Lyrarapax unguispinus
July 17, 2014

Lower Cambrian Predator Had A Simple Brain

April Flowers for - Your Universe Online

Approximately 520 million years ago, during the Lower Cambrian, the world's oldest known predator lived beneath the ocean's surface. An international team of scientists has identified what they call "an exquisitely preserved" brain in the fossil of a group of animals known as anomalocaridids, or "abnormal shrimp." The researchers were surprised to find that the brain of this predator was less complex than those found in fossils of some of the animal's prey.

The anomalocaridids, discovered in the 19th century but not properly identified until the early 1980s, were the top predators of their time. Scientists are still debating where these fierce looking creatures fit on the tree of life.

"Our discovery helps to clarify this debate," Nicholas Strausfeld, director of the University of Arizona's Center for Insect Science, said in a recent statement. "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."

The brain was found in the fossil of a new species of anomalocaridids called Lyrarapax unguispinus (Latin for "spiny-clawed lyre-shaped predator"). The team believes the structure of the brain suggests that this species is related to the modern day onychophorans, or velvet worms, which have stubby unjointed legs that end in tiny claws.

Velvet worms are exclusively predators that grow no more than a few inches in length with two long feelers that extend from the head, attached in front of a pair of small eyes. For the most part, they are found in the Southern Hemisphere. The worms' hunting ground is the undergrowth and leaf litter where their preferred prey are beetles and other small insects.

The Lyrarapax fossil bears an anatomical resemblance to the neuroanatomy of modern velvet worms in several ways. Velvet worms have a simple brain located in front of the mouth and a pair of ganglia located in front of the optic nerve and at the base of the long feelers. Strausfeld said that this is exactly the same architecture found in the fossil.

"These top predators in the Cambrian are defined by just their single pair of appendages, wicked-looking graspers, extending out from the front of their head," according to Strausfeld. "These are totally different from the antennae of insects and crustaceans. Such frontally disposed appendages are not found in any other living animals with the exception of velvet worms."

The team, which included scientists from the Natural History Museum of London and Yunnan University in China, say that the similarities of the brains and anatomies suggest that the fossil predators could have been distant relatives of the modern velvet worm.

"This is another contribution towards the new field of research we call neuropaleontology," said Xiaoya Ma of the Natural History Museum in London. "These grasping appendages are a characteristic feature of this most celebrated Cambrian animal group, whose affinity with living animals has troubled evolutionary scientists for almost a century. The discovery of preserved brain in Lyrarapax resolves specific anatomical correspondences with the brains of onychophorans."

"Being able to directly associate appendages with parts of the brain in Cambrian animals is a huge advantage," said Gregory Edgecombe, also at the Natural History Museum. "For many years now paleontologists have struggled with the question of how different kinds of appendages in Cambrian fossils line up with each other and with what we see in living arthropods. Now for the first time, we didn't have to rely just on the external form of the appendages and their sequence in the head to try and sort out segmental identities, but we can draw on the same tool kit we use for extant arthropods – the brain."

Combining this study with previous research, the team has identified the three groups of arthropods in existence today. The researchers believe these same groups coexisted in the Lower Cambrian.

The study results are scheduled to be published online in the journal Nature.

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