Product Code Database
Example Keywords: hair -playbook $90
barcode-scavenger
   » » Wiki: Nautiloid
Tag Wiki 'Nautiloid'.
Tag

Nautiloids are a group of () which originated in the and are represented today by the living Nautilus and . nautiloids are diverse and species rich, with over 2,500 recorded species. They flourished during the early era, when they constituted the main predatory animals. Early in their evolution, nautiloids developed an extraordinary diversity of shell shapes, including coiled morphologies and giant straight-shelled forms (). No orthoconic and only a handful of coiled species, the , survive to the present day.

In a broad sense, "nautiloid" refers to a major cephalopod subclass or collection of subclasses ( Nautiloidea sensu lato ). Nautiloids are typically considered one of three main groups of cephalopods, along with the extinct (ammonites) and living (such as , , and kin). While ammonoids and coleoids are with exclusive ancestor-descendant relationships, this is not the case for nautiloids. Instead, nautiloids are a grade of various early-diverging cephalopod lineages, including the ancestors of ammonoids and coleoids. Some authors prefer a narrower definition of Nautiloidea (Nautiloidea sensu stricto), as a singular subclass including only those cephalopods which are closer to living nautiluses than they are to either ammonoids or coleoids.


Taxonomic relationships
Nautiloids are among the group of animals known as , an advanced class of which also includes , and modern such as octopus and squid. Other mollusks include , and .

Traditionally, the most common classification of the cephalopods has been a four-fold division (by Bather, 1888), into the , nautiloids, , and . This article is about nautiloids in that broad sense, sometimes called Nautiloidea sensu lato.

speaking, nautiloids are a assemblage united by shared primitive () features not found in derived cephalopods. In other words, they are a grade group that is thought to have given rise to orthoceratoids, ammonoids and coleoids, and are defined by the exclusion of those descendent groups. Both ammonoids and coleoids have traditionally been assumed to have descended from , which in turn arose from . The ammonoids appeared early in the period (some 400 million years ago) and became abundant in the era, before their extinction at the end of the Cretaceous.

Some workers apply the name Nautiloidea to a more exclusive group, called Nautiloidea sensu stricto. This taxon consists only of those orders that are clearly related to the modern nautilus to the exclusion of other modern cephalopods. In this restricted definition, membership is somewhat variable between authors, but it usually includes Tarphycerida, Oncocerida, and Nautilida.


Shell
All nautiloids have a large external shell, divided into a narrowing chambered region (the ) and a broad, open occupied by the animal in life. The outer wall of the shell, also known as the conch, defines its overall shape and texture. The chambers (camerae) of the phragmocone are separated from each other by thin curved walls (septa), which formed during growth spurts of the animal. During a growth spurt, the rear of the mantle secretes a new septum, adding another chamber to the series of shell chambers. At the same time, shell material is added around the shell opening (aperture), enlarging the body chamber and providing more room for the growing animal. Sutures (or suture lines) appear where each septum contacts the wall of the outer shell. In life, they are visible as a series of narrow wavy lines on the outer surface of the shell. Like their underlying septa, the sutures of the nautiloids are simple in shape, being either straight or slightly curved. This is different from the "zigzag" sutures of the goniatites and the highly complex sutures of the ammonites.

The septa are perforated by the , a fleshy tube which runs through each of the internal chambers of the shell. Surrounding the fleshy tube of the siphuncle are structures made of (a polymorph of calcium carbonate – which during fossilisation is often recrystallized to calcite, a more stable form of calcium carbonate CaCO3): septal necks and connecting rings. Some of the earlier nautiloids deposited calcium carbonate in the empty chambers (called cameral deposits) or within the siphuncle ( endosiphuncular deposits), a process which may have been connected with controlling . The nature of the siphuncle and its position within the shell are important in classifying nautiloids and can help distinguish them from ammonoids. The siphuncle is on the shell periphery in most ammonoids whereas it runs through the center of the chambers in some nautiloids, including living nautiluses.

The subclass Nautiloidea, in its broader definition, is distinguished from other cephalopods by two main characteristics: the septa are smoothly concave in the forward direction, producing external sutures which are generally simple and smooth. The siphuncle is supported by septal necks which point to the rear (i.e. retrosiphonate) throughout the of the animal.

