Re: Teeth

Teeth, as far as vertibrates go, evolved from dermal scales, probably about
400 million years ago. The first vertibrates in the fossil record were
jawless. Teeth didn't develop until after jaws evolved.
I don't think teeth and jaws necessarily go together in the fossil
record. True teeth (and I include placoid scales in this
classification) probably preceded jaws by a long time. Teeth or
placoid scales have probably preceded the vertebrate.
Conodont fossils are very common and extent from the late Cambrian
to the Triassic. They have a dental like structure that until recently
was not associated with a more complete animal. Recently, trace
fossils have shown that the conodonts were jawless chordates, with
notochords instead of vertebrate. Conodont fossils have recognizable
dentin and something vaguely similar to enamel. Although there are no
preCambrian conodonts known, the fact of Cambrian conodonts points to
an origin that may date back to the Cambrian explosion. Therefore, I
would have to say that true teeth well proceeded jaws.
Furthermore, sharks and rays have scales (denticles) all over
their bodies that have a clear tooth like structure. These scales are
called placoid scales. Dentine, enamel, etc. However, they are not
attached to the jaws. The teeth in sharks are the placoid scales that
grow in the mouth. The barb on the tail of rays are specialized
placoid scales, and thus may be considered true teeth (in structure
anyway). Therefore, I find it doubtful that the placoid scales started
in the mouth. The jaw is the late structure here, not the teeth.
You should also point out that many structures that have a
superficial toothy appearance. Baracuda "teeth" have no dentine, no
enamel, and so are considered distant analogues to teeth. Some ducks
have a "teeth" which are mere pointed sections of their jaws. Just as
jaws without teeth are common. Saying that a tooth requires a jaw may
lead to trouble.

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