Researchers this week described about 100 fossil specimens of the fish unearthed at the Burgess Shale site in the Canadian Rockies and other locales.

Among them was a tiny jawless fish that lived more than half a billion years ago that has provided scientists with a treasure trove of information about the very dawn of vertebrate life.

The fish, called Metaspriggina, lived approximately 515 to 550 million years ago amid the flourishing of complex life during the Cambrian Period, according to Reuters.

Though two fragmentary specimens have already been found, the new ones showed unprecedented detail about one of the earliest known vertebrates.

Creatures like Metaspriggina started the lineage of vertebrates, or animals with backbones, that would later include a whole range of jawed fishes, birds, reptiles, amphibians, 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, according to Reuters. "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 that measured about 2-1/2 inches long, with a small head, a narrow, tapering body, a pair of large eyes and a pair of small nasal sacs.

Though it did not have any bones, Metaspriggina possessed a skull made of cartilage as well as precursors to vertebrae and a backbone-like skeletal rod called a "notochord," according to Reuters.

The researchers did not confirm if it had fins.

Metaspriggina boasted seven pairs of rod-like structures called gill arches, or branchial arches, that were used for both filtration of food particles and respiration, according to Reuters.

Caron said that the first pair of these gill arches were more robust than the others and presaged the first step in the evolution of jaws.

Scientists had never before been able to see such an early example, despite knowing about the importance of these arches in the evolution of vertebrates.

"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, according to Reuters.

Part of the jaw bones eventually e evolved into tiny middle ear bones in mammals, Caron added. The evolution of these arches "had a profound impact on how vertebrates look, live and function today."

The study was published this week in the journal Nature.

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