Download O-25 David Rudkin

The Life and Times of the
Earliest Horseshoe Crabs
Dave Rudkin
Department of Natural History (Palaeobiology)
Royal Ontario Museum
Toronto, Canada
Peter Van Roy
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
Geological Time – 4.6 Billion Years of Earth History
65 million years
186 million years
291 million years
4 BILLION years!
http://pubs.usgs.gov/gip/2008/58/geotimespiral_text.pdf
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
488
MYA
542
MYA
(after Xiao & Laflamme, Peterson et al & Dunn et al.)
The Great Ordovician Biodiversification Event
[Webby 2003]
“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]
GOBE marks abrupt rise of both “Paleozoic” &
“Modern” Evolutionary Faunas - mostly at
lower taxonomic levels & in “shelly” biotas
443.7
455.8
460.9
471.8
488.3
ORDOVICIAN
ORDOVICIAN
The Great Ordovician Biodiversification Event
• fossil record of family-level diversity through the Phanerozoic
25 MY
488
MYA
443
MYA
251
MYA
0
[Servais, et al., 2009]
The Great Ordovician Biodiversification Event
• a Cambrian hold-over & important new elements of the Paleozoic Fauna
The Ordovician World
• a dynamic global paleogeographic picture for the GOBE
[http://cpgeosystems.com/mollglobe.html - Ron Blakey, Colorado Plateau Geosystems, Inc.]
600 MYA
Early Cambrian - 540 MYA
Ediacaran
560 MYA
Late
LateOrdovician
Cambrian -- 500
450 MYA
MYA
• rapid seafloor spreading - maximum dispersal of continental land masses, island arcs &
rifted “terranes” - exceptionally high sea levels - maximum extent of tropical shelf areas
The Ordovician World
•global environmental context for the GOBE
• “greenhouse” climate for much of the Early & Middle Ordovician & a terminal ice age!
[Trotter, et al. 2008]
[Vandenbroucke, et al. 2010]
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-chondrite
parent body) & high influx of meteorites (incl. km-size impacters)
Reconstruction image courtesy of The Manitoba Museum
Ordovician Life
• extraordinary diversity in the seas – no comparable macroeukaryotic life on land!
Ordovician Life
© 1997 Philippe Janvier
Liopleurodon93 at en.wikipedia
Apokryltaros at en.wikipedia
• more appropriately … a sea without gnathostome (jaw-bearing vertebrate) predators
M. Purnell
• conodonts & agnathan
(“jawless”) craniate “fishes”
… small size & mostly
microphagous
G. Nowlan
Ordovician Life – the oldest horseshoe crab fossils
2008
2007
Lunataspis aurora
Ordovician Life – the oldest horseshoe crab fossils
443.7
*
455.8
460.9
471.8
488.3
Lunataspis aurora
Ordovician Life – fossils found with Lunataspis
•eurypterids
•medusans
•chlorophytes
•polychaetes
•pycnogonids
….. + + + + !
10 mm
10 mm
•shallow, nearshore, restricted
marine setting
0.5 mm
10 mm
Ordovician Life – new Lunataspis material
10 mm
NEW juvenile specimens
reveal proportional growth
changes
Ordovician Life – the NEWEST oldest horseshoe crab fossils!
2010
P. Van Roy
Van Roy, et al. 2008
Ordovician Life – the NEWEST oldest horseshoe crab fossils!
443.7
455.8
460.9
471.8
488.3
*
10 mm
Courtesy P. Van Roy
Van Roy & Briggs 2011
Ordovician Life – other Fezouata fossils
All images courtesy P. Van Roy
Model of Laggania by E. Horn
•anomalocaridids
•trilobites
•chlorophytes
•polychaetes
•diverse echinoderms
•graptolites
….. + + + + !
•deep, open water,
fully marine,
low-energy
setting
Early horseshoe crab fossils – the changing picture
?
• re-interpreting the telson of Lunataspis
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
Terminal Ordovician Extinctions
• second-most severe of the “Big 5” Phanerozoic Mass Extinctions
488
MYA
443
MYA
251
MYA
0
[Servais, et al., 2009]
Terminal Ordovician Extinctions
• second-most severe of the “Big 5” Phanerozoic Mass Extinctions
MAJOR CASUALTIES IN MARINE ECOSYSTEMS …
BUT HORSESHOE CRABS
SURVIVED!
The Post-Ordovician Record
4 extant species
… but for how much longer?
Very poor Tertiary record
Modest late Mesozoic presence
Survival & recovery
Reappearance & peak diversity
NO Silurian-Devonian horseshoe crabs … so far!
Earliest fossil record in Ordovician
? Probable, but as yet undetected, Cambrian origin
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 O2
extreme global “greenhouse” conditions
exceptionally high sea levels
no complex land life
no vertebrate predators
changing planktic trophic systems & benthic substrate utilization
meteor bombardment
rapid 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?
ACKNOWLEDGEMENTS
RESEARCH 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