bombardmentrapid plate movements, volcanism & mantle plumes
• horseshoe crab fortunes subsequently waxed & waned, but they have emerged as survivors of 5 major mass extinction events
• can they continue to adapt to rapid global change?
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ACKNOWLEDGEMENTSRESEARCH FUNDING: The Royal Ontario Museum
The Manitoba Museum Natural Sciences & Engineering Research Council of Canada
IN-KIND ASSISTANCE:Churchill Northern Studies Centre
FEZOUATA BIOTA IMAGES:Peter Van Roy
CO-AUTHORS / CO-RESEARCHERS:Graham Young, Michael Cuggy, Deborah Thompson, Ed Dobrzanski,
Sean Robson, Godfrey Nowlan
WORKSHOP ATTENDANCE: Cathay-Pacific Airways, Dr. Paul Shin & the
Workshop Planning Committee