A Large Cambrian Chaetognath with Supernumerary Grasping Spines

Area of Science:

• Paleontology
• Evolutionary Biology
• Marine Biology

Background:

• Chaetognaths, or arrow worms, are a distinct phylum of marine animals with an uncertain phylogenetic position.
• Despite their ancient origins in the Cambrian period, fossilized chaetognath bodies are exceptionally rare.

Purpose of the Study:

• To describe a new genus and species of chaetognath, Capinatator praetermissus, based on newly discovered fossils.
• To investigate the paleoecology and evolutionary history of early chaetognaths.

Main Methods:

• Description of approximately 50 fossil specimens from Middle Cambrian Burgess Shale localities.
• Analysis of preserved soft tissues, body size, and feeding apparatus morphology.

Main Results:

• Capinatator praetermissus represents a new genus and species, reaching up to 10 cm in length.
• Fossils indicate a benthic or near-benthic lifestyle and a feeding apparatus with up to 25 spines per side, nearly double that of modern chaetognaths.
• The large size and predatory adaptations suggest early chaetognaths occupied different ecological niches than their planktonic descendants.

Conclusions:

• The discovery of Capinatator praetermissus provides significant insight into the early evolution and paleoecology of chaetognaths.
• Miniaturization and a planktonic lifestyle may represent secondary adaptations in the evolution of chaetognaths.