This is an accepted version of this page
64-514: The Ichthyosauriformes are a group of marine reptiles , belonging to the Ichthyosauromorpha , that lived during the Mesozoic . The stem clade Ichthyosauriformes was in 2014 defined by Ryosuke Motani and colleagues as the group consisting of all ichthyosauromorphs that are more closely related to Ichthyosaurus communis than to Hupehsuchus nanchangensis . Their synapomorphies include
128-410: A branch-based total group clade containing Protorosaurus and all other saurians that are more closely related to Protorosaurus than to Lepidosauria. Gauthier, as an author for Phylonyms (2020), redefined Archosauromorpha as a node-based clade containing Gallus , Alligator , Mesosuchus , Trilophosaurus, Prolacerta, and Protorosaurus . The new name Pan-Archosauria was established for
192-555: A clade ( monophyletic group) including birds, though the precise definition of this clade varies between authors. Others prioritize the clade Sauropsida , which typically refers to all amniotes more closely related to modern reptiles than to mammals . The earliest known proto-reptiles originated from the Carboniferous period, having evolved from advanced reptiliomorph tetrapods which became increasingly adapted to life on dry land. The earliest known eureptile ("true reptile")
256-522: A polyphyletic grouping of various long-necked reptiles including Protorosaurus , tanystropheids , and Prolacerta . Other groups including pantestudines ( turtles and their extinct relatives) and the semiaquatic choristoderes have also been placed in Archosauromorpha by some authors. Archosauromorpha is one of the most diverse groups of reptiles, but its members can be united by several shared skeletal characteristics. These include laminae on
320-447: A temnospondyl ). A series of footprints from the fossil strata of Nova Scotia dated to 315 Ma show typical reptilian toes and imprints of scales. These tracks are attributed to Hylonomus , the oldest unquestionable reptile known. It was a small, lizard-like animal, about 20 to 30 centimetres (7.9 to 11.8 in) long, with numerous sharp teeth indicating an insectivorous diet. Other examples include Westlothiana (for
384-626: A large clade including Ichthyosauromorpha and Thalattosauria as opposed to the Pantestudine relations. Although the most diverse clade of living archosauromorphs are birds, early members of the group were evidently reptilian, superficially similar to modern lizards. When archosauromorphs first appeared in the fossil record in the Permian, they were represented by long-necked, lightly built sprawling reptiles with moderately long, tapering snouts. This body plan, similar to that of modern monitor lizards ,
448-509: A much more basal lineage of reptiles. The aquatic thalattosaurs and gliding kuehneosaurids are also irregularly considered archosauromorphs. Genetic studies have found evidence that modern testudines ( turtles and tortoises ) are more closely related to crocodilians than to lizards. If this evidence is accurate, then turtles are part of basal Archosauromorpha. Likewise, extinct turtle relatives known as Pantestudines would also fall within Archosauromorpha. Some geneticists have proposed
512-637: A name to refer to reptiles within the group formed by relatives of turtles and archosaurs. This name is the clade Archelosauria . Since Pantestudines may encompass the entire aquatic reptile order Sauropterygia , this means that Archosauromorpha (as Archelosauria) may be a much wider group than commonly believed. However, anatomical data disagrees with this genetic evidence, instead placing Pantestudines within Lepidosauromorpha but many modern studies have supported Archelosauria. Several recent studies place sauropterygians within Archosauromorpha group, forming
576-490: A section of the clade Amniota : The section that is left after the Mammalia and Aves have been hived off. It cannot be defined by synapomorphies , as is the proper way. Instead, it is defined by a combination of the features it has and the features it lacks: reptiles are the amniotes that lack fur or feathers. At best, the cladists suggest, we could say that the traditional Reptilia are 'non-avian, non-mammalian amniotes'. Despite
640-452: A tall dorsal process (vertical branch), a short anterior process (forward branch), and a tiny or absent posterior process (rear branch). The bones surrounding the quadratojugal also reconfigure to offset the changes to the quadratojugal. For example, the lower branch of the squamosal bone is shortened to offset the tall dorsal process of quadratojugal which connects to it. On the other hand, the rear branch jugal bone lengthens to fill some of
