Chondrichthyes: Difference between revisions

**†''[[Delphyodontos]]''<ref>{{Cite web|url=http://people.sju.edu/~egrogan/BearGulch/pages_fish_species/Delphyodontos_dacriformes.html|title=Bear Gulch - Delphyodontos dacriformes|work=Fossil Fishes of Bear Gulch|access-date=2019-05-15|archive-date=25 February 2015|archive-url=https://web.archive.org/web/20150225041927/http://people.sju.edu/~egrogan/BearGulch/pages_fish_species/Delphyodontos_dacriformes.html|url-status=dead}}</ref>

'''Chondrichthyes''' ({{IPAc-en|k|ɒ|n|ˈ|d|r|ɪ|k|θ|i|.|iː|z}}; {{etymology|grc|''{{wiktWikt-lang|grc|χόνδρος}}'' (khóndros{{grc-transl|χόνδρος}})|cartilage||''{{wiktWikt-lang|grc|ἰχθύς}}'' (ikhthús{{grc-transl|ἰχθύς}})|fish}}) is a [[class (biology)|class]] of [[jawed fish]] that contains the '''cartilaginous fishesfish''' thator '''chondrichthyans''', which all have skeletons[[skeleton]]s primarily composed of [[cartilage]]. They can be contrasted with the [[Osteichthyes]] or ''bony fishesfish'', which have skeletons primarily composed of [[bone tissue]]. Chondrichthyes are jawed[[aquatic animal|aquatic]] [[vertebrate]]s with paired [[Fishpaired fin|fins]], paired [[nare]]s, scales[[placoid scale]]s, and[[conus a heart with its chambersarteriosus]] in series.the Extant[[heart]], chondrichthyesand rangea inlack sizeof from[[operculum the(fish)|opercula]] 10and cm[[swim (3bladder]]s.9 in)Within [[finlessthe sleeperinfraphylum ray[[Gnathostomata]], tocartilaginous thefishes 10are mdistinct (32from ft)all [[whaleother shark]].jawed vertebrates.

The class is divided into two subclasses: [[Elasmobranchii]] ([[shark]]s, [[Batoidea|ray]]s, [[Skateskate (fish)|skate]]s, and [[sawfish]]) and [[Holocephali]] ([[chimaera]]s, sometimes called ghost sharks, which are sometimes separated into their own class). Extant chondrichthyans range in size from the {{cvt|10|cm}} [[finless sleeper ray]] to the over {{cvt|10|m}} [[whale shark]].

The skeleton is cartilaginous. The [[notochord]] is gradually replaced by a vertebral column during development, except in [[Holocephali]], where the notochord stays intact. In some deepwater sharks, the column is reduced.<ref>[{{Cite book|url=https://books.google.nocom/books?id=cxxSN4YA2i8C&pg=PA23&dq=Notochord:+Chimaeroids+%22Some+deepwater+squaloid,+hexanchoid,+and+lamnoid+sharks+%22&hlpg=no&saPA23|title=X&ved=0ahUKEwjK-YDWxYnbAhXhA5oKHZmtByAQ6AEIKDAA#v=onepage&q=Notochord%3A%20Chimaeroids%20%22Some%20deepwater%20squaloid%2C%20hexanchoid%2C%20and%20lamnoid%20sharks%20%22&f=false Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date]|first1=Leonard J. V.|last1=Compagno|first2=Food and Agriculture Organization of the United|last2=Nations|date=20 November 2001|publisher=Food & Agriculture Org.|isbn=9789251045435 |via=Google Books}}</ref>

In chondrichthyans, the nervous system is composed of a small brain, 8-108–10 pairs of cranial nerves, and a spinal chordcord with spinal nerves.<ref>{{Cite journal|last=Collin|first=Shaun P.|date=2012|title=The Neuroecology of Cartilaginous Fishes: Sensory Strategies for Survival|journal=Brain, Behavior and Evolution|language=en|volume=80|issue=2|pages=80–96|doi=10.1159/000339870|pmid=22986825|s2cid=207717002|issn=1421-9743}}</ref> They have several sensory organs which provide information to be processed. [[Ampullae of Lorenzini]] are a network of small jelly filled pores called [[Electroreception|electroreceptors]] which help the fish sense electric fields in water. This aids in finding prey, navigation, and sensing temperature. The [[Lateral line]] system has modified epithelial cells located externally which sense motion, vibration, and pressure in the water around them. Most species have large well-developed eyes. Also, they have very powerful nostrils and [[Olfactory bulb|olfactory]] organs. Their inner ears consist of 3 large [[semicircular canals]] which aid in balance and orientation. Their sound detecting apparatus has limited range and is typically more powerful at lower frequencies. Some species have [[Electric organ (biology)|electric organs]] which can be used for defense and predation. They have relatively simple brains with the forebrain not greatly enlarged. The structure and formation of myelin in their nervous systems are nearly identical to that of tetrapods, which has led evolutionary biologists to believe that Chondrichthyes were a cornerstone group in the evolutionary timeline of myelin development.<ref>{{Cite journal|last=de Bellard|first=Maria Elena|date=2016-06-15|title=Myelin in cartilaginous fish|journal=Brain Research|volume=1641|issue=Pt A|pages=34–42|doi=10.1016/j.brainres.2016.01.013|issn=0006-8993|pmc=4909530|pmid=26776480}}</ref>