Modern nautiluses have deeply coiled shells which are involute, meaning that the larger and more recent whorls overlap and obscure older whorls. The shells of fossil nautiloids may be either straight (i.e., as in and ), curved (as in ) coiled (as in ), or rarely a helical coil (as in ). Some species' shells—especially in the late Paleozoic and early Mesozoic—are ornamented with spines and ribs, but most have a smooth shell. The shells are formed of aragonite, although the cameral deposits may consist of primary calcite. The coloration of the shell of the modern nautilus is quite prominent, and, although somewhat rarely, the shell coloration has been known to be preserved in fossil nautiloids. They often show color patterns only on the dorsal side, suggesting that the living animals swam horizontally.


Modern nautiloids
Much of what is known about the extinct nautiloids is based on what we know about modern , such as the chambered nautilus, which is found in the southwest from to the , and in the off the coast of . It is not usually found in waters less than deep and may be found as far down as .

Nautili are free swimming animals that possess a head with two simple lens-free eyes and arms (or tentacles). They have a smooth shell over a large body chamber, which is divided into subchambers filled with an inert gas (similar to the composition of atmospheric air, but with more and less ) making the animal neutrally buoyant in the water. As many as 90 are arranged in two circles around the mouth. The animal is predatory, and has jaws which are horny and beak-like, allowing it to feed on .

Empty nautilus shells may drift a considerable distance and have been reported from , and . Undoubtedly the same applies to the shells of nautiloids, the gas inside the shell keeping it buoyant for some time after the animal's death, allowing the empty shell to be carried some distance from where the animal lived before finally sinking to the seafloor.

Nautili propel themselves by jet propulsion, expelling water from an elongated funnel called the , which can be pointed in different directions to control their movement. Unlike the and other cephalopods, modern nautili do not have an ink sac, and there is no evidence to suggest that the extinct forms possessed one either. Furthermore, unlike the extinct , the modern nautilus lacks an , a biomineralized plate which is proposed to act as an operculum which closes the shell to protect the body. However, aptychus-like plates are known from some extinct nautiloids, and they may be homologous to the fleshy hood of a modern nautilus.


Fossil record
Nautiloids are often found as in early rocks (less so in more recent strata).

The rocks of the period in the and parts of the United States contain a variety of nautiloid fossils, and specimens such as and Rayonnoceras may be found in the of the period in Ireland. The marine rocks of the period in often yield specimens of Cenoceras, and nautiloids such as are also found in the Pierre Shale formation of the period in the north-central United States.

Specimens of the nautiloid have been recorded measuring up to in shell length, and there is a description of a specimen estimated to have reached , although that specimen is reported as destroyed. These large nautiloids would have been formidable predators of other marine animals at the time they lived.

In some localities, such as and , the of nautiloids accumulated in such large numbers that they form limestones composed of nonspecific assemblages known as cephalopod beds, cephalopod limestones, nautiloid limestones, or Orthoceras limestones in the geological literature. Although the term now only refers to a genus, in prior times it was employed as a general name given to all nautiloids that lived from the Ordovician to the periods (but were most common in the early era).


Evolutionary history
Nautiloids are first known from the late Cambrian Fengshan Formation of northeastern , 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 named, there is no certainty that all of these are valid, and indeed it is likely that these taxa are seriously oversplit.

Most of these early forms died out, but a single family, the Ellesmeroceratidae, survived to the early , where it ultimately gave rise to all subsequent cephalopods. In the Early and Middle Ordovician the nautiloids underwent an evolutionary radiation. 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, , and 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 , with only the 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 and .

The massive extinctions at the end of the Permian were less damaging to nautiloids than to other and a few groups survived into the early , including , , nautilids and possibly . The last straight-shelled forms were long thought to have disappeared at the end of the , but a possible orthocerid has been found in rocks. Apart from this exception, only a single nautiloid suborder, the , continued throughout the , 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 (perhaps filling the niches vacated by the ammonoids in the end Cretaceous extinction), and maintained a worldwide distribution up until the middle of the Era. With the global cooling of the and , 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 (the pearly nautilus), and .

