Brachylophosaurus canadensis, STERNBERG, 1953

Cuthbertson, Robin S. & Holmes, Robert B., 2010, The first complete description of the holotype of Brachylophosaurus canadensis Sternberg, 1953 (Dinosauria: Hadrosauridae) with comments on intraspecific variation, Zoological Journal of the Linnean Society 159 (2), pp. 373-397 : 374-382

BRACHYLOPHOSAURUS CANADENSIS STERNBERG, 1953

Emended diagnosis of autapomorphies (revised from Prieto-Márquez, 2005): Nasals greatly developed into paddle-like solid crest extending posterodorsally, overhanging dorsal region of skull; prefrontal projecting posteriorly over frontal, and more posteriorly, ventromedially directed to underlie nasal crest and contribute to anterior border of supratemporal fenestra; quadratojugal with ‘noncrescentic’ posterior margin variably forming paraquadratic foramen with quadrate.

Holotype: NMC 8893; consists of skull, partial left and right hyoids, 14 cervicals, the anterior nine dorsal vertebrae, 12 ribs, complete right scapula, complete right coracoid, left and right humeri, left ulna and radius, and partial left manus.

During the original preparation, the skull was partially disarticulated, allowing the left maxilla and associated bones to be photographed and studied in medial view ( Sternberg, 1953: Pl. XXXIX). Subsequently, the skull was reassembled using steel armature for the purpose of mounting the skeleton for exhibition. Unfortunately, this armature obscures some details of the internal surface of the skull. Also, the centra of the vertebrae were drilled so that they could be strung along a steel rod, and were then backfilled with plaster. The vertebrae have since been separated from the steel rod, but permanent damage has been done to these bones, especially to the dorsal series.

Comparative material: TMP 90.104.01 (Oldman Formation of southern Alberta), MOR 794 and 1071 (lower Judith River Formation of north-eastern Montana) ( Prieto-Márquez, 2005).

Type locality and horizon: Little Sandhill Creek, northeast ¼, section 6, township 21, range 11, west of 4 th meridian, 60 feet above Red Deer River, Alberta. Oldman Formation of Belly River Group ( Weishampel et al., 2004), Upper Cretaceous (Late Campanian), 7.5 m below the Dinosaur Park Formation-Oldman Formation contact (David Evans, pers. comm.) .

DESCRIPTION

Sternberg (1953) provided a general description of the bones of the holotype, and this is not repeated here. Instead, we emphasize important anatomical features not mentioned by Sternberg, features of phylogenetic significance, and areas that exhibit variability in specimens of Brachylophosaurus . See Table 1 for cranial and postcranial measurements.

SKULL ( FIGS 1–3 )

The skull of the holotype of B. canadensis is virtually complete. Most elements remain in articulation, obscuring some aspects of their morphology. Nevertheless, the well-preserved skull provides the basis for a comprehensive description and comparison with other hadrosaurs.

Premaxilla: Anteriorly, the oral margin of the premaxilla is ventrally deflected rather than dorsally reflected as in other hadrosaurines such as Edmontosaurus regalis Lambe, 1917 (NMC 2288) and Gryposaurus notabilis Lambe, 1914 (NMC 2278). This margin is rugose, especially so on its anteroventral surface. Ventrally projecting denticles, although poorly preserved, are clearly present along the anterior premaxillary oral margin. Just posterior to these denticles, in a shallow sulcus on the palatal surface of the premaxilla, is a series of circular divots. This area is poorly preserved however, and the sulcus is most obvious on the left lateral premaxillary oral margin. The premaxilla is laterally and dorsally excavated just posterior to the oral margin at the base of the posterodorsal premaxillary process, forming the anterior extent of the outer narial depression. Positioned just posterior to the outer narial depression is the forward extent of a poorly developed circumnarial depression, the anterior margin of which is perforated C, cervical; D, dorsal; H., height; L., length; Max., maximum, Min., minimum; W., width.

