58-540: Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia , Australia , Europe , North America , and South America during the Ordovician living from about 480–460 mya , existing for approximately 20 million years . Baltoceratidae was named by Kobayashi (1935) and assigned to the Ellesmeroceratida by Flower and Kummel (1950) where it
116-502: A Baltic coast Ordovician genus, in prior times it was employed as a general name given to all straight-shelled nautiloids that lived from the Ordovician to the Triassic periods (but were most common in the early Paleozoic era). 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
174-675: A ' cold-blooded ' metabolism. However, the ancestors of mammals and birds also had these traits and so birds and mammals can be said to "have evolved from reptiles", making the reptiles, when defined by these traits, a grade rather than a clade. In microbiology , taxa that are thus seen as excluded from their evolutionary grade parent group are called taxa in disguise . Paraphyletic taxa will often, but not always, represent evolutionary grades. In some cases paraphyletic taxa are united simply by not being part of any other groups, and give rise to so-called wastebasket taxa which may even be polyphyletic . The traditional Linnaean way of defining taxa
232-501: A handful of coiled species, the nautiluses , 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 ammonoids (ammonites) and living coleoids (such as squid , octopus , and kin). While ammonoids and coleoids are monophyletic clades with exclusive ancestor-descendant relationships, this
290-400: 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 nitrogen and less oxygen ) making the animal neutrally buoyant in the water. As many as 90 tentacles are arranged in two circles around the mouth. The animal
348-430: A process which may have been connected with controlling buoyancy . 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,
406-410: 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 siphuncle , a fleshy tube which runs through each of the internal chambers of
464-525: 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 end Cretaceous extinction ), and maintained a worldwide distribution up until
522-417: 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. Much of what
580-545: A subclass of its own, Bactritoidea . Recently some workers in the field have come to recognize Dissidocerida as a distinct order, along with Pseudorthocerida, both previously included in Orthocerida as subtaxa. Cladistic approaches are rare in nautiloid systematics. Many nautiloid orders (not to mention the group as a whole) are not monophyletic clades , but rather paraphyletic grades . This means that they include some descendant taxa while excluding others. For example,
638-480: 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. 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
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#1732873601950696-467: Is a phylogenetic tree —a diagram containing a hypothesis of relationships that reflects the evolutionary history of a group of organisms. An evolutionary grade is a group of species united by morphological or physiological traits, that has given rise to another group that has major differences from the ancestral group's condition, and is thus not considered part of the ancestral group, while still having enough similarities that we can group them under
754-592: Is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley , to contrast with clade , a strictly phylogenetic unit. The concept of evolutionary grades arises in the context of phylogenetics : the study of the evolutionary history and relationships among or within groups of organisms . These relationships are determined by phylogenetic inference methods that focus on observed heritable traits, such as DNA sequences, protein amino acid sequences, or morphology . The result of such an analysis
812-613: Is about nautiloids in that broad sense, sometimes called Nautiloidea sensu lato . Cladistically speaking, nautiloids are a paraphyletic assemblage united by shared primitive ( plesiomorphic ) 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 bactritids , which in turn arose from straight-shelled orthoceratoids . The ammonoids appeared early in
870-591: Is available, organisms are preferentially grouped into clades . Where data is lacking, or groups of uncertain relationship are to be compared, the cladistic method is limited and grade provides a useful tool for comparing organisms. This is particularly common in palaeontology , where fossils are often fragmentary and difficult to interpret. Thus, traditional palaeontological works are often using evolutionary grades as formal or informal taxa, including examples such as labyrinthodonts , anapsids , synapsids , dinosaurs , ammonites , eurypterids , lobopodians and many of
928-402: 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 ontogeny of the animal. Modern nautiluses have deeply coiled shells which are involute, meaning that
986-562: Is known about the extinct nautiloids is based on what we know about modern nautiluses , such as the chambered nautilus , which is found in the southwest Pacific Ocean from Samoa to the Philippines , and in the Indian Ocean off the coast of Australia . It is not usually found in waters less than 100 meters (328 feet) deep and may be found as far down as 500 to 700 meters (1,640 to 2,300 feet). Nautili are free swimming animals that possess
1044-505: 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
1102-433: Is not the case for nautiloids. Instead, nautiloids are a paraphyletic 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. Nautiloids are among
