THE DEVELOPMENT OF ANTORBITAL, PARATYMPANIC AND PHARYNGEAL PNEUMATIC SINUSES IN MANIDENS CONDORENSIS (ORNITHISCHIA: HETERODONTOSAURIDAE)

BECERRA, MARCOS G.; POL, DIEGO; PAULINA-CARABAJAL, ARIANA

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Congreso; XXXV Jornadas Argentinas de Paleontologia de Vertebrados; 2022

Museo Paleontológico Egidio Feruglio

Skull pneumaticityis an archosaurian attribute, well-known in extant crocodilians and birds, anddescribed in many crurotarsan clades and saurischian dinosaurs. The skull ofornithischians, one of the two dinosaur subclades, is rather solid and lacks well-developedpneumatic recesses that invade within the bones, with derived speciescharacterized by forming complex airway arrangements. However, the skull pneumaticityof early ornithischians is poorly known. Only a recent description of Lesothosaurus (likely a basalgenasaurian) recognizes depressed regions in the antorbital fossa (maxilla),the palatine, and the basicranium (basioccipital, basisphenoid) that may berelated to pneumatic recesses. Here we present the 3D reconstructions of internalspaces and superficial pneumatic fossae in skull bones of the early Jurassicheterodontosaurid ornithischian Manidens condorensis (MPEF-PV3211 and 3809, Cañadón Asfalto Formation, Chubut), describing sinuses anddiverticula for three different cranial pneumatic systems: antorbital(paranasal), paratympanic and pharyngeal. The antorbital fenestra in themaxilla opens anteroventrally by a narrow and long slit into a wide spacewithin the maxilla and lateral to the tooth roots. These are interpreted as twodiverticula homologous to the interalveolar and promaxillary recesses of theantorbital paranasal air sinus in non-avian theropods and birds. The lacrimal showsa small internal space that opens laterally by a foramen and a notch, likelycorresponding to a lacrimal diverticulum of the antorbital sinus (as intheropods). The rostral, dorsal, and caudal tympanic recesses from theparatympanic system are recognized (with the first forming two uncommon dorsal diverticulawithin the basisphenoid). The connection to each other and their relation withthe cranial musculature are to be described. The basisphenoid shows a deepventral basisphenoidal recess, and a small pit-like subsellar recess betweenthe basipterygoid processes. Internal spaces are identified in the jugal,squamosal, ectopterygoid, quadrate, basisphenoid, basioccipital,supraoccipital, otoccipital, and prootics, identified as cancellous structures.No nasal or frontoparietal pneumatic recesses are present in Manidens condorensis.Comparisons indicate that similar pharingotympanic systems are present in Lesothosaurus,Heterodontosaurus, and Scelidosaurus, but the complex paranasal pneumatic system of Manidens seemsuncommon among ornithischians. Further research is needed to betterunderstand whether the presence of complex antorbital (paranasal) sinuses inornithischians is 1) a primitive feature shared with saurischians and otherarchosaurs and lost in more derived ornithischians, or 2) lost at the base of Ornithischiaand convergently appears among heterodontosaurids as a derived feature,characterizing the construction of the heterodontosaurid skull as more complexthan previously though.