by a conspicuous premaxillary foramen that bifurcates as it descends towards the palatal surface of the premaxilla. In contrast to the specimens described by Prieto-Márquez (2005), the type specimen lacks any evidence of an accessory premaxillary foramen. The circumnarial depression is continued posteriorly as a concavity running along the lateral surface of the ascending posterolateral premaxillary process, and terminates posteriorly as a gentle bowl-like depression just posterior to the external naris. The thin, posterolaterally directed, premaxillary process bears a horizontal trough on its medial surface to accommodate an anterior process of the maxilla. The trough is constant in width for most of its length, but opens slightly near its anterior limit as it slants ventromedially. The posterolateral process flattens to a thin slip of bone posterodorsally and overlaps the lateral surface of the nasal. A narrow gap between the ventral border of this process and the dorsal edge of the lacrimal exposes a small section of the more medially placed nasal. Posteriorly, the posterolateral process contacts the dorsal margin of the lacrimal and overlaps the anterior portion of the prefrontal before terminating at the contact of the prefrontal with the nasal above. The steeply ascending posterodorsal process projects dorsally and tapers to a point that inserts itself medial to the anterior segment of the nasal. The posterior extent of this process is approximately in line with the anterior limit of the anteroventral maxillary process.

Maxilla: Anteriorly, the dorsolateral surface of the maxilla is dominated by an excavation that forms a flattened, anteroventrally sloped shelf to receive the ventral surface of the posterolateral premaxillary process. Immediately posterior to the shelf, the maxilla is pierced by a large maxillary foramen, which may have delivered neurovasculature to the nasal vestibule ( Horner, Weishampel & Forster, 2004). Its medial perforation is not visible, but it may be obscured by steel mounting armature or the displaced left vomer. Three additional smaller maxillary foramina are present. Posterior to the rugose jugal facet, a flattened shelf accommodating the ectopterygoid forms the dorsolateral maxillary surface, which gently slopes ventrally at its posterior extent. A small, gently striated process (posterior maxillary process of Heaton, 1972) originates medial to the ectopterygoid shelf and projects posteriorly to articulate the pterygoid, reinforcing the contact between the two elements. Posteroventral to this process, the maxilla terminates in a rounded facet that is cupped from behind by the ectopterygoid ramus of the pterygoid. Projecting anteriorly from the anteromedial surface of the maxilla is an elongate, mediolaterally compressed, anterior maxillary process. The process is deepest posteriorly and tapers to a point anteriorly. A thin flange of bone projects dorsally from the posterior extent of the anterior maxillary process. Laterally offset from the dorsomedial surface of the maxilla, this flange articulates the medial surfaces of the anterior lacrimal and jugal. Deformation has obliterated its apex in the left maxilla and the entire flange is missing from the right element. However, it is typically triangular in shape in other hadrosaurs, and nothing about its preserved anatomy suggests that the shape was different in Brachylophosaurus . Posterior to this flange, the anteriorly rising dorsomedial edge of the maxilla articulates with both the pterygoid and palatine. This surface is incomplete in the right element, and the left has been crushed and is partially obscured by the pterygoid and palatine, thus obscuring the details of their sutural union. Some details of the medial aspect of the maxillae are not available from the holotype specimen. The left maxilla is obscured by the displaced left vomer, and both the right and left elements have steel armature attached to their medial surfaces. However, some observations can still be made. Much of the medial surface is occupied by the dental lamina, obscuring the dental battery. A dorsally arched row of dental foramina marking the dorsal limit of the dental lamina is visible on the medial surface of the right maxilla. Although poor preservation makes it difficult to clearly delineate individual foramina in some cases, the morphology suggests that one dental foramen is present for each tooth row. A small groove, most prominent at the approximate midlength of the tooth row, is present just above the ventromedial maxillary surface. It appears to meet the ventromedial maxillary edge well anterior the posterior end of the tooth row. As noted by Lull & Wright (1942), this groove may represent a vascular channel.

Nasal: Although the nasal shares the dorsal border of the external naris with the premaxilla anteriorly, the posterior portion of the external naris is formed solely by a triangular, wedge-like extension of nasal bone. Laterally, this anteroventral nasal process is partially obscured by the posterolateral premaxillary process. However, its ventral border follows the dorsal margin tained. However, there is no indication that the relationships of these bones differ significantly from that described in other B. canadensis specimens (Prieto- Márquez, 2005: Fig. 8A ). Posteriorly, the nasal crest overrides the anterior border of the upper temporal fenestra, covering all but its anterolateral corner.

