Antorbital fenestra

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

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 archosauriforms, 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.

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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]

See also

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This glossary explains technical terms commonly employed in the description of dinosaur body fossils. Besides dinosaur-specific terms, it covers terms with wider usage, when these are of central importance in the study of dinosaurs or when their discussion in the context of dinosaurs is beneficial. The glossary does not cover ichnological and bone histological terms, nor does it cover measurements.

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References

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  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.
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  4. Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. ISBN   1-4051-3413-5.