Fossil New to Science is Common Ancestor of Spiders and Scorpions


If there was an award show for fossils, one award given might be introduced by saying: “And the winner for the ancient fossil with the best-preserved nervous system goes to….” The clear winner of such an award would be one from 520 million years ago, a possible ancestor of both scorpions and spiders. The fossil shows that the creature had claws, and also nerve cords and a brain.

The research work done in analyzing the fossil, conducted by a group of international scientists, is presented in the journal Nature.

The fossil is one of a joint-legged arthropod of the great appendage variety. They’re called that because they have appendages or growths on their heads which are, basically, claws.

The study in Nature reveals that the fossil of the arthropod is an ancestor of scorpions and spiders, which are chelicerates. This sets it apart from other types of arthropods in it’s family tree, like centipedes, millipedes, lobsters, and insects.

Paleontologists such as Greg Edgecombe of London’s Natural History Museum can tell how major groups of animals are related through the study of their nervous systems.Similar groups have similar looking nervous systems.

Edgecombe calls the nervous system “one of the most reliable tool-kits we have.” He and his fellow paleontologists have been studying fossil records of the Cambrian period, learning from them information about the nerve cords, neural tissue, and brains of the animals which left their fossils behind.

The fossil of this 3-centimeter-long (a tad over an inch) creature was dug up from the famous Chengjiang formation. It’s near to Kunming, China. The fossil is an ancestor of the chelicerates, and it belongs to the genus Alalcomenaeus. The fossil, which is one that’s new to science, had 12 pairs of appendages that it used to walk of swim with, besides those on its head.

The study’s co-author, Xiaoya Ma, said that in a high-res image that they obtained of the fossil, she and the rest of the team of paleontologists could see the complete nervous system of the animal in detail.

She, Edgecombe, and the rest of their team could see both “concentrated neural structures” in the creature’s head, and the areas of the brain which had to do with the claw appendages.

They could also see how similar the brain seen in the fossil is to the brains of modern-day spiders and scorpions.

In an email, Xianoya Ma said through analyzing the neural anatomy of the fossil, the team was able “to sort out how fossil animals are related to animals today,”

The fossil depicts similarities to the brains found in scorpions and spiders. The brains of both are composed of three clusters of nerve cells called ganglia. The clusters are fused together along with some of the body ganglia of the animal. The ganglia of crustaceans are different, in that their ganglia are not as close together. They are also connected by long nerves, which gives them a ladder-like appearance.

Since the fossil belongs to a group of marine arthropods which have large claws, they’re also known as megacheirans — large claws in Greek.

According to Professor Nicholas Strausfeld, a team member from the University of Arizona, the central nervous systems of the megacheirans are “very similar to today’s horseshoe crabs and scorpions.”

Strausfeld added that, as the appendages are a part of the heads of the creatures, they evolved into “the biting mouthparts of spiders and their relatives.”

Both the so-called great appendages of these arthropods and the fangs of a spider or scorpion have elbow joints. These are situated between their pincer-like tip and the basal part.

The fossil, according to Strausfeld, is evidence that mandibulates (like crustaceans) and chelicerates were both around and distinct from each other at least as long as 520 million years ago.

The team of researchers will now turn their attentions to looking for common ancestors in the fossil records which are even older. The data they analyze will provide them with insights into the arthropods of today.

By analyzing the details the research team saw in the fossil of the Alalcomenaeus, they were able to determine that they had discovered a common ancestor to both spiders and scorpions.

Written by: Douglas Cobb

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