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52-560: Parareptilia ("near-reptiles") is an extinct subclass or clade of basal sauropsids / reptiles , typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near the end of the Carboniferous period and achieved their highest diversity during the Permian period . Several ecological innovations were first accomplished by parareptiles among reptiles. These include

104-525: A clade (from Ancient Greek κλάδος (kládos)  'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are

156-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it

208-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking

260-716: A clade of various early-diversing Permian and Triassic reptiles no longer included in the anapsids. Olsen's term "parareptiles" was chosen to refer to this clade, although its instability within their analysis meant that Gauthier et al. (1988) were not confident enough to erect Parareptilia as a formal taxon. Their cladogram is as follows: Synapsida [REDACTED] † Mesosauridae [REDACTED] † Procolophonidae [REDACTED] † Millerettidae [REDACTED] † Pareiasauria [REDACTED] † Captorhinidae [REDACTED] Testudines [REDACTED] † Protorothyrididae [REDACTED] Diapsida [REDACTED] Laurin & Reisz (1995) found

312-426: A large pit on the maxilla , a broad prefrontal - palatine contact, and the absence of a supraglenoid foramen of the scapula . Like many other so-called 'anapsids', parareptiles were historically understudied. Interest in their relationships were reinvigorated in the 1990s, when several studies argued that Testudines ( turtles and their kin) were members of Parareptilia. Although this would suggest that Parareptilia

364-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on

416-442: A slightly different topology, in which Reptilia is divided into Parareptilia and Eureptilia. They argued that Testudines (turtles) were members of Parareptilia; in fact, they explicitly defined Parareptilia as "Testudines and all amniotes more closely related to them than to diapsids". Captorhinidae was transferred to Eureptilia, while Parareptilia included turtles alongside many of the taxa named as such by Gauthier et al. (1988). There

468-497: A small part of the body of the sphenoid. It is the thinnest wall of the orbit, evidenced by pneumatized ethmoidal cells. The lateral wall is formed by the frontal process of zygomatic and more posteriorly by the orbital plate of the greater wing of sphenoid. The bones meet at the zygomaticosphenoid suture. The lateral wall is the thickest wall of the orbit, important because it is the most exposed surface, highly vulnerable to blunt force trauma. The base, orbital margin, which opens in

520-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,

572-402: Is a crucial structure in the orbit, as it is often the only source of collateral blood to the brain in cases of large internal carotid infarcts , as it is a collateral pathway to the circle of Willis . In addition, there is the optic canal , which contains the optic nerve, or cranial nerve II, and is formed entirely by the lesser wing of the sphenoid, separated from the supraorbital fissure by

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624-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,

676-399: Is formed by the articular (in the lower jaw) and the quadrate (in the upper jaw). In many parareptiles, the jaw joint is shifted forwards on the skull past the rear part of the braincase . Jaw muscles attach to the coronoid process , a triangular spur in the rear half of the jaw. Both the tooth-bearing dentary bone and the posterior foramen intermandibularis (a hole on the inner surface of

728-471: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution

780-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed

832-420: Is shared with other ‘cotylosaurs’ such as captorhinids , diadectomorphs , and seymouriamorphs . Another general ‘cotylosaurian’ feature in parareptiles is the ‘swollen’ appearance of their vertebrae , which have wide and convex upper surfaces. Parareptiles lacked a supraglenoid foramen on the scapula , a hole which is also absent in varanopids and neodiapsids. Most had a fairly short and thick humerus which

884-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with

936-403: The lamina papyracea , the most delicate bony structure in the skull, and one of the most commonly fractured bones in orbital trauma. The lacrimal bone also contains the nasolacrimal duct . The superior bony margin of the orbital rim, otherwise known as the orbital process , is formed by the frontal bone. The roof (superior wall) is formed primarily by the orbital plate frontal bone , and also

988-404: The optic strut . Injury to any one of these structures by infection, trauma or neoplasm can cause temporary or permanent visual dysfunction, and even blindness if not promptly corrected. The orbits also protect the eye from mechanical injury. In the orbit, the surrounding fascia allows for smooth rotation and protects the orbital contents. If excessive tissue accumulates behind the ocular globe,

