{{Short description|Extinct family of arthropods}} {{Automatic taxobox | taxon = Hurdiidae | fossil_range = {{Fossil range|Cambrian Stage 3|Emsian}} | image = 20220724 Hurdiidae.png | image_caption = ''Stanleycaris'' (top left), ''Hurdia'' (top right), ''Aegirocassis'' (middle), ''Peytoia'' (bottom left), ''Cambroraster'' (bottom right) | authority = Vinther ''et al.'', 2014 | subdivision_ranks = Genera | subdivision = See text }}
'''Hurdiidae''' (synonymous with the previously named '''Peytoiidae'''<ref name="McCall-2023">{{Cite journal |last=McCall |first=Christian R.A. |date=2023-12-13 |title=A large pelagic lobopodian from the Cambrian Pioche Shale of Nevada |url=https://www.cambridge.org/core/product/identifier/S002233602300063X/type/journal_article |journal=Journal of Paleontology |language=en |volume=97 |issue=5 |pages=1009–1024 |bibcode=2023JPal...97.1009M |doi=10.1017/jpa.2023.63 |issn=0022-3360 |s2cid=266292707|url-access=subscription }}</ref>) is an extinct cosmopolitan family of radiodonts, a group of stem-group marine arthropods, which lived during the Paleozoic Era. It is the most long-lived radiodont clade, lasting from the Cambrian period to the Devonian period.
==Description== <gallery widths="180"> File:20191213 Radiodonta frontal appendage Hurdiidae.png|Anatomy of the frontal appendage of a hurdiid File:20191229 Radiodonta frontal appendage Hurdiidae.png|Frontal appendages of various species of hurdiid File:20200803 Radiodonta Hurdiidae H-element.png|Dorsal carapaces of various species of hurdiid </gallery>
Hurdiidae is characterized by frontal appendages with distal region composed of 5 subequal blade-like endites, alongside the enlarged head carapaces and tetraradial mouthpart (oral cone).<ref name="Moysiuk-2019" />
The frontal appendages of hurdiids have a distinctive morphology, with the appendage of most species bearing five equally-sized elongate blade-like ventral spines known as endites.<ref name=Pates19/> Subsequent podomeres were reduced in size and with only small endites or none. Each podomere bore only a single endite, unlike other radiodonts, in which the endites were paired.<ref name=Pates19/> In most species, the endites were curved medially, so that the appendages formed a basket-like structure.<ref name="Moysiuk-2019" /> Some hurdiids had greater numbers of endites, with ''Cordaticaris'' bearing seven endites of equal length.<ref name=sun20/>
Hurdiids exhibited a wide range of body size. The smallest known hurdiid specimen, of an unnamed species, is estimated to have had a body length of {{convert|6|–|15|mm|in}}, but it is not known whether this specimen was a juvenile or an adult.<ref name=pates20/> ''Aegirocassis'', the largest known hurdiid, was over {{convert|2|m|ft}} long, comparable in size to the largest known arthropods.<ref name=vanroy15/>
==Paleobiology==
The majority of hurdiids appear to have been predators that fed by sifting sediment with their frontal appendages, but some members, like ''Aegirocassis'', ''Pseudoangustidontus'', and possibly ''Cambroraster'', were suspension feeders.<ref name="Moysiuk-2019" /><ref>{{Cite journal |last1=De Vivo |first1=Giacinto |last2=Lautenschlager |first2=Stephan |last3=Vinther |first3=Jakob |date=2021-07-28 |title=Three-dimensional modelling, disparity and ecology of the first Cambrian apex predators |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=288 |issue=1955 |article-number=20211176 |doi=10.1098/rspb.2021.1176 |issn=0962-8452 |pmc=8292756 |pmid=34284622}}</ref><ref name="Potin-2023" />