Lacrimal: The posterior surface of the lacrimal is pierced by a conspicuous lacrimal foramen; however, the path of the lacrimal duct is not clear because of poor preservation. Above the lacrimal foramen a triangular orbital prefrontal process helps unite the lacrimal to the prefrontal, and reinforce the anterior orbital margin. Ventrally, the lacrimal contacts the jugal with a stout jugal process. Its medial surface is difficult to interpret because of previous repair work, but this contact can be traced laterally where the lacrimal exhibits a distinct concavity that accommodates a small dorsal process of the anterior jugal process. Anterior to this depression, the lacrimal tapers to a slender anterior maxillary process that contacts the lateral surface of the lacrimal flange of the maxilla.

of the lacrimal posteriorly, and eventually contacts the prefrontal along this same border, which lies medial to the posterior limit of the posterolateral premaxillary process. Dorsally, a swelling is present on the dorsomedial surface of the nasal. This feature is similar to, although not as pronounced as, the condition seen in the holotype of Gryposaurus notabilis (NMC 2278) . A less prominent second swelling is present in the holotype of B. canadensis , just posterior to the first at the position of the anterior margin of the orbit. These swellings and resulting ‘flat’ dorsal profile do not appear to be as conspicuous in MOR 794. The nasal crest begins as a slightly raised ridge on the dorsolateral surface of the nasal, and extends posteriorly as a solid, raised spatulate crest, widening through the interorbital region. The crest is dorsoventrally compressed, raised medially, and gently concave lateral to its midline. The bilateral concavities are most exaggerated posteriorly, where the lateral edges of the crest are slightly dorsally reflected. As a result of the articulated nature of the holotype skull, the ventral contact surface of the nasal crest is not visible, so the relationship between the nasal and the underlying bones cannot be ascer- Jugal: The attenuating anterior tip of the maxillary process is incomplete in both left and right elements. A small triangular process projects from the dorsal margin of the maxillary process and fits into a concavity on the ventrolateral surface of the lacrimal. More posteriorly, the jugal projects an ascending postorbital process that bears a distinct groove on its proximal anterior face to cradle the distal tip of the descending jugal process of the postorbital. At its posterior extent, the jugal flares dorsoventrally to form the quadratojugal process. The medial surface of this process is gently excavated for its articulation with the quadratojugal. This excavation is more developed in E. regalis (NMC 2289) , in which the anteroventral margin of the excavation is deeper and ends abruptly in a distinct slot to accommodate the quadratojugal. Prieto-Márquez (2005) indicated the morphology of the ventrally projecting flange of the jugal to be an autapomorphy of Brachylophosaurus . However, based on the lack of quantifying data supporting this assertion, this feature is herein not recognized as an autapomorphy of the species.

Prefrontal: The prefrontal contacts the nasal anteromedially, although this suture is partially concealed by the overlapping posterolateral premaxillary process. At the approximate midlength of the dorsal orbital rim the prefrontal contacts the frontal. Sternberg (1953: Pl. XXXVIII) clearly indicated the ventral prefrontal–frontal orbital suture. Although the original ink tracing is still visible on the type specimen, some of the bone surface in this area has been restored, casting doubt on the accuracy of Sternberg’s identification of the suture. Dorsally, the contact of the prefrontal and frontal is clearly visible, as the prefrontal tapers medially with its dorsolateral suture overriding the frontal and paralleling the lateral margin of the nasal crest. The extension of the prefrontal continues posteriorly over the transverse contact of the parietal and frontal, and turns medially to form the anterior border of the upper temporal fenestra. This portion of the prefrontal is overridden by the nasal crest dorsally, but because of poor preservation its specific relationships remain unclear.

Postorbital: The anterodorsal portion of the postorbital is robust and its lateral surface is deeply pitted. Posteriorly, the postorbital is represented as an unbifurcated, dorsoventrally compressed squamosal process that forms the anterolateral border of the upper temporal fenestra. The ventromedial surface of the postorbital is obscured by steel armature, and its relationships with the parietal and laterosphenoid cannot be determined.

Squamosal: The prominent prequadratic process is oval shaped in cross-section and stouter and more robust than those observed in other hadrosaurs, such as Edmontosaurus saskatchewanensis Sternberg, 1926 (NMC 8509), Prosaurolophus maximus Brown, 1916 (NMC 2870), and Lambeosaurus lambei Parks, 1923 (NMC 2869, NMC 8633, and NMC 8703). The postquadratic process projects posteroventrally and slightly laterally from the quadrate cotyle, as its medial surface follows the contour of the opisthoticexoccipital of the paroccipital process. Approaching its posterior extent, the squamosal projects medially to enclose the upper temporal fenestra from behind. The left and right posteromedial processes converge on one another medially, but are separated by a posterior extension of the parietal sagittal crest. However, the specific articulation of the posteromedial squamosal processes and the parietal crest cannot be identified as a result of slight distortion to this area.

