Antorbital fenestra

An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosaurs, first appearing during the Triassic Period. Among extant archosaurs, birds still possess antorbital fenestrae, whereas crocodylians have lost them. The loss in crocodylians is believed to be related to the structural needs of their skulls for the bite force and feeding behaviours that they employ.[1][2] In some archosaur species, the opening has closed but its location is still marked by a depression, or fossa, on the surface of the skull called the antorbital fossa.

The antorbital fenestra houses a paranasal sinus that is confluent with the adjacent nasal capsule.[3] Although crocodylians walled over their antorbital fenestra, they still retain an antorbital sinus.[3]

In theropod dinosaurs, the antorbital fenestra is the largest opening in the skull. Systematically, the presence of the antorbital fenestra is considered a synapomorphy that unites tetanuran theropods as a clade. In contrast, most ornithischian dinosaurs reduce and even close their antorbital fenestrae[3] such as in hadrosaurs and the dinosaur genus Protoceratops. This closure distinguishes Protoceratops from other ceratopsian dinosaurs.[4]

Massospondylus Skull Steveoc 86
The antorbital fenestra in relation to the other skull openings in the dinosaur Massospondylus.

See also


  1. ^ Preushscoft, H., Witzel, U. 2002. Biomechanical Investigations on the Skulls of Reptiles and Mammals. Senckenbergiana Lethaea 82:207–222.
  2. ^ Rayfield, E.J., Milner, A.C., Xuan, V.B., Young, P.G. 2007. Functional Morphology of Spinosaur "Crocodile Mimic" Dinosaurs. JVP. 27(4):892–901.
  3. ^ a b c Witmer, L.M. 1997. The Evolution of the Antorbital Cavity of Archosaurs: A Study in Soft-Tissue Reconstruction in the Fossil Record with an Analysis of the Function of Pneumaticity. JVP 17(1 supp):1–76.
  4. ^ Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. ISBN 1-4051-3413-5.

External links


Asperoris is an extinct genus of archosauriform reptile known from the Middle Triassic Manda Beds of southwestern Tanzania. It is the first archosauriform known from the Manda Beds that is not an archosaur. However, its relationships with other non-archosaurian archosauriforms are uncertain. It was first named by Sterling J. Nesbitt, Richard J. Butler and David J. Gower in 2013 and the type species is Asperoris mnyama. Asperoris means "rough face" in Latin, referring to the distinctive rough texture of its skull bones.


Barberenasuchus is an extinct genus of an archosauriform. Fossils (poorly preserved skull and axis vertebra) have been found from the Santa Maria Formation of southern Brazil of Late Triassic age. Its phylogenetic position within Archosauriformes is uncertain; the author of its description classified it as a sphenosuchid crocodylomorph, while Kischlat (2000) considered it to be a rauisuchian. Irmis, Nesbitt and Sues (2013) stated that they "could not find any crocodylomorph character states preserved in the holotype specimen". Based on the presence of an antorbital fenestra the authors assigned Barberenasuchus to Archosauriformes, but stated that without further preparation and study it is not possible to assign it to any specific archosauriform group. It is named in honor of Mário Costa Barberena.


The Chaoyangopteridae are a family of pterosaurs within the Azhdarchoidea.

The clade Chaoyangopteridae was first defined in 2008 by Lü Junchang and David Unwin as: "Chaoyangopterus, Shenzhoupterus, their most recent common ancestor and all taxa more closely related to this clade than to Tapejara, Tupuxuara or Quetzalcoatlus". Based on neck and limb proportions, it has been suggested they occupied a similar ecological niche to that of azhdarchid pterosaurs, though it is possible they were more specialised as several genera occur in Liaoning, while azhdarchids usually occur by one genus in a specific location. The Chaoyangopteridae are mostly known from Asia, though the possible member Lacusovagus occurs in South America and there are possible fossil remains from Africa. Microtuban may extend the clade's existence into the early Late Cretaceous.Chaoyangopterids are distinguished from other pterosaurs by several traits of the nasoantorbital fenestra, a large hole on the side of the snout formed by the assimilation of the nares (nostril holes) into the antorbital fenestra. In members of this family, the nasoantorbital fenestra is massive, with the rear edge extending as far back as the braincase and jaw joint. The front edge is formed by a rod of bone known as the premaxillary bar, which is unusually slender in members of this family.Like their azhdarchid relatives, chaoyangopterids were terrestrial foragers.


