{{Short description|Extinct genus of Cambrian animals}} {{Automatic taxobox | fossil_range = Early-Middle Cambrian (Stage 3-Wuliuan), {{Fossil range|518|505}} | image2 = Orthrozanclus elongata fossil.png | image2_caption = Specimen of ''O. elongata'', from Zhao et al. (2017)<ref>{{Citation |author1=Fangchen, Zhao |author2=Smith, Martin |author3=Zongjun, Yin |author4=Han, Zang |author5=Maoyan, Zhu |year= 2017 |title= High resolution images of Orthrozanclus elongata |journal= Figshare | doi=10.6084/m9.figshare.c.3841387.v1}}</ref> | image = Orthrozanclus_elongata_reconstruction.jpg | image_caption = Reconstruction of ''O. elongata'' by Zhao ''et al''. (2017)<ref name=Zhao2017/> | display_parents = 3 | taxon = Orthrozanclus | authority = Conway Morris & Caron, 2007<ref name="ConwayMorrisCaron2007" /> | subdivision = {{species list | O. reburrus | Conway Morris & Caron, 2007<ref name="ConwayMorrisCaron2007" /> | O. elongata | Zhao & Smith, 2017<ref name=Zhao2017/> }} }}
'''''Orthrozanclus''''' (from Greek {{lang|el|ὄρθρος}} + {{lang|el|ζᾰ́γκλον}} ({{Transliteration|el|órthros}} + {{Transliteration|el|zánklon}}), "dawn scythe") is a genus of sea creatures known from two species, ''O. reburrus'' from the Middle Cambrian (~{{Ma|505}}) Burgess Shale and ''O. elongata'' from Early Cambrian (~{{Ma|518}}) Maotianshan Shales. Animals in this genus were one to two centimeters long, with spikes protruding from their armored bodies. The placement of this genus into a specific family is not universally accepted.<ref name=ButterfieldPalAss>{{cite conference |first = Butterfield |last = N.J. |date = 2007-12-18 |title = Lophotrochozoan roots and stems |conference = Palaeontological Association Annual Meeting |url = http://www.palass.org/modules.php?name=annual_meeting&page=1 |book-title = Programme with Abstracts |editor = Budd, G.E. |editor2 = Streng, M. |editor3 = Daley, A.C. |editor4 = Willman, S. |location = Uppsala, Sweden |pages = 26–7 |access-date = 2007-12-20 |archive-date = 2013-11-05 |archive-url = https://web.archive.org/web/20131105151402/http://www.palass.org/modules.php?name=annual_meeting&page=1 |url-status = dead }}</ref>
==History of discovery== Jean-Bernard Caron and Donald A. Jackson found a specimen in the Burgess Shale and in 2006 referred to it as "scleritomorph C" without a detailed description.<ref name=":0">{{cite journal |author1=Caron, J.-B. |author2=Jackson, D.A. |name-list-style=amp | title=Taphonomy of the Greater Phyllopod Bed Community, Burgess Shale | journal=PALAIOS | volume=21 | pages=451–465 | year=2006 | doi=10.2110/palo.2003.P05-070R | url=https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/21/5/451/145846/ | access-date=2008-08-04 | issue=5 |bibcode=2006Palai..21..451C |s2cid=53646959 | url-access=subscription}}</ref> In 2007 Caron and Simon Conway Morris published a description and named the fossil ''Orthrozanclus reburrus''. The genus name means "Dawn scythe" and derives from Greek, with the species name meaning "bristling hair" in Latin.<ref name="ConwayMorrisCaron2007">{{cite journal |author1=Conway Morris, S. |author2=Caron, J-B. |name-list-style=amp | title=Halwaxiids and the Early Evolution of the Lophotrochozoans | journal=Science | date=2 March 2007 | volume=315 | pages=1255–1258 | doi=10.1126/science.1137187 | issue=5816 | pmid=17332408 |bibcode = 2007Sci...315.1255M |s2cid=22556453 }}</ref>
The two known specimens of ''O. elongata'' were discovered from Maotianshan Shale in 2015 and 2016 and formally described the following year.<ref name="Zhao2017">{{Cite journal| doi= 10.1038/s41598-017-16304-6| pmid= 29176685 | pmc= 5701144 | title= ''Orthrozanclus elongata'' n. sp. And the significance of sclerite-covered taxa for early trochozoan evolution |journal= Scientific Reports |volume= 7 | issue= 1 | pages= 16232 |year= 2017 |last1= Zhao |first1= Fangchen |last2= Smith |first2= Martin R |last3= Yin |first3= Zongjun |last4= Zeng |first4= Han |last5= Li |first5= Guoxiang |last6= Zhu |first6= Maoyan|bibcode= 2017NatSR...716232Z }}</ref>
