Researchers from Northwest University have discovered a new ambulacrarian fossil species, dating back 518 million years, in the Chengjiang Biota of Yunnan province. This finding, published in Current Biology on Sept 16, provides crucial insights into the evolutionary development of starfish, acorn worms, and their relatives.

Ambulacraria today include echinoderms like starfish and sea urchins, and hemichordates such as acorn worms. Despite their genetic ties, these groups display significant morphological differences, and their common ancestral body plan has long been a mystery.

Led by Han Jian and He Kaiyue from Northwest University’s Department of Geology, the research team, in collaboration with international scholars, discovered four well-preserved specimens of a new species, Yujingia glutenotunica. These fossils, ranging from 8.5 mm to 22 mm in length, were found near Kunming, Yunnan.

“These fossils show complete cylindrical trunks, U-shaped guts, and two distinct sets of appendages. The feather-like appendages likely aided in food collection and transport,” explained Han Jian. Yujingia glutenotunica is a rare example of an early ambulacrarian lacking a mineralized skeleton.

Phylogenetic analysis reveals that Yujingia glutenotunica is one of the closest known stem-group fossils to the common ancestor of modern ambulacraria. Contrary to prior beliefs of a tentacle-free ancestor, this species had developed filter-feeding appendages.

“The discovery clarifies the origins of feeding modes among ambulacraria,” Han noted. Tentacle-based and pharyngeal filter-feeding evolved independently in separate evolutionary branches.

He Kaiyue, first author and doctoral candidate, described the naming of the species, likening its shape to a traditional Chinese jade vase. Its distinctive membranous layer led to its Chinese name, Jiaomo Yujingchong.

Academician Shu Degan remarked that this discovery bridges the evolutionary gap from primitive tentacle-bearing animals to modern echinoderms and hemichordates. It provides new insights into the evolutionary shift from bilateral to pentaradial symmetry in echinoderms, enriching the understanding of the deuterostome superphylum’s origins and diversification.

About Northwest University

Northwest University, a leading institution in northwest China, is renowned for its groundbreaking research on the Cambrian Chengjiang Biota, significantly contributing to the understanding of the Cambrian explosion and early animal evolution.