1040-411: The palate . A prominent hole, the foramen orbitonasale, is present at the intersection of the prefrontal, palatine, and lacrimal. Parareptilian palates also have toothless and reduced ectopterygoid bones, a condition taken to extremes in mesosaurs, which have lost the ectopterygoid entirely. Most parareptiles had large orbits (eye sockets), significantly longer (from front-to-back) than the region of

1092-501: The procolophonids , rediversified in the Triassic, but subsequently declined and became extinct by the end of the period. Compared to most eureptiles, parareptiles retained fairly "primitive" characteristics such as robust, low-slung bodies and large supratemporal bones at the back of the skull. While all but the earliest eureptiles were diapsids , with two openings at the back of the skull, parareptiles were generally more conservative in

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1144-411: The sphenoid bone . It is a major pathway for intracranial communication, containing cranial nerves III , IV , VI which control eye movement via the extraocular muscles , and the ophthalmic branches of cranial nerve V , or V1. The second division of the trigeminal nerve enters the skull base at the foramen rotundum , or V2. The inferior orbital fissure lies inferior and lateral to the ocular globe at

1196-408: The zygomatic bone laterally , the sphenoid bone , with its lesser wing forming the optic canal and its greater wing forming the lateral posterior portion of the bony orbital process, the maxillary bone inferiorly and medially which, along with the lacrimal and ethmoid bones , forms the medial wall of the orbital canal . The ethmoid air cells are extremely thin, and form a structure known as

1248-429: The ( cranial nerve II ) and the ophthalmic artery , and sits at the junction of the sphenoid sinus with the ethmoid air cells , superomedial and posterior to structures at the orbital apex. It provides a pathway between the orbital contents and the middle cranial fossa . The superior orbital fissure lies just lateral and inferior to the optic canal, and is formed at the junction of the lesser and greater wing of

1300-406: The extent of temporal fenestration . In its modern usage, Parareptilia was first utilized as a cladistically correct alternative to Anapsida , a term which historically referred to reptiles with solid skulls lacking holes behind the eyes. Nevertheless, not all parareptiles have 'anapsid' skulls, and some do have large holes in the back of the skull. They also had several unique adaptations, such as

1352-409: The eye can protrude, or become exophthalmic . Enlargement of the lacrimal gland , located superotemporally within the orbit, produces protrusion of the eye inferiorly and medially (away from the location of the lacrimal gland). Lacrimal gland may be enlarged from inflammation (e.g. sarcoid ) or neoplasm (e.g. lymphoma or adenoid cystic carcinoma ). Tumors (e.g. glioma and meningioma of

1404-494: The face, has four borders. The following bones take part in their formation: The orbit holds and protects the eyes . The movement of the eye is controlled by six distinct extraocular muscles, a superior , an inferior , a medial and a lateral rectus, as well as a superior and an inferior oblique . The superior ophthalmic vein is a sigmoidal vessel along the superior margin of the orbital canal that drains deoxygenated blood from surrounding musculature. The ophthalmic artery

1456-509: The first reptiles to return to marine ecosystems ( mesosaurs ), the first bipedal reptiles ( bolosaurids such as Eudibamus ), the first reptiles with advanced hearing systems ( nycteroleterids and others), and the first large herbivorous reptiles (the pareiasaurs ). The only parareptiles to survive into the Triassic period were the procolophonoids , a group of small generalists, omnivores, and herbivores. The largest family of procolophonoids,

1508-451: The fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over

1560-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"

1612-458: The head. Each consists of a base, an apex and four walls. There are two important foramina , or windows, two important fissures , or grooves, and one canal surrounding the globe in the orbit. There is a supraorbital foramen , an infraorbital foramen , a superior orbital fissure , an inferior orbital fissure and the optic canal , each of which contains structures that are crucial to normal eye functioning. The supraorbital foramen contains

