Deinonychus antirrhopus (Ostrom, 1969)

Brownstein, Chase Doran, 2021, Dromaeosaurid crania demonstrate the progressive loss of facial pneumaticity in coelurosaurian dinosaurs, Zoological Journal of the Linnean Society 191 (1), pp. 87-112 : 94

Deinonychus antirrhopus

The right nasal of Deinonychus is well preserved and in complete articulation with the right maxilla ( Fig. 1A–B ). This bone shows extensive superficial pneumaticity on its exterior and interior surfaces. Witmer (1997) briefly mentioned the exterior nasal pneumatic foramina of Deinonychus , but did not describe them in detail. Firstly, the exterior of the nasal is penetrated by a row of large, ovoid to circular pneumatic foramina that grow in size towards the posterior end of the bone. This row of pneumatic foramina is placed at the middle of the dorsoventral axis of the nasal. Two large, deep, ovoid foramina sit closely adjacent to each other at the middle of the nasal and are bordered dorsally by a raised ridge of bone and ventrally by the outer surface of the articular surface with the maxilla ( Fig. 1A ). Proximal to these two large foramina, the exterior pneumatic foramina row of the nasal transitions into a groove. The maxilla and nasal are tightly appressed in lateral view, and the rostral bone surface is smooth along this transition ( Fig. 1A ). This suggests that negligible distortion of this area occurred following burial. In the few other theropods where large pneumatic foramina are present on the exterior of the nasal, the foramina connect with the antorbital sinus through fenestrae in the nasal extension of the antorbital fenestra (e.g. Gold et al., 2013). This feature is probably present in Deinonychus based on the presence of a cavity along the anterodorsal end of the antorbital fenestra. The interior of the nasal shows a row of large, widelyspaced pneumatic foramina that are set in a slightly depressed line of bone. This interior row mirrors the exterior row in being dorsoventrally centred on the nasal. The foramina of the interior row, of which four are immediately observable, are ovoid and shallow. Another important feature of the interior surface of the nasal in Deinonychus is the presence of a hollow chamber between the maxilla and nasal in medial view and the apparent lack of a tight interior articulation of these two bones. This chamber would have housed the nasal airways (e.g. Witmer & Ridgely, 2008; Gold et al., 2013).

Figures

Figure 1. Craniofacial pneumaticity of Deinonychus. Maxilla YPM VP 5232 in (A, C) lateral and (B, D) medial views. Abbreviations: aofen, antorbital fenestra; aof, antorbital fossa; nepf, nasal exterior pneumatic foramina; mf, maxillary fenestra; na, nasal; pmf, promaxillary fenestra; mi, maxilla interior; ammf, anteromedial maxillary fenestra; mipf, interior maxillary pneumatic foramina; pmr, promaxillary recess; suas, suprantral strut; nipf, interior nasal pneumatic foramina; pras, preantral strut; mes, medial shelf; man, maxillary antrum; air, airway space; ear, epiantral recess; pmmf, posteromedial maxillary fenestra; rugose, rugose bone surface; smooth, smooth bone surface. In (C) and (D), light red are nasal pneumatic foramina, dark green is the maxillary fenestra, orange is the promaxillary fenestra, tan are maxillary pneumatic foramina, light green is the promaxillary recess, light blue is the anteromedial maxillary fenestra, pink is the epiantral recess, and red is the posteromedial maxillary recess. Courtesy of the Division of Vertebrate Paleontology, Peabody Museum of Natural History, Yale University, New Haven, CT, USA (peabody.yale.edu).