Eosuchians are an extinct order of diapsid reptiles. Depending on which taxa are included the order may have ranged from the late Carboniferous to the Eocene but the consensus is that eosuchians are confined to the Permian and Triassic.

Eosuchia was initially defined to include all "thecodontian" reptiles which did not have an antorbital fenestra but did retain tabulars, postparietals and a large pineal foramen (Broom, 1914). Broom coined the term as a new suborder for Youngina.

A definition for inclusion in the order is difficult: it is almost easier to list the primitively-diapsid reptiles that have not been included at one time or another. The order has almost been treated as a dustbin for diapsids that are not obviously lepidosaurian or archosaurian. One consequence has been Romer's suggestion of the alternative order Younginiformes to be applied strictly to those forms with the primitive diapsid form, in particular, a complete lowermost arch as the quadratojugal and jugal bones of the skull meet.The one constant eosuchian has been Youngina, a small lizard-shaped reptile from the Upper Permian of South Africa. This and a couple of other genera, which may or may not be synonymous with Youngina, make up the family Younginidae.

The tangasaurids, a family that includes forms apparently adapted for swimming in fresh water, is also usually included.In some phylogenies Eosuchia has been treated (probably erroneously) as a sister lepidosaur taxon to Squamata and Rhynchocephalia.


Hupehsuchia is an order of diapsid reptiles closely related to ichthyosaurs. The group was short-lasting, with a temporal range restricted to the late Olenekian age, spanning only a few million years of the Early Triassic. The order gets its name from Hubei Province, China, from which many specimens have been found. They are probable members of the newly defined clade Ichthyosauromorpha.

Infratemporal fenestra

An infratemporal fenestra, also called the lateral temporal fenestra is an opening in the skull behind the orbit in some animals. An opening in front of the eye sockets, conversely, is called an antorbital fenestra. Both of these openings reduced the weight of the skull. Infratemporal fenestrae are commonly (although not universally) seen in the fossilized skulls of dinosaurs.


Jidapterus is a genus of azhdarchoid pterodactyloid pterosaur from the Aptian-age Lower Cretaceous Jiufotang Formation of Chaoyang, Liaoning, China. The genus was in 2003 named by Dong Zhiming, Sun Yue-Wu and Wu Shao-Yuan. The type species is Jidapterus edentus. The genus name is derived from Jílín Dàxué or "Jilin University" and a Latinised Greek pteron, "wing". The specific name means "toothless" in Latin.

The genus is based on holotype CAD-01, a nearly complete skeleton with partial skull. The skull is toothless and relatively long, with a straight and very pointed beak, and a large hole where the antorbital fenestra is joined with the nostrils. The eye sockets are small, and there is no crest along the lower jaw as seen in ornithocheiroids, although a short projection was present at the back of the skull. The wingspan of this individual was estimated to be 1.7 m (5.58 ft). Its classification has been unstable; the original authors did not assign it to a group. Some of the original authors later suggested it was a more basal azhdarchoid, whereas another group suggested it was closer to Pteranodon and possibly the same genus as Chaoyangopterus. David Unwin assigned it to Tapejaridae without comment in The Pterosaurs: From Deep Time, but later, in a collaboration with Lü, agreed that it belonged to another azhdarchoid group and was a close relative of Chaoyangopterus, placing both in the new family Chaoyangopteridae. A redescription of the genus in 2017 corroborated these results, and also presented evidence distinguishing it from Chaoyangopterus.


