The evolution of vertebrates raises countless questions, and we have only answered a few of them. One of the key distinguishing features in this evolutionary path is the introduction of jaws, but scientists have difficulty pinpointing exactly when this feature originated. The latest discovery of fossilized Metaspriggina, a jawless vertebrate clocking in at 505 million years old, is giving scientists an exciting look at the early formation of jaw structures.

The Metaspriggina fossils, which are exceptionally well preserved, display seven pairs of arches near the front of the head. Most of these structures were early forms of gills, or branchial arches, used to filter out food and breathe. The pairs of arches closest to the front of the head, however, were discovered to be thicker than the others, and closely match early jaw structures. Scientists studied the thicker arches and discovered that they are, indeed, the predecessors of vertebrate jaws. The identification is likely the earliest evidence of jaw formation in the fossil record, and is exciting news for those attempting to unravel the mysteries of complex vertebrate evolution. 

The fossils, found in the Burgess Shale site in Canada in 2012, are revealing additions to the two incomplete specimens of Metaspriggina that have been discovered so far. Approximately 44 fossils were collected from the site for this study, which was published in the Journal Nature on June 11. The primary goal of this project is, based on these fossilized finds, to reclassify Metaspriggina as one of the earliest vertebrate organisms. 

Metaspriggina lived during the Cambrian explosion, a period of immense evolutionary formation of life so long ago that fossils of this kind are quite rare, providing a treasure chest of information for researchers from the University of Cambridge and the University of Toronto. The soft tissue that made up the bodies of such fish specimens (Metaspriggina had no bones) do not preserve well over time, yet the fossils are remarkably intact. "The detail in this Metaspriggina fossil is stunning. Even the eyes are beautifully preserved and clearly evident," says lead author of the study, Professor Simon Conway Morris. 

The formation of jaws was one of the earliest vertebrate features to evolve, making it one of the most significant. Metaspriggina's jaw-like features not only pave the way for the evolution of feeding mechanisms, they also shed light on the evolution of all vertebrates, including humans. While the origin of jaws was, before now, a muddled theory due to lack of well-preserved fossils, the Metaspriggina findings give scientists hope that the evolutionary mysteries of our ancestors are one step closer to being solved. 

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