Quadrate bone

The quadrate bone is part of a skull in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In these animals it connects to the quadratojugal and squamosal in the skull, and forms part of the jaw joint (the other part is the articular bone at the rear end of the lower jaw).

It is formed by endochondral ossification and is formed from the hindmost part of the primitive cartilaginous upper jaw.

Skull anapsida 1
Anapsid skull, Quadrate bone marked q

Evolutionary variation

In snakes, the quadrate bone has become elongated and very mobile, and contributes greatly to their ability to swallow very large prey items. In some lizards and dinosaurs also the quadrate is articulated at both ends and movable. In certain reptiles, the variation and stability of the morphology of the quadrate bone has help paleontologist in the species-level taxonomy and identification of mosasaur squamates [1] and spinosaurine dinosaurs.[2]

In mammals the articular and quadrate bones have migrated to the middle ear and are known as the malleus and incus. This migration was first described by Reichert in 1837. In pig embryos he discovered that the mandible ossifies on the side of Meckel's cartilage, while the posterior part of that cartilage is ossified and then detaches from the rest of the cartilage to enter the middle ear where it becomes the incus.[3]

See also


  1. ^ DeBraga, M. and Carroll, R.L., 1993. The origin of mosasaurs as a model of macroevolutionary patterns and processes. In Evolutionary biology (pp. 245-322). Springer US.
  2. ^ Hendrickx, C., Mateus O., & Buffetaut E. (2016). Morphofunctional Analysis of the Quadrate of Spinosauridae (Dinosauria: Theropoda) and the Presence of Spinosaurus and a Second Spinosaurine Taxon in the Cenomanian of North Africa.. PLoS ONE. 11, e0144695., 01, Number 1: Public Library of Science
  3. ^ Scott 2000, Paragraph starting with "The original jaw bones changed also. [...] "


  • Gilbert, Scott F. (c. 2000). "The anatomical tradition: Evolutionary Embryology: Embryonic homologies". Developmental Biology. Sunderland (MA): Sinauer Associates, Inc. (NCBI). Retrieved January 2010. Check date values in: |accessdate= (help)

External links


Allokotosauria is a clade of early archosauromorph reptiles from the Middle to Late Triassic known from Asia, Africa, North America and Europe. Allokotosauria was first described and named when a new monophyletic grouping of specialized herbivorous archosauromorphs was recovered by Sterling J. Nesbitt, John J. Flynn, Adam C. Pritchard, J. Michael Parrish, Lovasoa Ranivoharimanana and André R. Wyss in 2015. The name Allokotosauria is derived from Greek meaning "strange reptiles" in reference to unexpected grouping of early archosauromorph with a high disparity of features typically associated with herbivory. Nesbitt et al. (2015) defined the group as a stem-based taxon containing Azendohsaurus madagaskarensis and Trilophosaurus buettneri and all taxa more closely related to them than to Tanystropheus longobardicus, Proterosuchus fergusi, Protorosaurus speneri or Rhynchosaurus articeps. Therefore, Allokotosauria includes the families Azendohsauridae and Trilophosauridae by definition, as well as the potentially more basal Pamelaria which is closer to them than to other early archosauromorphs. Pamelaria is the earliest known allokotosaur, dating to the Anisian of India. Azendohsauridae is currently represented by a single genus Azendohsaurus known from the Ladinian to Carnian of Africa, while trilophosaurids are mostly known from the Carnian to Norian stages of North America, England and potentially European Russia, though one member of the latter group, Variodens inopinatus, is known from Rhaetian. According to studies of Arctosaurus material from Cameron Island in Canada, the latter may have been an allokotosaurian because of the similarities with Azendohsaurus due to the presence of a posterior ridge from the centrum to the diapophyses which extends from the diapophysis all the way to the posterior ventrolateral corner of the centrum. This ridge overhangs a deep groove in the lateral surface of the centrum.Allokotosauria is most notably characterized by wrinkled side surface of orbital border of the frontal bone, expanded and hooked quadrate bone head on the posterior side, and a prominent tubercle developed above to the glenoid fossa of the scapula, although there are other unambiguous traits that differentiate it from other early archosauromorphs. Below is a cladogram showing the phylogenetic relationships of Allokotosauria within Archosauromorpha as recovered by Nesbitt et al. (2015). Ezcurra (2016) also recovered a highly supported Allokotosauria with the same topology (including only Pamelaria, Azendohsaurus madagaskarensis and Trilophosaurus buettneri in his analysis), but noted that Pamelaria is nearly as likely to represent a basal azendohsaurid instead.

