A new species, the common ancestor of scorpions and spiders, has been discovered!

Paleontologists have discovered that a tiny creature that lived in the seas about half a billion years ago was the oldest known ancestor of spiders, scorpions and horseshoe crabs. Let’s take a look at the details together.

The oldest ancestor of scorpions and spiders discovered

This tiny creature, called Setapedites abundantis, was just 5 millimeters long and lived 478 million years ago in an ocean covering what is now Morocco. This creature, whose fossils were first discovered in the early 2000s, has been waiting to be examined since then. Since fossil analysis is a time-consuming process, researchers are just now uncovering the secrets of this tiny creature.

Detailed studies of the fossils of Setapedites abundantis revealed that this creature belongs to the arthropod clade, specifically the Euchelicerata group. Arthropods are a diverse group of invertebrates that include insects, myriapods, crustaceans, and arachnids, and represent approximately 75 percent of animal life on Earth.

The Euchelicerata subgroup includes creatures such as spiders, scorpions, horseshoe crabs, mites and ticks, which have mouthparts called chelicerae that are used to grasp and poison their prey. However, it is not known exactly when and how these different animals diverged from other arthropods and embarked on their own evolutionary paths.

Paleontologist Lorenzo Lustri and his team examined the fossils of Setapedites abundantis found in the Fezouata Shale formation. The fossils showed anatomical features such as two branched appendages on the back of the animal. These features confirmed that Setapedites abundantis belongs to the Offacolidae family. Previously, only Offacolus kingi was known in this family, and this species lived during the Silurian period, between 444 and 420 million years ago.

The inclusion of Setapedites abundantis in this family revealed this creature to be the oldest known member of the Euchelicerata in the arthropod family tree. This finding fills the evolutionary gap between early arthropods and Euchelicerata.

The location of the fossil has now been determined. The next step will be to examine this fossil in more detail to better understand how its unique features emerged and the evolution of these features. This will allow us to learn more about how the spiders we know and love today evolved.