TOKYO • The discovery of a five-eyed shrimp-like creature that lived about 520 million years ago may end a long-running debate about the evolution of Earth's most common animals.
Arthropods, ranging from lobsters and crabs to spiders and millipedes, make up about 80 per cent of all animal species alive today and are characterised by their hard exoskeleton. But their evolution has long been something of a mystery because their ancient ancestors had a variety of features their modern counterparts do not.
The discovery of Kylinxia zhangi, a shrimp-like creature preserved in fossils found in China's Yunnan province this week holds the key to the "missing link" in arthropod evolution.
Like today's arthropods, Kylinxia had a hard shell, a segmented body and legs with joints. But the ancient creature also had characteristics in common with even older animals, leading researchers to name it after "Kylin", a creature in Chinese mythology with attributes from a variety of animals.
Like an ancient creature called Opabinia, known informally as a "weird wonder", Kylinxia had three smaller eyes in a row on its head, with two larger ones behind. It also had two spiky front appendages, just like another creature thought to be an arthropod ancestor: the Anomalocaris.
But scientists have, in the past, had difficulties linking both those ancient creatures to modern arthropods - until they found Kylinxia zhangi.
"Kylinxia represents a crucial transitional fossil predicted by Darwin's evolutionary theory," said Dr Han Zeng, first author of a study published in the journal Nature on Wednesday.
"It bridges the evolutionary gap from Anomalocaris to true arthropods and forms a key 'missing link' in the origin of arthropods," said Dr Zeng at the Nanjing Institute of Geology and Palaeontology.
Professor Huang Diying, the study's corresponding author, said: "It looked strange, like a frontal appendage of Anomalocaris attached to the body of a common arthropod. After careful preparation, I knew it was a new and very important arthropod."