==Description== left|thumb|Reconstruction of ''O. reburrus'', possibly with opposite orientation of peripheral sclerites<ref name="Zhao2017" /> ''Orthrozanclus reburrus'' was {{convert|6|-|10.3|mm|in}} long including its long spines, and had a fairly slim, roughly oval body that tapered towards the rear, was distinctly convex on top but was surrounded by a flatter rim. The underside was soft and unarmored, but the upward-facing surfaces were armored by: a small shell, near the front end; three zones of armor plates called "sclerites", which fitted close to the body and one of which ran all the way round the animal; 16 to 20 long, upwards-curving spines on each side of the body. The sclerites and spines were unmineralized, and had internal cavities that appear to have been circular in cross-section. The shell was convex and shaped like a triangle with rounded corners. It had a bulge at the front, a raised rear edge and a ridge along the middle that flared out towards the rear. It also had finely spaced rings that indicate growth by addition of material round the edges, and coarser ridges which may indicate that the animal was metameric, in other words built out of repeated "modules". The function of the shell at the front is unknown.<ref name="ConwayMorrisCaron2007" />
The animal clearly lived on the sea-floor, and is thought to have had a muscular foot rather like that of a snail.<ref name="ConwayMorrisCaron2007" />
==Classification== {{Further|Halwaxiid}} [[Image:Wiwaxia corrugata.jpg| thumb | 150px | A reconstruction of ''Wiwaxia'' ]] ''Orthrozanclus''′ sclerites are very similar to those of its Burgess Shale contemporary ''Wiwaxia''.<ref name=":0" /> Its shell is very similar to: one of the two Burgess Shale shell types labelled ''Oikozetetes''; the forward shell of Halkieriids, most of which are dated to the Early Cambrian; and those of other Early Cambrian fossils such as ''Ocruranus'' and ''Eohalobia''. These similarities suggest that ''Orthrozanclus'' was an intermediate form between ''Wiwaxia'' and the Halkieriids and that all three of these taxa formed a monophyletic clade, in other words a group that consists of a common ancestor and ''all'' of its descendants.<ref>{{Cite book |last1=Ponder |first1=Winston Frank |url=https://books.google.com/books?id=6KvQDwAAQBAJ&pg=PT56 |title=Biology and Evolution of the Mollusca, Volume 2 |last2=Lindberg |first2=David R. |last3=Ponder |first3=Juliet Mary |date=2020-02-14 |publisher=CRC Press |isbn=978-1-351-11523-0 |pages=56 |language=en}}</ref> However this draws ''Orthrozanclus'' into a complex debate that has gone on since 1990 about whether ''Wiwaxia'' is more closely related to molluscs or to polychaete worms, and therefore about the entire "family tree" of the Lophotrochozoa, a "super-phylum" that is thought to contain modern molluscs, annelids and brachiopods as well as some extinct groups.<ref name="ConwayMorrisCaron2007" /> The main opponent of this view, Nicholas Butterfield, proposes that ''Wiwaxia'' is more closely related to annelids while Halkieriids are very close to molluscs.<ref name="ButterfieldPalAss" /><ref name=Butterfield2006>{{cite journal | author = Butterfield, N.J. | year = 2006 | title = Hooking some stem-group ''worms'': fossil lophotrochozoans in the Burgess Shale | journal = BioEssays | volume = 28 | issue = 12 | pages = 1161–6 | doi = 10.1002/bies.20507 | url=http://www3.interscience.wiley.com/journal/113471993/abstract | archive-url=https://archive.today/20110813124946/http://www3.interscience.wiley.com/journal/113471993/abstract | url-status=dead | archive-date=2011-08-13 | access-date=2008-08-06 | pmid = 17120226 | s2cid = 29130876 | url-access = subscription}}</ref><ref name="Butterfield2008EarlyCambrianRadula">{{ cite journal | author=Butterfield, N.J. | title=An Early Cambrian Radula | journal=Journal of Paleontology | date=May 2008 | volume=82 | issue=3 | pages=543–554 | doi=10.1666/07-066.1 | bibcode=2008JPal...82..543B | s2cid=86083492 | url=https://dx.doi.org/10.1666/07-066.1 | access-date=2008-08-20 | url-access=subscription}}</ref> {{clear left}} {| border="0" cellspacing="0" cellpadding="3" <!