Editing Nautiloid (section)

==Evolutionary history==
Nautiloids are first known from the late Cambrian Fengshan Formation of northeastern [[China]], where they seem to have been quite diverse (at the time this was a warm shallow sea rich in marine life). However, although four orders have been proposed from the 131 [[species]] named, there is no certainty that all of these are valid, and indeed it is likely that these taxa are seriously oversplit.

[[File:Cyrtoceras NT small.jpg|thumb|Reconstruction of ''[[Cyrtoceras|Cyrtoceras sp]]'']]
[[File:Gyronaedyceras eryx.jpg|thumb|''[[Gyronaedyceras|Gyronaedyceras eryx]]'', an oncocerid from the Middle Devonian of Wisconsin]]
[[File:Acleistoceras whitfieldi.jpg|thumb|''[[Acleistoceras|Acleistoceras whitfieldi]]'', an oncocerid from the Middle Devonian of Wisconsin]]
[[File:A coiled cephalopods imprint from Dane county, Wisconsin.jpg|thumb|''[[Trocholites]]'', an [[Tarphycerida|tarphycerid]] from the Upper Ordovician of Wisconsin]]

Most of these early forms died out, but a single family, the [[Ellesmeroceratidae]], survived to the early [[Ordovician]], where it ultimately gave rise to all subsequent cephalopods. In the Early and Middle Ordovician the nautiloids underwent an evolutionary radiation.<ref name="KR2008">{{Cite journal | vauthors = Kroeger B, Landing E | journal = Geological Magazine| volume = 145 | title = Onset of the Ordovician cephalopod radiation – evidence from the Rochdale Formation (middle Early Ordovician, Stairsian) in eastern New York| doi = 10.1017/S0016756808004585| year = 2008 | issue = 4 | pages = 490–520| bibcode = 2008GeoM..145..490K| s2cid = 129441156| url = http://edoc.hu-berlin.de/18452/22517}}</ref><ref name="Kr2009">{{cite journal | vauthors = Kroeger B, Yun-Bai Z | title = Pulsed cephalopod diversification during the Ordovician | journal =  Palaeogeography, Palaeoclimatology, Palaeoecology | volume = 273 | issue = 1–2| pages = 174–201 | year = 2009 | doi = 10.1016/j.palaeo.2008.12.015 | bibcode = 2009PPP...273..174K}}</ref> Some eight new orders appeared at this time, covering a great diversity of shell types and structure, and ecological lifestyles.

Nautiloids remained at the height of their range of adaptations and variety of forms throughout the Ordovician, [[Silurian]], and [[Devonian]] periods, with various straight, curved and coiled shell forms coexisting at the same time. Several of the early orders became extinct over that interval, but others rose to prominence.

Nautiloids began to decline in the Devonian, perhaps due to competition with their descendants and relatives the Ammonoids and [[Coleoid]]s, with only the [[Nautilida]] holding their own (and indeed increasing in diversity). Their shells became increasingly tightly coiled, while both numbers and variety of non-nautilid species continued to decrease throughout the [[Carboniferous]] and [[Permian]].

The massive extinctions at the end of the Permian were less damaging to nautiloids than to other [[taxon|taxa]] and a few groups survived into the early [[Mesozoic]], including [[Pseudorthocerida|pseudorthocerids]], [[Bactritida|bactritids]], nautilids and possibly [[Orthocerida|orthocerids]]. The last straight-shelled forms were long thought to have disappeared at the end of the [[Triassic]], but a possible orthocerid has been found in [[Cretaceous]] rocks. Apart from this exception, only a single nautiloid suborder, the [[Nautilina]], continued throughout the [[Mesozoic]], where they co-existed quite happily with their more specialised ammonoid cousins. Most of these forms differed only slightly from the modern nautilus. They had a brief resurgence in the early [[Tertiary]] (perhaps filling the niches vacated by the ammonoids in the [[Cretaceous–Paleogene extinction event|end Cretaceous extinction]]), and maintained a worldwide distribution up until the middle of the [[Cenozoic]] Era. With the global cooling of the [[Miocene]] and [[Pliocene]], their geographic distribution shrank and these hardy and long-lived animals declined in diversity again. Today there are only six living species, all belonging to two genera, ''[[Nautilus (genus)|Nautilus]]'' (the pearly nautilus), and ''[[Allonautilus]]''.

