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Here, we describe a large stem chaetognath,\n            <jats:italic>Timorebestia koprii<\/jats:italic>\n            gen. et sp. nov., from the lower Cambrian Sirius Passet Lagerst\u00e4tte, which exhibits lateral and caudal fins, a distinct head region with long antennae and a jaw apparatus similar to\n            <jats:italic>Amiskwia sagittiformis<\/jats:italic>\n            .\n            <jats:italic>Amiskwia<\/jats:italic>\n            has previously been interpreted as a total-group chaetognathiferan, as either a stem-chaetognath or gnathostomulid. We show that\n            <jats:italic>T. koprii<\/jats:italic>\n            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\n            <jats:italic>T. koprii<\/jats:italic>\n            suggest that early chaetognaths occupied a higher trophic position in pelagic food chains than today.\n          <\/jats:p>","DOI":"10.1126\/sciadv.adi6678","type":"journal-article","created":{"date-parts":[[2024,1,3]],"date-time":"2024-01-03T18:58:17Z","timestamp":1704308297000},"update-policy":"https:\/\/doi.org\/10.34133\/aaas_crossmark","source":"Crossref","is-referenced-by-count":21,"title":["A giant stem-group chaetognath"],"prefix":"10.1126","volume":"10","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8985-930X","authenticated-orcid":true,"given":"Tae-Yoon S.","family":"Park","sequence":"first","affiliation":[{"name":"Division of Earth Sciences, Korea Polar Research Institute, 26 Songdomirae-ro Yeonsu-gu, Incheon 21990, Republic of Korea."},{"name":"University of Science and Technology, 217 Gajeong-ro, Daejeon 34113, Republic of Korea."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4719-6317","authenticated-orcid":true,"given":"Morten Lunde","family":"Nielsen","sequence":"additional","affiliation":[{"name":"Division of Earth Sciences, Korea Polar Research Institute, 26 Songdomirae-ro Yeonsu-gu, Incheon 21990, Republic of Korea."},{"name":"School of Earth Sciences, Palaeobiology Research Group, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK."},{"name":"British Geological Survey, Nicker Hill, Keyworth NG12 5GG, UK."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3910-0346","authenticated-orcid":true,"given":"Luke A.","family":"Parry","sequence":"additional","affiliation":[{"name":"Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Martin Vinther","family":"S\u00f8rensen","sequence":"additional","affiliation":[{"name":"Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350, Denmark."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4415-2447","authenticated-orcid":true,"given":"Mirinae","family":"Lee","sequence":"additional","affiliation":[{"name":"Division of Earth Sciences, Korea Polar Research Institute, 26 Songdomirae-ro Yeonsu-gu, Incheon 21990, Republic of Korea."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8605-6272","authenticated-orcid":true,"given":"Ji-Hoon","family":"Kihm","sequence":"additional","affiliation":[{"name":"Division of Earth Sciences, Korea Polar Research Institute, 26 Songdomirae-ro Yeonsu-gu, Incheon 21990, Republic of Korea."},{"name":"University of Science and Technology, 217 Gajeong-ro, Daejeon 34113, Republic of Korea."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Inhye","family":"Ahn","sequence":"additional","affiliation":[{"name":"Division of Earth Sciences, Korea Polar Research Institute, 26 Songdomirae-ro Yeonsu-gu, Incheon 21990, Republic of Korea."},{"name":"University of Science and Technology, 217 Gajeong-ro, Daejeon 34113, Republic of Korea."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1206-6803","authenticated-orcid":true,"given":"Changkun","family":"Park","sequence":"additional","affiliation":[{"name":"Division of Earth Sciences, Korea Polar Research Institute, 26 Songdomirae-ro Yeonsu-gu, Incheon 21990, Republic of Korea."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6979-8319","authenticated-orcid":true,"given":"Giacinto","family":"de Vivo","sequence":"additional","affiliation":[{"name":"Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Napoli, Italy."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5141-1577","authenticated-orcid":true,"given":"M. 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