1160-426: Is predatory, and has jaws which are horny and beak-like, allowing it to feed on crustaceans . Empty nautilus shells may drift a considerable distance and have been reported from Japan , India and Africa . Undoubtedy the same applies to the shells of fossil 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
1218-511: Is somewhat variable between authors, but it usually includes Tarphycerida, Oncocerida, and Nautilida. All nautiloids have a large external shell, divided into a narrowing chambered region (the phragmocone ) and a broad, open body chamber 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
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#17328736019501276-571: 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
1334-496: Is through the use of anatomical traits. When the actual phylogenetic relationship is unknown, well defined groups sometimes turn out to be defined by traits that are primitive rather than derived. In Linnaean systematics , evolutionary grades are accepted in higher taxonomic ranks , though generally avoided at family level and below. In phylogenetic nomenclature evolutionary grades (or any other form of paraphyly) are not accepted. Where information about phylogenetic relationships
1392-628: The Carboniferous and Permian . The massive extinctions at the end of the Permian were less damaging to nautiloids than to other taxa and a few groups survived into the early Mesozoic , including pseudorthocerids , bactritids , nautilids and possibly 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
1450-534: The Devonian period (some 400 million years ago) and became abundant in the Mesozoic 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
1508-655: The Ordovician period in the Baltic coast and parts of the United States contain a variety of nautiloid fossils, and specimens such as Discitoceras and Rayonnoceras may be found in the limestones of the Carboniferous period in Ireland . The marine rocks of the Jurassic period in Britain often yield specimens of Cenoceras , and nautiloids such as Eutrephoceras are also found in
1566-544: The Baltoceratidae are restricted to forms with a siphuncle that is tubular or slightly expanded within the chambers, excluding genera with a more ellesmeroceratid aspect in which connecting rings thicken inwardly, such as Amsleroceras , Cyptendoceras , and Rioceras . Nautiloidea Nautiloids are a group of marine cephalopods ( Mollusca ) which originated in the Late Cambrian and are represented today by
1624-527: The Baltoceratidae, those with a calcareous rod secreted on the lower surface of the inside of the siphuncle known as "rod-bearing" and those without, in which the interior of the siphuncle tube is empty, known as "vacuosiphonate". Empty siphuncled forms, the vacuosiphonate, gave rise to the Michelinoceratidae , commonly known as the Orthoceratidae, which has its beginning in the lower Cassinian stage in
1682-479: 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, Silurian , and Devonian periods, with various straight, curved and coiled shell forms coexisting at
1740-510: The Palcephalopod/Neocephalopod question, since the only cephalopods included were Nautilus and coleoids. 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 protoconch morphology, connecting ring structure, and
1798-499: The Pierre Shale formation of the Cretaceous period in the north-central United States. Specimens of the Ordovician nautiloid Endoceras have been recorded measuring up to 5.7 meters (19 feet) in shell length, and there is a description of a specimen estimated to have reached 9.1 meters (30 feet), although that specimen is reported as destroyed. These large nautiloids would have been formidable predators of other marine animals at
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1856-456: 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, Bactritida , which is derived from Orthocerida , is sometimes included with Nautiloidea, sometimes with Ammonoidea , and sometimes placed in
1914-603: The ancestral group, to the Orthocerida where assigned by Kroger et al. (2007) The Baltorceratidae are characterized by dominantly straight, slender, smooth shells with a moderately large ventral siphuncle composed of orthochoanitic septal necks and thin connecting rings, free of diaphragms and which in advanced forms becomes more central in position. Septa are close spaced, resulting in short camerae and may form shallow ventral lobes. Cameral deposits are normal which develop apically and more ventrally. Two stocks are found within
1972-426: The animal lived before finally sinking to the seafloor. Nautili propel themselves by jet propulsion, expelling water from an elongated funnel called the hyponome , which can be pointed in different directions to control their movement. Unlike the belemnites 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
2030-412: 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
2088-417: The basis of their usefulness for laymen and field researchers. In bacteriology , the renaming of species or groups that turn out to be evolutionary grades is kept to a minimum to avoid misunderstanding, which in the case of pathogens could have fatal consequences. When referring to a group of organisms, the term "grade" is usually enclosed in quotation marks to denote its status as a paraphyletic term. With
2146-408: 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
2204-405: The development of OMZs , preventing nautiloids from retreating into deeper water, are also cited as other potential causes of extinction. 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
2262-423: 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
