Page 339 - Introduction to Paleobiology and The Fossil Record

Chapter 13

Spiralians 2: mollusks

Key points

• The Phylum Mollusca can be traced back to at least the Late Precambrian, when
Kimberella probably fed on algae in Ediacaran communities.
• Early mollusks were characterized by some short-lived, unusual forms but with the
molluskan features of a mantle, mineralized shell and radula; these were members of
the small shelly fauna.
• Mollusk shell shape and even ornament can be modeled by a variety of microcomputer-
based software packages; only a small percentage of theoretical morphospace is occu-
pied by living and fossil mollusks.
• Bivalves are characterized by a huge variety of shell shapes, dentitions and muscle
scars, adapted for a wide range of life strategies in marine and some freshwater
environments.
• Most gastropods undergo torsion in early life; they have a single shell, often coiled. The
group adapted to a wide range of environments from marine to terrestrial.
• Cephalopods are the most advanced mollusks, with a well-developed head, senses and
a nervous system; they include the nautiloids, ammonoids and the coleoids. The group
is carnivorous.
• During the Mesozoic many mollusks developed a number of protective strategies such
as robust armor or deep infaunal life modes. The group may also have relied on multi-
formity of shape and color to confuse predator search images.
• Annelid worms were a sister group to the mollusks; their jaws, the scolecodonts, are
relatively common in Paleozoic faunas.

She sells seashells on the seashore;
The shells that she sells are seashells I’m sure.
So if she sells seashells on the seashore,
I’m sure that the shells are seashore shells.

Old nursery rhyme