The recent decrease in the once worldwide distribution of nautiloids is now believed to have been caused by the spread of . From the onward, the appearance of pinnipeds in the geological record of a region coincides with the disappearance of nautiloids from that region. As a result, nautiloids are now limited to their current distribution in the tropical Indo-Pacific Ocean, where pinnipeds are absent. The genus seem to have temporarily survive regions where pinnipeds were present through adaptations to fast and agile swimming, but eventually went extinct as well. Predation by short-snouted whales and the development of OMZs, preventing nautiloids from retreating into deeper water, are also cited as other potential causes of extinction.


Timeline of orders
ImageSize = width:1000px height:auto barincrement:15px PlotArea = left:10px bottom:50px top:10px right:10px

Period = from:-542 till:-0 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:25 start:-542 ScaleMinor = unit:year increment:5 start:-542 TimeAxis = orientation:hor AlignBars = justify

Colors =

#legends
 id:black        value:black
 id:white        value:white
 id:paleozoic     value:rgb(0.6,0.75,0.55)
 id:cambrian   value:rgb(0.49,0.63,0.33)
 id:ordovician   value:rgb(0,0.57,0.44)
 id:silurian   value:rgb(0.70,0.88,0.71)
 id:devonian   value:rgb(0.8,0.55,0.22)
 id:carboniferous   value:rgb(0.4,0.65,0.6)
 id:permian   value:rgb(0.94,0.25,0.24)
 id:mesozoic     value:rgb(0.38,0.77,0.79)
 id:triassic     value:rgb(0.51,0.17,0.57)
 id:jurassic     value:rgb(0.2,0.7,0.79)
 id:cretaceous   value:rgb(0.5,0.78,0.31)
 id:cenozoic     value:rgb(0.95,0.98,0.11)
 id:paleogene   value:rgb(0.99,0.6,0.32)
 id:neogene   value:rgb(0.999999,0.9,0.1)
 id:quaternary   value:rgb(0.98,0.98,0.50)
     

BarData=

bar:eratop
bar:space
bar:periodtop
bar:space
bar:NAM1
bar:NAM2
bar:NAM3
bar:NAM4
bar:NAM5
bar:NAM6
bar:NAM7
bar:NAM8
     

bar:space
bar:period
bar:space
bar:era
     

PlotData=

align:center textcolor:black fontsize:M mark:(line,black) width:25
shift:(7,-4)
     

bar:periodtop
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:[[Neog.|Neogene]]
from: -2.588    till: 0   color:quaternary    text:[[Q.|Quaternary]]
     

bar:eratop
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]]
     

PlotData=

align:left fontsize:M mark:(line,white) width:5 anchor:till align:left
     

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]]
     

PlotData=

align:center textcolor:black fontsize:M mark:(line,black) width:25
     

bar:period
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:[[Neog.|Neogene]]
from: -2.588    till: 0   color:quaternary    text:[[Q.|Quaternary]]
     

bar:era
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]]
     


Classification

Older classification systems
A consensus on nautiloid classification has traditionally been elusive and subject to change, as different workers emphasize different fundamental traits when reconstructing evolutionary events. The largest and most widely cited publication on nautiloid taxonomy is the Treatise on Invertebrate Paleontology Part K by Teichert et al. 1964, though new information has rendered this volume outdated and in need of revision. Treatise Part K was based on previous classification schemes by Flower & Kummel (1950) and the Russian Osnovy Paleontologii Vol. 5 (1962) textbook.

Other comprehensive taxonomic schemes have been devised by Wade (1988), Teichert (1988), and Shevyrev (2006). Wade (1988) divided the subclass Nautiloidea ( sensu lato) into 6 superorders, incorporating orders that are phylogenetically related. They are:

Three of these superorders were established for orders of uncertain placement: Endocerida, Actinocerida, and Discosorida. The other three unite related orders which share a common ancestor and form a branch of the nautiloid taxonomic tree: Plectronoceratoidea, which consists mostly of small Cambrian forms that include the ancestors of subsequent stocks; Orthoceratoidea, which unites different primarily orthoconic orders (including the ancestors for Bacritida and Ammonoidea); and Nautilitoidea, which includes the first coiled cephalopods, Tarphycerida, as well as Nautilida, which includes the recent Nautilus. Another order, , which is derived from , is sometimes included with Nautiloidea, sometimes with , and sometimes placed in a subclass of its own, .

Recently some workers in the field have come to recognize Dissidocerida as a distinct order, along with Pseudorthocerida, both previously included in as subtaxa.