Kalisuchus ('Kali's crocodile') was a genus of basal archosauriform known from remains unearthed from the Arcadia Formation (Rewan Group) of the Early Triassic of the Crater, Southwest of Rolleston, south central Queensland, Australia. It was named after Kali, the Hindu goddess of destruction, a reference to the very fragmentary nature of its remains. The type species of Kalisuchus is K. rewanensis, which refers to the Rewan Group. The Arcadia formation is dated to the Induan age at the very beginning of the Triassic, making Kalisuchus one of the oldest archosauromorphs known in Australia.


Kunpengopterus is a genus of wukongopterid pterosaur from the middle-late Jurassic or early Cretaceous of northeastern China.

Kunpengopterus is known from holotype IVPP V16047, an almost complete skeleton with complete skull and lower jaws recovered from rocks of the Tiaojishan Formation or Daohugou Beds in Linglongta, Jianchang County, western Liaoning. The age of these layers is controversial. This compression fossil is of an adult individual. Aside from the bones some soft parts were also preserved and the remains of a possibly regurgitated fish.

Kunpengopterus was named and described by Wang Xiaolin, Alexander Wilhelm Armin Kellner, Jiang Shunxing, Cheng Xin, Meng Xi and Taissa Rodrigues in 2010. The type species is Kunpengopterus sinensis. The generic name combines the Kun, a large fish or whale from Chinese folklore that could transform itself into the Peng, a gigantic colourful bird providing a mythological explanation of the northern lights, with a Latinised Greek pteron, "wing". The specific name refers to the Chinese origin.In 2017, an additional specimen, IVPP V 23674, was referred and described. It consists of a skeleton with skull.Kunpengopterus has an elongated head, 106.9 millimetres long. The cervical vertebrae too are relatively long. The naris is confluent with the antorbital fenestra, but these large openings are still partly separated by a broad and anteriorly directed processus nasalis which has itself a small vertical tear-shaped opening. A low bony crest is present on the skull, just behind the eyes; preserved soft tissue shows it was elongated by cartilage and a yellow discolouration indicates it was perhaps enlarged to the back by a skin flap. There is no sign of a crest on the snout or of a keel under the lower jaws. The back of the skull is rounded. Kunpengopterus has a long stiff tail. The fifth toe is also long and strongly curved.Kunpengopterus was assigned to the Wukongopteridae, a group of pterosaurs showing a mix of basal and derived traits.


Lacusovagus (meaning "lake wanderer") is a genus of azhdarchoid pterodactyloid pterosaur from the Lower Cretaceous of Brazil. It is based on SMNK PAL 4325, a partial upper jaw comprising sections of the skull in front of the eyes. This specimen was found in rocks of the Early Cretaceous-age (probably Aptian stage, about 120 million years ago) Nova Olinda Member of the Crato Formation. The skull was long, and unusually wide. The section in front of the combined nasal-antorbital fenestra was relatively short. Also unusual was the combination of its toothless jaws and no bony head crest. Lacusovagus was described in 2008 by Mark Witton. The type species is L. magnificens, meaning "grand lake wanderer", in reference to its large size—it is currently the largest pterosaur known from the Crato Formation with an estimated wingspan of 4.1 meters (13 feet).Lacusovagus shares many characteristics with the basal azhdarchoid family Chaoyangopteridae, and preliminary studies suggested it was a member of that clade. However, in 2017, a phylogenetic analysis found it to be within the genus Tupuxuara, a member of the Thalassodromidae.


