Siberiidae

{{Short description|Extinct family of Cambrian lobopodians}} {{Taxobox | fossil_range = {{Fossil range|Cambrian Stage 3|Cambrian Series 2}} | image = 20191217 Siberiida Siberion Megadictyon Jianshanopodia.png | image_caption = Reconstructions of the known siberiids | regnum = Animalia | phylum = Lobopodia | classis = †Xenusia | ordo = †'''Siberiida''' | familia = †'''Siberiidae''' | familia_authority = Dzik, 2011 | subdivision_ranks = Genera | subdivision = * {{extinct}}''Siberion'' * {{extinct}}''Jianshanopodia'' * {{extinct}}''Megadictyon'' * {{extinct}}''Parvibellus''?<ref name="McCall2023" /> {{small|(may represent the larva of any described siberiids) }} }}

'''Siberiidae''' is a family of Cambrian lobopodians, sometimes called "jianshanopodians"<ref name="ReferenceA">{{cite journal |last1=Smith |first1=Martin R. |last2=Ortega-Hernández |first2=Javier |year=2014 |title=Hallucigenia's onychophoran-like claws and the case for Tactopoda |url=http://dro.dur.ac.uk/19108/1/19108.pdf |url-status=live |journal=Nature |volume=514 |issue=7522 |pages=363–366 |bibcode=2014Natur.514..363S |doi=10.1038/nature13576 |pmid=25132546 |s2cid=205239797 |archive-url=https://ghostarchive.org/archive/20221010/http://dro.dur.ac.uk/19108/1/19108.pdf |archive-date=2022-10-10}}</ref> or "giant lobopodians".<ref>{{Cite journal |last=Edgecombe |first=Gregory D. |date=2020-11-02 |title=Arthropod Origins: Integrating Paleontological and Molecular Evidence |url=https://www.annualreviews.org/doi/10.1146/annurev-ecolsys-011720-124437 |journal=Annual Review of Ecology, Evolution, and Systematics |volume=51 |issue=1 |pages=1–25 |doi=10.1146/annurev-ecolsys-011720-124437 |issn=1543-592X |s2cid=225478171|url-access=subscription }}</ref> They are suggested to be more closely related to "gilled lobopodians" and arthropods than to other lobopodians, providing important evidence for the origin of the arthropod body plan.

== Morphology == Siberiids often reach large sizes, achieving as much as 22 cm,<ref name=":0" /> or even over 30 cm in length as seen in ''Jianshanopodia''.<ref name="McCall2023" />

=== Cephalon === The anterior of the cephalon is blunt, prominent appendages equipped with endites protrude laterally from it.<ref name=":92">{{Cite journal |last=Dzik |first=Jerzy |date=2011-07-01 |title=The xenusian-to-anomalocaridid transition within the lobopodians |url=http://paleoitalia.org/media/u/archives/7.Dzik_-_BollSPI_50-1.pdf |url-status=usurped |journal=Bollettino della Società Paleontologica Italiana |volume=50 |pages=65–74 |archive-url=https://web.archive.org/web/20170808022647/http://paleoitalia.org/media/u/archives/7.Dzik_-_BollSPI_50-1.pdf |archive-date=2017-08-08 |df=dmy-all}}</ref> In the case of ''Megadictyon'' the appendages terminate with sclerotized spines. The bottom of the head exposes an oral opening surrounded by an array of layers of plates and teeth which has been compared to the oral cones of radiodonts;<ref name=":0">{{Cite journal |author=Liu, J.-N. |author2=Shu, D.-G. |author3=Han, J. |author4=Zhang, Z.-F. |author5=Zhang, X.-L. |year=2007 |title=Morpho-anatomy of the lobopod ''Magadictyon'' cf. ''haikouensis'' from the Early Cambrian Chengjiang Lagerstätte, South China |journal=Acta Zoologica |volume=88 |issue=4 |pages=279–288 |doi=10.1111/j.1463-6395.2007.00281.x}}</ref> the pharynx houses numerous pharyngeal teeth,<ref name="Liu2006">{{cite journal |author1=Jianni Liu |author2=Degan Shu |author3=Jian Han |author4=Zhifei Zhang |author5=Xingliang Zhang |year=2006 |title=A large xenusiid lobopod with complex appendages from the Lower Cambrian Chengjiang Lagerstätte |url=http://www.app.pan.pl/article/item/app51-215.html |journal=Acta Palaeontologica Polonica |volume=51 |issue=2 |pages=215–222 |accessdate=2015-03-13}}</ref> and has been compared to that of priapulids.<ref name=":1">{{Cite journal |last1=Vannier |first1=Jean |last2=Liu |first2=Jianni |last3=Lerosey-Aubril |first3=Rudy |last4=Vinther |first4=Jakob |last5=Daley |first5=Allison C |year=2014 |title=Sophisticated digestive systems in early arthropods |journal=Nature Communications |volume=5 |pages=3641 |bibcode=2014NatCo...5.3641V |doi=10.1038/ncomms4641 |pmid=24785191 |doi-access=free}}</ref> No eyes have been observed.<ref name="McCall2023" />