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1664-513: The jaw) reach as far back as the coronoid process. The surangular bone, which forms the upper rear part of the jaw, is narrow and plate-like. There was some variation in the body shape of parareptiles, with early members of the group having an overall lizard -like appearance, with thin limbs and long tails. The most successful and diverse groups of parareptiles, the pareiasaurs and procolophonids , had massively-built bodies with reduced tails and stout limbs with short digits. This general body shape

1716-420: The jugal, squamosal, and quadratojugal firmly sutured together without any gaps or slits between them. This principle still holds true for some subgroups, such as pareiasaurs. However, a growing number of parareptile taxa are known to have had an infratemporal fenestra , a large hole or emargination lying among the bones behind the eye. In some taxa, the margins of such openings may include additional bones such as

1768-1364: The largest turtle data set to date in their analysis and concluded that turtles are likely a sister group of crocodilians and birds (Archosauria). This placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics, since turtles possess an anapsid skull. This would make Parareptilia a totally extinct group with skull features that resemble those of turtles through convergent evolution . With turtles positioned outside of parareptiles, Tsuji and Müller (2009) redefined Parareptilia as "the most inclusive clade containing Milleretta rubidgei and Procolophon trigoniceps , but not Captorhinus aguti ." The cladogram below follows an analysis by M.S. Lee, in 2013. Synapsida [REDACTED] † Millerettidae [REDACTED] † Eunotosaurus † Lanthanosuchoidea [REDACTED] † Procolophonoidea [REDACTED] † Pareiasauromorpha [REDACTED] † Captorhinidae [REDACTED] † Paleothyris † Araeoscelidia [REDACTED] † Claudiosaurus [REDACTED] † Younginiformes [REDACTED] Lepidosauromorpha [REDACTED] † Choristodera [REDACTED] † Trilophosaurus [REDACTED] † Rhynchosauria [REDACTED] Archosauriformes [REDACTED] Clade In biological phylogenetics ,

1820-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"

1872-445: The lateral wall of the maxillary sinus. It is not as important in function, though it does contain a few branches of the maxillary nerve and the infraorbital artery and vein. Other minor structures in the orbit include the anterior and posterior ethmoidal foramen and zygomatic orbital foramen . The bony walls of the orbital canal in humans do not derive from a single bone, but a mosaic of seven embryologically distinct structures:

1924-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of

1976-401: The lesser wing of sphenoid near the apex of the orbit. The orbital surface presents medially by trochlear fovea and laterally by lacrimal fossa. The floor (inferior wall) is formed by the orbital surface of maxilla , the orbital surface of zygomatic bone and the minute orbital process of palatine bone . Medially, near the orbital margin, is located the groove for nasolacrimal duct . Near

2028-481: The maxilla or postorbital . When seen from above, the rear edge of the skull is straight or has a broad median embayment. From inside to outside, the rear edge of the skull is formed by three pairs of bones: the postparietals , tabulars , and supratemporals . Parareptiles have particularly large supratemporals, which often extend further backwards than the tabulars. Apart from the long, slender jaws of mesosaurs, most parareptile jaws were short and thick. The jaw joint

2080-410: The mid-to-late 1990s by Olivier Rieppel and Michael deBraga argued that turtles were actually lepidosauromorph diapsids related to the sauropterygians . The diapsid affinities of turtles have been supported by molecular phylogenies . The first genome-wide phylogenetic analysis was completed by Wang et al. (2013). Using the draft genomes of Chelonia mydas and Pelodiscus sinensis, the team used

2132-403: The middle of the floor, located infraorbital groove, which leads to the infraorbital foramen. The floor is separated from the lateral wall by inferior orbital fissure , which connects the orbit to pterygopalatine and infratemporal fossa . The medial wall is formed primarily by the orbital plate of ethmoid , as well as contributions from the frontal process of maxilla, the lacrimal bone , and

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2184-434: The rest of the reptiles or Eureptilia ("true reptiles"). Olsen's term was generally ignored, and various taxa later known as parareptiles were generally not placed into exclusive groups with each other. Many were classified as 'cotylosaurs' (a wastebasket taxon of stout-bodied 'primitive' reptiles or reptile-like tetrapods) or ' anapsids ' (reptiles without temporal fenestrae , such as modern turtles). Parareptilia's usage