704-565: A tiny gecko, Sphaerodactylus ariasae , which can grow up to 17 mm (0.7 in) to the saltwater crocodile , Crocodylus porosus , which can reach over 6 m (19.7 ft) in length and weigh over 1,000 kg (2,200 lb). In the 13th century, the category of reptile was recognized in Europe as consisting of a miscellany of egg-laying creatures, including "snakes, various fantastic monsters, lizards, assorted amphibians, and worms", as recorded by Beauvais in his Mirror of Nature . In
SECTION 10
#1732891670004768-570: Is also shared by Triassic archosauromorphs such as tanystropheids and Prolacerta . Other early groups such as trilohpsaurids, azendohsaurids, and rhynchosaurs deviate from this body plan by evolving into stockier forms with semi-erect postures and higher metabolisms. The archosauriforms went to further extremes of diversity, encompassing giant sauropod dinosaurs, flying pterosaurs and birds, semiaquatic crocodilians , phytosaurs , and proterochampsians , and apex predators such as erythrosuchids , pseudosuchians , and theropod dinosaurs. Despite
832-479: Is equivalent to the more common definition of Sauropsida, which Modesto and Anderson synonymized with Reptilia, since the latter is better known and more frequently used. Unlike most previous definitions of Reptilia, however, Modesto and Anderson's definition includes birds, as they are within the clade that includes both lizards and crocodiles. General classification of extinct and living reptiles, focusing on major groups. The cladogram presented here illustrates
896-512: Is generally considered paraphyletic or polyphyletic , and few modern studies use it. Apart from these four groups, Archosauromorpha is sometimes considered to encompass several additional groups of reptiles. One of the most common additions is Choristodera , a group of semiaquatic reptiles with mysterious origins. Although choristodere fossils are only known from the Jurassic through the Miocene , it
960-987: Is particularly prominent in the ancient relatives of crocodylians, but it first appeared earlier at the last common ancestor of allokotosaurs, rhynchosaurs, and archosauriforms. The presence of a calcaneal tuber (sometimes known as a lateral tuber of the calcaneum) is a synapomorphy of the group Crocopoda, and is also responsible for its name. The cladogram shown below follows the most likely result found by an analysis of turtle relationships using both fossil and genetic evidence by M.S. Lee, in 2013. Pan-Lepidosauria / Lepidosauromorpha [REDACTED] † Eosauropterygia [REDACTED] † Placodontia [REDACTED] † Sinosaurosphargis † Odontochelys † Proganochelys Testudines [REDACTED] † Choristodera [REDACTED] † Prolacertiformes [REDACTED] † Trilophosaurus [REDACTED] † Rhynchosauria [REDACTED] Archosauriformes [REDACTED] The following cladogram
1024-503: Is theorized that they first appeared during the Permian alongside the earliest archosauromorphs. Choristoderes share numerous otherwise unique traits with archosauromorphs, but they share an equal or greater number of unique traits with lepidosauromorphs as well, so there is still some debate over their inclusion within either group. The chameleon - or tamandua -like drepanosaurs are also semi-regularly placed within Archosauromorpha, although some studies have considered them to be part of
1088-685: The Ichthyopterygia which again include the Ichthyosauria . [REDACTED] [REDACTED] [REDACTED] [REDACTED] Reptiles See text for extinct groups. Reptiles , as commonly defined, are a group of tetrapods with an ectothermic ('cold-blooded') metabolism and amniotic development . Living reptiles comprise four orders : Testudines ( turtles ), Crocodilia ( crocodilians ), Squamata ( lizards and snakes ), and Rhynchocephalia (the tuatara ). As of May 2023, about 12,000 living species of reptiles are listed in
1152-853: The Reptile Database . The study of the traditional reptile orders, customarily in combination with the study of modern amphibians , is called herpetology . Reptiles have been subject to several conflicting taxonomic definitions. In Linnaean taxonomy , reptiles are gathered together under the class Reptilia ( / r ɛ p ˈ t ɪ l i ə / rep- TIL -ee-ə ), which corresponds to common usage. Modern cladistic taxonomy regards that group as paraphyletic , since genetic and paleontological evidence has determined that birds (class Aves), as members of Dinosauria , are more closely related to living crocodilians than to other reptiles, and are thus nested among reptiles from an evolutionary perspective. Many cladistic systems therefore redefine Reptilia as
