The half-billion-year-old brains of an ancient predator were discovered preserved in 15 fossils found in Greenland. Their existence is helping researchers understand how brains evolved into the complex organs they are today.
Over the years, other fossils with preserved nervous tissue have come loose from rocks battered by weather, but this is the first time researchers have found the tissue remains of an ancient marine predator called Kerygmachela kierkegaardi not destroyed by exposure to the elements.
The fossilized brains are some of the oldest on record, but that’s not what sets them apart. Rather, it’s their surprisingly simple structure that is shedding light on how the organ has evolved over millions of years.
Just shy of 0.3 meters (1 foot) at its longest, the creepy-looking water beast used 11 pairs of wrinkly flaps to swim through the waters, attacking prey with two spiny limbs. Inhabiting the oceans during the Cambrian Explosion, fossils from this time period represent one of the most important evolutionary histories of life.
K. kierkegaardi is related to today’s panarthropods – a group of animals that includes water bears (tardigrades) and velvet worms – and the arthropods that make up crustaceans and insects.
Today, the arthropod brain is made of three distinct segments that migrate together via a bundle of nerves that fuse together with two other brain segments. These segments innervate corresponding appendages and, due to this structure, some insects can live for days or even a week without their head.
Until now, researchers thought the ancestor of all vertebrates and arthropods surely also had a three-segmented brain. Instead, they found the ancient creatures had a single-segmented brain. This means their brains were much simpler than the ones we see in arthropods and is more similar to that of tardigrades.
Not everyone buys the story, however
“If they’re going to say that the brain of Kerygmachela is like that of a tardigrade, you have to be really, really careful,” Nicholas Strausfeld, from the University of Arizona, told National Geographic. “Because it might not be.”
Little is known about the brain structure of tardigrades in general. In fact, they might not even have a one-segmented brain. It's possible they use a unique nerve structure that works much differently.
Led by Jakob Vinther and Tae-Yoon Park of the Korea Polar Research Institute, the study used anatomical analysis to show that the creature's brain innervated the large eyes and frontal appendages. This is an intermediate step between the relatively simple eyes of today’s panarthropods and the complex eyes of arthropods.
The fossils were found in the Buen Formation of Sirius Passet in North Greenland in 2011 and 2016. The study is published in Nature Communications.