The Paranasal Sinuses: The Last Frontier in Craniofacial Biology The Paranasal Air Sinuses of Predatory and Armored Dinosaurs (Archosauria: Theropoda and Ankylosauria) and Their Contribution to Cephalic Structure

The paranasal air sinuses and nasal cavities were studied along with other cephalic spaces (brain cavity, paratympanic sinuses) in certain dinosaurs via CT scanning and 3D visualization to document the anatomy and examine the contribution of the sinuses to the morphological organization of the head as a whole. Two representatives each of two dinosaur clades are compared: the theropod saurischians Majungasaurus and Tyrannosaurus and the ankylosaurian ornithischians Panoplosaurus and Euoplocephalus. Their extant archosaurian outgroups, birds and crocodilians (exemplified by ostrich and alligator), display a diversity of paranasal sinuses, yet they share only a single homologous antorbital sinus, which in birds has an important subsidiary diverticulum, the suborbital sinus. Both of the theropods had a large antorbital sinus that pneumatized Anatomical abbreviations used (taxonomic representation indicated in parentheses): airway 5 main nasal airway (respiratory region of the nasal cavity; all); antorb 5 antorbital sinus (archosaurs); aofen 5 internal antorbital fenestra in the skull; the external antorbital fenestra is the rim around the antorbital fossa (Majungasaurus, Tyrannosaurus); caudal loop 5 caudal loop of the nasal airway (Panoplosaurus, Euoplocephalus); ch 5 choana (all); dalv 5 dorsal alveolar canal, transmitting branches of the maxillary nerves and large vessels (Euoplocephalus); con 5 conchal spaces in the airway of the ostrich, where the mucosal nasal conchae reside; ect 5 ectopterygoid sinus (source of diverticulum uncertain, probably not from antorbital sinus; Tyrannosaurus); endocast 5 cranial endocast of brain cavity (all); eth 5 ethmoidal sinus (human); fr 5 frontal sinus (human; in ostrich, frontal portion of fronto-ethmoidal sinus; Majungasaurus); ialv 5 interalveolar sinuses (a maxillary sinus, from antorbital sinus via other maxillary sinuses; Tyrannosaurus); jug 5 jugal sinus (from antorbital sinus; Tyrannosaurus); lac 5 lacrimal sinus proper (from antorbital sinus in nonavian theropods including most birds but from suborbital sinus in ostrich); lacm 5 medial lacrimal sinus (from antorbital sinus in nonavian theropods); mant 5 maxillary antral sinus (a maxillary sinus, from antorbital sinus; Tyrannosaurus); max 5 maxillary sinus (human, alligator, theropods— nonhomologous); mes 5 mesethmoidal portion of fronto-ethmoidal sinus (ostrich); mfen 5 maxillary fenestra of skull (Tyrannosaurus); mnas 5 medial nasal canal, transmitting the medial nasal branches of the ophthalmic nerve and enlarged medial nasal branches of the ethmoidal vessels (Euoplocephalus); nar 5 nostril (fossil skulls); nas 5 nasal sinus (from antorbital sinus; Majungasaurus); npdu 5 nasopharyngeal duct (alligator); nvas 5 neurovascular canals in the premaxilla derived principally from the medial nasal canal (Euoplocephalus); olf 5 olfactory region of the nasal cavity (all); orbit 5 orbit or eye socket (fossil skulls); pf 5 prefrontal sinus (alligator); pal 5 palatine sinus (alligator, Tyrannosaurus, Panoplosaurus, Euoplocephalus—not homologous); pmax 5 promaxillary sinus (a maxillary sinus, from antorbital sinus; Tyrannosaurus); pter 5 pterygoid sinus (from nasopharyngeal duct in alligator, from suborbital sinus in ostrich); pterpal 5 pterygopalatine sinus of nasopharyngeal duct (alligator); pv5 postvestibular sinus (alligator); rostral loop5 rostral loop of the nasal airway (Panoplosaurus, Euoplocephalus); sph 5 sphenoidal sinus (human); squ 5 squamosal sinus (perhaps from antorbital sinus via suborbital sinus; Tyrannosaurus); sub 5 suborbital sinus (from antorbital sinus in theropods, including ostrich); tymp 5 main middle ear cavity and paratympanic sinuses (all); *5 position of the putative ‘‘paranasal aperture,’’ which is not demonstrably separate either externally or internallyfromthetruenarialaperture(Euoplocephalus). Grant sponsor: National Science Foundation; Grant numbers: NSF BSR-9112070, NSF IBN-9601174, NSF IBN-0343744, NSF IOB-0517257; Grant sponsor: Ohio University College of Osteo-