=== Limbs === Siberiids bear stout, unarthropodized, annulated limbs called lobopods. They bear gill-like papillae protruding dorsally from the series of annuli; These papillae were weakly sclerotized in ''Siberion'' and form branched feather-like structures in ''Jianshanopodia'' in order to greatly increase the surface area for respiration;<ref name=":92" /><ref name="McCall2023" /> the lobopods house internal fine canals which branch off into the papillae.<ref name="Liu2006" /> Their trunk limbs also lack claws.<ref name="McCall2023" />

=== Trunk === Numerous uniform annulations ornament the broad trunk of siberiids,<ref name=":0" /><ref name=":92" /> however ''Jianshanopodia'' exhibits primitive segmentation in its trunk region comprising at least 9 segments.<ref name="Liu2006" /> The dorsal surface on ''Siberion'' is adorned by tw rows of small lateral tubercles corresponding to the annuli.<ref name=":92" /> left|thumb|262x262px|A fossil of ''Jianshanopodia'' presenting the gut diverticulae and the caudal area.

=== Caudal area === Siberiids exhibit a differentiated terminal caudal (tail) protrusion.<ref name=":92" /> In ''Jianshanopodia'' the caudal end forms a trilobed tail fan comprising the terminal protrusion and a pair of lobes positioned laterally to the median lobe, and pointing posteriorly; in front of the tail fan is a pair of smaller, distinct laterally oriented lobopods.<ref name="Liu2006" />

=== Internal anatomy === The digestive system is generally equipped with gut diverticulae allowing for more efficient digestion and metabolism;<ref name=":1" /> however ''Siberion'' may be an exception to that.<ref name=":92" /> Based on ''Jianshanopodia'', the respiratory papillae also house fine canals.

=== Other members of Siberiidae === thumb|291x291px|The holotype and only specimen of Parvibellus. ''Parvibellus'' was initially described as a lower stem group arthropod; however, a recent study has suggested ''Parvibellus'' to be an early developmental stage of a siberiid based on the features such as a ventral mouth opening surrounded by circlets of tooth plates, and the lack of eyes and claws. It lacks the respiratory papillae generally possessed by siberiids, but that can be explained by its small size which allows it to respirate without any specialized structures.<ref name="McCall2023" />

There are also several more indeterminate siberiids from the Chengjiang Lagerstätte which have not been described yet.<ref name="McCall2023" /><ref name=":1" /> One of them bears anterior papillae which are not seen in other siberiids, terminal spines on the frontal appendages, and gut diverticulae.<ref name=":1" /><ref>{{Cite journal |last1=Vannier |first1=Jean |last2=Martin |first2=Emmanuel L. O. |date=2017-02-15 |title=Worm-lobopodian assemblages from the Early Cambrian Chengjiang biota: Insight into the "pre-arthropodan ecology"? |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=468 |pages=373–387 |doi=10.1016/j.palaeo.2016.12.002 |issn=0031-0182|doi-access=free |bibcode=2017PPP...468..373V }}</ref>

== Ecology == The respiratory papillae likely supported an active predatory lifestyle, similar to opabiniids, and radiodonts which too bear specialized respiratory structures, and raptorial appendages. This lifestyle is also supported by the gut diverticulae allowing for more efficient digestion and metabolism present in ''Jianshanopodia'' and ''Megadictyon''.<ref name=":1" /> Siberiids have been found in the Chengjiang Biota and the Sinsk Biota.<ref name=":92" />

