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| © Mikhail Shekhanov for the Ukhta Local Museum his is the Sosnogorsk lagoon just before a deadly storm. |
The 372-million-year-old fossils of tetrapod -- creatures that
evolved from fish living in water to creatures that walked on land --
have been discovered by researchers in Russia. And given how well they
were preserved, we can tell this was one weird-looking creature.
Had humans been around at the time, they might have seen large,
oval-shaped eyes hovering just above the water line looking back at
them.
This tetrapod, dubbed Parmastega aelidae, looked similar to
a crocodile, except its protruding eyes were on top of its head. Its
nose and jaws, concealing a combination of sharp fangs on the upper jaw
and needle-like teeth on the bottom jaw, would have been below the
surface of the water, the researchers said. And the way they curved
together looked a bit like a menacing grin.
Tetrapods began evolving from fish during the Devonian period. They
would eventually give rise to all creatures who walked on land,
including reptiles, birds, amphibians and mammals.
Until the
discovery of these fossils, everything researchers knew about Devonian
tetrapods relied on nearly complete fossils from Ichthyostega and
Acanthostega that lived at the end of the Devonian period 360 million
years ago, as well as pieces of other species.
But scientists know that tetrapods lived as long as 390 million years ago due to fossilized footprints.
The
newly discovered example was an early tetrapod, which maintained
characteristics similar to fish in some of its bones. It was discovered
in the Sosnogorsk Formation where limestone formed from a once-tropical
lagoon. Now, it's an exposed area on the banks of the Izhma River in
Ukhta. The study published Wednesday in the journal Nature.
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| © Pavel Beznosov Some of the newly uncovered tetrapod fossils. |
Researchers believe its eyes were above water while the rest of its
body lurked below because there are lines in the skull where sensory
organs once helped the tetrapod sense vibrations in the water. It used
gills to breath beneath the water and was likely more than three feet
long.
Crocodiles also lurk in the water this way, usually to keep
an eye on prey that walks on land. But the fossil of this tetrapod held
another surprise: it likely never left the water. Its shoulder girdle
was partially comprised of cartilage. The vertebra and limbs haven't
been preserved, so they may have been as well. Cartilage is softer than
bone, so it's unlikely that this creature was walking around.
Perhaps it grabbed prey on the shoreline.
"Far
from presenting a progressive cavalcade of ever more land-adapted
animals, the origin of tetrapods is looking more and more like a tangled
bush of ecological experimentation," the researchers said in a release.
Given
their eye shape and position, these tetrapods would have been most
comparable to modern mudskippers, according to Nadia Fröbish and Florian
Witzman at the Natural History Museum in Berln, authors of a News and
Views article that accompanied the study. They were not involved in the
study.
But mudskippers use their eyes to watch for predators on
land or in the sky. When this tetrapod was alive, neither threat existed
yet.
Understanding how vertebrates transitioned from water to
land is like following the plot of a crime novel, Fröbish and Witzman
said.
"The P. aelidae fossils offer a treasure trove of
information that could help to disentangle some of the complex
evolutionary changes that took place when vertebrates made the
transition from aquatic to terrestrial life," they said. "This discovery
also reminds us that much still remains to be learnt in the next
gripping chapter of this detective story."
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