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
Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian (roughly 252 million years ago). It was defined by Jacques Gauthi ...
, first appearing during the
Triassic Period. Among
extant
Extant is the opposite of the word extinct. It may refer to:
* Extant hereditary titles
* Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English
* Extant taxon, a taxon which is not extinct, ...
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.
[Preushscoft, H., Witzel, U. 2002. Biomechanical Investigations on the Skulls of Reptiles and Mammals. Senckenbergiana Lethaea 82:207–222.][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.] In some archosaur species, the opening has closed but its location is still marked by a depression, or
fossa
Fossa may refer to:
Animals
* Fossa (animal), the common name of a carnivoran mammal of genus ''Cryptoprocta'' endemic to Madagascar
* ''Fossa'', the Latin genus name of the Malagasy civet, a related but smaller mammal endemic to Madagascar
Pla ...
, 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.
[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.] Although crocodylians walled over their antorbital fenestra, they still retain an antorbital sinus.
In
theropod dinosaurs
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
, 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
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
. In contrast, most
ornithischian dinosaurs reduce and even close their antorbital fenestrae
such as in
hadrosaurs and the dinosaur genus ''
Protoceratops''. This closure distinguishes ''Protoceratops'' from other
ceratopsian dinosaurs.
[Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. .]
See also
*
Fenestra (anatomy)
References
{{reflist
External links
Archosaur Morphology
Dinosaur anatomy
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