Opening in the skull in front of the eye sockets, largely associated with archosauriforms
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.
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]
^Preushscoft, H., Witzel, U. 2002. Biomechanical Investigations on the Skulls of Reptiles and Mammals. Senckenbergiana Lethaea 82:207–222.
^ abcWitmer, 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.
^Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. ISBN 1-4051-3413-5.
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An antorbitalfenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated...
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fenestra. Zhuchengtyrannus also possesses a ventral margin of the antorbitalfenestra that lies well above that of the ventral rim of the antorbital fossa...
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ridge which terminates at the rear lower corner of the antorbitalfenestra. The antorbitalfenestra itself takes the form of a very large and elongated triangular...
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Archosauria and later Archosauriformes, such as the presence of an antorbitalfenestra and serrated teeth, are now known to have evolved prior to those...
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and unusually wide. The section in front of the combined nasal-antorbitalfenestra was relatively short. Also unusual was the combination of its toothless...
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to the genus. However, C. iguidensis has antorbital fossae limited to the proximity of the antorbitalfenestra, a crest running along the medial face of...
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