- People often say,
"Where are the intermediate fossils?
Show us your intermediate fossils"
There are plenty of intermediate fossils,
and one of the best examples is whales.
The modern whales are up there.
Here's a series of fossils back in time:
Dorudon about 36 million years ago,
Rodhocetus about 47 1/2 million years,
Pakicetus about 48 1/2 million years.
And you can see they form
a lovely series of intermediates.
As you go from old to young,
Pakicetus, Rodhocetus,
you're gradually losing the hind legs to Dorudon,
which has almost lost the hind legs completely.
Modern whales have completely lost the hind
legs.
There are some vestigial bones,
some remnant bones buried deep inside the
body.
A lovely series of intermediates
getting progressively more and more specialized
in living in the sea.
If you look at Pakicetus,
which is an old fossil whale,
you see that the nostril is just about where
you'd expect the nostril to be, near the tip
of the snout.
If we move on a million years to Rodhocetus,
you see that the nostril has moved backwards,
backwards on the skull,
backwards along the snout.
Now if you look at a modern whale -
that's a dolphin, a modern dolphin -
you see that the nostril
is right up near the top of the head.
That's the blowhole.
The nostril has moved right backwards.
Now, a really surprising thing
is which animal is the most closely related
to modern whales among modern animals,
and the answer, astonishingly, is the hippopotamus,
which is classified in the even-toed ungulates,
the cloven-hoofed animals.
So what we now believe is that there was an
ancestor,
which was a cloven hoofed animal,
before 55 million years ago.
A little bit before that,
the ancestor gave rise to other cloven-hoofed
animals.
And the later than that,
there was a split between the lineage leading
to whales
and the lineage leading to modern hippopotamuses.
It's molecular evidence as well as fossil
evidence
that shows that hippos
are the most closely related modern animals.
