Hyoliths are Palaeozoic lophophorates.

Area of Science:

• Paleontology
• Evolutionary Biology
• Cambrian Fossils

Background:

• Hyoliths are abundant, globally distributed Cambrian fossils with unresolved ecological and evolutionary importance.
• Their poorly understood soft anatomy and unique scleritome have led to varied taxonomic classifications, often as incertae sedis or related to molluscs.

Purpose of the Study:

• To reconstruct the soft anatomy and ecological role of the mid-Cambrian hyolith Haplophrentis.
• To clarify the phylogenetic position of hyoliths within the animal kingdom.

Main Methods:

• Examination of over 1,500 specimens of Haplophrentis from the Burgess Shale and Spence Shale Lagerstätten.
• Reconstruction of soft tissues, including feeding and digestive organs, based on exceptionally preserved specimens.

Main Results:

• Haplophrentis is reconstructed as a semi-sessile, epibenthic suspension feeder.
• Exceptionally preserved soft tissues reveal a lophophore and a U-shaped digestive tract with a dorsolateral anus.
• These features indicate an affinity with lophophorates (brachiopods, phoronids, tommotiids).

Conclusions:

• The findings establish a clear relationship between hyoliths and lophophorates.
• This significantly increases the known morphological disparity of hyoliths.
• The study resolves the long-standing taxonomic uncertainty surrounding this prominent fossil group.