Sengupta et al. (2017) described a new azendohsaurid and recovered Pamelaria as an azendohsaurid.


Arcticodactylus is a genus of basal pterosaur living during the Late Triassic in the area of present Greenland. Its only species was previously attributed to Eudimorphodon, and its closest relatives may have been Eudimorphodon or Austriadraco.

Articular bone

The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as Stem-mammal. In these animals it is connected to two other lower jaw bones, the suprangular and the angular. It forms the jaw joint by articulating with the quadrate bone of the skull.

In mammals, the articular bone has migrated to the middle ear to become the malleus, while the quadrate bone becomes the incus. Paleontologists regard this as a defining characteristic of mammalian fossils.It is analogous to, but not homologous to the articular process of the lower jaw.


Baurusuchinae is a subfamily of baurusuchid crocodyliforms from the Late Cretaceous of Brazil. Named in 2011, it contains the baurusuchids Baurusuchus and Stratiotosuchus. Baurusuchinae is one of two subfamilies of Baurusuchidae, the other being Pissarrachampsinae.Several features distinguish baurusuchines from pissarrachampsines and help diagnose the subfamily. The two prefrontal bones on the top of the skull are connected along a small length of midline of the skull, while those of pissarrachampsines touch only at a small point. The frontal bone, situated behind the prefrontals, is very wide. Baurusuchines also have ridges on parts of their palate. The quadratojugal, a bone within a depression of the skull behind the eye called the laterotemporal fenestra, extends up to the rim of the fenestra or ends just below it. There is also a straight or somewhat curved muscle scar on the medial surface of the quadrate bone.Baurusuchinae is a stem-based taxon defined in 2011 as Baurusuchus pachecoi and all crocodyliforms more closely related to it than to Pissarrachampsa sera, Notosuchus terrestris, Mariliasuchus amarali, Armadillosuchus arrudai, Araripesuchus gomesi, Sebecus icaeorhinus, Bretesuchus bonapartei, Peirosaurus torminni, and Crocodylus niloticus.Baurusuchines are only found in the Bauru Basin of Brazil, and are therefore endemic to the Bauru Group. Because of their restricted stratigraphic and geographic range, baurusuchines were probably sympatric, living in the same environment at the same time. Alternatively, they may have been stratigraphically separated, meaning that each species lived at a slightly different time.


Europelta is an extinct genus of struthiosaurine nodosaurid dinosaur known from the Early Cretaceous (early Albian stage) lower Escucha Formation of Teruel Province, northeastern Spain. It contains a single species, Europelta carbonensis. It is known from two associated partial skeletons, and represents the most complete ankylosaur known from Europe.


Hadrosauromorpha is a cohort of iguanodontian ornithopods, defined in 2014 by David B. Norman to divide Hadrosauroidea into the basal taxa with compressed manual bones and a pollex, and the derived taxa that lack them. The clade is defined as all the taxa closer to Edmontosaurus regalis than Probactrosaurus gobiensis. This results in different taxon inclusion depending on the analysis.


Huanansaurus is an extinct genus of oviraptorid dinosaur that lived approximately 72 million years ago, between the Campanian and Maastrichtian, during the latter part of the Cretaceous period in what is now China, in the Nanxiong Formation.


Ilokelesia is an abelisaur found in 1991, preserved in the layers of the earliest Late Cretaceous of the Río Limay Formation, Neuquén Group, located near Plaza Huincul, Neuquén Province, Argentina. The specimen, consisting of very fragmentary elements of the skull and the axial and appendicular skeleton, was described by Rodolfo Coria and Leonardo Salgado in late 1998.


The Leptotyphlopidae (commonly called slender blind snakes or thread snakes) are a family of snakes found in North America, South America, Africa, & Asia. All are fossorial and adapted to burrowing, feeding on ants and termites. Two subfamilies are recognized.

Middle ear

The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the inner ear. The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear is also known as the tympanic cavity and is surrounded by the tympani bone. The auditory tube (also known as the Eustachian tube or the pharyngotympanic tube) joins the tympanic cavity with the nasal cavity (nasopharynx), allowing pressure to equalize between the middle ear and throat.

