110 / 2025-03-31 23:07:09

Exploring the mineralization and evolutionary significance of early Cambrian hyoliths

biomineralization,Cambrian,hyoliths

Theme 3: Earth-Life Co-evolution Through Time > Session 3a: Precambrian Earth and Life Co-evolution

Hyoliths are one of the earliest groups within the superphylum Lophotrochozoa to acquire mineralization capabilities. Their morphology and microstructure of mineralized skeletons evolved radially during the early Cambrian, making them a significant component of the Cambrian marine communities. However, their systematization and phylogenetic relationships with other lophotrochozoans remain disputed. In this study, hyolith fossils from the Xinji Formation (Series 2, Cambrian) in North China were reported. Some of hyolith conchs displayed unique bidirectional or unidirectional foliated aragonite structures. These structures, typically preserved close to the aperture of the conchs, exhibit a characteristic complex shell microstructure with multiple layers. The layers of the bidirectional foliated aragonite are arranged in a staircase-mode along the dorsoventral axis in mirror symmetry, whereas crystallites of unidirectional foliated aragonite structures are consistently arranged in a counterclockwise direction. Very interestingly, similar foliated aragonite structures were also discovered in some helcionelloid species from the Cambrian Terreneuvian in southwestern Mongolia. These unique foliated-like microstructure in hyoliths and molluscs sustain the deep homology of biomineralization between the two groups, further confirming their closer phylogenetic relationships. This study also demonstrates the significant value of biomineralization in phylogenetic analyses, particularly in solving the long-standing puzzle concerning the phylogenetic affinity of extinct biomineralizers like hyoliths.