Paleontologists led by Dr Nicholas Strausfeld from the University of Arizona’s Center for Insect Science have discovered the fossilized remains of Lyrarapax unguispinus – one of the world’s first known predators that lived in what in now southwest China during the Cambrian period, about 520 million years ago.

Lyrarapax unguispinus (Latin for ‘spiny-clawed lyre-shaped predator’) belongs to Anomalocarididae (abnormal shrimps), a group of early marine animals known from fossils found in Cambrian deposits in Australia, China, United States, Canada and Europe.

The Lyrarapax fossil with well-preserved traces of muscles, digestive tract and brain was unearthed in 2013 near Kunming in the Chinese province of Yunnan.

“Because its detailed morphology is exquisitely preserved, Lyrarapax unguispinus is amongst the most complete anomalocaridids known so far,” said Dr Peiyun Cong of Yunnan University, China, who is the first author of a paper describing Lyrarapax unguispinus in the journal Nature.

Over 12 cm long, Lyrarapax unguispinus was dwarfed by some of the larger anomalocaridids, which reached 1 meter in length.

“Paleontologists excavating lower Cambrian rocks in southern Australia found that some anomalocaridids had huge compound eyes, up to 10 times larger than the biggest dragonfly eye, befitting what must have been a highly efficient hunter,” Dr Strausfeld said.

Anomalocaridids were first discovered as fossils in the late 19th century but not properly identified until the early 1980s. They still have paleontologists arguing over where they belong in the tree of life.

“Our discovery helps to clarify this debate. It turns out the top predator of the Cambrian had a brain that was much less complex than that of some of its possible prey and that looked surprisingly similar to a modern group of rather modest worm-like animals,” Dr Strausfeld said.

According to Dr Strausfeld and his colleagues, the brain in the Lyrarapax fossil suggests its relationship to a branch of animals whose living descendants are known as onychophorans (velvet worms). These wormlike animals are equipped with stubby unjointed legs that end in a pair of tiny claws.

Onychophorans, which are also exclusively predators, grow to no more than a few centimeters in length and are mostly found in the Southern Hemisphere, where they roam the undergrowth and leaf litter in search of beetles and other small insects, their preferred prey.

The Lyrarapax fossil resembles the neuroanatomy of today’s onychophorans in several ways. Onychophorans have a simple brain located in front of the mouth and a pair of ganglia – a collection of nerve cells – located in the front of the optic nerve and at the base of their long feelers.

“The similarities of their brains and other attributes suggest that the anomalocaridid predators could have been very distant relatives of today’s velvet worms,” Dr Strausfeld concluded.

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Peiyun Cong et al. Brain structure resolves the segmental affinity of anomalocaridid appendages. Nature, published online July 16, 2014; doi: 10.1038/nature13486