The Monofenestrata are an unranked group of pterosaurs that includes the family Wukongopteridae and the suborder Pterodactyloidea.The clade Monofenestrata was in 2009/2010 defined as the group consisting of Pterodactylus and all species sharing with Pterodactylus the synapomorphy, shared derived trait, of an external nostril confluent with the antorbital fenestra, the major skull opening on the side of the snout. The name is derived from Greek monos, "single", and Latin fenestra, "window". The concept was inspired by the discovery of Darwinopterus, a species combining a pterodactyloid-type skull with a more basal build of the remainder of the body. The Darwinoptera, a primitive subgroup of monofenestratans showing this transitional anatomy, was also named for Darwinopterus and defined as all descendants of its common ancestor with Pterorhynchus.The earliest known monofenestrate fossils have been found in the Stonesfield Slate formation of the United Kingdom, which dates to the Bathonian stage of the Middle Jurassic, dated to about 166 million years ago. Identified elements include cervical vertebrae, fourth metacarpals and a possible pterodactyloid synsacrum. Below is a cladogram showing the results of a phylogenetic analysis presented by Andres, Clark & Xu, 2014. This study found the two traditional groupings of ctenochasmatoids and kin as an early branching group, with all other pterodactyloids grouped into the Eupterodactyloidea.


Morrinhosuchus is an extinct genus of notosuchian crocodyliform from the Late Cretaceous Adamantina Formation of Brazil. It is known from a mandible and a portion of the front of the skull collected from the municipality of Monte Alto in São Paulo state. Morrinhosuchus refers to Morrinho de Santa Luzia, a hill nearby the collection site of the holotype, while luziae refers to the chapel of Santa Luzia, which is located on top of the hill.The skull and jaws are posteriorly broad but narrow significantly toward the front. The teeth at the back of the jaw are bulbous in shape and circular in cross-section (this shape is only found in one other notosuchian, Mariliasuchus, also from the Adamantina Formation). The mandible arches upward. The symphysis, or area where the two sides of the lower jaw meet, is formed mostly by the mandibles but also partly by the splenials. The skull preserves an antorbital fenestra, or opening in front of the eyes. The nasal, a bone at the top of the skull behind the nostrils, is relatively long. There is also a small notch at the contact between the premaxilla and the maxilla near the front of the snout.Morrinhosuchus can be distinguished from Mariliasuchus on the basis of several unique features. For example, there is a gap between the maxilla and the palatine bone around the midline of the palate. The palate itself is also wider than that of Mariliasuchus. While the teeth of the two genera are very similar, their number and placement in the jaw differs slightly. Morrinhosuchus has seven post-caniniform teeth while Mariliasuchus has only six. There are also differences in the shape of the rostrum between the two genera, as Morrinhosuchus has a higher, more pointed snout with less constriction than in Mariliasuchus.The Adamantina Formation, which is Turonian to Santonian in age, was deposited in semi-arid conditions around 95 million years ago. Morrinhosuchus was found in an outcrop of reddish sandstone with carbonate nodules, concretions, and areas of intense bioturbation. The Adamantina Formation is part of the larger Bauru Basin, from which several other notosuchians have been found. These include Sphagesaurus, Mariliasuchus, Adamantinasuchus, Armadillosuchus, and Baurusuchus.


Parapsicephalus (meaning "beside arch head") is a genus of long-tailed rhamphorhynchid pterosaurs from the Lower Jurassic Whitby, Yorkshire, England. It contains a single species, P. purdoni, named initially as a species of the related rhamphorhynchid Scaphognathus in 1888 but moved to its own genus in 1919 on account of a unique combination of characteristics. In particular, the top surface of the skull of Parapsicephalus is convex, which is otherwise only seen in dimorphodontians. This has been the basis of its referral to the Dimorphodontia by some researchers, but it is generally agreed upon that Parapsicephalus probably represents a rhamphorhynchid. Within the Rhamphorhynchidae, Parapsicephalus has been synonymized with the roughly contemporary Dorygnathus; this, however, is not likely given a large number of differences between the two taxa, including the aforementioned convex top surface of the skull. Parapsicephalus has been tentatively referred to the Rhamphorhynchinae subgrouping of rhamphorhynchids, but it may represent a basal member of the group instead.


