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Published on: June 16, 2020
Machaeridians are Palaeozoic armoured annelids
Jakob Vinther1, Peter Van Roy, Derek E G Briggs
1Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520, USA.
Nature
|January 11, 2008
Summary
Exceptionally preserved fossils reveal machaeridians, enigmatic Palaeozoic animals, are annelids. This discovery clarifies their worm-like ancestry and early evolution of plated skeletons in marine invertebrates.
Area of Science:
- Paleontology and Evolutionary Biology
- Invertebrate Zoology
Background:
- Machaeridians are enigmatic Palaeozoic marine invertebrates known from shell plates dating from the Early Ordovician to the Carboniferous.
- Their classification has been debated for 150 years, with proposed affinities including barnacles, echinoderms, molluscs, and annelids.
Observation:
- A new machaeridian specimen from the Upper Tremadocian of Morocco preserves soft-tissue morphology, including parapodia and chaetae.
- These features are characteristic of annelid worms.
Findings:
- The discovery of soft parts definitively demonstrates the annelid affinity of machaeridians.
- This finding indicates that a lineage of annelids evolved a dorsal skeleton of calcareous plates early in their evolutionary history.
Implications:
- Resolves the long-standing systematic enigma of machaeridian classification.
- Provides insights into the early evolution of skeletal structures within the Annelida.
- Highlights the importance of exceptionally preserved fossils in understanding invertebrate paleontology and evolution.
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