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RE: Timeline: "Sinemurian - first grazing echinoids"
The echinoid "lantern" or jaw apparatus was actually present in Paleozoic
echinoids dating back to the Ordovician, although it did not become strongly
developed for true "rasping" until the early Mesozoic. So, "grazing" in the
broad sense evolved much earlier than Mesozoic, but the kind of rasping of
algae and bioerosion that modern sea urchins can do on hard surfaces probably
originated in the early Jurassic.
What is more significant for the changing ecology of the seas in
Mesozoic time was the evolution of *burrowing* echinoids - the forebearers of
modern "heart urchins" or "sea biscuits" and sand dollars - that also took
place in the Sinemurian. This was part of a general "invasion" of the soft sea
floor by various marine bottom dwellers (Thayer's "biological bulldozers")
during the Mesozoic. This may have been linked to events on land: a response
to a rise in input of terrestrial plant matter from the vast land area of
Pangaea or different flavors of plant matter from newly evolved forms...
(Apologies for this digression from an invertebrate-type, but it does
bring up the importance of considering linkages between events of vertebrate
and invertebrate evolution, as well as connections between terrestrial and
marine events. Keep in mind that those hearty echinoids - grazers and
burrowers - went charging through the K/T "crisis" w/ hardly a twitch of a tube
Pertinent sources: Boardman, Cheetham, & Rowell, 1987, Fossil Invertebrates,
Blackwell Scientific, p.608-611, esp. Fig. 18.79; also Smith, A., 1984,
Echinoid Palaeobiology, Allen & Unwin.
Dave Meyer, Geology, Univ. of Cincinnati, Cincinnati, OH 45221, 513-556-4530,
FAX 513-556-6931, e-mail DAVID.MEYER@UC.EDU.