The recent decrease in the once worldwide distribution of nautiloids is now believed to have been caused by the spread of [[pinniped]]s.<ref name=":1">{{Cite web |date=2022-10-15 |title=How seals made Nautilus a 'Living Fossil' |url=https://journalofbiogeographynews.org/2022/10/15/how-seals-made-nautilus-a-living-fossil/ |url-status=live |archive-url=https://web.archive.org/web/20221023145840/https://journalofbiogeographynews.org/2022/10/15/how-seals-made-nautilus-a-living-fossil/ |archive-date=2022-10-23 |access-date=2023-03-29 |website=Journal of Biogeography |language=en-US}}</ref> From the [[Oligocene]] onward, the appearance of pinnipeds in the geological record of a region coincides with the disappearance of nautiloids from that region.<ref name=":2">{{Cite journal |last1=Kiel |first1=Steffen |last2=Goedert |first2=James L. |last3=Tsai |first3=Cheng-Hsiu |date=2022-09-22 |title=Seals, whales and the Cenozoic decline of nautiloid cephalopods |journal=Journal of Biogeography |language=en |volume=49 |issue=11 |pages=1903–1910 |doi=10.1111/jbi.14488 |s2cid=252576418 |issn=0305-0270 |doi-access=free |bibcode=2022JBiog..49.1903K }}</ref> As a result, nautiloids are now limited to their current distribution in the tropical Indo-Pacific Ocean, where pinnipeds are absent.<ref name=":1" /> The genus ''[[Aturia]]'' seem to have temporarily survive regions where pinnipeds were present through adaptations to fast and agile swimming, but eventually went extinct as well.<ref name=":2" /> Predation by short-snouted whales and the development of [[Oxygen minimum zone|OMZs]], preventing nautiloids from retreating into deeper water, are also cited as other potential causes of extinction.<ref name=":2" />

===Timeline of orders===

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 from: -542    till:  -488.3   color:cambrian  text:[[Cambrian]]          
 from: -488.3    till: -443.7    color:ordovician    text:[[Ordovician]]
 from: -443.7    till: -416    color:silurian    text:[[Silurian]]
 from: -416    till: -359.2   color:devonian    text:[[Devonian]]
 from: -359.2    till: -299   color:carboniferous    text:[[Carboniferous]]
 from: -299    till: -251   color:permian    text:[[Permian]]
 from: -251    till: -199.6  color:triassic    text:[[Triassic]]
 from: -199.6    till: -145.5   color:jurassic    text:[[Jurassic]]
 from: -145.5   till: -65.5   color:cretaceous    text:[[Cretaceous]]
 from: -65.5    till: -23.03   color:paleogene    text:[[Paleogene]]
 from: -23.03    till: -2.588   color:neogene    text:[[Neogene|Neog.]]
 from: -2.588    till: 0   color:quaternary    text:[[Quaternary|Q.]]

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 from:  -542   till:  -251    color:paleozoic    text:[[Paleozoic Era]]
 from:  -251   till:  -65.5    color:mesozoic    text:[[Mesozoic Era]]
 from:  -65.5   till:  0   color:cenozoic    text:[[Cenozoic]]

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 color:cambrian bar:NAM1  from:-497    till:-488.3 text:[[Plectronocerida]]
 color:paleozoic bar:NAM2  from:-497    till:-453 text:[[Ellesmerocerida]]
 color:paleozoic bar:NAM3  from:-485.4    till:-358.9 text:[[Actinocerida]]
 color:ordovician bar:NAM4 from:-477.7    till:-443.8 text:[[Endocerida]]
 color:paleozoic bar:NAM5 from:-485.4    till:-358.9 text:[[Tarphycerida]]
 color:paleozoic bar:NAM6 from:-470     till:-323.2 text:[[Oncocerida]]
 color:paleozoic bar:NAM7 from:-470     till:-358.9 text:[[Discosorida]]
 color:mesozoic bar:NAM8 from:-419.2     till:0 text:[[Nautilida]]

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 from: -443.7    till: -416    color:silurian    text:[[Silurian]]
 from: -416    till: -359.2   color:devonian    text:[[Devonian]]
 from: -359.2    till: -299   color:carboniferous    text:[[Carboniferous]]
 from: -299    till: -251   color:permian    text:[[Permian]]
 from: -251    till: -199.6  color:triassic    text:[[Triassic]]
 from: -199.6    till: -145.5   color:jurassic    text:[[Jurassic]]
 from: -145.5   till: -65.5   color:cretaceous    text:[[Cretaceous]]
 from: -65.5    till: -23.03   color:paleogene    text:[[Paleogene]]
 from: -23.03    till: -2.588   color:neogene    text:[[Neogene|Neog.]]
 from: -2.588    till: 0   color:quaternary    text:[[Quaternary|Q.]]

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 from:  -542   till:  -251    color:paleozoic    text:[[Paleozoic Era]]
 from:  -251   till:  -65.5    color:mesozoic    text:[[Mesozoic Era]]
 from:  -65.5   till:  0   color:cenozoic    text:[[Cenozoic]]
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