The primary function of the middle ear is to efficiently transfer acoustic energy from compression waves in air to fluid–membrane waves within the cochlea.

Oceanic eclectus parrot

The oceanic eclectus parrot (Eclectus infectus) is an extinct parrot species which occurred on Tonga, Vanuatu and possibly on Fiji. The only living relative in the genus is the eclectus parrot (Eclectus roratus), which has proportionally larger wings than the oceanic eclectus parrot. The fossil material unearthed in November 1989 in Late Pleistocene and Holocene deposits on 'Eua, Lifuka, 'Uiha and Vanuatu and described in 2006 by David William Steadman include a complete femur, five radii, a quadrate bone, a mandible, a coracoid, two sterna, two humeri, two ulnae, two tibiotarsi, a carpometacarpus, a tarsometatarsus, and three pedal phalanges.The oceanic eclectus parrot became extinct on Tonga during the early settlement 3000 years ago, presumably due to human-caused factors. On Vava'u, it may have survived into historic times because among the drawings which were created in 1793 during Alessandro Malaspina's Pacific expedition, there is one sketch which appears to portray an Oceanic eclectus parrot.


The Odontoanserae is a purposed clade that includes the family Pelagornithidae (pseudo-toothed birds) and the clade Anserimorphae (the order Anseriformes and their stem-relatives). The placement of the pseudo-toothed birds in the evolutionary tree of birds has been problematic, with some supporting the placement them near the orders Procellariformes and Pelecaniformes based on features in the sternum.In 2005 a cladistic analysis had found support in placing pseudo-toothed birds as the sister group to waterfowl. Evidence for this comes from shared characteristics in the skull such as lack a crest on the underside of the palatine bone and two condyles on the mandibular process of the quadrate bone, with the middle condyle beakwards of the side condyle. In addition to that both groups have similar features in their pelvic and pectoral regions. Furthermore a 2013 study on the growth pattern and structure of the pseudoteeth in Pelagornis mauretanicus shows more support of Odontoanserae as both groups have "soft rhamphotheca, or delayed hardening of the rhamphotheca." In addition to Pelagornithidae and Anseriformes paleontologists also have support in placing mihirungs (Dromornithidae) and Gastornithids into this group, as they too also share anatomical features in the skull and pelvic bones with waterfowl. The mihirungs and the gastornithids are more derived than the pseudo-tooth birds and are closer to Anseriformes. One hypothesis is that diatryams and mihirungs are successive sister groups to anseriforms and another hypothesis places mihirungs as crowned anseriforms closely related to the screamers (Anhimidae).Below is the general consensus of the phylogeny.

However, a 2017 paper by Worthy and colleagues have found an alternative phylogeny concerning Anserimorphae. By adding additional new characters, as well as incorporating several new taxa into established matrices, the authors have found gastornithids and mihirungs to be sister taxa and could be placed in the order Gastornithiformes. In addition they have found support that the family Vegaviidae (usually classified as crowned anseriforms or their sister taxon) are more related to gastornithiforms than to anseriforms (which they have created the monotypic order Vegaviiformes). The authors did note the bootstrap support is weakly supported and several alternative phylogenies in their paper found gastornithiforms to be stem galliforms instead. These too were also weakly supported as well. Below is a simplified phylogeny showing their one phylogeny supporting gastornithiforms as anserimorphs.

In 2019 a new species Conflicto antarcticus was described from Early Paleocene deposits in Antarctica. Known completely from associated bones from a single individual, Tambussi et al. (2019) incorporated the new taxon into a phylogenetic analysis using the matrix data from Worthy et al. (2017). Their results not only supported the sister grouping of vegaviids with gastornithids and mihirungs (which they included Vegaviidae into Gastornithiformes), but also found two taxa Anatalavis rex and the tall, wading presbyornithids, traditionally placed as crowned members of Anseriformes, have found to be stem-anseriforms. Below is the Tambussi et al. (2019) phylogeny.


Oligokyphus is an extinct genus of advanced herbivorous cynodonts of the late Triassic to early Jurassic periods. Originally considered to be an early mammal, it is now classified as a Mammaliamorph (nearly a mammal) because Oligokyphus does not have the mammalian jaw attachments and it retains a vestigial joint between the quadrate bone and the squamosal bone in the skull.


