CAMBRIAN-
544-500 Ma
The
Cambrian marks the first appearance of hard shelled marine invertebrates, a
milestone achievement in the evolution of life. The base of the Cambrian
(544 Ma) is considered by many to be the first occurrence of the burrowing trace
fossil Phycodes pedum, designated the Nemakit-Daldynian stage,
which is followed by the Tommotian stage.
TOMMOTIAN FAUNA
The first appearance of
hard shelled metazoans are referred to as the Tommotian Fauna, also known as SSF
(small shelly fossils).
EARLY CAMBRIAN
By
the Early Cambrian, most of the major phyla existing today had developed. The
massive diversification of life forms has seen no equal prior to or since this
evolutionary achievement.
A
number of factors converged to provide the impetus for the growth and
diversification observed in the Cambrian Period. These factors included
the:
-rise
of metazoans, a springboard event in evolution
-availability of free oxygen in the atmosphere
-supercontinent rift & passive margin development
-development of sunlit continental shelves
-equatorial position of the continents
BURGESS SHALE-
SLOSS
SEQUENCES
LATE CAMBRIAN
The
Late Cambrian was marked by equatorial
land masses and marginal seas, and the continued transgression of the
Sauk Seas. At this point in time, the shallow seas were
awash in widespread shelled marine invertebrates
which included:
Arthropods (Trilobites)
http://www.ualberta.ca/~kbrett/triloclass.html
Brachiopods
Algae
Sponges
Archeocyathids
http://www.ucmp.berkeley.edu/porifera/archaeo.html
Cnidera
Mollusks
Echinoderms
1st Fish- the first vertebrates!
Cambrian Fossils in Wisconsin
QUESTIONS
http://www.gps.caltech.edu/~devans/iitpw/science.html