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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