| align=center | 5-75–7

| align=center | 5-75–7

Cartilaginous fish are considered to have evolved from [[acanthodians]]. The discovery of ''[[Entelognathus]]'' and several examinations of acanthodian characteristics indicate that bony fish evolved directly from placoderm like ancestors, while acanthodians represent a paraphyletic assemblage leading to Chondrichthyes. Some characteristics previously thought to be exclusive to acanthodians are also present in basal cartilaginous fish.<ref>{{cite journal |author1=Min Zhu |author2=Xiaobo Yu |author3=Per Erik Ahlberg |author4=Brian Choo |author5=Jing Lu |author6=Tuo Qiao |author7=Qingming Qu |author8=Wenjin Zhao |author9=Liantao Jia |author10=Henning Blom |author11=You'an Zhu |year=2013 |title=A Silurian placoderm with osteichthyan-like marginal jaw bones |journal=[[Nature (journal)|Nature]] |volume=502 |issue=7470 |pages=188–193 |doi=10.1038/nature12617 |pmid=24067611|bibcode=2013Natur.502..188Z |s2cid=4462506 }}</ref> In particular, new phylogenetic studies find cartilaginous fish to be well nested among acanthodians, with ''[[Doliodus]]'' and ''[[Tamiobatis]]'' being the closest relatives to Chondrichthyes.<ref>{{cite journal|doi=10.26879/601|title=The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland|journal=Palaeontologia Electronica|year=2016|last1=Burrow|first1=CJ|last2=Den Blaauwen|first2=J.|last3=Newman|first3=MJ|last4=Davidson|first4=RG|doi-access=free}}</ref> Recent studies vindicate this, as ''[[Doliodus]]'' had a mosaic of chondrichthyan and acanthodian traits.<ref>{{cite journal|doi=10.1206/3875.1|title=Pectoral Morphology in ''Doliodus'': Bridging the 'Acanthodian'-Chondrichthyan Divide|journal=American Museum Novitates|issue=3875|pages=1–15|year=2017|last1=Maisey|first1=John G.|last2=Miller|first2=Randall|last3=Pradel|first3=Alan|last4=Denton|first4=John S.S.|last5=Bronson|first5=Allison|last6=Janvier|first6=Philippe|s2cid=44127090|url=https://www.archive.org/download/pectoralmorphol00mais/pectoralmorphol00mais.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.archive.org/download/pectoralmorphol00mais/pectoralmorphol00mais.pdf |archive-date=2022-10-09 |url-status=live}}</ref> Dating back to the Middle and Late [[Ordovician]] Period, many isolated scales, made of [[dentine]] and bone, have a structure and growth form that is chondrichthyan-like. They may be the remains of [[stem group|stem]]-chondrichthyans, but their classification remains uncertain.<ref name="Andreev2015">{{cite journal |last1 = Andreev |first1 = Plamen S.|last2=Coates |first2 =Michael I. |last3=Shelton |first3=Richard M. |last4=Cooper |first4=Paul R. |last5=Smith |first5=M. Paul |last6=Sansom |first6=Ivan J. |year=2015 |title=Ordovician chondrichthyan-like scales from North America |journal=[[Palaeontology (journal)|Palaeontology]] |volume=58 |issue=4 |pages=691–704 |doi=10.1111/pala.12167|s2cid = 140675923|doi-access=free }}</ref><ref name="Sansom2012">{{cite journal |last1=Sansom |first1=Ivan J. |last2=Davies |first2= Neil S. |last3=Coates |first3=Michael I. |last4=Nicoll |first4=Robert S. |last5=Ritchie |first5=Alex |year=2012 |title=Chondrichthyan-like scales from the Middle Ordovician of Australia |journal=[[Palaeontology (journal)|Palaeontology]] |volume=55 |issue=2 |pages=243–247 |doi=10.1111/j.1475-4983.2012.01127.x|bibcode=2012Palgy..55..243S |doi-access=free }}</ref><ref name="Andreev2016">{{cite journal |last1=Andreev |first1=Plamen |last2=Coates |first2=Michael I. |last3=Karatajūtė-Talimaa |first3=Valentina |last4=Shelton |first4=Richard M. |last5=Cooper |first5=Paul R. |last6=Wang |first6=Nian-Zhong |last7=Sansom |first7=Ivan J. |year=2016 |title=The systematics of the Mongolepidida (Chondrichthyes) and the Ordovician origins of the clade |journal=PeerJ |volume=4 |page=e1850 |doi=10.7717/peerj.1850|pmid=27350896 |pmc=4918221 |doi-access=free }}</ref>

