Yujingia glutenotunica fossil challenges starfish ancestor origins
- Fossils discovered in southwestern China suggest that an extinct animal called Yujingia glutenotunica lived close to the evolutionary roots of ambulacrarians, challenging the long-standing scientific picture of how...
- Yujingia lived during the Cambrian explosion, when most major animal groups first appeared in the fossil record.
- Two sets of appendages reveal how the animals likely lived on the ancient seafloor.
Fossils discovered in southwestern China suggest that an extinct animal called Yujingia glutenotunica lived close to the evolutionary roots of ambulacrarians, challenging the long-standing scientific picture of how the starfish family began.
Discovering Yujingia glutenotunica in the Maotianshan Shales
Yujingia lived during the Cambrian explosion, when most major animal groups first appeared in the fossil record. Much of the evidence from this period comes from creatures with hard shells or skeletons, because soft bodies usually decayed before leaving detailed traces. However, the Maotianshan Shales in China’s Yunnan Province offered a rare window into that otherwise missing history by preserving the bodies, guts, and appendages of Yujingia without mineralized skeletons. The recovered specimens measure 8 to 22 millimeters, which is about 0.31 to 0.87 inches long.
Two sets of appendages reveal how the animals likely lived on the ancient seafloor. Suspended organic debris was collected by feather-shaped feeding tentacles, while an additional set probably kept the creatures temporarily pinned against the ocean floor. Although they spent time attached to the bottom, researchers indicate they probably could move to some degree. Its outline closely resembles a traditional Chinese ritual vase known as a yujingping, and a pale, original membrane enclosing the visceral mass inspired the species name for its gelatinous appearance.
Reconstructing the Ambulacrarian Common Ancestor
Ambulacraria is one of the two major branches of deuterostome animals, first classified in the 1880s, and includes echinoderms like starfish alongside hemichordates like acorn worms. Chordates represent the other major branch and include humans. Reconstructing the ancestral ambulacrarian helps researchers understand how these lineages developed different bodies and ways of feeding. To place Yujingia in the animal family tree, co-author Dr. Giovanni Mussini from the University of Cambridge and lead author Kaiyue He assembled a dataset of 505 anatomical characteristics across 100 living and extinct taxa using Bayesian phylogenetic reconstruction.
There has been a tendency to think of the last common ancestor of ambulacrarians as more closely resembling a worm living in its seafloor burrow, filtering food from the water,
Mussini said in the published findings. This new fossil suggests instead that the common ancestor of the ambulacrarians might have actually fed with tentacles and may have been more like starfish and their relatives.
Mussini added that the fivefold radial symmetry of starfish and the bilaterally symmetrical, worm-like bodies of acorn worms had remained a mystery until now.
Connecting Early Cambrian Fossils to Modern Lineages
The phylogenetic analysis placed Yujingia closer to the last common ancestor of living ambulacrarians than previously described fossils. Rather than establishing it as the ancestor itself, the statistical evaluation identifies it as a particularly informative relative near that ancestral branch. Bridging early Cambrian tentacled organisms with the modern branches of echinoderms and hemichordates, its mixed features imply that a complex nutritional apparatus developed prior to the evolution of rigid echinoderm skeletons.
How the major deuterostome groups diverged during the Cambrian explosion is one of the central questions in animal evolution. Yujingia helps connect primitive, tentacle-bearing animals living on the seafloor with modern echinoderms and hemichordates. It offers a new way to understand the profound transition from bilateral symmetry to the fivefold radial body plan of echinoderms and adds an important fossil to a crucial gap in the early animal tree of life.
Degan Shu
The fossils also connect anatomy with lifestyle by showing how ecological demands can drive different lineages onto distinct paths. Chordates became reliant on movement to find food, streamlining their bodies and developing brains, while members of the starfish lineage remained anchored to the seafloor and specialized in particle feeding. The research, published in Current Biology, was supported in part by the Natural Environment Research Council, which is part of UK Research and Innovation.