1216-418: The amniotic egg . The terms Sauropsida ("lizard faces") and Theropsida ("beast faces") were used again in 1916 by E.S. Goodrich to distinguish between lizards, birds, and their relatives on the one hand (Sauropsida) and mammals and their extinct relatives (Theropsida) on the other. Goodrich supported this division by the nature of the hearts and blood vessels in each group, and other features, such as
1280-405: The capitulum and trochlea (elbow joints) of the humerus are poorly developed. Early archosauromorphs retain well-developed elbow joints, but all archosauromorphs apart from Aenigmastropheus have a trochlea ( ulna joint) which is shifted towards the outer surface of the humerus, rather than the midpoint of the elbow as in other reptiles. In conjunction with this shift, the olecranon process of
1344-410: The nasal bones on the upper edge of the snout. A few advanced archosauriforms reacquired the plesiomorphic ("primitive") state present in other reptiles, that being a short or absent posterodorsal process of the premaxilla, with the rear edge of the nares formed primarily by the maxilla bones instead. As for the nares themselves, they were generally large and oval-shaped, positioned high and close to
SECTION 20
#17328916700041408-1674: The "family tree" of reptiles, and follows a simplified version of the relationships found by M.S. Lee, in 2013. All genetic studies have supported the hypothesis that turtles are diapsids; some have placed turtles within Archosauromorpha, though a few have recovered turtles as Lepidosauromorpha instead. The cladogram below used a combination of genetic (molecular) and fossil (morphological) data to obtain its results. Synapsida ( mammals and their extinct relatives) [REDACTED] † Millerettidae [REDACTED] † Eunotosaurus † Lanthanosuchidae [REDACTED] † Pareiasauromorpha [REDACTED] † Procolophonoidea [REDACTED] † Captorhinidae [REDACTED] † Paleothyris † Araeoscelidia [REDACTED] † Claudiosaurus [REDACTED] † Younginiformes [REDACTED] † Kuehneosauridae [REDACTED] Rhynchocephalia ( tuatara and their extinct relatives) [REDACTED] Squamata ( lizards and snakes ) [REDACTED] [REDACTED] † Eosauropterygia [REDACTED] † Placodontia [REDACTED] † Sinosaurosphargis † Odontochelys † Proganochelys Testudines ( turtles ) [REDACTED] † Choristodera [REDACTED] † Prolacertiformes [REDACTED] † Rhynchosauria [REDACTED] † Trilophosaurus [REDACTED] Archosauriformes ( crocodiles , birds , dinosaurs and extinct relatives) [REDACTED] [REDACTED] The placement of turtles has historically been highly variable. Classically, turtles were considered to be related to
1472-453: The 18th century, the reptiles were, from the outset of classification, grouped with the amphibians . Linnaeus , working from species-poor Sweden , where the common adder and grass snake are often found hunting in water, included all reptiles and amphibians in class "III – Amphibia" in his Systema Naturæ . The terms reptile and amphibian were largely interchangeable, reptile (from Latin repere , 'to creep') being preferred by
1536-473: The 1980s by Gauthier, Michael J. Benton , and Susan E. Evans implemented Gauthier's classification scheme within large studies of reptile relations. Michel Laurin (1991) defined Archosauromorpha as a node-based clade containing the most recent common ancestor of Prolacerta , Trilophosaurus , Hyperodapedon and all of its descendants. David Dilkes (1998) formulated a more inclusive (and more common) definition of Archosauromorpha, defining it as
1600-480: The French. J.N. Laurenti was the first to formally use the term Reptilia for an expanded selection of reptiles and amphibians basically similar to that of Linnaeus. Today, the two groups are still commonly treated under the single heading herpetology . It was not until the beginning of the 19th century that it became clear that reptiles and amphibians are, in fact, quite different animals, and P.A. Latreille erected
1664-657: The anapsid condition has been found to occur so variably among unrelated groups that it is not now considered a useful distinction. By the early 21st century, vertebrate paleontologists were beginning to adopt phylogenetic taxonomy, in which all groups are defined in such a way as to be monophyletic ; that is, groups which include all descendants of a particular ancestor. The reptiles as historically defined are paraphyletic , since they exclude both birds and mammals. These respectively evolved from dinosaurs and from early therapsids, both of which were traditionally called "reptiles". Birds are more closely related to crocodilians than
