O S T R A C O D E R M
J A W L E S S F I S H
We have to go back 450,000,000 years to find
our first sign of an animal having a vertebra, or a
close likeness. Prior to that there were plenty
of jellyfish populating the oceans as well as
assorted animals of the kind you find in tidepools.
The earliest vertebrate species were simple
in plan and may have looked like oversize worms
wiggling through water. The specimen above has
two dorsal fins to stabilize the animal, behaving much
like a sailboat's keel to keep it upright.
The animal leads with its armored head,
flattened and taking the shape of a shovel blade.
The eyes are new, as is a distinct and enlarged
neural center that becomes the individual's brain.
The mind discovers light, quickly learning it is
the best and most reliable source for information,
far more than either touch or smell delivers.
Now the animal can identify something from a
distance, know its size, its headed direction
and know whether it is food or foe.
P L A C O D E R M
30,000,000 years later and we enter the
Devonian Period - The Age of Fishes.
The basic body plan of a fish is revealed
with the Placoderm. The name means
Plated Skin in Greek, referring to the animal's
armored head. Vertebrates now have a
lower jaw and with it, the ability to bite
like a true carnivore, capturing its prey with
fangs.
Then, after 60,000,000 years of life's further
development, a global environmental catastrophe
occurs, killing off most living species on Earth.
The Placoderms disappear from the fossil record.
S H A R K
20,000,000 million years have passed.
The land is now covered in thick forest.
This time of great plant abundance is
know as the Carboniferous Period, a later
source for stored energy in the form of
its buried oil, coal and natural gas.
The first animals capable of dwelling on land
would find these vast forests a never-ending
buffet.
Sharks appear in the fossil record.
Their skeleton made of cartilage makes them
lighter, faster and more maneuverable than bony fish.
The shark pictured above sports an anvil-shaped,
front dorsal fin. Its bulk hinders swimming but
the flat-head fin is a male display device important
in courtship.
A C A N T H O D I I
S P I N Y F I N N E D F I S H
Every fin attaches to a spine, except for the tail.
Its skeleton is cartilage but the head is bone.
Bone makes for a stronger helmet.
Cartilage is used to boost performance while
bone provides strength for protection.
How is it the two separate developments of
cartilage and bone, manage to combine
in one group of vertebrates?
The spiny finned fish succeeded for millions of years.
It ended with an environmental catastrophe that destroyed
most of life on Earth. The spiny-finned fish were swept
from the fossil record along with the placoderms.
O S T E I C H T H Y E S
M O D E R N B O N Y F I S H
Over 95% of all vertebrate species
in existence today are fish. They are found
most everywhere life can exist. Fish have
an exceedingly adaptable genetic makeup.
Some notable features:
M. Gills for respiration. Exchanging gases
with the surrounding water. They can't breathe
without water constantly moving over the gills.
A shark must continually swim in order to breathe.
A modern fish has an operculum, a bony gill cover
that flaps while the fish is hovering, enabling the
animal to breath while standing still.
E. Swim Bladder for buoyancy.
It gives the fish neutral buoyancy, enabling it to
hover in the water and not sink. It is a thin walled,
gas-filled sac that has proven highly adaptive.
Some species of fish that live in stagnant ponds
are able to supplement their gills with using their
swim-bladder for respiration when water becomes
oxygen deprived. Lungs replace gills for respiration
as the fish's gas bladder fulfills a new purpose.
I. Nostrils for smelling, only.
As yet they have no roll in breathing.
They are sensors that detect chemical cues
in the water for feeding and navigation.
This is a vital sensory organ behind the salmon's
remarkable journey home to the stream of their birth
for the purpose of reproduction.
A C T I N O P T E R Y G I I
R A Y - F I N N E D F I S H
Fins supported by thin, bony rays provides for
superior responsiveness and overall performance.
The design is powered by competition and
responses to continuing environmental changes.
Somehow the code to life was written.
It's instructions have been coded in molecular
verse and passed from individual to individual
for hundreds of millions of generations now.
The mystery only deepens with the additional
knowledge we gain. It's a principle of science.
* * * * *
OVER EASY
No comments:
Post a Comment