Early Critters in Microbial Mats: Evolution or Just a Strange Environment?

For many billions of years, the only life that existed on Earth was
microbial, that is, microscopic organisms that we generally call bacteria.
These were commonly so abundant that microbial mats basically covered
much of the Earth’s ocean seafloors.

Then during the Cambrian, a little more than a half billion years ago,
animals evolved and burrowed into the microbial mats and took advantage
of this rich food source. Of course, that means they eventually ate up
the mats.

Many Cambrian animals have a seemingly strange morphology, and have been
thought by many to represent early “evolutionary experiments.” Among
these are the helicoplacoids — the earliest known echinoderms and
ancestors of modern animals like the starfish. Shaped like a football,
a helicoplacoid had “armor” that was essentially small mineralized plates
formed into spirals. Even its food-gatherng organ was a spiral that
wound around its body.

David Bottjer, of the University of Southern California, does not agree
with the “evolutionary experiment” interpretation of how these animals
came about. He will outline a different approach to understanding these
strange morphologies on Thursday, November 8, at the Geological Society
of America’s annual meeting in Boston. “Many early animals were well-
adapted, via evolutionary processes, to the unusual (and now usually
non-existent) microbial-mat-covered seafloor environments that were
typical for the Cambrian. So, rather than the animals being particularly
unusual, we are saying that the environments were!” explained Bottjer.
“And, being evolutionarily well-adapted to an unusual environment gives
an animal a strange morphology, to our modern eyes. So we are suggesting
a different evolutionary explanation than what has been offered before,
and, in that sense, are breaking from tradition.”

This discovery provides a piece for the ongoing puzzle work of
understanding how animal life first evolved on Earth.

CONTACT INFORMATION

During the GSA Annual Meeting, November 4-8, contact Ann Cairns or
Christa Stratton at the GSA Newsroom in the Hynes Convention Center,
Boston, Massachusetts, for assistance and to arrange for interviews:
(617) 954-3214.

The abstract for this presentation is available at:
http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_24298.htm

Post-meeting contact information:

David Bottjer

Department of Earth Sciences

University of Southern California

Los Angeles, CA 90089-0740

E-mail: dbottjer@usc.edu

Phone: 213-740-6100

Ann Cairns

Director of Communications

Geological Society of America

Phone: 303-357-1056

Fax: 303-357-1074

E-mail: acairns@geosociety.org