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55-483: See text Rhynchocephalia ( / ˌ r ɪ ŋ k oʊ s ɪ ˈ f eɪ l i ə / ; lit.   ' beak-heads ' ) is an order of lizard-like reptiles that includes only one living species, the tuatara ( Sphenodon punctatus ) of New Zealand . Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a speciose group with high morphological and ecological diversity. The oldest record of

110-461: A cohors (plural cohortes ). Some of the plant families still retain the names of Linnaean "natural orders" or even the names of pre-Linnaean natural groups recognized by Linnaeus as orders in his natural classification (e.g. Palmae or Labiatae ). Such names are known as descriptive family names. In the field of zoology , the Linnaean orders were used more consistently. That is,

165-509: A capital letter. For some groups of organisms, their orders may follow consistent naming schemes . Orders of plants , fungi , and algae use the suffix -ales (e.g. Dictyotales ). Orders of birds and fishes use the Latin suffix -iformes meaning 'having the form of' (e.g. Passeriformes ), but orders of mammals and invertebrates are not so consistent (e.g. Artiodactyla , Actiniaria , Primates ). For some clades covered by

220-399: A corresponding quadrate conch, similar to those found in lizards, these have been lost in the tuatara and likely other derived rhynchocephalians. This loss may be connected to the development of back and forth motion of the lower jaw. The dentition of most rhynchocephalians, including the tuatara, is described as acrodont , which is associated with the condition of the teeth being attached to

275-570: A distinct rank of biological classification having its own distinctive name (and not just called a higher genus ( genus summum )) was first introduced by the German botanist Augustus Quirinus Rivinus in his classification of plants that appeared in a series of treatises in the 1690s. Carl Linnaeus was the first to apply it consistently to the division of all three kingdoms of nature (then minerals , plants , and animals ) in his Systema Naturae (1735, 1st. Ed.). For plants, Linnaeus' orders in

330-403: A hooked fifth metatarsal . Like some lizards, the tuatara possesses a parietal eye (also called a pineal eye or a third eye) covered by scales at the top of the head formed by the parapineal organ, with an accompanying hole in the skull roof enclosed by the parietal bones , dubbed the "pineal foramen", which is also present in fossil rhynchocephalians. The parietal eye detects light (though it

385-399: A posteriorly directed process (extension) of the jugal bone. All known rhynchocephalians lack the splenial bone present in the lower jaw of more primitive reptiles, with the skulls of all members of Sphenodontia lacking lacrimal bones . The majority of rhynchocephalians also have fused frontal bones of the skull. While early rhynchocephalians possessed a tympanic membrane in the ear and

440-410: A single tooth row, with the presence of an additional isolated tooth. The unranked clade Neosphenodontia is defined as the most inclusive clade containing Sphenodon but not Clevosaurus hudsoni, which is supported by the presence of six synapomorphies, including the increased relative length of the antorbital region of the skull (the part of the skull forward of the eye socket), reaching 1/4 to 1/3 of

495-471: A talus fracture may result in complications and long-term morbidity. A 2015 review came to the conclusion that isolated talar body fractures may be more common than previously thought. A fractured talar body often has a displacement that is best visualised using CT imaging. In case a talus fracture is accompanied by a dislocation, restoration of articular and axial alignment is necessary to optimize ankle and hindfoot function. Dice were originally made from

550-1154: Is a cladogram of Rhynchocephalia after DeMar et al. 2022 (based on maximum parsimony , note that cladogram collapses into a polytomy under Bayesian analysis ): Gephyrosaurus bridensis Diphydontosaurus avonis Planocephalosaurus robinsonae Rebbanasaurus jaini Godavarisaurus lateefi Theretairus antiquus Polysphenodon mulleri Opisthiamimus gregori Clevosaurus convallis Clevosaurus brasiliensis Clevosaurus hadroprodon Clevosaurus bairdi Clevosaurus hudsoni Clevosaurus cambrica Brachyrhinodon taylori Colobops noviportensis Sphenodon punctatus (tuatara) Cynosphenodon huizachalensis Sphenovipera jimmysjoyi Kawasphenodon expectatus Kawasphenodon peligrensis Pelecymala robustus Fraserosphenodon latidens Opisthias rarus Eilenodon robustus Sphenotitan leyesi Toxolophosaurus cloudi Priosphenodon avelasi Homoeosaurus maximiliani Kallimodon pulchellus Sigmala sigmala Vadasaurus herzogi Order (biology) What does and does not belong to each order