The earliest unequivocal fossils of acanthodian-grade cartilaginous fishes are ''[[Qianodus]]'' and ''[[Fanjingshania]]'' from the early Silurian ([[Aeronian]]) of [[Guizhou]], China around 439 million years ago, which are also the oldest unambigousunambiguous remains of any jawed vertebrates.<ref name=":12">{{cite journal |last1=Andreev |first1=Plamen S. |last2=Sansom |first2=Ivan J. |last3=Li |first3=Qiang |last4=Zhao |first4=Wenjin |last5=Wang |first5=Jianhua |last6=Wang |first6=Chun-Chieh |last7=Peng |first7=Lijian |last8=Jia |first8=Liantao |last9=Qiao |first9=Tuo |last10=Zhu |first10=Min |date=September 2022 |title=Spiny chondrichthyan from the lower Silurian of South China |url=https://www.nature.com/articles/s41586-022-05233-8 |journal=Nature |volume=609 |issue=7929 |pages=969–974 |doi=10.1038/s41586-022-05233-8 |pmid=36171377 |bibcode=2022Natur.609..969A |s2cid=252570103}}</ref><ref name=":02">{{Cite journal |last1=Andreev |first1=Plamen S. |last2=Sansom |first2=Ivan J. |last3=Li |first3=Qiang |last4=Zhao |first4=Wenjin |last5=Wang |first5=Jianhua |last6=Wang |first6=Chun-Chieh |last7=Peng |first7=Lijian |last8=Jia |first8=Liantao |last9=Qiao |first9=Tuo |last10=Zhu |first10=Min |date=2022-09-28 |title=The oldest gnathostome teeth |url=http://dx.doi.org/10.1038/s41586-022-05166-2 |journal=Nature |volume=609 |issue=7929 |pages=964–968 |bibcode=2022Natur.609..964A |doi=10.1038/s41586-022-05166-2 |issn=0028-0836 |pmid=36171375 |s2cid=252569771}}</ref> ''Shenacanthus vermiformis'', which lived 436 million years ago, had thoracic armour plates resembling those of placoderms.<ref>[{{cite journal | url=https://pubmed.ncbi.nlm.nih.gov/36171378/ | pmid=36171378 | year=2022 | last1=Zhu | first1=Y. A. | last2=Li | first2=Q. | last3=Lu | first3=J. | last4=Chen | first4=Y. | last5=Wang | first5=J. | last6=Gai | first6=Z. | last7=Zhao | first7=W. | last8=Wei | first8=G. | last9=Yu | first9=Y. | last10=Ahlberg | first10=P. E. | last11=Zhu | first11=M. | title=The oldest complete jawed vertebrates from the early Silurian of China | journal=Nature | volume=609 | issue=7929 | pages=954–958 | doi=10.1038/s41586-022-05136-8 PubMed]| bibcode=2022Natur.609..954Z | s2cid=252569910 }}</ref>

| [[File:Stethacanthus BWSymmorium1DB.jpg|140px147x147px]]

| align=center | [[Symmoriidae|Symmoriids]]

| align=center | <small></small>Zangerl, 1981 (sensu Maisey, 2007)

| align=center | 4

| valign=top | Members of the holocephali, they were heavily [[sexually dimorphic]].<ref>{{cite journal | last1 = Coates | first1 = M. | last2 = Gess | first2 = R. | last3 = Finarelli | first3 = J. | last4 = Criswell | first4 = K. | last5 = Tietjen | first5 = K. | year = 2016 | title = A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes | journal = Nature | volume = 541| issue = 7636| pages = 208–211| doi = 10.1038/nature20806 | pmid = 28052054 | bibcode = 2017Natur.541..208C | s2cid = 4455946 }}</ref>

| align=center style="background:rgb(165,100,165)" | [[Eugeneodontida|<span style="color:white;">†Eugeneodontida</span>]]

| align=center | [[Eugeneodontida|Eugeneodonts]]

| align=center | <small></small>Eugeneodontida

| valign=top | Members of the holocephali, they are characterized by large tooth whorls in their jaws.<ref>{{cite journal |last1=Tapanila |first1=L |last2=Pruitt |first2=J |last3=Pradel |first3=A |last4=Wilga |first4=C |last5=Ramsay |first5=J |last6=Schlader |first6=R |last7=Didier |first7=D |year=2013 |title=Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion |journal=Biology Letters |volume=9 |issue= 2|page=20130057 |doi=10.1098/rsbl.2013.0057 |pmid=23445952 |pmc=3639784 }}</ref>

| align=center | <small></small>Cappetta et al., 1993

| align=center | 1

| align=center | 1

| [[File:Early SharkCladoselache.jpgpng|140px140x140px]]

| align=center | <small></small>Dean, 1894

| [[File:Triodus1dbXenacanth.jpgpng|140px147x147px]]

| [[File:Sphenacanthus1DBDracopristis hoffmanorum.jpgpng|140px147x147px]]

| [[File:Hybodus modelhauffianus.jpgpng|140px147x147px]]