Osteodontornis is an extinct seabird genus. It contains a single named species, Osteodontornis orri (Orr's Bony-toothed Bird, in literal translation of its scientific name), which was described quite exactly one century after the first species of the Pelagornithidae (Pelagornis miocaenus) was. O. orri was named after then-recently deceased naturalist Ellison Orr.The bony-toothed or pseudotooth birds were initially believed to be related to albatrosses in the Procellariiformes, but actually they seem to be rather close relatives of either pelicans and storks, or of waterfowl, and are here placed in the order Odontopterygiformes to account for this uncertainty. Also, their internal taxonomy is not well-resolved. An earlier-described pseudotooth bird, Cyphornis magnus from Vancouver Island (Canada), was believed to be of Eocene age but is nowadays assumed to have lived about twenty million years ago in the Early Miocene, not too long before the Clarendonian (Middle/Late Miocene) O. orri. It may be that Osteodontornis is a junior synonym of Cyphornis.

Pelecanus schreiberi

Pelecanus schreiberi is a fossil pelican described by Storrs Olson from Early Pliocene (5.3 to 3.6 million year old) deposits in the Yorktown Formation of North Carolina. It was a large species with distinctive features suggesting that it represents an extinct lineage with no living descendants. The specific epithet commemorates Ralph W. Schreiber (1942–1988), a former curator of birds at the Natural History Museum of Los Angeles County and an authority on pelicans.Collected in 1972 by one Gerard R. Case from a mine on the southern side of the Pamlico River near Aurora, North Carolina, the holotype is a right lower third of a femur of an egg-laying female. The denseness of the medullary bone indicated this last fact as it is a feature of living egg-laying female pelicans. The features of the femur allowed it to be classified as a pelican, but quite different from living species. Some foot bones (phalanges) have also been found. An incomplete quadrate bone and axis vertebra without a spine from a mine of the same age in Polk County in central Florida are tentatively considered to be the same species. These remains are from the Bone Valley Formation, of nearly the same age as the Yorktown Formation.The female is around the same size as the largest individual great white pelicans (Pelecanus onocrotalus) or Dalmatian pelicans (P. crispus), so a male could have been even larger – possibly the largest living or fossil pelican recorded, rivalled only by subfossil remains of a New Zealand pelican that has been described as a subspecies of the Australian pelican (P. conspicillatus) and a mysterious late Miocene species Pelecanus odessanus from the Ukraine.


Potamornis is a prehistoric bird genus that dated back to the late Maastrichtian age of the late Cretaceous period. Its scrappy remains were found in the Lance Formation at Buck Creek, USA, and additional possible remains were found in the upper Hell Creek Formation of Montana, dated to the Danian age of the Paleogene period, though these may have been reworked. A single species was named and described in 2001: Potamornis skutchi.This was almost certainly a member of the Hesperornithes, the hefty and toothed flightless diving birds of the Mesozoic seas. Its precise relationships are not all too clear; the quadrate bone is unique in some respects but apparently shares more apomorphies with the family Hesperornithidae - the "typical" Hesperornithes - in cladistic analysis. Consequently, it might be considered a fossil hesperornithid with a different feeding specialization. Though it was heavily built like many (flying and flightless) diving birds, it weighed perhaps 1.5 or 2 kg. This raises the possibility that the Hesperornithes not only included flying members (see also Enaliornis), but that their families might have evolved flightlessness independently.


Quadrate may refer to:

Quadrate bone

Quadrate (heraldry)

Quadrate lobe of liver

Quadratojugal bone

The quadratojugal is a cranial bone that is present in many tetrapods and their close relatives. It forms the rear lower corner of the skull, typically connecting to the jugal (cheek bone) from the front and the squamosal from above. The inner face of the quadratojugal also connects to the quadrate bone which forms the cranium's contribution to the jaw joint. Many living and extinct reptiles and amphibians possess a quadratojugal, but the bone has been lost or fused to other bones in several lineages. Modern examples of tetrapods without a quadratojugal include salamanders, mammals, birds, and squamates (lizards and snakes).

Varanus amnhophilis

Varanus amnhophilis, the Samos dragon, is an extinct species of monitor lizard from the Miocene of Greece. It was named in 2012 and placed in its own subgenus, Varaneades. It is only known from a partial skull and several vertebrae, but comparisons with other species of monitor lizard put its size between 60 and 80 centimetres (2.0 and 2.6 ft) in length. The fossil was found in the Turolian-age Mytilini Formation on the island of Samos and is currently housed in the American Museum of Natural History.

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