605-401: Is convex, triangular, or semi-oval in shape, and rests on the plantar calcaneonavicular ligament ; the lateral , named the anterior calcaneal articular surface, is somewhat flattened, and articulates with the facet on the upper surface of the anterior part of the calcaneus . The neck of talus is directed anteromedially, and comprises the constricted portion of the bone between the body and

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660-419: Is determined by a taxonomist , as is whether a particular order should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing an order. Some taxa are accepted almost universally, while others are recognized only rarely. The name of an order is usually written with

715-508: Is highly variable. The tuatara has an average total length of 34.8 and 42.7 centimetres (13.7 and 16.8 in) for females and males respectively. Clevosaurus sectumsemper has an estimated total length of 12 centimetres (4.7 in), while large individuals of the largest known terrestrial sphenodontian, Priosphenodon avelasi reached total lengths of just over 100 centimetres (39 in). The aquatic pleurosaurs reached lengths of up to 150 centimetres (59 in). The tuatara has among

770-451: Is probably not capable of detecting movement or forming images), monitoring the day-night and seasonal cycles, helping to regulate the circadian rhythm , among other functions. While pineal eyes were widespread among early vertebrates, including early reptiles, they have been lost among most living groups. Rhynchocephalians are distinguished from squamates by a number of traits, including the retention of gastralia (rib-like bones present in

825-402: Is semi-cylindrical, and it is flanked by the articulate facets for the two malleoli. The ankle mortise, the fork-like structure of the malleoli, holds these three articulate surfaces in a steady grip, which guarantees the stability of the ankle joint. However, because the trochlea is wider in front than at the back (approximately 5–6 mm) the stability in the joint vary with the position of

880-528: The International Code of Zoological Nomenclature , several additional classifications are sometimes used, although not all of these are officially recognized. In their 1997 classification of mammals , McKenna and Bell used two extra levels between superorder and order: grandorder and mirorder . Michael Novacek (1986) inserted them at the same position. Michael Benton (2005) inserted them between superorder and magnorder instead. This position

935-815: The Systema Naturae and the Species Plantarum were strictly artificial, introduced to subdivide the artificial classes into more comprehensible smaller groups. When the word ordo was first consistently used for natural units of plants, in 19th-century works such as the Prodromus Systematis Naturalis Regni Vegetabilis of Augustin Pyramus de Candolle and the Genera Plantarum of Bentham & Hooker, it indicated taxa that are now given

990-466: The ball-and-socket -shaped talocalcaneonavicular joint . The talus is the second largest of the tarsal bones ; it is also one of the bones in the human body with the highest percentage of its surface area covered by articular cartilage . It is also unusual in that it has a retrograde blood supply, i.e. arterial blood enters the bone at the distal end. In humans, no muscles attach to the talus, unlike most bones, and its position therefore depends on

1045-422: The flexor hallucis longus . Exceptionally, the lateral of these tubercles forms an independent bone called os trigonum or accessory talus; it may represent the tarsale proximale intermedium . On the bone's inferior side, three articular surfaces serve for the articulation with the calcaneus, and several variously developed articular surfaces exist for the articulation with ligaments. For descriptive purposes

1100-415: The herbivorous eilenodontines , and there were other rhynchocephalians with specialised ecologies like the durophagous sapheosaurs . There were even successful groups of aquatic sphenodontians, such as the pleurosaurs . Tuatara were originally classified as agamid lizards when they were first described by John Edward Gray in 1831. They remained misclassified until 1867, when Albert Günther of

1155-410: The infraorder Eusphenodontia which is defined by the least inclusive clade containing Polysphenodon , Clevosaurus hudsoni and Sphenodon , which is supported by the presence of three synapomorphies , including the presence of clearly visible wear facets on the teeth of the dentary or maxilla, the premaxillary teeth are merged into a chisel like structure, and the palatine teeth are reduced to

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1210-403: The intermedium , between the bases of the tibia and fibula , and the fourth centrale , lying in the mid-part of the tarsus. These bones are still partially separate in modern amphibians, which therefore do not have a true talus. The talus forms a considerably more flexible joint in mammals than it does in reptiles. This reaches its greatest extent in artiodactyls , where the distal surface of

