The Chengjiang Biota in southwestern China is famous for its Maotianshan Shale and wealth of fossils. The formation recently revealed another important find. Paleontologists discovered a preserved marine Megacheiran specimen described October 16 in the journal Nature. Megacheiran are a group of arthropods (any invertebrate with an exoskeleton) characterized by a large appendage. Megacheiran literally means “large claw” in Greek.
The newly discovered fossil, Alalcomenaeus, is from around 520 million years ago, dating to the Cambrian. This is an important find because it is now the earliest known fossil to have a complete nervous system. The specimen represents a distant relative of modern day scorpions and spiders. It provides an important evolutionary step between scorpions and spiders and other arthropods like millipedes and crustaceans.
The central nervous system of this animal was the key in linking it to living creatures of today. Looking at the configuration of the nervous system of the specimen through micro-computed tomography (CT scans), the authors of the recently published paper in Nature showed that organization of nerves and associated structures correspond most closely to the nervous system of the Chelicerata (scorpions and horseshow crabs) – this is why Alalcomenaeus was assigned to the Megacheiran.
Alalcomenaeus was an average of 3-6 cm long. It could crawl on land and swim in ancient seas using 12 paired legs that came off of a segmented body. To aid in swimming it had a paddle-like tail which ended in elongated, flat spines. Its foremost appendages had long claw-like tools for pinching and grasping. Based on multiple findings of this creature it has been determined to be the dominant fauna of the area.
Source: Tanaka, G., Hou, X., Ma, X., Edgecombe, G. D., & Strausfeld, N. J. (2013). Chelicerate neural ground pattern in a Cambrian great appendage arthropod. Nature, 502(7471), 364-367.
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