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Science Forum Index » Bio Evolution Forum » Ostracoderm Head Shields: Skulls?
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| Guest |
 Posted: Sun Mar 11, 2007 12:24 pm |
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Three questions related to the early evolution of bone in the chordate
phylum.
1) Are the head shields of ostracoderms homologous to skulls?
2) Is there any indication that they had hard bone other than their
head shields?
3) Were ostraderm scales placoidal (i.e., homologous to vertebrate
teeth) or something else (e.g., like teleost scales)?
The ostracoderms were a group of jawless fish that lived 600-650 MYA,
who had bony head shields. Their name means "bone-shelled", implying
that these shields grew over the skin.
Some of the scientific literature implies that the head shields have
nothing to do with our modern skulls. To me the head shields have a
superficial resemblance to skulls. |
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| Guest |
| Posted: Mon Mar 12, 2007 7:59 am |
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I made a mistake that I am correcting here. The ostracoderms were a
group of jawless fish that appeared 420 MYA. The ostracoderms did not
lived 600 - 650 MYA, or at least they left no fossils at that time. In
any case, my question is the same. Are ostracoderm head shields skulls
or shells? |
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| Bill Morse |
| Posted: Sat Mar 24, 2007 7:15 am |
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Guest
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drosen0000@yahoo.com wrote:
Quote: I made a mistake that I am correcting here. The ostracoderms were a
group of jawless fish that appeared 420 MYA. The ostracoderms did not
lived 600 - 650 MYA, or at least they left no fossils at that time. In
any case, my question is the same. Are ostracoderm head shields skulls
or shells?
The only reference I've got - "The Evolution of Vertebrate Design" by
Leonard Radinsky - states that the head shields are bone - which I think
would make them skulls.
--
Yours, Bill Morse |
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