1265-436: The palatine , vomer and pterygoid bones, though the vomer and/or the pterygoid teeth are lost in some groups, including the living tuatara, which only has palatine teeth. A distinctive character found in all rhynchocephalians is the enlargement of the tooth row present on the palatine bones. While in other rhynchocephalians the palatine tooth row is oblique to the teeth of the maxilla , in members of Sphenodontinae (including

1320-534: The 7th to 8th intrauterine month an ossification center is formed in the anklebone. The talus bone lacks a good blood supply. Because of this, healing a broken talus can take longer than most other bones. One with a broken talus may not be able to walk for many months without crutches and will further wear a walking cast or boot of some kind after that. Talus injuries may be difficult to recognize, and lateral process fractures in particular may be radiographically occult. If not recognized and managed appropriately,

1375-648: The British Museum noted features similar to birds, turtles, and crocodiles. He proposed the order Rhynchocephalia (from ῥύγχος / rhúnkhos 'beak' and κεφαλή / kephalḗ 'head', meaning "beak head") for the tuatara and its fossil relatives. In 1925, Samuel Wendell Williston proposed the Sphenodontia to include only tuatara and their closest fossil relatives. Sphenodon is derived from Greek σφήν ( sphḗn ) 'wedge' and ὀδούς ( odoús ) 'tooth'. Many disparately related species were subsequently added to

1430-519: The Rhynchocephalia, resulting in what taxonomists call a " wastebasket taxon ". These include the superficially similar (both in shape and name) but unrelated rhynchosaurs , which lived in the Triassic . Studies in the 1970s and 1980s demonstrated that rhynchosaurs were unrelated, with computer-based cladistic analysis conducted in the 1980s providing a robust diagnosis for the definition of

1485-449: The belly of the body, ancestrally present in tetrapods and also present in living crocodilians ). Unlike squamates, but similar to the majority of birds, the tuatara lacks a penis. This is a secondary loss, as a penis or squamate-like hemipenes were probably present in the last common ancestor of rhynchocephalians and squamates. The complete lower temporal bar (caused by the fusion of the jugal and quadtrate / quadratojugal bones of

1540-447: The bone has a smooth keel to allow greater freedom of movement of the foot, and thus increase running speed. In non-mammal amniotes , the talus is generally referred to as the astragalus. In modern crocodiles , the astragalus bears a peg which inserts into a corresponding socket on the calcaneum , and the hinge of the ankle joint runs between the two tarsals; this condition is referred to as "croc-normal"; this "croc-normal" condition

1595-420: The crest of the jaw bone, lacking tooth replacement and having extensive bone growth fusing the teeth to the jaws resulting in the boundary between the teeth and bone being difficult to discern. This differs from the condition found in most lizards (except acrodontans ), which have pleurodont teeth which are attached to the shelf on the inward-facing side of the jaw, and are replaced throughout life. The teeth of

1650-424: The elongation of the fourth metacarpal, the presence of a posterior process on the ischium, and the antorbital region of the skulls is between a third and a quarter of the total skull length. The clade Opisthodontia has been used for the grouping of all sphenodontians more closely related to Priosphenodon (a member of Eilenodontinae ) than to Sphenodon. Not all studies use this clade, as some studies have found

1705-400: The foot. The talus has joints with the two bones of the lower leg , the tibia and thinner fibula . These leg bones have two prominences (the lateral and medial malleoli ) that articulate with the talus. At the foot end, within the tarsus, the talus articulates with the calcaneus (heel bone) below, and with the curved navicular bone in front; together, these foot articulations form

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1760-402: The foot: with the foot dorsiflexed (toes pulled upward) the ligaments of the joint are kept stretched, which guarantees the stability of the joint; but with the foot plantarflexed (as when standing on the toes) the narrower width of the trochlea causes the stability to decrease. Behind the trochlea is a posterior process with a medial and a lateral tubercle separated by a groove for the tendon of

1815-529: The group is dated to the Middle Triassic around 238 to 240 million years ago, and they had achieved global distribution by the Early Jurassic . Most rhynchocephalians belong to the group Sphenodontia ('wedge-teeth'). Their closest living relatives are lizards and snakes in the order Squamata , with the two orders being grouped together in the superorder Lepidosauria . Once representing

