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A giant stem-group chaetognath.

Tae-Yoon S Park1,2, Morten Lunde Nielsen1,3,4, Luke A Parry5

  • 1Division of Earth Sciences, Korea Polar Research Institute, 26 Songdomirae-ro Yeonsu-gu, Incheon 21990, Republic of Korea.

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Summary
This summary is machine-generated.

A new fossil, *Timorebestia koprii*, from the Cambrian Sirius Passet Lagerstätte, reveals early chaetognaths were large pelagic predators. Its unique features confirm its position on the chaetognath stem, suggesting a higher trophic role in ancient marine ecosystems.

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Area of Science:

  • Paleontology
  • Evolutionary Biology
  • Marine Biology

Background:

  • Chaetognaths, or arrow worms, are ancient pelagic predators dating back to the Cambrian period.
  • Previous interpretations of related fossils like *Amiskwia sagittiformis* were uncertain regarding their phylogenetic placement.
  • Understanding early chaetognath evolution is key to reconstructing ancient marine food webs.

Purpose of the Study:

  • To describe a new large stem chaetognath fossil, *Timorebestia koprii*, from the lower Cambrian Sirius Passet Lagerstätte.
  • To determine the phylogenetic position of *T. koprii* within the chaetognath lineage.
  • To infer the ecological role of early chaetognaths in Cambrian marine ecosystems.

Main Methods:

  • Fossil description and morphological analysis of *Timorebestia koprii*.
  • Comparative anatomy with known chaetognaths and related taxa.
  • Phylogenetic analysis based on shared anatomical features, particularly the ventral ganglion.

Main Results:

  • *Timorebestia koprii* is described with features including lateral and caudal fins, antennae, and a jaw apparatus.
  • The presence of a shared ventral ganglion firmly places *T. koprii* on the chaetognath stem lineage.
  • The large size and gut contents indicate early chaetognaths were significant predators.

Conclusions:

  • *Timorebestia koprii* represents a large, early chaetognath, expanding our understanding of their ancestral morphology.
  • This discovery solidifies the phylogenetic position of certain Cambrian fossils within the chaetognath stem group.
  • Early chaetognaths likely occupied a more dominant predatory role in Cambrian pelagic ecosystems than their modern counterparts.