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 A tiny jawless fish that lived more than half a billion years ago
is providing scientists with a treasure trove of information about
the very dawn of vertebrate life on Earth.
Researchers on Wednesday described about 100 fossil specimens of the
fish unearthed at the Burgess Shale site in the Canadian Rockies and
other locales, many exquisitely preserved showing the primitive body
structures that would later evolve into jaws.
The fish, Metaspriggina, lived about 515 to 500 million years ago
amid the astonishing flourishing of complex life during the Cambrian
Period. While two fragmentary specimens had been found previously,
the new ones revealed unprecedented detail about one of the earliest
known vertebrates.
Creatures like Metaspriggina began the lineage of vertebrates -
animals with backbones - that later would include the whole range of
jawed fishes, amphibians, reptiles, birds and mammals including
people.
"It allows an understanding of where we come from and what our most
distant relatives might have looked like," said Jean-Bernard Caron,
a paleontologist at the Royal Ontario Museum in Toronto. "Because of
its great age - more than half a billion year old - Metaspriggina
provides a deep down view at the origins of the vertebrates."
Metaspriggina was a soft-bodied jawless fish no bigger than a
person's thumb - about 2-1/2 inches (6 cm) long, with a small head,
a narrow, tapering body, a pair of large eyes atop the head and a
pair of small nasal sacs.
It did not have bones but possessed a skull possibly made of
cartilage as well as precursors to vertebrae and a skeletal rod
called a "notochord" that provided body support like backbones would
do in later vertebrates. It is unclear if it had fins.
The scientists were especially excited about the gill structure of
the fish because of the preview it gives to the anatomy of later
vertebrates - paving the way for the jaws that would open a world of
possibilities for so many later creatures.
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Metaspriggina boasted seven pairs of rod-like structures called gill
arches, or branchial arches, that functioned for both filtration of
food particles and respiration. The first pair of these gill arches
was more robust than the others and presaged the first step in the
evolution of jaws, Caron said.
Scientists have known about the importance of these arches in the
evolution of vertebrates but had never before been able to see such
an early example.
"Metaspriggina is important because it both fills an important gap
in our understanding of the early evolution of the group to which we
belong, but in particular shows with remarkable clarity the
arrangement of the so-called branchial arches," University of
Cambridge paleontologist Simon Conway Morris said.
Part of the jaw bones eventually evolved into tiny middle ear bones
in mammals, Caron added, noting that the evolution of these arches
"had a profound impact on how vertebrates look, live and function
today."
The study was published in the journal Nature.
(Reporting by Will Dunham; Editing by Tom Brown)
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