A team of researchers has discovered what they believe to be the missing link in the evolution of complex cells. In a study, published in the journal Nature on Wednesday, the researchers said the new findings will help them better understand how complex cell types, including plants, fungi, animal and humans, evolved from simple microbes billions of years ago.

The origin of complex cell types -- collectively called “eukaryotes” -- has so far baffled the scientific community. But, as part of the new study, the scientists have discovered a new group of microorganisms, called Lokiarchaeota or “Loki” for short, which can solve mysteries about the evolutionary transition from simple to complex cells.

“The puzzle of the origin of the eukaryotic cell is extremely complicated, as many pieces are still missing,” Thijs Ettema, a microbiologist at Upssala University in Sweden, and the study’s lead author, said in a statement. “We hoped that Loki would reveal a few more pieces of the puzzle, but when we obtained the first results, we couldn’t believe our eyes. The data simply looked spectacular.”

The researchers studied Loki’s genome and found that the microorganism represented an intermediate form between the simple cells of microbes and the complex cell types of eukaryotes. According to the researchers, when they placed Loki in the "Tree of Life," it formed a well-supported group with the eukaryotes in their analysis.

“In addition, we found that Loki shares many genes uniquely with eukaryotes, suggesting that cellular complexity emerged in an early stage in the evolution of eukaryotes," Anja Spang, a researcher at the Uppsala University, and one of the co-authors of the study, said in the statement.

The term Lokiarchaeota is derived from “Loki’s Castle,” a field of hydrothermal vents, where the microorganism was found. Loki's Castle is located on the Mid-Atlantic Ridge between Greenland and Norway at a depth of 2,352 meters, or about 7,717 feet.

According to the researchers, hydrothermal vents are volcanic systems located at the ocean floor. Although the site where Loki was found is heavily influenced by volcanic activity, it is quite low in temperature, they said.

“In a way, we are just getting started. There is still a lot out there to discover … to revise our biology textbooks more often in the near future," Ettema said.