Editing Endocerida

{{short description|Fossil order of cephalopods}}
{{Automatic taxobox
| fossil_range = {{fossil range|Floian|Hirnantian|latest=early Silurian|ref=<ref name=Kroger2009/><ref name="Barskov2008"/>}}
| image = Cameroceras_trentonese.jpg
| image_caption = The massive endocerid ''[[Cameroceras]]'' (middle) alongside other nautiloids
| taxon = Endocerida
| authority = Teichert, 1933
| subdivision_ranks = Families
| subdivision = † [[Cyrtendoceratidae]]<br>
† [[Endoceratidae]]<br>
† [[Proterocameroceratidae]]<br>
† [[Yorkoceratidae]]
}}

'''Endocerida''', from [[Ancient Greek]] ἔνδον (''éndon''), meaning "inside", and κέρας (''kéras''), meaning "horn", is an extinct [[Nautiloidea|nautiloid]] order, a group of [[cephalopod]]s from the Lower Paleozoic with cone-like deposits in their [[siphuncle]]. Endocerida was a diverse group of [[cephalopod]]s that lived from the Early [[Ordovician]] possibly to the Late [[Silurian]]. Their shells were variable in form. Some were straight ([[orthoconic]]), others curved (cyrtoconic); some were long (longiconic), others short (breviconic). Some long-shelled forms like ''[[Endoceras]]'' attained shell lengths close to {{convert|6|m|ft}}. The related ''[[Cameroceras]]'' is anecdotally reported to have reached lengths approaching {{convert|9|m|ft}}, but these claims are problematic. The overwhelming majority of endocerids and nautiloids in general are much smaller, usually less than a meter long when fully grown.

== Morphology==
[[Image:Endoceras.JPG|thumb|left|''[[Endoceras]]'' fossils]] 
Endocerids had a relatively small [[body chamber]] as well as a proportionally large [[siphuncle]], which in some genera reached nearly half the shell diameter. This suggests that much of the visceral mass may have been housed within the siphuncle itself rather than just in the body chamber as with other nautiloids (Teichert, 1964). Endocerids are primarily distinguished by the presence of conical calcareous deposits, known as endocones, found in the more apical portion of the siphuncle. They are thought to act as a counterweight for the animal’s body. The chambers ([[Camera (cephalopod)|camerae]]) of endocerids are always free of organic deposits, unlike [[Orthoceratoidea|orthoceratoid]] cephalopod orders such as the Orthocerida and [[Actinocerida]].

===Body size===

Endocerids reached enormous body sizes. The largest confirmed specimen, belonging to ''[[Endoceras|Endoceras giganteum]]'', is {{convert|3|m|ft}} long as preserved, but is missing a substantial portion of its aboral end.<ref name=Teichert1960/><ref name=Klug2015/> The reconstructed length of the shell is nearly {{convert|6|m|ft}}.<ref name=Teichert1960/><ref name=Klug2015/> An alleged endocerid specimen {{convert|30|ft|m}} long is unconfirmed.<ref name=Teichert1960/>

== Ecology==
[[File:Endoceras sp.png|left|thumb|Life restoration of ''Endoceras'']]
The mode of life of endocerids is debated.<ref name=Mironenko2018/> Endocerids may have been the [[apex predator]]s of the Ordovician, probably living close to the sea floor, and preying on [[trilobite]]s, molluscs, [[brachiopod]]s and other bottom-dwelling organisms.<ref name=Kroger2009/> They were probably not active [[nekton]]ic swimmers, but rather crawled over the floor of epicontinental seas or lay there in ambush.{{Citation needed|date=July 2018}} Although there is study that supports [[Filter feeder|filter feeding]] ecology,<ref name=Mironenko2018/> according to [[Hydrostatics|hydrostatic]] properties, it is not likely and still supports benthic predators.<ref>{{Cite journal |last1=Peterman |first1=David J. |last2=Barton |first2=Christopher C. |last3=Yacobucci |first3=Margaret M. |date=2019-05-21 |title=The hydrostatics of Paleozoic ectocochleate cephalopods (Nautiloidea and Endoceratoidea) with implications for modes of life and early colonization of the pelagic zone |url=https://palaeo-electronica.org/content/2019/2521-cephalopod-hydrostatics |journal=Palaeontologia Electronica |language=English |volume=22 |issue=2 |pages=1–29 |doi=10.26879/884 |s2cid=181794320 |issn=1094-8074|doi-access=free }}</ref>

===Reproduction===

Endocerids laid relatively large eggs, and hatched at a relatively large body size.<ref name=Laptikhovsky2018/> It is likely that endocerids were [[demersal]] after hatching, as large eggs would make an easy target for predators in the pelagic zone.<ref name=Laptikhovsky2018/> Endocerids may have migrated from their habitat in the open ocean to shallower water to lay their eggs.<ref name=Mironenko2018/>

