The fossilised 520-million-year-old creature shown above had five eyes on stalks, but that’s only part of its attraction. Its body structure combines features from different groups of arthropods, researchers have discovered, providing new insights into the early evolutionary history of the most successful animals on Earth.
Three-quarters of all modern animals are anthropods but understanding their early history has been a challenge in evolutionary biology.
“Kylinxia represents a crucial transitional fossil predicted by Darwin’s evolutionary theory,” says Zeng Han from Nanjing Institute of Geology and Palaeontology in China, first author of a paper in the journal Nature.
The previously undescribed species Kylinxia zhangi is named after a chimeric creature in Chinese mythology called Kylin and the Chinese word for shrimp. Six specimens were discovered in the Chengjiang Biota in Yunnan, which offers the most complete early animal fossils of the Cambrian era.
“Owing to very special taphonomic conditions, the Kylinxia fossils exhibit exquisite anatomical structures,” says co-author Zhao Fangchen. “For example, nervous tissue, eyes and digestive system: these are soft body parts we usually cannot see in conventional fossils”
Detailed anatomical examination shows that Kylinxia has distinctive features of true arthropods, including a hardened cuticle, a segmented trunk and jointed legs.
However, it also has characteristics present in very ancestral forms, including the five eyes of Opabinia, known as the Cambrian “weird wonder”, and the raptorial appendages of Anomalocaris, the giant apex predator in the Cambrian ocean.
Anomalocaris, which could reach two metres in length, has been regarded as an ancestral form of arthropod, but there are big morphological differences between it and true arthropods, and this has been considered a crucial “missing link” in the origin of arthropods.
“Our results indicate that the evolutionary placement of Kylinxia is right between Anomalocaris and the true arthropods,” says co-author Zhu Maoyan. “Therefore, our finding reached the evolutionary root of the true arthropods.”
As such, adds Zheng, it contributes “strong fossil evidence for the evolutionary theory of life”.
Related reading: Meet a 500-million-year-old micro monster