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The
Diversity of The World of Life
Vertebrates
(Vertebrata)
Placoderms
(Placodermi)
Representatives
Placoderms
Biology
ENVIRONMENTS
Placoderms are extinct marine species.
DESCRIPTION
Placoderms and similar species were more adapted to
swimming than more primitive species (like ostracoderms):
Placoderms and the like had a relatively streamlined body with paired
"pectoral" fins (towards the front of the body) and paired
"pelvic" fins (towards the rear).
Perhaps
more importantly (for their success and that of their ancestors, including
us), placoderms were amongst the first vertebrates with jaws,
which evolved from the bones and skin of the front-most "gill
arches" of more primitive fish.
Although
placoderms and the like had a scaly body, there was typically less bony armor than in ostracoderms,
although the head and "neck" area of many placoderms were well
protected by a heavy, bony armor, as with a movable shield (as for a Triceratops).
Although most placoderms were relatively small, some grew
up to ten feet long!
FEEDING HABITS
Significantly,
jaws allow vertebrates to feed on more food sources than jawless creatures
can exploit.
MOTION
The fins of fish typically help provide stability,
guidance, propulsion, and even lift during swimming.
RESPIRATION
Although
some of the gills were lost in the evolution of jaws, gases dissolved in
water were exchanged over the remaining gills.
COORDINATION
Placoderms
and other primitive jawed fishes had well developed eyes, one on either
side of the head. These fish were efficient predators, which
undoubtedly contributed to the extinction of more primitive species.
Vertebrates
(Vertebrata)
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