It's one of the places where these organisms like to still live and
they're called horseshoe crabs.
So one example in North America is
Florida Bay is a place that horseshoe crabs do extremely well.
They also live up and down the entirety of the east coast of the US, but
they occur anyplace around the world where you have those right environments.
The horseshoe crabs are remarkable.
First of all, they are very, very closely related to the trilobites.
And so the trilobites went extinct at the end of the fauna,
that was one of the organisms that did very well and
then was out competed at the environment changed.
And so we don't have any modern day trilobites, but the trilobites that we do
have living are an ancestor of the trilobites called the horseshoe crabs.
And if you look at the very earliest stages of horseshoe crab development, they
look identical to many of the types of trilobites we have in the fossil record.
What we see commonly, one of strategies within evolution,
is that as time goes on and organisms evolve and
become more successful environments, some of their earlier stages of development,
they're actually pushed further into the history of the life of one organism.
So in other words, things that evolve through time as they change and
adapt to environmental constraints and competition and predation,
some of the earlier forms of what the organism looked like are actually pushed
into the early stages of the growth of the individual organisms.
And we describe that with a phrase that is ontogeny recapitulates phylogeny.
Ontogeny is the growth history of one single organism.
Phylogeny is the history of evolution of
all lineages of that organism through time.
And so, what we see is that ontogeny,
the history of the growth of one organism going from a baby to an adult.
What we see is during ontogeny the very earliest stages of phylogeny,
which is evolution from an earlier ancestor to later organisms,
we see that those natural environmental, those natural
experiments in the face of natural selection and other processes that go on.
They're actually captured and preserved in that individual organism but
they're only shown and expressed when the organism is very young and very small.
And as they grow to be older then they have different morphologies.
So the early stages of horseshoe crabs are in that same ilk.
Another thing that's critically important about horseshoe crabs is that they're
the only Metazoan that we know of that had blood based on copper,
so their blood is actually blue.
Most organisms, like ourselves, we have an iron-based blood system.
And it has to do with, the reason that's been successful is it
is a very effective means for having iron then reacts with oxygen and it's
a good way to transport oxygen throughout the internal system of the medazone.
But the blue blooded horseshoe crabs are one that have done extremely well
in terms of being successful, but they have this unique history
of having a copper based blood, which turns the blood blue.
So the horseshoe crabs are one good example of how we have a living record of
ancient organisms that are still alive and, if you will, living fossils.
But in the history of the development of any one of these living fossils going from
juvenile into an adult, we have buried within that,
the record of the earlier stages of evolution and phylogeny,
that were part of the development of these organisms.
So the horseshoe crabs have been around since the but
they have actually evolved significantly beyond that and
their earliest ancestors were very very closely related to the trilobites.
So these organisms that live on the sea floor were, they dominated and
proliferated.
And they created these great assemblages of life on the sea
floor that we call reefs.
And the word reef, R-E-E-F is a word that, again,
most people know, but is very poorly known how to define it by most people.
And the idea there is that a reef is a structure on the sea floor, or
it could be a lake floor.
But in this case it's a sea floor.
It's a structure on the sea floor that is stuck together and
rigid, and it can resist waves.
In other words, when waves come along, if there's a bump on the sea floor, that bump
is resistant enough to push back and not be pulverized and spread out by the wave.
Now, the word reef then can be a group of organisms on the sea floor, but
it can also be a group of rocks on the sea floor.
And this word reef was actually derived from the norse word rif, R-I-F and
that means the human rib.
And so a coral reef is a group of corals along with some of the other organisms
that we talked about, the brachiopods and the bivalves and the clams and
snails and all these other groups that are living on the sea floor.
So the whole notion of having a group of animals get together and
create a community on the sea floor.
And when they live and conduct their everyday life together in these
assemblages, again, they're invertebrates.
And because they have an exoskeleton, their skeletons all accumulate in place.
And it makes an accumulation of rock.
And then that accumulation of rock, based on these exoskeletons,
is wave resistant and it sticks off a sea floor.
So the idea of communities on the sea floor, when corals were dominant,
we called them coral reefs.
When brachiopods are dominant, we call them brachiopod bryozoan bivalve reefs.
Whatever makes up the major part of the community living on the sea floor,
that's what we use as their name.
So the Cambrian fauna was the initiation and the introduction to the sea floor of
these invertebrates that would live in communities, create these
accumulations and these accumulations through time become fossilized.
And so these fossilized reef communities provided us with a dramatically detailed
record of the ecology of what was happening on the sea floor.
And again, the thinking here is that these communities of the Cambrian fauna
that were developed in these reef organizational entities on the sea floor,
the date then ended up setting the template for
the early oceans within the Paleozoic.
Now, there were a whole series of other events that took place.
Things like meteor impacts.
We had additional formation of ice.
We had other events, volcanic eruptions that took place in that early Paleozoic,
the Cambrian, the Ordovician, the Silurian, and then into the Devonian.
So, as an accumulation of all these events together with the ongoing exchange
going from some organisms originating, radiating, evolving,
and then going extinct, that Cambrian community did well, but more or
less went extinct by about the time of the Devonians.
Some of them got through, but others did not.