1728-638: The broader total group of Archosauromorpha, similar to the definition of Dilkes (1998). In 2016, Martin Ezcurra named a subgroup of Archosauromorpha, Crocopoda ("crocodile feet"). Crocopoda is defined as all archosauromorphs more closely related to allokotosaurs (specifically Azendohsaurus and Trilophosaurus ), rhynchosaurs (specifically Rhynchosaurus ), or archosauriforms (specifically Proterosuchus ) rather than Protorosaurus or tanystropheids (specifically Tanystropheus ). This group roughly corresponds to Laurin's definition of Archosauromorpha. Since
1792-421: The class Batracia (1825) for the latter, dividing the tetrapods into the four familiar classes of reptiles, amphibians, birds, and mammals. The British anatomist T.H. Huxley made Latreille's definition popular and, together with Richard Owen , expanded Reptilia to include the various fossil " antediluvian monsters", including dinosaurs and the mammal-like ( synapsid ) Dicynodon he helped describe. This
1856-493: The concept of Prolacertiformes as a traditional monophyletic group (i.e. one whose members have a single common ancestor). He argued that Prolacerta was much closer to Archosauriformes than to other "prolacertiforms", invalidating the name. Likewise, Pamelaria is now considered an allokotosaur, Macrocnemus is a tanystropheid, and Protorosaurus may be too basal ("primitive") to form a clade with any of its supposed close relatives. As such, this final group of Archosauromorpha
1920-554: The early proposals for replacing the paraphyletic Reptilia with a monophyletic Sauropsida , which includes birds, that term was never adopted widely or, when it was, was not applied consistently. When Sauropsida was used, it often had the same content or even the same definition as Reptilia. In 1988, Jacques Gauthier proposed a cladistic definition of Reptilia as a monophyletic node-based crown group containing turtles, lizards and snakes, crocodilians, and birds, their common ancestor and all its descendants. While Gauthier's definition
1984-574: The end of the Triassic period, but the most famous group of archosauromorphs not only survived, but have continued to diversify and dominate beyond the Triassic-Jurassic extinction . These were the Archosauriformes, a diverse assortment of animals including the famous dinosaurs and pterosaurs . Two subclades of Archosauriformes survive to the present day: the semiaquatic crocodilians and the last of
Ichthyosauriformes - Misplaced Pages Continue
2048-503: The exception of Aenigmastropheus , the vertebrae lack notochordal canals, holes which perforate the centra. This also sets the archosauromorphs apart from most other Permian and Triassic reptiles. The humerus (upper arm bone) is solid in archosauromorphs, completely lacking a hole near the elbow known as the entepicondylar foramen . This hole, present in most other tetrapods, is also absent in choristoderes yet not fully enclosed in some proterosuchids. In many advanced archosauromorphs,
2112-402: The feathered dinosaurs: birds. Gauthier used the name Archosauria to refer to what is now called the Archosauriformes; in modern studies, the name Archosauria has a more restricted definition that only includes the ancestors of crocodilians (i.e. Pseudosuchia ) and birds (i.e. Avemetatarsalia ). The final unambiguous members of Archosauromorpha represent the most controversial group. These were
2176-453: The fetus develops within the mother, using a (non-mammalian) placenta rather than contained in an eggshell . As amniotes, reptile eggs are surrounded by membranes for protection and transport, which adapt them to reproduction on dry land. Many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals , with some providing initial care for their hatchlings. Extant reptiles range in size from
2240-434: The first archosauromorphs to appear, and can be characterized by their long necks, sprawling posture, and carnivorous habits. One name for the group, Protorosauria , is named after Protorosaurus , the oldest archosauromorph known from good remains. Another name, Prolacertiformes, is in reference to a different member, Prolacerta . Protorosauria/Prolacertiformes has had a complicated history, and many taxa have entered and left