==Diversity==
Endocerids were among some half a dozen cephalopod orders that appeared in the Lower Ordovician. They reached their greatest diversity during the Lower to Mid-Ordovician, but were already in decline by the middle of this period with most genera becoming extinct by the end of the [[Sandbian]] (late Ordovician), while some rare hangers on lasted into the [[Silurian]].<ref name='Barskov2008'>{{cite journal
 | doi = 10.1134/S0031030108110014
 | title = Cephalopods in the marine ecosystems of the Paleozoic
 | year = 2008
 | author = Barskov, I. S.
 | journal = Paleontological Journal
 | volume = 42
 | pages = 1167
 | last2 = Boiko
 | first2 = M. S.
 | last3 = Konovalova
 | first3 = V. A.
 | last4 = Leonova
 | first4 = T. B.
 | last5 = Nikolaeva
 | first5 = S. V.
 | issue = 11 | s2cid = 83608661
 }}</ref>  In any case, the endocerid lineage became completely extinct relatively early on in cephalopod history.

==Classification==

=== Evolution ===
Endocerids evolved from the earlier [[Ellesmerocerida|ellesmerocerids]], most likely from a genus similar to ''[[Pachendoceras]]''. This ellesmerocerid gave rise to ''[[Proendoceras]]'', the earliest representative of the [[Proterocameroceratidae]] and hence of the Endocerida. Endocerids evolved from ellesmerocerids by reduction of siphuncle diaphragms and the development of endocones. In the early part of the mid-Lower Ordovician, the Endocerida quickly diversified into many different families. In true endocerids, there was a trend of overall increasing size, eventually resulting in massive orthoconic genera such as ''[[Endoceras]]'' and ''[[Cameroceras]]''. In another lineage (now known as [[Bisonocerida]]), the siphuncle grew more complex, resulting in genera such as ''[[Chihlioceras]]'' and ''[[Allotrioceras]]''.

=== Taxonomy ===
Citing its diversity, Curt Teichert (1964) placed the Endocerida in its own subclass called the Endoceroidea or '''Endoceratoidea''' (which some Russian paleontologists ranked as a [[superorder]] instead. [[Rousseau Flower]] rejected this separation on the grounds that endocerids were no more diverse or complex than any other order. He considered them to be simply another order within the Nautiloidea.

Flower (1958) divided the Endocerida into two suborders, the Proterocamerocerina and the Endocerina. As he defined the two suborders, Proterocamerocerina included the [[Proterocameroceratidae]], [[Manchuroceratidae]], and [[Emmonsoceratidae]], while Endocerina included the [[Piloceratidae]] and [[Endoceratidae]]. Endocerid classification since then has relied on a dichotomy between short-shelled forms with complex endocones and long-shelled forms with simple endocones.

Endocerid relationships have been difficult to establish both within the order and relative to other nautiloids. Their generally orthoconic shell shape and dorsomyarian muscle scars are similar to the subclass [[Orthoceratoidea]], which are ancestral to [[Ammonoidea|ammonoids]] (ammonites) and [[Coleoidea|coleoids]] (squid, octopus, etc.).<ref name=":2">{{Cite journal |last1=King |first1=Andy H. |last2=Evans |first2=David H. |date=2019 |title=High-level classification of the nautiloid cephalopods: a proposal for the revision of the Treatise Part K |journal=[[Swiss Journal of Palaeontology]] |language=en |volume=138 |issue=1 |pages=65–85 |doi=10.1007/s13358-019-00186-4 |s2cid=133647555 |issn=1664-2384|doi-access=free }}</ref> However, their nautilosiphonate [[connecting ring]] structure and lack of [[cameral deposit]]s are more similar to living [[nautilus]] and their proposed ancestors, the subclass [[Multiceratoidea]]. Some studies have re-established Endoceratoidea to clarify that endocerids occupy a unique subclass of nautiloids.<ref name=":1">{{Cite journal |last1=Pohle |first1=Alexander |last2=Kröger |first2=Björn |last3=Warnock |first3=Rachel C. M. |last4=King |first4=Andy H. |last5=Evans |first5=David H. |last6=Aubrechtová |first6=Martina |last7=Cichowolski |first7=Marcela |last8=Fang |first8=Xiang |last9=Klug |first9=Christian |date=2022-04-14 |title=Early cephalopod evolution clarified through Bayesian phylogenetic inference |journal=BMC Biology |volume=20 |issue=1 |pages=88 |doi=10.1186/s12915-022-01284-5 |pmid=35421982 |pmc=9008929 |s2cid=248158390 |issn=1741-7007 |doi-access=free }}</ref>