==Distribution==
Hurdiids had a global distribution.<ref name=sun20/> The earliest known hurdiid in the fossil record is ''Peytoia infercambriensis'', which lived during the third age of the Cambrian in what is now the country of Poland.<ref name=daley15/> The group increased in diversity during the Miaolingian epoch.<ref name=sun20/> Post-Cambrian records of the group are rare, but the group lasted into the Devonian period, with the last known taxon being the Emsian ''Schinderhannes bartelsi'' from what is now Germany.<ref name=daley15/><ref name=pates20/>
==Classification==
Hurdiidae is classified within Radiodonta, a clade of stem-group arthropods. Hurdiidae is defined phylogenetically as the most inclusive clade containing ''Hurdia victoria'' but not ''Amplectobelua symbrachiata'', ''Anomalocaris canadensis'', or ''Tamisiocaris borealis''.<ref name=vinther14/> Some authors have argued that Peytoiidae, which was named by Conway Morris and Robison, 1982, has priority over Hurdiidae, and that Hurdiidae has "yet to be properly established following ICZN standards", due to its first definition not having a character-based diagnosis, and the second being published in an online-only journal without being registered in the ZooBank database.<ref name="McCall-2023" /><ref>{{cite web |last1=Greenfield |first1=Tyler |date=17 January 2023 |title="Hurdiidae" versus Peytoiidae |url=https://incertaesedisblog.wordpress.com/2023/01/17/hurdiidae-versus-peytoiidae/ |website=Incertae Sedis |language=en}}</ref>
Cladogram of Hurdiidae after Moysiuk & Caron, 2025:<ref name="MoysiukCaron2025">{{cite journal |last1=Moysiuk |first1=Joseph |last2=Caron |first2=Jean-Bernard |date=May 2025 |title=Early evolvability in arthropod tagmosis exemplified by a new radiodont from the Burgess Shale |journal=Royal Society Open Science |volume=12 |issue=5 |bibcode=2025RSOS...1242122M |doi=10.1098/rsos.242122 |doi-access=free|pmc=12076883 |pmid=40370603 |article-number=242122}}</ref> {{clade| style=font-size: 100%; line-height:100% |label1=Hurdiidae |1={{clade |1=''Mosura fentoni'' 80px |2= {{clade |1=''Schinderhannes bartelsi'' 70px |2={{clade |1={{clade |1=''Stanleycaris hirpex'' 80px |2=''Peytoia nathorsti'' 80px }} |label2= |2={{clade |1=''Aegirocassis benmoulai'' 100px |label2=Hurdiinae |2={{clade |1={{clade |1=''Hurdia victoria'' 80px |2=''Hurdia triangulata'' 80px }} |2={{clade |1=''Pahvantia hastata'' 70px |2={{clade |1=''Cordaticaris striatus'' 70px |2={{clade |1=''Titanokorys gainesi'' 70px |2=''Cambroraster falcatus'' 80px }} }} }} }} }} }} }} }} }}
Species include:
* ''Falciscaris mumakiana''<ref>{{cite journal |last1=Gaëtan J.-M. |first1=Potin |last2=Claisse |first2=Pénélope |date=2 December 2025 |title=A new giant nektobenthic radiodont benthivore from the Early Ordovician Fezouata Biota in Morocco |journal=Acta Palaeontologica Polonica |volume=70 |issue=4 |pages=709–722 |doi=10.4202/app.01278.2025}}</ref> * ''Mosura fentoni''<ref name="MoysiukCaron2025" /> * ''Peytoia nathorsti''<ref name="CaronMoysiuk" /> * ''Peytoia infercambriensis''<ref name="Pates19" /> * ''Schinderhannes bartelsi''<ref name="CaronMoysiuk" /> * ''Stanleycaris hirpex''<ref name="CaronMoysiuk" /> * ''Stanleycaris qingjiangensis''<ref>{{Cite journal |last=Wu |first=Yu |last2=Pates |first2=Stephen |last3=Zhang |first3=Mingjing |last4=Lin |first4=Weiliang |last5=Ma |first5=Jiaxin |last6=Liu |first6=Cong |last7=Wu |first7=Yuheng |last8=Zhang |first8=Xingliang |last9=Fu |first9=Dongjing |date=2024 |title=Exceptionally preserved radiodont arthropods from the lower Cambrian (Stage 3) Qingjiang Lagerstätte of Hubei, South China and the biogeographic and diversification patterns of radiodonts |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/spp2.1583 |journal=Papers in Palaeontology |language=en |volume=10 |issue=4 |article-number=e1583 |doi=10.1002/spp2.1583 |issn=2056-2802}}</ref> * ''Ursulinacaris grallae''<ref name="Pates19" /> *'''Hurdiinae''' ** ''Buccaspinea cooperi''<ref name="Patesetal">Pates S, Lerosey-Aubril R, Daley AC, Kier C, Bonino E, Ortega-Hernández J. 2021. The diverse radiodont fauna from the Marjum Formation of Utah, USA (Cambrian: Drumian) PeerJ 9:e10509 https://doi.org/10.7717/peerj.10509</ref> ** ''Cambroraster falcatus''<ref name="CaronMoysiuk">{{cite journal |last1=Caron |first1=Jean-Bernard |last2=Moysiuk |first2=Joe |date=2021 |title=A giant nektobenthic radiodont from the Burgess Shale and the significance of hurdiid carapace diversity |journal=R. Soc. Open Sci. |volume=8 |article-number=210664 |bibcode=2021RSOS....810664C |doi=10.1098/rsos.210664 |doi-access=free|pmc=8424305 |pmid=34527273}}</ref> ** ''Cordaticaris striatus''<ref name="CaronMoysiuk" /> ** ''Hurdia triangulata''<ref name="CaronMoysiuk" /> ** ''Hurdia victoria''<ref name="CaronMoysiuk" /> ** ''Pahvantia hastata''<ref name="CaronMoysiuk" /> ** ''Titanokorys gainesii''<ref name="CaronMoysiuk" /> ** ''Zhenghecaris shankouensis''?<ref name="CaronMoysiuk" /> *'''Aegirocassisinae''' ** ''Aegirocassis benmoulai''<ref name="CaronMoysiuk" /> ** ''Pseudoangustidontus duplospineus''<ref name="Potin-2023">{{cite journal |last1=Potin |first1=G. J.-M. |last2=Gueriau |first2=P. |last3=Daley |first3=A. C. |year=2023 |title=Radiodont frontal appendages from the Fezouata Biota (Morocco) reveal high diversity and ecological adaptations to suspension-feeding during the Early Ordovician |journal=Frontiers in Ecology and Evolution |volume=11 |bibcode=2023FrEEv..1114109P |doi=10.3389/fevo.2023.1214109 |doi-access=free |article-number=1214109}}</ref> ** ''Pseudoangustidontus izdigua'' ''Tauricornicaris'' was previously considered as a member of Hurdiidae, but fossils of it were later reinterpreted to be euarthropod tergites.<ref>{{Cite journal |last1=Guo |first1=J. |last2=Pates |first2=S. |last3=Cong |first3=P. |last4=Daley |first4=A. |last5=Edgecombe |first5=G. |last6=Chen |first6=T. |last7=Hou |first7=X. |date=2018 |title=A new radiodont (stem Euarthropoda) frontal appendage with a mosaic of characters from the Cambrian (Series 2 Stage 3) Chengjiang biota |url=https://ora.ox.ac.uk/objects/uuid:a2d090f6-c0cb-4603-8d89-a4894fe55f02 |journal=Papers in Palaeontology |language=en |volume=5 |issue=1 |page=99 |bibcode=2019PPal....5...99G |doi=10.1002/spp2.1231 |issn=2056-2799}}</ref><ref>{{Cite journal |last1=Cong |first1=Pei-Yun |last2=Edgecombe |first2=Gregory D. |last3=Daley |first3=Allison C. |last4=Guo |first4=Jin |last5=Pates |first5=Stephen |last6=Hou |first6=Xian-Guang |date=2018 |editor-last=Zhang |editor-first=Xi-Guang |title=New radiodonts with gnathobase-like structures from the Cambrian Chengjiang biota and implications for the systematics of Radiodonta |url=https://onlinelibrary.wiley.com/doi/10.1002/spp2.1219 |journal=Papers in Palaeontology |language=en |volume=4 |issue=4 |pages=605–621 |bibcode=2018PPal....4..605C |doi=10.1002/spp2.1219 |issn=2056-2799}}</ref>
