Several fossil specimens of a Cambrian fish called Metaspriggina walcotti recently discovered in Canada shed new light on the development of the earliest vertebrates, including the origin of jaws.
Reconstruction of Metaspriggina walcotti. Image credit: M. Collins.
Fish fossils from the Cambrian period are very rare and usually poorly preserved.
Previously, only two incomplete specimens of Metaspriggina walcotti had been identified.
About 44 well-preserved specimens of this prehistoric species were collected from the famous Burgess Shale Formation in British Columbia in 2012.
Paleontologists Prof Simon Morris of the University of Cambridge and Dr Jean-Bernard Caron from the University of Toronto and Royal Ontario Museum used these fossils, along with several more specimens from the eastern United States, to reclassify Metaspriggina walcotti as one of the first vertebrates.
“The details in the fossils are stunning. Even the eyes are beautifully preserved and clearly evident,” said Prof Conway Morris, who is the first author of a paper published in the journal Nature.
The fossils, which date from 505 million years ago, also show pairs of exceptionally well-preserved arches near the front of the fish’s body.
Overall view showing approximately 44 individuals of Metaspriggina walcotti, white numbers, including several preserving eyes, blue arrows. Image credit: Simon Conway Morris / Jean-Bernard Caron.
“These arches have long been known to have played a key role in the evolution of vertebrates, including the origin of jaws, and some of the tiny bones in the ear which transmit sound in mammals.”
“Until now, however, a lack of quality fossils has meant that the arrangement of these arches in the first vertebrates had been hypothetical.”
The first of these pairs, closest to the head of Metaspriggina walcotti, eventually led to the evolution of jaws in vertebrates, according to the paleontologists.
The arrangement of the muscles shows Metaspriggina walcotti were active swimmers, not unlike a trout, and the animals saw the world through a pair of large eyes and sensed their surrounding environment with nasal structures.
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Simon Conway Morris & Jean-Bernard Caron. A primitive fish from the Cambrian of North America. Nature, published online June 11, 2014; doi: 10.1038/nature13414