1870-521: The group. Rhynchocephalia and their sister group Squamata (which includes lizards, snakes and amphisbaenians ) belong to the superorder Lepidosauria , the only surviving taxon within Lepidosauromorpha . Squamates and rhynchocephalians have a number of shared traits ( synapomorphies ), including fracture planes within the tail vertebrae allowing caudal autotomy (loss of the tail when threatened), transverse cloacal slits, an opening in

1925-414: The highest known ages of sexual maturity among reptiles, at around 9 to 13 years of age, and has a high longevity in comparison to lizards of similar size, with wild individuals likely reaching 70 years, and possibly over 100 years in age. Such a late onset of sexual maturity and longevity may have or not have been typical of extinct rhynchocephalians. While the grouping of Rhynchocephalia is well supported,

1980-459: The jaw bone, and are fused to the bone at the base of the socket (ankylothecodont). In many derived sphenodontians, the premaxillary teeth at the front of the upper jaw are merged into a large chisel-like structure. Rhynchocephalians possess palatal dentition (teeth present on the bones of the roof of the mouth). Palatal teeth are ancestrally present in tetrapods, but have been lost in many groups. The earliest rhynchocephalians had teeth present on

2035-708: The orders in the zoology part of the Systema Naturae refer to natural groups. Some of his ordinal names are still in use, e.g. Lepidoptera (moths and butterflies) and Diptera (flies, mosquitoes, midges, and gnats). In virology , the International Committee on Taxonomy of Viruses 's virus classification includes fifteen taxomomic ranks to be applied for viruses , viroids and satellite nucleic acids : realm , subrealm , kingdom , subkingdom, phylum , subphylum , class, subclass, order, suborder, family, subfamily , genus, subgenus , and species. There are currently fourteen viral orders, each ending in

2090-399: The oval head. Its upper and medial surfaces are rough, for the attachment of ligaments; its lateral surface is concave and is continuous below with the deep groove for the interosseous talocalcaneal ligament . The body of the talus comprises most of the volume of the talus bone (ankle bone). It presents with five surfaces; a superior, inferior, medial, lateral and a posterior: During

2145-414: The pelvis known as the thyroid fenestra, the presence of extra ossification centres in the limb bone epiphyses , a knee joint where a lateral recess on the femur allows the articulation of the fibula, the development of a sexual segment of the kidney, and a number of traits of the feet bones, including a fused astralago - calcaneun and enlarged fourth distal tarsal , which creates a new joint, along with

2200-408: The position of the neighbouring bones. Though irregular in shape, the talus can be subdivided into three parts. Facing anteriorly, the head carries the articulate surface of the navicular bone, and the neck , the roughened area between the body and the head, has small vascular channels. The body features several prominent articulate surfaces: On its superior side is the trochlea tali, which

2255-489: The posterior border of the ischium is characterised by a distinctive process. In 2021 the clade Acrosphenodontia was defined, which is less inclusive than Sphenodontia and more inclusive than Eusphenodontia, and includes all sphenodontians with fully acrodont dentition, excluding basal partially acrodont sphenodontians. In 2022 the extinct clade Leptorhynchia was defined, including a variety of neosphenodontians, at least some of which were aquatically adapted, characterised by

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2310-564: The precursor of the currently used International Code of Nomenclature for algae, fungi, and plants . In the first international Rules of botanical nomenclature from the International Botanical Congress of 1905, the word family ( familia ) was assigned to the rank indicated by the French famille , while order ( ordo ) was reserved for a higher rank, for what in the 19th century had often been named

2365-502: The rank of family (see ordo naturalis , ' natural order '). In French botanical publications, from Michel Adanson 's Familles naturelles des plantes (1763) and until the end of the 19th century, the word famille (plural: familles ) was used as a French equivalent for this Latin ordo . This equivalence was explicitly stated in the Alphonse Pyramus de Candolle 's Lois de la nomenclature botanique (1868),

2420-406: The relationships of many taxa to each other are uncertain, varying substantially between studies. In modern cladistics, the clade Sphenodontia includes all rhynchocephalians other than Wirtembergia , as well as Gephyrosaurus and other gephyrosaurids . Gephyrosaurids have been found as more closely related to squamates in some analyses. In 2018, two major clades within Sphenodontia were defined,

