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| Reconstruction of Timorebestia koprii gen et sp. nov. in the pelagic ecosystem preserved in Sirius Passet. Other taxa shown in the foreground are Kiisortoqia, Siricaris, Kerygmachela, Pauloterminus, Kleptothule, and Isoxys. Further in the background is two radiodonts: Tamisiocaris and an amplectobeluid. Park, Nielsen, Parry, Sørensen, Lee, ... et Vinther, 2024. Artwork by Robert Nicholls/BobNichollsArt. |
Abstract
Chaetognaths, with their characteristic grasping spines, are the oldest known pelagic predators, found in the lowest Cambrian (Terreneuvian). Here, we describe a large stem chaetognath, Timorebestia koprii gen. et sp. nov., from the lower Cambrian Sirius Passet Lagerstätte, which exhibits lateral and caudal fins, a distinct head region with long antennae and a jaw apparatus similar to Amiskwia sagittiformis. Amiskwia has previously been interpreted as a total-group chaetognathiferan, as either a stem-chaetognath or gnathostomulid. We show that T. koprii shares a ventral ganglion with chaetognaths to the exclusion of other animal groups, firmly placing these fossils on the chaetognath stem. The large size (up to 30 cm) and gut contents in T. koprii suggest that early chaetognaths occupied a higher trophic position in pelagic food chains than today.
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| Holotype (MGUH 34286) of Timorebestia koprii gen et sp. nov. (A to C) Entire specimen. (D and E) Jaw apparatus in the anterior region of trunk. |
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| Isoxys predation (A to C) Timorebestia koprii gen et sp. nov. MGUH 34291, specimen with several specimens of the bivalved arthropod Isoxys volucris in its gut. (A) Specimen photographed with reflective light. (B) Specimen photographed with low angle light illuminated from top left. (C) Interpretative drawing (color guide: green, gut; dark yellow, Isoxys specimens). |
Systematic paleontology
Unranked clade Spiralia Scleip, 1929
Unranked clade Chaetognathifera Bekkouche and Gąsiorowski, 2022
Phylum Chaetognatha Leuckart, 1854 (stem group)
Timorebestia koprii gen. et sp. nov.
Diagnosis for genus and species: Wide-bodied “amiskwiiform” with lateral fins along most of the trunk length. The body and the lateral fins taper distally and terminate in a well-developed rounded caudal fin. Distinct fin rays are present with no rayless zone separating the trunk and tail fins. Anterior region of trunk tapers markedly into a short head bearing a pair of long antennae, which are about half the length of the body. An internal jaw apparatus in the anterior trunk region consists of a pair of larger subtriangular elements connected by a symphysis, a pair of blunt anterior elements, and a single anterior, presumed ventral/basal, plate. Longitudinal muscles occurring in discrete bands are present in the trunk with additional sparse and delicate outer circular/transverse muscles. The digestive tract extends from the trunk-head transition and terminates anterior to the caudal fin with no septum separating the caudal region from the trunk.
Locality and horizon: T. koprii occurs in several horizons at the main Lagerstätte locality in Sirius Passet, ..., Peary Land, North Greenland. Collections from which material is derived have been focused on an exposed section that totals 12 m, with collection focused on a particular fossiliferous interval between 5 and 7 m.
Etymology: Genus name: Timor, (Latin) for causing fear or dread and bestia (Latin), meaning beast. The species name is after Korea Polar Research Institute (KOPRI) for their support of the past, and ongoing, field expeditions to Sirius Passet.
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| evolution of food web tiering. Schematic presentation of the preserved and inferred components of the pelagic food web in Sirius Passet during the early Cambrian in comparison to modern pelagic food webs, highlighting the downward shift of arthropods and chaetognaths that took place during the Paleozoic as jawed vertebrates evolved to dominate the upper tiers in the food chain. |
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| Reconstruction of Timorebestia koprii gen et sp. nov. in the pelagic ecosystem preserved in Sirius Passet. Other taxa shown in the foreground are Kiisortoqia, Siricaris, Kerygmachela, Pauloterminus, Kleptothule, and Isoxys. Further in the background is two radiodonts: Tamisiocaris and an amplectobeluid. Artwork by Robert Nicholls/BobNichollsArt. |
Tae-Yoon S. Park, Morten Lunde Nielsen, Luke A. Parry, Martin Vinther Sørensen, Mirinae Lee, ... and Jakob Vinther. 2024. A GIANT STEM-GROUP CHAETOGNATH. SCIENCE ADVANCES. 10(1); DOI: 10.1126/sciadv.adi6678
