74 | SCIENCE ILLUSTRATEDO
ur ability to breathe above the water originated long
before we began to live on dry land. The earliest boney
fish, which were the ancestors of anything from cod to
humans, had already developed primitive lungs. One of
them was the 33-cm-long Guiyu, discover in 2009. Guiyu is
the oldest known bony fish, and unlike the earliest
vertebrates, it had a spine consisting of robust bones
instead of cartilage. Moreover, the skull had been
furnished with an important addition: a lower jaw,
allowing the fish more possibilities of consuming food.
The Guiyu fossil also demonstrates that the foundation
stones of our arms and legs were being laid. Whereas other
fish moved their fins by means of muscles close to the spine,
Guiyu's muscles were probably located in its fins. This new
evolutionary trait made the fins much more flexible.
Although Guiyu’s lungs have not been preserved,
scientists are quite sure that they must have existed. The
ancestor of bony fish must have had lungs, because all
modern bony fish have lungs of some kind. In many fish,
but not all, the primitive lungs have been converted into
swim bladders, which help the animals control their
upward momentum in the water. Like the modern bowfin,
Guiyu used its lungs as a supplement to its gills to get
extra oxygen for an active life in the water.Early Fish Had Lungs
Early bony
fish gave us:
Lungs
Jaw
Primitive limbsThis fossil filled a gaping hole
in scientists’ knowledge about
a major stage in vertebrate
evolutionary historyF
or almost three decades, its
bones had been forgotten in
the basement of a Scottish
museum. It had been categorised
as a fish shortly after its
discovery in 1971. That is, until
British palaeontologist Jennifer
Clack got hold of the fossil in- She determined the
creature, which was named
Pederpes, was not a fish, but
rather one of the first vertebrates
to live on dry land. Before Clack’s
exhaustive investigation of
Pederpes, scientists lacked high-
quality fossils from this epoch.
They knew about early animal
fossils, which did not yet live on
dry land, and later fossils of
animals that were fully adapted
to life on dry land, but had until
then found nothing in between.
Pederpes’ primitive arms and
legs gave scientist a long-awaited
idea of the adaptations that
made life on dry land possible.
Pederpes’ aquatic ancestors had
limbs that pointed down along
their bodies and could not be
used for very much other than
swimming or pushing the
animals away from the ocean
floor. Pederpes’ limbs pointed
away from the body, towards the
ground, keeping the 1-m-long
animal's body off the ground.
And Pederpes was not alone.
Last year, Clack contributed to
naming five new coexisting
species, all showing similar
forms of dray land adaptation.Scottish Amphibian
Took Crucial Step
348 million years ago419 million years agoCREATIVE COMMONSThe amphibian-like Pederpes
could probably move about in
both water and on dry land,
where it caught insects, etc.HUMANS EVOLUTION