Editing Chaetognatha (section)

== Fossil record ==
Due to their soft bodies, chaetognaths fossilize poorly. Even so, several fossil chaetognath species have been described.<ref name="Vannier2007" /> Chaetognaths first appear during the [[Cambrian]] Period. Complete body fossils have been formally described from the Lower [[Cambrian]] [[Maotianshan shales]] of [[Yunnan, China]] (''Eognathacantha ercainella'' Chen & Huang<ref>{{cite journal | vauthors = Chen JY, Huang DY | title = A possible Lower Cambrian chaetognath (arrow worm) | journal = Science | volume = 298 | issue = 5591 | pages = 187 | date = October 2002 | pmid = 12364798 | doi = 10.1126/science.1075059 | s2cid = 544495 }}</ref> and ''Protosagitta spinosa'' Hu<ref>{{cite journal | vauthors = Hu SX |year=2005 |title=Taphonomy and palaeoecology of the Early Cambrian Chengjiang Biota from Eastern Yunnan, China |journal=Berliner Paläobiologische Abhandlungen |volume=7 |pages=1–197}}</ref>) and the Middle Cambrian [[Burgess Shale]] of British Columbia (''[[Capinatator praetermissus]]''.) A Cambrian [[stem-group]] chaetognath, ''[[Timorebestia]]'', first described in 2024, was much larger than modern species, showing that chaetognaths occupied different roles in marine ecosystems compared to today.<ref name="Park2024">{{cite journal |doi=10.1126/sciadv.adi6678 |title=A giant stem-group chaetognath |date=2024 |last1=Park |first1=Tae-Yoon S. |last2=Nielsen |first2=Morten Lunde |last3=Parry |first3=Luke A. |last4=Sørensen |first4=Martin Vinther |last5=Lee |first5=Mirinae |last6=Kihm |first6=Ji-Hoon |last7=Ahn |first7=Inhye |last8=Park |first8=Changkun |last9=De Vivo |first9=Giacinto |last10=Smith |first10=M. Paul |last11=Harper |first11=David A. T. |last12=Nielsen |first12=Arne T. |last13=Vinther |first13=Jakob |journal=Science Advances |volume=10 |issue=1 |pages=eadi6678 |doi-access=free |pmid=38170772 |pmc=10796117 |bibcode=2024SciA...10I6678P }}</ref> A more recent chaetognath, ''Paucijaculum samamithion'' Schram, has been described from the [[Mazon Creek]] biota from the [[Pennsylvanian (geology)|Pennsylvanian]] of Illinois. 


Chaetognaths were thought possibly to be related to some of the animals grouped with the [[conodont]]s. The conodonts themselves, however, have been shown to be dental elements of [[vertebrates]]. It is now thought that [[protoconodont]] elements (e.g., ''[[Protohertzina]] anabarica'' Missarzhevsky, 1973), are probably grasping spines of chaetognaths rather than teeth of conodonts. Previously chaetognaths in the Early Cambrian were only suspected from these protoconodont elements, but the more recent discoveries of body fossils have confirmed their presence then.<ref>{{cite journal | vauthors = Szaniawski H |year=2002 |title=New evidence for the protoconodont origin of chaetognaths |journal=[[Acta Palaeontologica Polonica]] |volume=47 |issue=3 |url=http://www.app.pan.pl/archive/published/app47/app47-405.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.app.pan.pl/archive/published/app47/app47-405.pdf |archive-date=2022-10-09 |url-status=live | pages=405–419 }}</ref> There is evidence that chaetognaths were important components of the oceanic [[food web]] already in the Early Cambrian.<ref>{{cite journal |doi=10.1098/rspb.2006.3761 |title=Early Cambrian origin of modern food webs: Evidence from predator arrow worms |date=2007 |last1=Vannier |first1=J. |last2=Steiner |first2=M. |last3=Renvoisé |first3=E. |last4=Hu |first4=S.-X |last5=Casanova |first5=J.-P |journal=Proceedings of the Royal Society B: Biological Sciences |volume=274 |issue=1610 |pages=627–633 |pmid=17254986 |pmc=2197202 }}</ref>