Quadrate: A small depression, located just ventral to the head of the quadrate on the anteromedial surface of the shaft, accommodates the prequadratic process of the squamosal. A small process projects posterolaterally from the posterior margin of the dorsal shaft, also just ventral to the head. The anterior face of the quadrate shaft is embayed just below its approximate midheight. Much of the surface area forming the embayment is roughened, including the dorsal and ventral margins that form the articular facets for the quadratojugal. However, the bone surface of the embayment between the facets is smooth and does not appear to have contacted the quadratojugal. The ventral end of the quadrate expands mediolaterally to form a triangular-shaped mandibular condyle. The lateral surangular condyle is rugose and rounded with an anteroposteriorly compressed flange radiating dorsomedially from its ventral tip. The anterior surface of this medial flange is concave. Its medial border ascends dorsomedially to contribute to the pterygoid flange. The medial flange does not appear to have contacted the articular. The broad pterygoid flange is posteromedially concave and complements the anterolateral surface of the posterior alar projection of the pterygoid. The portion of the pterygoid flange that overlaps the pterygoid is easily identified by its roughened and striated surface.

Quadratojugal: The mediolaterally thickened posterior border of the quadratojugal lacks the crescentic shape observed in Edmontosaurus and other hadrosaurs. As a result, a small paraquadratic foramen occurs between the posterodorsal and posteroventral contact of the quadratojugal with the quadrate (see Discussion for further interpretation of this feature). A depression on the anterolateral surface of the quadratojugal marks the point of articulation with the jugal.

Frontal: The co-ossified frontals are obscured by the nasal crest in B. canadensis . The only portion of the frontal visible in the holotype is its contribution to the dorsal orbital rim, which is more rugose and robust than the orbital contribution of the prefrontal. Anteromedially, the frontal undercuts the prefrontal, and posterodorsally, forms an interdigitating suture with the postorbital. Ventrally, its sutural contacts with the prefrontal and postorbital are not as clearly visible as originally figured by Sternberg (1953), making the true sutural path difficult to trace.

Parietal: The co-ossified parietals bear a conspicuous sagittal crest separating the upper temporal fenestrae. The anterior margin of the parietal of hadrosaurs contacts the frontal along a broad, transverse interdigitated suture; however, the specific relationship of this contact is obscured in the holotype by an overhanging posteromedial extension of the prefrontal. A process extends anterolaterally to the postorbital, but the specific structure of its articulation with the postorbital is unclear because of poor preservation, the presence of steel armature, and previous repair work. A near-horizontal suture marks the ventral articulation of the lateral surface of the parietal with the anterior positioned laterosphenoid and the more posterior opisthotic. The specific relationship between the posterior portion of the parietal and its contact with the squamosal and supraoccipital is unclear because of unpreserved sutures and damaged bone surface. Although distorted, a mediolaterally thickened posterior extension of the parietal sagittal crest clearly prevents the posteromedial processes of the squamosal from contacting at the midline.

Braincase: The braincase is preserved with good detail ( Fig. 4 ); however, co-ossification is advanced and the sutures indicating the mutual relationships of individual bones cannot be traced. Viewed in posterior aspect, the exoccipital articulates with the rugose supraoccipital along a broad horizontal contact. The supraoccipital contacts the squamosal laterally, and possibly the posterior extension of the parietal sagittal crest dorsally. However, this area is slightly distorted and the suture between the parietal and supraoccipital is not obvious. The constituent bones forming the margins of the braincase foramina cannot be confirmed because of the advanced state of co-ossification. A deep transverse groove, indicating the articulation of the basal tubera of the basioccipital and the more anterior basisphenoid, is one of the few remnants of sutural contacts on the braincase. Large, paired alar processes project posterolaterally from the lateral surface of the basisphenoid. Each alar process is triangular in outline, anteroposteriorly thin, and bears fluting on both its anterior and posterior surfaces. A prominent pterygoid process lies just anterior to each of the alar processes and projects ventrolaterally from the basisphenoid. Medial to the pterygoid processes, a smaller near-straight anteroposteriorly compressed process projects posteroventrally from the basisphenoid. This process is also present in E. regalis (NMC 2289) and E. saskatchewanensis (NMC 8509), although it is not nearly as pronounced.