''Zhenghecaris'' was originally described as a thylacocephalan, but it was later considered a hurdiid dorsal carapace.<ref>{{Cite journal |last1=Pates |first1=Stephen |last2=Daley |first2=Allison C. |last3=Butterfield |first3=Nicholas J. |date=2019-06-11 |title=First report of paired ventral endites in a hurdiid radiodont |journal=Zoological Letters |volume=5 |issue=1 |page=18 |doi=10.1186/s40851-019-0132-4 |issn=2056-306X |pmc=6560863 |pmid=31210962 |doi-access=free}}</ref><ref name="Moysiuk-2019">{{Cite journal |last1=Moysiuk |first1=J. |last2=Caron |first2=J.-B. |date=2019-08-14 |title=A new hurdiid radiodont from the Burgess Shale evinces the exploitation of Cambrian infaunal food sources |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=286 |issue=1908 |article-number=20191079 |doi=10.1098/rspb.2019.1079 |issn=0962-8452 |pmc=6710600 |pmid=31362637}}</ref> However, its placement is questioned by some researchers, since its classification as a radiodont is largely based on the characters of ''Tauricornicaris''.<ref name="Patesetal" />
While ''Schinderhannes'' was originally described as a stem-arthropod with characters of both euarthropods and radiodonts, this interpretation was denied and most researchers now agree that it is a hurdiid radiodont.<ref>{{Cite journal |last1=Vinther |first1=Jakob |last2=Stein |first2=Martin |last3=Longrich |first3=Nicholas R. |last4=Harper |first4=David A. T. |date=2014 |title=A suspension-feeding anomalocarid from the Early Cambrian |url=https://www.nature.com/articles/nature13010 |journal=Nature |language=en |volume=507 |issue=7493 |pages=496–499 |bibcode=2014Natur.507..496V |doi=10.1038/nature13010 |hdl=1983/88f89453-e81f-4767-a74d-1794c33e6b34 |issn=1476-4687 |pmid=24670770 |s2cid=205237459 |hdl-access=free}}</ref><ref>{{Cite journal |last1=Cong |first1=Peiyun |last2=Ma |first2=Xiaoya |last3=Hou |first3=Xianguang |last4=Edgecombe |first4=Gregory D. |last5=Strausfeld |first5=Nicholas J. |date=2014 |title=Brain structure resolves the segmental affinity of anomalocaridid appendages |url=https://www.nature.com/articles/nature13486 |journal=Nature |language=en |volume=513 |issue=7519 |pages=538–542 |bibcode=2014Natur.513..538C |doi=10.1038/nature13486 |issn=1476-4687 |pmid=25043032 |s2cid=4451239|url-access=subscription }}</ref><ref>{{Cite journal |last1=Van Roy |first1=Peter |last2=Daley |first2=Allison C. |last3=Briggs |first3=Derek E. G. |date=2015 |title=Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps |url=https://www.nature.com/articles/nature14256 |journal=Nature |language=en |volume=522 |issue=7554 |pages=77–80 |bibcode=2015Natur.522...77V |doi=10.1038/nature14256 |issn=1476-4687 |pmid=25762145 |s2cid=205242881|url-access=subscription }}</ref><ref>{{Cite journal |last1=Lerosey-Aubril |first1=Rudy |last2=Pates |first2=Stephen |date=2018-09-14 |title=New suspension-feeding radiodont suggests evolution of microplanktivory in Cambrian macronekton |journal=Nature Communications |language=en |volume=9 |issue=1 |page=3774 |bibcode=2018NatCo...9.3774L |doi=10.1038/s41467-018-06229-7 |issn=2041-1723 |pmc=6138677 |pmid=30218075}} [https://datadryad.org/stash/dataset/doi:10.5061/dryad.1cf2fb0 Dryad Data]</ref><ref