2236-399: The same skull. While most synapsids and many early eureptiles had a caniform region of enlarged fang-like teeth in the front half of the skull, very few parareptiles possessed caniform teeth. Many amniotes have a row of small pits running along bones at the edge of the mouth, but parareptiles have only a few pits, with one especially large pit near the front of the maxilla . The rest of

2288-477: The skull behind the eyes. The jugal bone, which forms the lower and rear edge of the orbit, has a very thin suborbital process (front branch), usually no subtemporal process (lower rear branch), and a thick dorsal process (upper rear branch). The squamosal and quadratojugal bones, which lie behind the jugal, are quite large and are embayed from behind to accommodate the internal ears. Parareptiles were traditionally considered to have an ‘ anapsid ’-type skull, with

2340-405: The skull was often strongly-textured by pits, ridges, and rugosities in most parareptile groups, occasionally culminating in complex bosses or spines. The maxilla is usually low, while the prefrontal and lacrimal bones in front of the eye are both fairly large. In all parareptiles except mesosaurs, the prefrontal has a plate-like inner branch which forms a broad contact with the palatine bone of

2392-439: The spine to the ilium, were usually slender or fan-shaped, with large gaps between them. The hindlimbs were typically not much longer than the forelimbs, and had thick reptilian ankle bones and short toes. There are some exceptions, such as Eudibamus , an early Permian bolosaurid with very elongated hindlimbs. The name Parareptilia was coined by Olson in 1947 to refer to an extinct group of Paleozoic reptiles, as opposed to

2444-499: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Orbit (anatomy) The orbits are conical or four-sided pyramidal cavities, which open into the midline of the face and point back into

2496-463: The supraorbital nerve, the first division of the trigeminal nerve or V1 and lies just lateral to the frontal sinus . The infraorbital foramen contains the second division of the trigeminal nerve, the infraorbital nerve or V2, and sits on the anterior wall of the maxillary sinus . Both foramina are crucial as potential pathways for cancer and infections of the orbit to spread into the brain or other deep facial structures. The optic canal contains

2548-471: Was expanded near the elbow. Unlike early eureptiles, the outer part of the lower humerus possessed both a small supinator process and an ectepicondylar foramen and groove. The ulna generally has a poorly developed olecranon process , another trait in contrast with the earliest eureptiles. Most parareptiles had an ilium which was fan-shaped and vertically (rather than horizontally) oriented, an unusual trait among early amniotes. The sacral ribs, which connect

2600-551: Was not extinct after all, the origin of turtles is still heavily debated. Many other morphological or genetic analyses find more support for turtles among diapsid eureptiles such as sauropterygians or archosauromorphs , rather than parareptiles. Parareptilian skulls were diverse, from mesosaurs with elongated snouts filled with hundreds of thin teeth, to the snub-nosed, knob-encrusted skulls of pareiasaurs . Parareptile teeth were quite variable in shape and function between different species. However, they were relatively homogenous on

2652-715: Was one major exception: mesosaurs were placed outside both groups, as the sister taxon to the crown group Reptilia. Mesosaurs were still considered sauropsids, as they were closer to reptiles than to synapsids. The traditional group 'Anapsida' was rejected as a paraphyletic assemblage. The cladogram of Laurin & Reisz (1995) is provided below: Synapsida [REDACTED] † Mesosauridae [REDACTED] † Millerettidae [REDACTED] † Pareiasauria [REDACTED] † Procolophonidae [REDACTED] Testudines [REDACTED] † Captorhinidae [REDACTED] † Protorothyrididae [REDACTED] Diapsida [REDACTED] In contrast, several studies in

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2704-413: Was revived by cladistic studies, to refer to those traditional 'anapsids' that were thought to be unrelated to turtles. Gauthier et al. (1988) provided the first phylogenetic definitions for the names of many amniote taxa and argued that captorhinids and turtles were sister groups, constituting the clade Anapsida (in a much more limited context than typically applied). A name had to be found for

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