2304-531: The first few dorsal (back) vertebrae as well. The centrum (main body) of each vertebra is parallelogram -shaped, with a front surface typically positioned higher than the rear surface. The transverse processes (rib facets) of these vertebrae extend outwards to a greater extent than in other early reptiles. In many long-necked archosauromorphs, the rib facets are slanted, connecting to cervical ribs that are often long, thin, and dichocephalous (two-headed). Thin, plate-like ridges known as laminae develop to connect
2368-442: The group as paleontologists discover and re-evaluate reptiles of the Triassic. By far the most famous of these are tanystropheids such as Tanystropheus , known for having necks longer than their entire body. Other notable genera include Boreopricea , Pamelaria , and Macrocnemus , as well as strange gliding reptiles such as Sharovipteryx and Mecistotrachelos . A landmark 1998 study by David Dilkes completely deconstructed
2432-460: The hypothesis that turtles belong to a separate clade within Sauropsida , outside the saurian clade altogether. The origin of the reptiles lies about 310–320 million years ago, in the steaming swamps of the late Carboniferous period, when the first reptiles evolved from advanced reptiliomorphs . The oldest known animal that may have been an amniote is Casineria (though it may have been
2496-463: The late Middle Permian or Late Permian , though they became much more common and diverse during the Triassic period . Although Archosauromorpha was first named in 1946, its membership did not become well-established until the 1980s. Currently Archosauromorpha encompasses four main groups of reptiles: the stocky, herbivorous allokotosaurs and rhynchosaurs , the hugely diverse Archosauriformes , and
2560-508: The late 19th century, a number of definitions of Reptilia were offered. The biological traits listed by Lydekker in 1896, for example, include a single occipital condyle , a jaw joint formed by the quadrate and articular bones, and certain characteristics of the vertebrae . The animals singled out by these formulations, the amniotes other than the mammals and the birds, are still those considered reptiles today. The synapsid/sauropsid division supplemented another approach, one that split
2624-499: The latter are to the rest of extant reptiles. Colin Tudge wrote: Mammals are a clade , and therefore the cladists are happy to acknowledge the traditional taxon Mammalia ; and birds, too, are a clade, universally ascribed to the formal taxon Aves . Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class Reptilia is not a clade. It is just
Ichthyosauriformes - Misplaced Pages Continue
2688-796: The living reptiles, there are many diverse groups that are now extinct , in some cases due to mass extinction events . In particular, the Cretaceous–Paleogene extinction event wiped out the pterosaurs , plesiosaurs , and all non-avian dinosaurs alongside many species of crocodyliforms and squamates (e.g., mosasaurs ). Modern non-bird reptiles inhabit all the continents except Antarctica. Reptiles are tetrapod vertebrates , creatures that either have four limbs or, like snakes, are descended from four-limbed ancestors. Unlike amphibians , reptiles do not have an aquatic larval stage. Most reptiles are oviparous , although several species of squamates are viviparous , as were some extinct aquatic clades –
2752-431: The midline of the skull. Many early archosauromorphs, including Protorosaurus , tanystropheids, Trilophosaurus , and derived rhynchosaurs, have a blade-like sagittal crest on the parietal bones at the rear part of the skull roof , between a pair of holes known as the supratemporal (or upper temporal) fenestrae. However, in other allokotosaurs, the basal rhynchosaur Mesosuchus , and more crownward archosauromorphs,
2816-604: The moment considered a reptiliomorph rather than a true amniote ) and Paleothyris , both of similar build and presumably similar habit. However, microsaurs have been at times considered true reptiles, so an earlier origin is possible. Archosauromorpha Archosauromorpha ( Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs , including birds ) rather than lepidosaurs (such as tuataras , lizards , and snakes ). Archosauromorphs first appeared during
2880-422: The other euryapsids, and given the older name Parapsida. Parapsida was later discarded as a group for the most part (ichthyosaurs being classified as incertae sedis or with Euryapsida). However, four (or three if Euryapsida is merged into Diapsida) subclasses remained more or less universal for non-specialist work throughout the 20th century. It has largely been abandoned by recent researchers: In particular,