name="Moysiuk-2019" /><ref>{{Cite journal |last1=Liu |first1=Jianni |last2=Lerosey-Aubril |first2=Rudy |last3=Steiner |first3=Michael |last4=Dunlop |first4=Jason A |last5=Shu |first5=Degan |last6=Paterson |first6=John R |date=2018-06-01 |title=Origin of raptorial feeding in juvenile euarthropods revealed by a Cambrian radiodontan |journal=National Science Review |volume=5 |issue=6 |pages=863–869 |doi=10.1093/nsr/nwy057 |issn=2095-5138 |doi-access=free}}</ref><ref>{{Cite journal |last1=Moysiuk |first1=Joseph |last2=Caron |first2=Jean-Bernard |date=2021 |title=Exceptional multifunctionality in the feeding apparatus of a mid-Cambrian radiodont |journal=Paleobiology |language=en |volume=47 |issue=4 |pages=704–724 |bibcode=2021Pbio...47..704M |doi=10.1017/pab.2021.19 |issn=0094-8373 |doi-access=free}}</ref><ref>{{Cite journal |last1=Moysiuk |first1=Joseph |last2=Caron |first2=Jean-Bernard |date=2022 |title=A three-eyed radiodont with fossilized neuroanatomy informs the origin of the arthropod head and segmentation |journal=Current Biology |volume=32 |issue=15 |pages=3302–3316.e2 |bibcode=2022CBio...32E3302M |doi=10.1016/j.cub.2022.06.027 |issn=0960-9822 |pmid=35809569 |doi-access=free}}</ref><ref>{{Cite journal |last1=Zeng |first1=Han |last2=Zhao |first2=Fangchen |last3=Zhu |first3=Maoyan |date=2023-01-06 |title=Innovatiocaris, a complete radiodont from the early Cambrian Chengjiang Lagerstätte and its implications for the phylogeny of Radiodonta |url=https://www.lyellcollection.org/doi/10.1144/jgs2021-164 |journal=Journal of the Geological Society |language=en |volume=180 |issue=1 |bibcode=2023JGSoc.180..164Z |doi=10.1144/jgs2021-164 |issn=0016-7649 |article-number=jgs2021-164}}</ref> A few researchers have raised questions about its classification as a hurdiid.<ref>{{cite journal |author1=Zhu, X. |author2=Lerosey-Aubril, R. |author3=Ortega-Hernández, J. |year=2021 |title=Furongian (Jiangshanian) occurrences of radiodonts in Poland and South China and the fossil record of the Hurdiidae |url=https://www.researchgate.net/publication/352983445 |journal=PeerJ |language=en |volume=9 |doi=10.7717/peerj.11800 |pmc=8312493 |pmid=34386302 |doi-access=free |article-number=e11800}}</ref><ref>{{cite journal |last1=Potin |first1=Gaëtan J.-M. |last2=Daley |first2=Allison C. |date=2023 |title=The significance of ''Anomalocaris'' and other Radiodonta for understanding paleoecology and evolution during the Cambrian explosion |journal=Frontiers in Earth Science |volume=11 |bibcode=2023FrEaS..1160285P |doi=10.3389/feart.2023.1160285 |issn=2296-6463 |doi-access=free |article-number=1160285}}</ref>
''Huangshandongia yichangensis'', ''Liantuoia inflata''<ref>{{cite journal |last1=Zhilin |first1=Cui |last2=Shicheng |first2=Huo |date=1990 |title=鄂西下寒武统甲壳类化石新发现 |journal=Acta Palaeontologica Sinica |volume=29 |issue=3}}</ref> and ''Proboscicaris hospes<ref>{{cite journal |last1=Chlupač |first1=Ivo |last2=Kordule |first2=Vratislav |date=2002 |title=Arthropods of Burgess Shale type from the Middle Cambrian of Bohemia (Czech Republic) |url=http://www.geology.cz/bulletin/fulltext/3-02-chlupac |journal=Bulletin of the Czech Geological Survey |volume=77 |issue=3 |pages=167–182}}</ref>'' may represent species of ''Hurdia''.