== Phylogeny == In the past siberiids have been considered a transitional group between 'Xenusia' and Radiodonta,<ref name=":92" /> but newer studies have recovered the phylogenetic relationships to be more complex and siberiids as basal total-group arthropods near ''Aysheaia''<ref name="McCall2023">{{cite journal |last1=McCall |first1=Christian |date=13 December 2023 |title=A large pelagic lobopodian from the Cambrian Pioche Shale of Nevada |url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/large-pelagic-lobopodian-from-the-cambrian-pioche-shale-of-nevada/11B0704C49A7730AA3E8F46EB2CA1C95 |journal=Journal of Paleontology |volume=97 |issue=5 |pages=1009–1024 |bibcode=2023JPal...97.1009M |doi=10.1017/jpa.2023.63 |access-date=13 December 2023|url-access=subscription }}</ref> which too bears differentiated raptorial frontal appendages.<ref name=":92" />

Phylogeny of Panarthropoda after Knecht et al. 2025:<ref name="knecht2025">{{cite journal |last1=Knecht|first1=Richard J.|last2=McCall|first2=Christian R. A.|last3=Tsai|first3=Cheng-Chia|last4=Rabideau Childers|first4=Richard A.|last5=Yu|first5=Nanfang|date=23 July 2025|title=''Palaeocampa anthrax'', an armored freshwater lobopodian with chemical defenses from the Carboniferous|journal=Communications Biology|volume=8|issue=1|doi=10.1038/s42003-025-08483-0|article-number=1080|pmid=40702124|doi-access=free|pmc=12287526}}</ref>{{clade|{{extinct}}''Diania'' 80px|{{clade |1={{extinct}}''Lenisambulatrix'' 80px |2={{clade |label1= |1={{clade |1={{extinct}}''Paucipodia'' 80px |2={{clade |1={{extinct}}''Thanahita'' 80px |2={{clade |label1={{extinct}}Eoconchariidae |1={{clade |1={{extinct}}''Microdictyon'' 80px |2={{extinct}}''Fusuchoncharium'' |3={{extinct}}''Quadratapora'' }} |2={{clade |1={{clade |1={{extinct}}''Xenusion'' 80px |2={{extinct}}''Onychodictyon'' 80px }} |2={{clade |1={{extinct}}''Strictocorniculum'' |2={{extinct}}''Rhombocorniculum'' |3={{extinct}}''Orstenotubulus''80px |4={{extinct}}''Carbotubulus'' |5={{extinct}}''Hallucigenia fortis'' |6={{extinct}}''Hallucigenia sparsa'' 80px |7={{clade |1={{extinct}}''Hallucigenia hongmeia'' |2={{clade |1={{extinct}}''Cardiodictyon'' 80px |2={{clade |1=Tardigrada 80px |label2={{extinct}}Luolishaniida |2={{clade |1={{clade |1={{extinct}}''Ovatiovermis'' 60px |2={{extinct}}''Facivermis'' 80px }} |2={{clade |1={{extinct}}''Luolishania'' 80px |label2={{extinct}}Collinsovermidae |2={{clade |1={{extinct}}''Acincocricus'' |2={{clade |1={{extinct}}''Collinsovermis'' 80px |2={{clade |1={{extinct}}''Collinsium'' |2={{extinct}}''Entothyreos'' 80px }}}}}}}}}}}}}}}}}}}}}}}}}} |2={{clade |label1={{extinct}}Aysheaiidae |1={{clade |1={{extinct}}''Aysheaia'' 80px |2={{clade |1={{extinct}}''Hadranax'' 80px |2={{extinct}}''Palaeocampa'' 80px }}}} |label2=Antennopoda |2={{clade |1={{clade |1={{extinct}}''Antennacanthopodia'' 80px |2=Onychophora (velvet worms) 80px

}} |2={{clade |label1={{extinct}}Siberiidae |1={{clade |1={{extinct}}''Siberion'' 80px |2={{extinct}}''Megadictyon'' 80px |3={{extinct}}''Jianshanopodia'' 80px }} |2={{clade |1={{clade |1={{extinct}}''Pambdelurion'' 80px |2={{extinct}}Kerygmachelidae 80px }} |2={{clade |1={{extinct}}Opabiniidae 80px |2={{clade |1={{extinct}}Radiodonta (e.g. ''Anomalocaris'') 80px |2=Deuteropoda (modern arthropods) 100px }}}}}}}}}}}}}}}}|style=font-size:90%}}

== References == {{reflist}}

Category:Fossil taxa described in 2011 Category:Lobopodia Category:Xenusia Category:Cambrian animals Category:Prehistoric arthropod families