2944-425: The parietal bones have an additional lowered area which extends transversely (from left to right) behind the supratemporal fenestrae and sagittal crest (when applicable). The lower temporal fenestra is not fully enclosed in early archosauromorphs (and choristoderes) due to alterations to the structure of the quadratojugal bone at the rear lower corner of the skull. This bone is roughly L-shaped in these taxa, with
3008-501: The possession of a long nasal bone , stretching to the front beyond the nostril; large scleral rings , filling the eye sockets; a narrow snout in top view; and converging digits with little space between them. The Ichthyosauriformes probably split off in the Early Triassic , about 250 million years ago; the last known forms lived in the middle Cretaceous . A basal ichthyosauriform is Cartorhynchus ; more derived species are part of
3072-416: The primitive anapsid reptiles. Molecular work has usually placed turtles within the diapsids. As of 2013, three turtle genomes have been sequenced. The results place turtles as a sister clade to the archosaurs , the group that includes crocodiles, non-avian dinosaurs, and birds. However, in their comparative analysis of the timing of organogenesis , Werneburg and Sánchez-Villagra (2009) found support for
3136-438: The reptiles into four subclasses based on the number and position of temporal fenestrae , openings in the sides of the skull behind the eyes. This classification was initiated by Henry Fairfield Osborn and elaborated and made popular by Romer 's classic Vertebrate Paleontology . Those four subclasses were: The composition of Euryapsida was uncertain. Ichthyosaurs were, at times, considered to have arisen independently of
3200-451: The rhynchosaurs. Gauthier used the name "Trilophosauria" for this group, but a 2015 study offered an alternative name. This study found that Azendohsauridae , Triassic reptiles previously mistaken for " prosauropod " dinosaurs, were in fact close relatives of Trilophosaurus and the rest of Trilophosauridae . Trilophosaurids and azendohsaurids are now united under the group Allokotosauria ("strange reptiles"). These two groups did not survive
3264-415: The sagittal crest is weakly differentiated, although the inner edge of each supratemporal fenestra still possessed a depressed basin of bone known as a supratemporal fossa. Ezcurra (2016) argued that presence of supratemporal fossae and an absence or poor development of the sagittal crest could be used to characterize Crocopoda. He also noted that in almost all early archosauromorphs (and some choristoderes ),
SECTION 50
#17328916700043328-567: The seminal studies of the 1980s, Archosauromorpha has consistently been found to contain four specific reptile groups, although the definitions and validity of the groups themselves have been questioned. The least controversial group is Rhynchosauria ("beak reptiles"), a monophyletic clade of stocky herbivores. Many rhynchosaurs had highly modified skulls, with beak-like premaxillary bones and wide heads. Another group of archosauromorphs has traditionally been represented by Trilophosaurus , an unusual iguana -like herbivorous reptile quite different from
3392-443: The space left by the shortening of the anterior process of the quadratojugal. In archosauriforms, the jugal even re-encloses the lower temporal fenestra. The stapes are long, thin, and solid, without a perforating hole (stapedial foramen) present in the more robust stapes of other reptiles. In conjunction with their long, S-shaped necks, early archosauromorphs had several adaptations of the cervical (neck) vertebrae , and usually
3456-445: The staggering diversity of archosauromorphs, they can still be united as a clade thanks to several subtle skeletal features. Most archosauromorphs more "advanced" than Protorosaurus possessed an adaptation of the premaxilla (tooth-bearing bone at the tip of the snout) known as a posterodorsal or postnarial process. This was a rear-facing branch of bone that stretched up below and behind the external nares (nostril holes) to contact
