Paleontologists from Yunnan University, the University of Leicester and the Natural History Museum, London have conducted a microtomographic study of new specimens of the Early Cambrian shrimp-like arthropod Kylinxia zhangi.
Life reconstruction of Kylinxia zhangi. Image credit: X. Wang.
Kylinxia zhangi swam in the Early Cambrian seas, approximately 518 million years ago
First described in 2020, the ancient arthropod was about 5 cm (2 inches) long and about 1.2 cm (0.5 inches) wide.
Kylinxia zhangi was part of the Chengjiang biota of China’s Yunnan Province, from which over 250 species of exceptionally preserved fossil organisms have been described.
The size of a large shrimp, its surprising features include three eyes on the head and a pair of fearsome limbs presumably used to catch prey.
“Kylinxia zhangi occupies a pivotal position in arthropod evolution, branching from the euarthropod stem lineage between radiodonts (Anomalocaris and relatives) and ‘great-appendage’ arthropods,” said University of Leicester Ph.D. student Robert O’Flynn and colleagues.
“Its combination of appendage and exoskeletal features is viewed as uniquely bridging the morphologies of so-called ‘lower’ and ‘upper’ stem-group euarthropods.”
In their research, O’Flynn and co-authors examined several new specimens of Kylinxia zhangi.
Because the new material is preserved nearly complete, they were able to image the animal’s head, identifying six segments: the front one bearing eyes, the second with a pair of large grasping limbs, and the other four each bearing a pair of jointed limbs.
“The preservation of the fossil animal is amazing,” O’Flynn said.
“After CT-scanning we can digitally turn it around and literally stare into the face of something that was alive over 500 million years ago.”
“As we spun the animal around, we could see that its head possesses six segments, just as in many living arthropods.”
“Kylinxia zhangi, and the Chengjiang biota whence it came, are instrumental to building our understanding of early euarthropod evolution,” said University of Leicester’s Professor Mark Williams.
“We were examining the micro-CT data in the hope of refining and correcting previous interpretation of head structures in this genus, Kylinxia,” said Yunnan University’s Professor Yu Liu.
“Amazingly, we found that its head is composed of six segments, as in, e.g., insects.”
“Most of our theories on how the head of arthropods evolved were based on these early-branching species having fewer segments than living species,” said Dr. Greg Edgecombe, a paleontologist at Yunnan University and the Natural History Museum, London.
“Discovering two previously undetected pairs of legs in Kylinxia zhangi suggests that living arthropods inherited a six-segmented head from an ancestor at least 518 million years ago.”
The team’s results appear in the journal Current Biology.
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Robert J. O’Flynn et al. The early Cambrian Kylinxia zhangi and evolution of the arthropod head. Current Biology, published online August 28, 2023; doi: 10.1016/j.cub.2023.08.022