Polonosuchus is a genus of rauisuchian known from the late Triassic (Carnian age) of Poland. It was a huge predator about 5–6 metres in length and, like all rauisuchians, was equipped with a large head of long sharp teeth. The legs were placed almost underneath the body, unlike most reptiles, which would have made it quite fast and a powerful runner. The appearance was very similar to that of the more known Postosuchus, of North America, and shared with the latter the ecological niche of the apex predator.It was described as Teratosaurus silesiacus in 2005 by Tomasz Sulej, and was transferred to the genus Polonosuchus by Brusatte et al. in 2009. However, it is still considered closely related to the remaining Teratosaurus species, Teratosaurus suevicus. In Polonosuchus, the rostromedial foramen is on the medial surface of the maxilla, and the foramina for replacement teeth are not connected by a dental groove but are set together in a straight line, unlike in Teratosaurus. It also had a larger first dental alveolus than Teratosaurus, no different in size from alveoli 2-4, shorter overall maxillae (165 mm as opposed to 245 mm), and a large ridge between the palatal process and the dental alveoli which is not present in Teratosaurus at all.


Shansisuchus (meaning "Shansi Province crocodile") is an extinct genus of archosauriform reptile belonging to the family Erythrosuchidae that lived during the Middle Triassic in what is now China. The first fossils of Shansisuchus were discovered from the Ermaying Formation of Shansi Province in 1964 by Chinese paleontologist Yang Zhongjian. Like other erythrosuchids, Shansisuchus was a large-bodied carnivore with a large, deep skull. Shansisuchus is unique among early archosauriforms in having a hole in its skull called a subnarial fenestra.

Smok (archosaur)

Smok (meaning "dragon" in Polish) is an extinct genus of large carnivorous archosaur. It lived during the latest Triassic period (latest Norian to early Rhaetian stage, between 205–200 Ma). Its remains have been found in Lisowice, southern Poland. The type species is Smok wawelski (after the Wawel Dragon) and was named in 2012. It is larger than any other known predatory archosaur from the Late Triassic or Early Jurassic of central Europe. The relation of Smok to other archosaurs has not yet been thoroughly studied; it may be a rauisuchid, prestosuchid or ornithosuchid crurotarsan (part of the crocodile line of archosaurs) or a theropod dinosaur (part of the bird line of archosaurs).


Tasmaniosaurus ('lizard from Tasmania'), although this genus is not a true lizard) is an extinct genus of archosauromorph reptile known from the Knocklofty Formation (Early Triassic) of West Hobart, Tasmania, Australia. The type species is T. triassicus. This genus is notable not only due to being one of the most complete Australian Triassic reptiles known, but also due to being a very close relative of Archosauriformes. Once believed to be a proterosuchid, this taxon is now believed to have been intermediate between advanced non-archosauriform archosauromorphs such as Prolacerta, and basal archosauriforms such as Proterosuchus. Features traditionally used to define Archosauria and later Archosauriformes, such as the presence of an antorbital fenestra and serrated teeth, are now known to have evolved prior to those groups due to their presence in Tasmaniosaurus.


Teraterpeton (meaning "wonderful creeping thing" in Greek) is an extinct genus of trilophosaurid archosauromorphs. It is known from a partial skeleton from the Late Triassic Wolfville Formation of Nova Scotia, described in 2003. It has many unique features seen in no other related form, including an elongated, toothless snout and large openings for the nostrils. Because of this, Teraterpeton was originally placed in its own family, Teraterpetidae, related to Trilophosaurus. Newer studies generally place it within Trilophosauridae.


Wannia is an extinct genus of basal phytosaur reptile known from the Late Triassic (late Carnian or early Norian stage) of Texas, southern United States. It contains a single species, Wannia scurriensis, which is known from a single specimen. This species was originally named as a species referred to Paleorhinus and later was considered as a possible junior synonym of Paleorhinus bransoni. However its re-description revealed five autapomorphies, and a phylogenetic position as the most basal known phytosaur, justifying the erection of a new generic name for the species.

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