Kylinxia zhangi: Cambrian Shrimp-Like Arthropod Had Five Eyes
Paleontologists in China have uncovered exceptionally preserved fossils of a previously unknown genus and species of extinct arthropod, Kylinxia zhangi, that provides important insights into the phylogenetic relationships among early arthropods, the evolutionary transformations and disparity of their frontal appendages, and the origin of crucial evolutionary innovations in the phylum Euarthropoda.
Kylinxia zhangi swam in the Early Cambrian seas, approximately 518 million years ago.
The six specimens with well-preserved soft parts of this ancient creature were found in the Yu’anshan Formation in Yunnan province, southern China.
They show an unexpected mix of distinctive features of true arthropods as well as more ancient features.
Kylinxia zhangi had a fused head shield, a segmented trunk, and jointed legs.
But it also had raptorial frontalmost appendages and five stalked compound eyes, of which the anterior (forward-facing) two are at least twice as large as the posterior three.
“This configuration of eyes is reminiscent of the peculiar five eyes in Opabinia regalis,” the paleontologists said.
Kylinxia zhangi was a member of the Chengjiang biota, the most diverse assemblage of Early Cambrian marine fossils known.
“Among the Chengjiang fauna, the giant top predator Anomalocaris is considered the ancestral form of arthropod,” the researchers said.
“But huge morphological differences exist between Anomalocaris and true arthropods. There is a great evolutionary gap between the two that can hardly be bridged.”
“Our results indicate that the evolutionary placement of Kylinxia zhangi is right between Anomalocaris and the true arthropods,” said co-author Professor Maoyan Zhu, a paleontologist at the Nanjing Institute of Geology and Palaeontology.
“Therefore, our finding reached the evolutionary root of the true arthropods.”
“Kylinxia zhangi represents a crucial transitional fossil predicted by Darwin’s evolutionary theory,” added lead author Dr. Han Zeng, also from the Nanjing Institute of Geology and Palaeontology.
“It bridges the evolutionary gap from Anomalocaris to true arthropods and forms a key ‘missing link’ in the origin of arthropods, contributing strong fossil evidence for the evolutionary theory of life.”
The team’s paper was published in the journal Nature.
H. Zeng et al. An early Cambrian euarthropod with radiodont-like raptorial appendages. Nature, published online November 4, 2020; doi: 10.1038/s41586-020-2883-7