2320-430: The extinct ammonoids , the modern nautilus lacks an aptychus , 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. Nautiloids are often found as fossils in early Palaeozoic rocks (less so in more recent strata). The rocks of
2378-434: The group of animals known as cephalopods , an advanced class of mollusks which also includes ammonoids , belemnites and modern coleoids such as octopus and squid. Other mollusks include gastropods , scaphopods and bivalves . Traditionally, the most common classification of the cephalopods has been a four-fold division (by Bather, 1888), into the orthoceratoids , nautiloids, ammonoids , and coleoids . This article
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2436-628: The larger and more recent whorls overlap and obscure older whorls. The shells of fossil nautiloids may be either straight (i.e., orthoconic as in Orthoceras and Rayonnoceras ), curved (as in Cyrtoceras ) coiled (as in Cenoceras ), or rarely a helical coil (as in Lorieroceras ). Some species' shells—especially in the late Paleozoic and early Mesozoic—are ornamented with spines and ribs, but most have
2494-518: The latter part of the Lower Ordovician. Rod bearing forms gave rise to the Troedsonnellidae with early members, Buttsoceras and Tajaroceras found in the upper Cassinian. The Baltoceratidae and Orthoceratidae both have a spherical apex that lacks a cicatrix, and similar, two-layered thin connecting rings which clearly places the Baltoceratidae in the Orthocerida as well. Furthermore,
2552-422: The living Nautilus and Allonautilus . Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. They flourished during the early Paleozoic 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 ( orthocones ). No orthoconic and only
2610-536: 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 (the pearly nautilus), and Allonautilus . The recent decrease in the once worldwide distribution of nautiloids is now believed to have been caused by
2668-460: The more well known taxa of human evolution . Organizing organisms into grades rather than strict clades can also be very useful to understand the evolutionary sequence behind major diversification of both animals and plants. Evolutionary grades, being united by gross morphological traits, are often eminently recognizable in the field. While taxonomy seeks to eliminate paraphyletic taxa, such grades are sometimes kept as formal or informal groups on
2726-720: The order level (although various isolated families also originated during this diversification event): Plectronocerida Yanhecerida Ellesmerocerida ( paraphyletic to Endoceratoidea, Multiceratoidea, and Orthoceratoidea) Endocerida Bisonocerida Cyrtocerinida Tarphycerida (possibly paraphyletic to Nautilida ) Oncocerida (paraphyletic to Ascocerida and Discosorida) Ascocerida Discosorida Riocerida (possibly paraphyletic to later orthoceratoids) Dissidocerida (paraphyletic to later orthoceratoids) Lituitida Actinocerida Pseudorthocerida Orthocerida (paraphyletic to Bactritida , Ammonoidea , and Coleoidea ) Evolutionary grade A grade
2784-507: 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 Neocephalopoda (the rest of
2842-488: The rise of phylogenetic nomenclature , the use of evolutionary grades as formal taxa has come under debate. Under a strict phylogenetic approach, only monophyletic taxa are recognized. This differs from the more traditional approach of evolutionary taxonomy . The difference in approach has led to a vigorous debate between proponents of the two approaches to taxonomy, particularly in well established fields like vertebrate palaeontology and botany . The difference between
2900-578: The same clade. The ancestral group will not be phylogenetically complete (i.e. is not a clade ), and so will represent a paraphyletic taxon. The most commonly cited example is that of reptiles . In the early 19th century, the French naturalist Latreille was the first to divide tetrapods into the four familiar classes of amphibians, reptiles, birds, and mammals. In this system, reptiles are characterized by traits such as laying membranous or shelled eggs, having skin covered in scales or scutes , and having
2958-622: 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 Coleoids , 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
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#17328736019503016-441: The shell. Surrounding the fleshy tube of the siphuncle are structures made of aragonite (a polymorph of calcium carbonate – which during fossilisation is often recrystallized to calcite, a more stable form of calcium carbonate [CaCO 3 ]): 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 ),
3074-588: The spread of pinnipeds . From the Oligocene 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 Aturia 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
3132-447: 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
3190-444: 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
3248-402: The time they lived. In some localities, such as Scandinavia and Morocco , the fossils of orthoconic 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 Orthoceras now only refers to
3306-468: 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 cladogram , showing early cephalopod relationships to
3364-475: Was retained by Unklesbay and Young (1956), again by Flower (1964) , and by Furnish and Glenister in Teichert et al. (1964). Flower (1964) included the Baltoceratidae in the ellesmeroceratid suborder Ellesmeroceratina. Further study of baltoceratid interiors, namely regarding the generally thin connecting rings and lack of siphuncular diaphragms, showed they are distinct from the typical ellesmerocerids and belong, as
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