Restudy of piloceratid-like families with complex endocones has suggested that Endocerida in its broadest form is [[Polyphyly|polyphyletic]], with piloceratid-like and proterocameroceratid-like members having independent origins from ellesmerocerids. In light of this issue, the numerous piloceratid-like families were placed within a new order, [[Bisonocerida]].<ref name=":0">{{Cite journal |last1=Evans |first1=David H. |last2=King |first2=Andrew H. |date=2012-01-01 |title=Resolving polyphyly within the Endocerida: The Bisonocerida nov., a new order of early palaeozoic nautiloids |url=https://www.sciencedirect.com/science/article/pii/S0016699511001100 |journal=Geobios |language=en |volume=45 |issue=1 |pages=19–28 |doi=10.1016/j.geobios.2011.11.015 |issn=0016-6995|url-access=subscription }}</ref> Bisonocerida may still be related to endocerids within Endoceratoidea.<ref name=":1" />

== See also ==
* [[Cephalopod size]]

== References ==
{{Reflist|refs=
<ref name=Klug2015>
{{cite journal
 | first1 = Christian
 | last1 = Klug
 | first2 = Kenneth
 | last2 = De Baets
 | first3 = Björn
 | last3 = Kröger
 | first4 = Mark A.
 | last4 = Bell
 | first5 = Dieter
 | last5 = Korn
 | first6 = Jonathan L.
 | last6 = Payne
 | year = 2015
 | title = Normal giants? Temporal and latitudinal shifts of Palaeozoic marine invertebrate gigantism and global change
 | journal = Lethaia
 | volume = 48
 | issue = 2
 | pages = 267–288
 | doi = 10.1111/let.12104
}}
</ref>
<ref name=Kroger2009>
{{cite journal
 | doi = 10.1016/j.palaeo.2008.12.015
 | title = Pulsed cephalopod diversification during the Ordovician
 | year = 2008
 | last1= Kröger
 | first1 = Björn
 | last2 = Yun-Bai
 | first2 = Zhang
 | journal = Palaeogeography, Palaeoclimatology, Palaeoecology
 | volume = 273
 | issue = 1–2
 | pages = 174–183
}}
</ref>
<ref name=Laptikhovsky2018>
{{cite journal
 | first1 = Vladimir
 | last1 = Laptikhovsky
 | first2 = Svetlana
 | last2 = Nikolaeva
 | first3 = Mikhail
 | last3 = Rogov
 | year = 2018
 | title = Cephalopod embryonic shells as a tool to reconstruct reproductive strategies in extinct taxa
 | journal = Biological Reviews
 | volume = 93
 | issue = 1
 | pages = 270–83
 | doi = 10.1111/brv.12341
 | pmid = 28560755
| doi-access = free
 }}
</ref>
<ref name=Mironenko2018>
{{cite journal
 | first1 = Aleksandr A.
 | last1 = Mironenko
 | title = Endocerids: suspension feeding nautiloids?
 | journal = Historical Biology
 | doi = 10.1080/08912963.2018.1491565
 | year = 2018
 | volume = 32
 | issue = 2
 | pages = 1–9
| s2cid = 89799876
 }}
</ref>
<ref name=Teichert1960>
{{cite journal
| first1 = Curt
| last1 = Teichert
| first2 = Bernhard
| last2 = Kummel
| year = 1960
| title = Size of endoceroid cephalopods
| journal = Breviora
| volume = 128
}}
</ref>
}}

==Further reading==
*Clarke, J.M. 1897. [https://www.biodiversitylibrary.org/page/14923672 The Lower Silurian Cephalopoda of Minnesota]. In: E.O. Ulrich, J.M. Clarke, W.H. Scofield & N.H. Winchell  ''The Geology of Minnesota. Vol. III, Part II, of the final report. Paleontology.'' Harrison & Smith, Minneapolis. pp.&nbsp;761–812.
*Flower, 1955, ''Status of Endoceroid Classification''; ''Jour. Paleon.'' V 29. n.3 May 1955, pp 327–370; figs, plts.
*Flower,1958, ''Some Chazyan and Mohawkian Endoceratida''; ''Jour. Paleon'' V32, n.3, pp 433–468; figs, plts. 
*Flower, 1976, ''Ordovician Cephalopod Faunas and Their Role in Correlation'', in Bassett, M.C.(Ed); ''The Ordovician System: Proceedings of a Paleontological Association Symposium''; Birmingham, Eng.1974; Univ of Wales and Welsh Nat’l Mus Press.    
*Teichert, C. 1964, ''Endoceratoidea'', in the ''[[Treatise on Invertebrate Paleontology]]'', Part-K (Nautiloidea; Geol Soc of America and University of Kansas Press; pp K160–K188; figs.
*Neale Monks and Philip Palmer. ''Ammonites''. Smithsonian Institution Press, Washington D.C. 2002.

{{fossil cephalopods}}
{{Taxonbar|from=Q144946}}

[[Category:Endocerida]]
[[Category:Prehistoric cephalopod orders]]
[[Category:Ordovician cephalopods]]
[[Category:Early Ordovician first appearances]]
[[Category:Late Ordovician extinctions]]
[[Category:Fossil taxa described in 1933]]