3520-789: The structure of the forebrain. According to Goodrich, both lineages evolved from an earlier stem group, Protosauria ("first lizards") in which he included some animals today considered reptile-like amphibians , as well as early reptiles. In 1956, D.M.S. Watson observed that the first two groups diverged very early in reptilian history, so he divided Goodrich's Protosauria between them. He also reinterpreted Sauropsida and Theropsida to exclude birds and mammals, respectively. Thus his Sauropsida included Procolophonia , Eosuchia , Millerosauria , Chelonia (turtles), Squamata (lizards and snakes), Rhynchocephalia , Crocodilia , " thecodonts " ( paraphyletic basal Archosauria ), non- avian dinosaurs , pterosaurs , ichthyosaurs , and sauropterygians . In
3584-465: The term Archosauromorpha for the archosaur lineage at the 1982 annual meeting of the American Society of Zoologists , and later used it within his 1984 Ph.D. thesis. Archosauromorpha, as formulated by Gauthier, included four main groups of reptiles: Rhynchosauria, "Prolacertiformes", "Trilophosauria", and Archosauria (now equivalent to the group Archosauriformes ). Cladistic analyses created during
3648-472: The term Archosauromorpha was seldom used until many years after its creation. The advent of cladistics helped to sort out at least some of the relationships within Reptilia, and it became clear that there was a split between the archosaur lineage and the lepidosaur lineage somewhere within the Permian, with certain reptiles clearly closer to archosaurs and others allied with lepidosaurs. Jacques Gauthier reused
3712-440: The ulna is poorly developed in archosauromorphs apart from Aenigmastropheus and Protorosaurus . The ankle bones of archosauromorphs tend to acquire complex structures and interactions with each other, and this is particularly the case with the large proximal tarsal bones: the astragalus and calcaneum . The calcaneum, for example, has a tube-like outer extension known as a calcaneal tuber in certain archosauromorphs. This tuber
3776-404: The vertebrae, a posterodorsal process of the premaxilla, a lack of notochordal canals, and the loss of the entepicondylar foramen of the humerus. The term Archosauromorpha was first used by Friedrich von Huene in 1946 to refer to reptiles more closely related to archosaurs than to lepidosaurs. However, there was little consensus on ancient reptile relationships prior to the late 20th century, so
3840-434: The vertebral components, sloping down from the elongated transverse processes to the centra. Laminae are practically unique to archosauromorphs, being present even in the earliest Permian genera such as Aenigmastropheus and Eorasaurus . However, they are also known to occur in the bizarre semiaquatic reptile Helveticosaurus , as well as the biarmosuchian synapsid Hipposaurus . In all adult archosauromorphs with
3904-585: The years following Gauthier's paper. The first such new definition, which attempted to adhere to the standards of the PhyloCode , was published by Modesto and Anderson in 2004. Modesto and Anderson reviewed the many previous definitions and proposed a modified definition, which they intended to retain most traditional content of the group while keeping it stable and monophyletic. They defined Reptilia as all amniotes closer to Lacerta agilis and Crocodylus niloticus than to Homo sapiens . This stem-based definition
SECTION 60
#17328916700043968-625: Was Hylonomus , a small and superficially lizard-like animal which lived in Nova Scotia during the Bashkirian age of the Late Carboniferous , around 318 million years ago . Genetic and fossil data argues that the two largest lineages of reptiles, Archosauromorpha (crocodilians, birds, and kin) and Lepidosauromorpha (lizards, and kin), diverged during the Permian period. In addition to
4032-592: Was close to the modern consensus, nonetheless, it became considered inadequate because the actual relationship of turtles to other reptiles was not yet well understood at this time. Major revisions since have included the reassignment of synapsids as non-reptiles, and classification of turtles as diapsids. Gauthier 1994 and Laurin and Reisz 1995's definition of Sauropsida defined the scope of the group as distinct and broader than that of Reptilia, encompassing Mesosauridae as well as Reptilia sensu stricto . A variety of other definitions were proposed by other scientists in
4096-615: Was not the only possible classification scheme: In the Hunterian lectures delivered at the Royal College of Surgeons in 1863, Huxley grouped the vertebrates into mammals , sauroids, and ichthyoids (the latter containing the fishes and amphibians). He subsequently proposed the names of Sauropsida and Ichthyopsida for the latter two groups. In 1866, Haeckel demonstrated that vertebrates could be divided based on their reproductive strategies, and that reptiles, birds, and mammals were united by
#3996