<ref>{{Cite journal |last1=Daley |first1=Allison C. |last2=Budd |first2=Graham E. |last3=Caron |first3=Jean-Bernard |date=2013 |title=Morphology and systematics of the anomalocaridid arthropod Hurdia from the Middle Cambrian of British Columbia and Utah |url=http://www.tandfonline.com/doi/full/10.1080/14772019.2012.732723 |journal=Journal of Systematic Palaeontology |language=en |volume=11 |issue=7 |pages=743–787 |bibcode=2013JSPal..11..743D |doi=10.1080/14772019.2012.732723 |issn=1477-2019|url-access=subscription }}</ref><ref>{{Cite journal |last1=Sun |first1=Zhixin |last2=Zeng |first2=Han |last3=Zhao |first3=Fangchen |date=2020 |title=A new middle Cambrian radiodont from North China: Implications for morphological disparity and spatial distribution of hurdiids |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=558 |bibcode=2020PPP...55809947S |doi=10.1016/j.palaeo.2020.109947 |issn=0031-0182 |article-number=109947}}</ref>
==References== {{Reflist|refs= <ref name="daley15">{{Cite journal |last1=Daley |first1=Allison C. |last2=Legg |first2=David A. |date=2015 |title=A morphological and taxonomic appraisal of the oldest anomalocaridid from the Lower Cambrian of Poland |journal=Geological Magazine |volume=152 |issue=5 |pages=949–955 |bibcode=2015GeoM..152..949D |doi=10.1017/S0016756815000412 |s2cid=130745134}}</ref> <ref name="Pates19">{{Cite journal |last1=Pates |first1=Stephen |last2=Daley |first2=Allison C. |last3=Butterfield |first3=Nicholas J. |date=2019 |title=First report of paired ventral endites in a hurdiid radiodont |journal=Zoological Letters |volume=5 |issue=1 |page=18 |doi=10.1186/s40851-019-0132-4 |issn=2056-306X |pmc=6560863 |pmid=31210962 |doi-access=free}}</ref> <ref name="pates20">{{Cite journal |last1=Pates |first1=Stephen |last2=Botting |first2=Joseph P. |last3=McCobb |first3=Lucy M. E. |last4=Muir |first4=Lucy A. |date=2020 |title=A miniature Ordovician hurdiid from Wales demonstrates the adaptability of Radiodonta |journal=Royal Society Open Science |volume=7 |issue=6 |article-number=200459 |bibcode=2020RSOS....700459P |doi=10.1098/rsos.200459 |pmc=7353989 |pmid=32742697 |doi-access=free}}</ref> <ref name="sun20">{{Cite journal |last1=Sun |first1=Zhixin |last2=Zeng |first2=Han |last3=Zhao |first3=Fangchen |date=2020 |title=A new middle Cambrian radiodont from North China: Implications for morphological disparity and spatial distribution of hurdiids |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=558 |bibcode=2020PPP...55809947S |doi=10.1016/j.palaeo.2020.109947 |issn=0031-0182 |s2cid=224868404 |article-number=109947}}</ref> <ref name="vanroy15">{{cite journal |last1=Van Roy |first1=Peter |last2=Daley |first2=Allison C. |last3=Briggs |first3=Derek E. G. |year=2015 |title=Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps |journal=Nature |volume=522 |issue=7554 |pages=77–80 |bibcode=2015Natur.522...77V |doi=10.1038/nature14256 |pmid=25762145 |s2cid=205242881}}</ref> <ref name="vinther14">{{cite journal |last1=Vinther |first1=Jakob |last2=Stein |first2=Martin |last3=Longrich |first3=Nicholas R. |last4=Harper |first4=David A. T. |year=2014 |title=A suspension-feeding anomalocarid from the Early Cambrian |url=http://dro.dur.ac.uk/21270/1/21270.pdf |journal=Nature |volume=507 |issue=7493 |pages=496–499 |bibcode=2014Natur.507..496V |doi=10.1038/nature13010 |pmid=24670770 |s2cid=205237459 |author-link4=David Harper (palaeontologist)}}</ref> }}
{{Radiodonta}} {{Taxonbar|from=Q19587147}}
Category:Radiodonta Category:Cambrian Series 2 first appearances Category:Early Devonian extinctions Category:Prehistoric arthropod families