King of Cambrian predators had brain of a worm

16 July 2014

A team of scientists has used the spectacular discovery of a rare fossil brain to reassign the ancestry of a 520-million-year-old animal. 

The exquisitely preserved brain of the ancient fossil, one of three new specimens given the name Lyrarapax unquispinus, was discovered in 2009 as part of the Chengjiang fossil deposits in the Chinese province of Yunnan, originally uncovered in 1984. 

Controversial origins

Scientists have always argued over where the group of long-extinct animals known as anomalocaridids, meaning 'abnormal shrimp', belongs in the tree of life. 

Anomalocaridids are one of the first-known predators and lived during the Cambrian, when life only existed in the sea.

new species Lyrarapax unquispinus

Artist impression of Lyararapax, one of the first known predators chasing primitive fishes © Nicholas Strausfeld/University of Arizona.

Traditionally, the animal's set of claw-like appendages at the front of its head were associated with either insect antennae or to pincers of living arthropods, such as scorpions. 

But geochemical analysis and electron microscope scanning suggest that the structure of its brain and single pair of appendages at the front of the head compare most closely to a group of living animals known as onychophorans, or velvet worms. 

The research was carried out at the Museum by Cambrian experts Dr Greg Edgecombe and Dr Xiaoya Ma and their collaborators in China and the US.

Onychophorans, also exclusively predators, grow to about 10cm 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. 

Dr Ma said the preserved brain discovery is the first time a complete overview of the Cambrian predator has been possible, and has provided information not previously available from external morphology, the study of the form and structure of organisms. 

'This has further established the new field of research we call neuropalaeontology, which has only existed for the past few years,' she said.

Evolutionary answers

Dr Ma also said the research, which was presented in a paper in Nature this week, provided crucial information to help answer evolutionary questions about arthropods. 

How the mouth parts of ancient animals evolved remains debatable. This recent research suggests that a pair of appendages, as seen in anomalocaridids, could have migrated backwards to form the labrum, a structure that borders the mouth in contemporary arthropods.

Adapting to survive

The biggest of three Lyrarapax fossils now known was about 8cm long. Some anomalocaridids reached more than a metre in length, all had swimming flaps, one pair of spiny grasping legs and huge compound eyes, up to 10 times larger than the biggest dragonfly eye, making them highly efficient hunters.

The Cambrian Period, between approximately 541 and 486 million years ago, marked a profound change in life on Earth with an explosion of complex organisms.

Lead author of the paper Dr Nicholas Strausfeld, Director of the University of Arizona's Center for Insect Science, said that the fossil brain discovery provides hugely valuable evidence for sorting out how Cambrian fossils line up with living arthropods.

'It also suggests that these ancient predators drove the evolution of more complex brains to be able to recognise potential danger and rapidly coordinate escape movements in order to survive.'

  • by Nicola Pearson
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