Palaeoxyris

{{Short description|Egg fossil}} {{ichnobox | fossil_range = {{fossil range|Carboniferous|Cretaceous}} | image = Palaeoxyris diagram.jpg | image_caption = Diagram of a Mesozoic type ''Palaeoxyris'' specimen | taxon = Palaeoxyris | authority = Brongniart, 1828 }} [[File:Sgff a 1907442 f0011 c.jpg|left|thumb|Early Jurassic estuarine ecosystem, with ''Palaeoxyris'' egg cases attached via tendril to ''Neocalamites'', with hybodonts in the background]]

'''''Palaeoxyris''''' is a morphogenus of eggs cases, widely thought to have been produced by hybodonts, with a predominant occurrence in ancient freshwater environments. They comprise a beak, a body and a pedicle. They display a conspicuous right-handed spiral of collarettes around the body, and in some cases, the pedicle, resulting in a rhomboidal pattern when flattened during fossilisation.<ref name="Böttcher">{{cite journal |author=Ronald Böttcher |year=2010 |title=Description of the shark egg capsule ''Palaeoxyris friessi'' n. sp. from the Ladinian (Middle Triassic) of SW Germany and discussion of all known egg capsules from the Triassic of the Germanic Basin |journal=Palaeodiversity |volume=3 |pages=123–139 |url=http://www.palaeodiversity.org/pdf/03/Palaeodiversity_Bd3_Boettcher.pdf }}</ref> At the end of the beak was a tendril which attached the egg to vegetation during development.<ref>{{Cite journal |last1=Krüger |first1=Ashley |last2=Slater |first2=Sam |last3=Vajda |first3=Vivi |date=2021-07-03 |title=3D imaging of shark egg cases ( Palaeoxyris ) from Sweden with new insights into Early Jurassic shark ecology |journal=GFF |language=en |volume=143 |issue=2–3 |pages=229–247 |doi=10.1080/11035897.2021.1907442 |bibcode=2021GFF...143..229K |issn=1103-5897|doi-access=free }}</ref> The body of the egg ranges in length from {{Convert|1.2-8.9|cm|in}}, depending on the species.<ref>{{Cite journal |last1=Fischer |first1=Jan |last2=Axsmith |first2=Brian J. |last3=Ash |first3=Sidney R. |date=2010-03-01 |title=First unequivocal record of the hybodont shark egg capsule Palaeoxyris in the Mesozoic of North America |url=http://dx.doi.org/10.1127/0077-7749/2009/0028 |journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen |volume=255 |issue=3 |pages=327–344 |doi=10.1127/0077-7749/2009/0028 |bibcode=2010NJGPA.255..327F |issn=0077-7749|url-access=subscription }}</ref>

Originally described as plant remains (being named after the plant genus ''Xyris''), it took decades before their true nature as animal eggs was revealed.<ref>{{cite journal |author1=Jan Fischer |author2=Ilja Kogan |name-list-style=amp |year=2008 |title=Elasmobranch egg capsules ''Palaeoxyris'', ''Fayolia'' and ''Vetacapsula'' as subject of palaeontological research – an annotated bibliography |journal=Freiberger Forschungshefte |volume=C 528 |pages=75–91}}</ref> Nearly 30 different ''Palaeoxyris'' species are currently known with a stratigraphic range from the Carboniferous to the Cretaceous.<ref name="Böttcher"/><ref name=":0">{{cite journal |author1=Jan Fischer |author2=Sebastian Voigt |author3=Jörg W. Schneider |author4=Michael Buchwitz |author5=Silke Voigt |year=2011 |title=A selachian freshwater fauna from the Triassic of Kyrgyzstan and its implication for Mesozoic shark nurseries |journal=Journal of Vertebrate Paleontology |volume=31 |issue=5 |pages=937–953 |doi=10.1080/02724634.2011.601729|bibcode=2011JVPal..31..937F |s2cid=85753690 }}</ref> Mesozoic ''Palaeoxyris'' specimens differ from Paleozoic specimens by having the twisting of the collarette end at the beginning of the pedicle, rather than the spiraling continuing down the pedicle as in Paleozoic specimens.<ref>{{Cite journal |last1=Fischer |first1=Jan |last2=Licht |first2=Martin |last3=Kriwet |first3=Jürgen |last4=Schneider |first4=Jörg W. |last5=Buchwitz |first5=Michael |last6=Bartsch |first6=Peter |date=2014-04-03 |title=Egg capsule morphology provides new information about the interrelationships of chondrichthyan fishes |url=http://www.tandfonline.com/doi/abs/10.1080/14772019.2012.762061 |journal=Journal of Systematic Palaeontology |language=en |volume=12 |issue=3 |pages=389–399 |doi=10.1080/14772019.2012.762061 |bibcode=2014JSPal..12..389F |issn=1477-2019|url-access=subscription }}</ref> Likely hybodont producers of some of the eggs assigned to the genus include the genus ''Lonchidion''.<ref name=":0" />

==References== {{Reflist|32em}}

Category:Egg fossils Category:Carboniferous cartilaginous fish Category:Permian cartilaginous fish Category:Triassic cartilaginous fish Category:Jurassic cartilaginous fish Category:Cretaceous cartilaginous fish Category:Madygen Formation