Peter Van Roy

The Life and Times of the Earliest Horseshoe Crabs

Dave RudkinDepartment of Natural History (Palaeobiology)

Royal Ontario MuseumToronto, Canada

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 291 million years186 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

542 MYA

488 MYA

(after Xiao & Laflamme, Peterson et al & Dunn et al.)

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

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

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

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.]

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]

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)

Ordovician Life• extraordinary diversity in the seas – no comparable macroeukaryotic life on land!

Reconstruction image courtesy of The Manitoba Museum

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

Ordovician Life – the oldest horseshoe crab fossils

20072008

Lunataspis aurora

488.3

443.7

460.9

471.8

455.8

Ordovician Life – the oldest horseshoe crab fossils

*

Lunataspis aurora

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….. + + + + !

Ordovician Life – new Lunataspis material

10 mm

NEW juvenile specimensreveal proportional growth

changes

Ordovician Life – the NEWEST oldest horseshoe crab fossils!

Van Roy, et al. 2008

P. Van Roy

2010

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

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

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

488 MYA

443 MYA

251 MYA

0

Terminal Ordovician Extinctions• second-most severe of the “Big 5” Phanerozoic Mass Extinctions

[Servais, et al., 2009]

MAJOR CASUALTIES IN MARINE ECOSYSTEMS …

Terminal Ordovician Extinctions• second-most severe of the “Big 5” Phanerozoic Mass Extinctions

BUT HORSESHOE CRABS SURVIVED!

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?

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?

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