2475-446: The scope of the clade to be identical to Eilenodontinae. The family Sphenodontidae has been used to include the tuatara and its closest relatives within Rhynchocephalia. However the grouping has lacked a formal definition, with the included taxa varying substantially between analyses. The closest relatives of the tuatara are placed in the clade Sphenodontinae , which are characterised by a completely closed temporal bar. The following

2530-416: The skull) of the tuatara, often historically asserted to be a primitive feature retained from earlier reptiles, is actually a derived feature among sphenodontians, with primitive lepidosauromorphs and many rhynchocephalians including the most primitive ones having an open lower temporal fenestra without a temporal bar. While often lacking a complete temporal bar, the vast majority of rhynchocephalians have

2585-408: The suffix -virales . Talus bone The talus ( / ˈ t eɪ l ə s / ; Latin for ankle or ankle bone; pl. : tali ), talus bone , astragalus ( / ə ˈ s t r æ ɡ ə l ə s / ), or ankle bone is one of the group of foot bones known as the tarsus . The tarsus forms the lower part of the ankle joint . It transmits the entire weight of the body from the lower legs to

2640-409: The talus bone is divided into three sections, neck, body, and head. The talus bone of the ankle joint connects the leg to the foot. The head of talus looks forward and medialward ; its anterior articular or navicular surface is large, oval, and convex. Its inferior surface has two facets, which are best seen in the fresh condition. The medial , situated in front of the middle calcaneal facet,

2695-433: The talus of hoofed animals, leading to the nickname "bones" for dice. Colloquially known as " knucklebones ", these are approximately tetrahedral . Modern Mongolians still use such bones as shagai for games and fortune-telling , with each piece relating to a symbolic meaning. The talus apparently derives from the fusion of three separate bones in the feet of primitive amphibians; the tibiale , articulating with tibia,

2750-429: The total skull length, the posterior (hind) edge of the parietal bone is only slightly curved inward, the parietal foramen is found at the same level or forward of the anterior border of the supratemporal fenestra (an opening of the skull), the palatine teeth are further reduced from the condition in eusphenodontians to a single lateral tooth row, the number of pterygoid tooth rows are reduced to one or none, and

2805-493: The tuatara have no roots, though the teeth of some other rhynchocephalians possess roots. The acrodont dentition appears to be a derived character of rhynchocephalians not found in more primitive lepidosauromorphs. The most primitive rhynchocephalians have either pleurodont teeth or a combination of both pleurodont front and acrodont posterior teeth. Some rhynchocephalians differ from these conditions, with Ankylosphenodon having superficially acrodont teeth that continue deeply into

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2860-447: The tuatara) and Eilenodontinae it is orientated parallel to the maxilla. In these groups, during biting, the teeth of the dentary in the lower jaw slot between the maxillary and palatine tooth rows. This arrangement, which is unique among amniotes, permits three point bending of food items, and in combination with propalinal movement (back and forward motion of the lower jaw) allows for a shearing bite. The body size of rhynchocephalians

2915-532: The world's dominant group of small reptiles, many of the niches occupied by lizards today were held by rhynchocephalians during the Triassic and Jurassic . Rhynchocephalians underwent a great decline during the Cretaceous , and they had disappeared almost entirely by the beginning of the Cenozoic . While the modern tuatara is primarily insectivorous and carnivorous , the diversity of the group also included

2970-418: Was adopted by Systema Naturae 2000 and others. In botany , the ranks of subclass and suborder are secondary ranks pre-defined as respectively above and below the rank of order. Any number of further ranks can be used as long as they are clearly defined. The superorder rank is commonly used, with the ending -anae that was initiated by Armen Takhtajan 's publications from 1966 onwards. The order as

3025-405: Was likely ancestral for archosaurs . In dinosaurs (including modern birds) and pterosaurs , the hinge of the ankle instead is distal to the two tarsals. Far rarer are archosaurs with a "croc-reversed" ankle joint, in which the calcaneus bears a peg whilst the astragalus bears a socket. In the theropod dinosaur lineage leading to birds, the astragalus gradually increases in size until it forms

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