A new fossil of a prehistoric underwater creature, which swam across the Earth's oceans even before dinosaurs fully evolved, has been discovered. And guess what, the fossil – which is of a 245-million-year-old horseshoe crab – has joined the dark side of the Force as the animal has been named Vaderlimulus because its shield head resembles the helmet worn by Darth Vader, the infamous villain from the Star Wars film series.

Palaeontologists discovered the fossil in Idaho. Researchers believe that over 240 million years ago, the oddly shaped horseshoe crab likely lived in the shallow waters of Idaho's then-existing coastline.

According to the New Mexico Department of Cultural Affairs, the newly discovered fossil dates back to the Triassic Period, which was the first period of the Mesozoic era (252 to 201 million years ago). It was the time when dinosaurs and mammals were just beginning their evolutionary development. Meanwhile, the horseshoe crab was "already ancient" at the same time as the animal goes back as far as 470 million years.

In a paper published in the German journal Neues Jahrbuch für Geologie und Paläontologie, palaeontologists say that the new discovery provides more information about the evolution of ancient underwater creature.

The fossil is also the first ever horseshoe crab from the Triassic Period to be found in North America.

Only four known species of horseshoe crabs are alive today. But unfortunately, their population is declining. These modern relatives of the prehistoric creatures are often referred to as "living fossils" because their physical appearance seems to have undergone little change, despite having lived for centuries.

260-million-year-old fossils reveal Antarctica had tree-filled forests before dinosaurs existed

Researchers say that the fossil reveals the ancient creature had "heightened enlargement and proportional reduction of body elements, sometimes resulting in bizarre forms".

"Vaderlimulus, however, has unusual body proportions that give it an odd appearance," Allan J Lerner, the study's lead author, said.

Palaeontologist concluded that Vaderlimulus belonged to an extinct horseshoe crab species called Austrolimulidae. The underwater creatures of this particular family were evolving to adjust from marine to freshwater settings during the Triassic Period, which likely explains its bizarre physical appearance.

Horseshoe crab Darth Vader fossil
Drawing of Vaderlimulus NM Museum of Natural History & Science