-- row of cladograms side by side --> |- valign="top" | <div style="width:auto; border:solid 1px silver; padding:2px; margin:2px; font-size:90%;"> <div style="width:auto; border:solid 1px silver; padding:5px"> {| border="0" cellspacing="0" cellpadding="3" <!-- CM & C 2007 cladograms side by side --> |- valign="top" | <!-- Conway Morris and Caron (2007) Hypothesis 1 --> {{clade |1={{clade |1={{clade |1=''Kimberella'' |2={{clade |1=''Odontogriphus'' |2={{clade |1={{clade |1=<span style="background-color:#ffffcc">'''''Wiwaxia'''''</span> |2={{clade |1=Siphogonotuchida |2={{clade |1=''Orthrozanclus'' |2=Halkieriids }} }} }} |2={{clade |1=MOLLUSCA<br />(crown group) }} }} }} }} |2={{clade |1={{clade |1=''Canadia'' |2=ANNELIDA<br />(crown group) }} |2={{clade |1=''Micrina'' |2=BRACHIOPODA<br />(crown group) }} }} }} }} | <!-- spacer --> | align="right" | <!-- Conway Morris and Caron (2007) Hypothesis 2 --> {{clade |1={{clade |1=''Kimberella'' |2={{clade |1=''Odontogriphus'' |2={{clade |1=MOLLUSCA<br />(crown group) |2={{clade |1={{clade |1=Siphogonotuchida |2={{clade |1=Halkieriids |2={{clade |1=''Orthrozanclus'' |2=<span style="background-color:#ffffcc">'''''Wiwaxia'''''</span> }} }} }} |2={{clade |1={{clade |1=''Canadia'' |2=ANNELIDA<br />(crown group) }} |2={{clade |1=''Micrina'' |2=BRACHIOPODA<br />(crown group) }} }} }} }} }} }} }} |} </div>Cladograms: Conway Morris and Caron (2007) — Hypothesis 1 (left) and 2 (right).<br />The authors regard Hypothesis 1 as better supported by the evidence, but not robust.<ref name="ConwayMorrisCaron2007" /></div> | <div style="width:auto; border:solid 1px silver; padding:2px; margin:2px; font-size:90%;"> <div style="width:auto; border:solid 1px silver; padding:5px"> {{clade |1={{clade |1=''Kimberella'' |2=''Odontogriphus'' |3={{clade |1={{clade|1={{clade|"'''Halsiphonids'''"<br />(halkieriids + <br />siphogonotuchids) }}}} |2={{clade|1={{clade|MOLLUSCA<br />(crown group) }}}} |3={{clade |1=<span style="background-color:#ffffcc">'''''Wiwaxia'''''</span> |2={{clade |1=''Canadia'' |2=ANNELIDA<br />(crown group) }} }} |4={{clade|1={{clade|''Micrina''|BRACHIOPODA<br />(crown group)}}}} }} }} }} </div>Butterfield's alternative.<ref name="ButterfieldPalAss"/> </div> |}
Zhao et al. (2017) propose an alternative - that halkieriids (including orthrozanclus and halkieria) are unrelated to ''Wiwaxia'', but are instead related to the camenellan tommotiids and thus belong in the brachiopod stem lineage.<ref name=Zhao2017/>
==See also== {{Portal|Paleontology}} *Burgess Shale *Halwaxiida
==References== {{Reflist}}
== External links == * {{Cite web|date=2011|title=''Orthrozanclus reburrus''|work=Burgess Shale Fossil Gallery|publisher=Virtual Museum of Canada|url=http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=94|archive-url=https://web.archive.org/web/20201112025257/http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=94|archive-date=2020-11-12|url-status=dead|access-date=2023-01-21}} *[https://web.archive.org/web/20070305173024/http://uk.news.yahoo.com/02032007/80-132/spiky-oddball-prowled-ocean-half-billion-years.html Spiky oddball prowled ocean half billion years ago. Yahoo UK & Ireland News] *[https://arstechnica.com/journals/science.ars/2007/3/1/7278 New fossil unites three branches of life in the Cambrian. Ars Technica]
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Category:Burgess Shale fossils Category:Taxa named by Simon Conway Morris Category:Fossil taxa described in 2007 Category:Maotianshan shales fossils Category:Cambrian genus extinctions