Early cladistic efforts
approaches are rare in nautiloid systematics. Many nautiloid orders (not to mention the group as a whole) are not , but rather grades. This means that they include some descendant taxa while excluding others. For example, the paraphyletic order Orthocerida includes numerous orthocerids stretching through the Paleozoic, but it excludes colloids, despite colloids having a well-established ancestry among the orthocerids. Interpretations by Engeser (1996–1998) suggests that nautiloids, and indeed cephalopods in general, should be split into two main clades: Palcephalopoda (including all the nautiloids except Orthocerida and Ascocerida) and (the rest of the cephalopods). Palcephalopoda is meant to correspond to groups which are closer to living nautilus, while Neocephalopoda is meant to correspond to groups closer to living coleoids. One issue which this scheme is the necessity of establishing a firm ancestry for nautilus, to contextualize which cephalopods are closer to which of the two living end members. On the basis of morphological traits, Nautilida is most similar to coiled early nautiloids such as the Tarphycerida and Oncocerida. However, these orders diverged from coleoid ancestors in the early Ordovician at the latest, while genetic divergence estimates suggest that Nautilida diverged in the Silurian or Devonian.

A more recent phylogenetic study by Lindgren et al. (2004), which supports the monophyly of cephalopods, does not bear on the Palcephalopod/Neocephalopod question, since the only cephalopods included were Nautilus and coleoids.


Recent revisions
For an in-process revision of Treatise Part K, King & Evans (2019) reclassified nautiloids sensu lato into five subclasses. Major groups were primarily defined by variation in their muscle attachment types. Other traits referenced during this reclassification include morphology, connecting ring structure, and the extent of cameral and endosiphuncular deposits. While most previous studies referred to subclasses with the suffix '-oidea', these authors instead opted for the suffix '-ia', to prevent confusion between group levels. For example, Nautiloidea sensu stricto was renamed to Nautilia, to differentiate it from the informal broader definition of "nautiloid". In addition, they used the unsimplified names for orders, with the suffix '-atida' rather than the common simplified form, '-ida'.

Traditional nautiloid classification schemes emphasize certain character traits over others, potentially involving personal bias as to which traits are worth emphasizing according to different authors. This issue may be resolved by sampling all morphological traits equally through bayesian phylogenetic inference. The first cephalopod-focused paper to use this technique was published by Pohle et al. (2022). They recovered several previously hypothesized groups, though many orders were determined to be paraphyletic. The study was focused on early cephalopod diversification in the Late Cambrian and Ordovician, and did not discuss in detail the origin of post-Ordovician groups. The following is a simplified version of their , showing early cephalopod relationships to the order level (although various isolated families also originated during this diversification event):


Gallery
File:Nautilus pompilius 3.jpg|The , one of only two surviving nautiloid genera File:Allonautilus scrobiculatus.jpg| , the other surviving nautliod genus File:Endoceras_sp.png| was one of the largest nautiloids to have ever lived File:Alaskoceras sewardi.jpg| was a member of the , the first cephalopods to evolve coiled shells File:Plectronoceras.png| was one of the earliest known nautiloids, existing in the late Cambrian File:Diorama of a Devonian seafloor - Goldringia nautiloid cephalopod eating a trilobite (45654169671).jpg| was a nautiloid from the middle of the File:Lorieroceras lorieri.jpg| was a bizarre nautiloid from the Devonian that possessed a coiled shell File:Cenoceras NT.jpg|A reconstruction of the nautiloid File:Hoko River Nautilids.jpg|Two nautiloids from the aged Hoko River Formation, Nautilus cookanum and Aturia alabamensis File:Diorama of a Permian seafloor - coiled cephalopod, sponges, brachiopods (43887749560).jpg| was a nautiloid from the Late that possessed hollow recurved spines running along its shell


See also


Further reading
  • http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/cephalopoda.php (retrieved on May 11, 2014)


External links

Page 1 of 1
1
Page 1 of 1
1

Account

Social:
Pages:  ..   .. 
Items:  .. 

Navigation

General: Atom Feed Atom Feed  .. 
Help:  ..   .. 
Category:  ..   .. 
Media:  ..   .. 
Posts:  ..   ..   .. 

Statistics

Page:  .. 
Summary:  .. 
1 Tags
10/10 Page Rank
5 Page Refs
6s Time