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An Early Cambrian stem polychaete with pygidial cirri
Jakob Vinther1, Danny Eibye-Jacobsen, David A T Harper
1Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA.
Biology Letters
|July 8, 2011
Summary
A new fossil polychaete, Pygocirrus butyricampum, from the Early Cambrian Sirius Passet fauna reveals pygidial cirri. This finding indicates key annelid crown group traits evolved earlier than previously thought.
Area of Science:
- Paleontology
- Evolutionary Biology
- Zoology
Background:
- The oldest annelid fossils, polychaetes from the Cambrian Period, are crucial for understanding annelid evolution.
- Annelid crown group diversification occurred during the Cambrian-Ordovician transition.
- Pygidial cirri are a defining characteristic of the annelid crown group.
Purpose of the Study:
- To describe a new fossil polychaete species from the Early Cambrian Sirius Passet fauna.
- To investigate the evolutionary origins of key annelid crown group characteristics.
Main Methods:
- Fossil description and analysis of morphological features.
- Comparative analysis with existing annelid fossil records and extant taxa.
Main Results:
- Description of Pygocirrus butyricampum gen. et sp. nov., a slender-bodied polychaete with biramous parapodia and chaetae.
- Identification of pygidial cirri in Pygocirrus butyricampum, representing the first record of this structure in Cambrian annelids.
- Evidence that pygidial cirri, a defining character of the annelid crown group, were present in the total group by the Early Cambrian.
Conclusions:
- Pygocirrus butyricampum provides insights into the early evolution of annelids.
- The presence of pygidial cirri in this Early Cambrian fossil suggests an earlier origin for the annelid crown group than previously established.
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