PALATE

The palate of B. canadensis has been described by Heaton (1972). The following is intended as a supplement to this excellent work.

Pterygoid: The central plate of the right pterygoid is slightly disarticulated from the maxilla and ectopterygoid, revealing a distinct groove on its anterolateral surface to accommodate the posteromedial pterygoid process of the maxilla. The quadrate ramus of the pterygoid is composed of the posteroventral projection and the posterior alar projection. Distally, the posteroventral projection flares dorsoventrally. This projection was damaged and lost in the right pterygoid of the holotype and the left posteroventral projection is somewhat distorted, but essentially remains in its proper position abutting the quadrate. The triangular, mediolaterally compressed posterior alar projection forms a broad wing as it tapers distally to a point, and conforms to the contour of the pterygoid flange of the quadrate. Two processes project anteriorly from the central plate. The ventrally directed ectopterygoid ramus bears the maxillary facet and a gentle depression on its lateral face identifying the articular surface for the ectopterygoid. The second process, the anterodorsally projecting palatine ramus, is an elongate, thin wing of bone bearing a convex lateral surface and a concave ventromedial surface, the latter of which contributed to the posteroventral nasal passage. An anteroposteriorly elongate, dorsoventrally compressed, laterally facing palatine articular facet is present on the distal tip of the palatine ramus. This differs from the conspicuous dorsoventrally expanded facet observed in E. regalis .

Vomer: The vomer is an elongate, triangular-shaped bone forming the medial surface of the internal naris. The left vomer has been displaced and now rests against the medial surface of the left maxilla. It is mediolaterally compressed, tallest posteriorly, and tapers anteriorly to a mediolaterally thickened point that indicates where the vomers contacted one another medially ( Heaton, 1972: fig. 1). The medial surface is gently concave. The posterodorsal margin of the vomer curves medially before descending anteriorly to a process, rounded in outline, on the posteroventral corner of the vomer. This process, as well as the ventral surface of the vomer, is partially obscured by steel armature.

Ectopterygoid: The dorsoventrally compressed anterior process has a slight anteroposterior dorsal arch to accommodate the ectopterygoid shelf of the maxilla. The medial and lateral margins of the anterior process are near parallel, diverging only slightly posteriorly. Posteriorly, the ectopterygoid projects ventrolaterally as a semicircular slip of bone. The posteromedial border of the ectopterygoid is reflected dorsally. However, its ventral surface is incomplete and obscured in both the right and left elements.

Palatine: Although the right palatine is missing, the left is nearly complete and close to its natural position. Its central portion is mediolaterally compressed, with anterodorsal and anterolateral processes diverging from its forward margin, and an expanded posteroventral border. Its smooth medial surface appears to lack the gently concave contour described by Heaton (1972) for E. regalis (NMC 2289) . However, the absence of this character may be the result of postmortem distortion. The mediolaterally compressed anterodorsal process expands from the central palatine and tapers at its neck before flaring anteroposteriorly at its distal margin. The dorsal margin of the distal ‘fan’ is posterolaterally directed and offset from the more parasagittally aligned central portion of the palatine. The laterally directed anterolateral jugal process is slightly thicker than the central portion of the palatine. The distal margin of the anterolateral jugal process has been mounted in articulation with both the lacrimal and the jugal process of the maxilla. However, poor preservation of the distal tip of the anterolateral jugal process makes it impossible to confirm this relationship.

LOWER JAW ( FIGS 2B , 5 )

Dentary: As in the maxilla, a thin dental lamina obscures much of the medial face of the dental battery. A narrow, ventromedially directed ridge separates the dental lamina from the circular dental foramina at the base of the dental battery ( Fig. 5B ). There are 38 foramina in the sequence, nearly one foramen for each of the 39 vertical tooth row positions; however, immediately dorsal to the 17th dental foramen, an additional foramen pierces the dentary. A shallow groove on the ventromedial surface of the dentary originates more or less immediately below the first vertical tooth row, deepening as it progresses posteriorly until it opens medially to the Meckelian canal. The mediolaterally thin edentulous portion of the ramus anterior to the tooth row flares slightly laterally from the dentary. Its dorsal margin is especially thin, and has been partially reconstructed to smooth out the damaged edge. The portion of the diastema contributing to the mental symphysis has not been preserved in either the left or right dentary, and the facet for the articulation with the unpreserved predentary has been lost. Although Sternberg (1953) indicated only three dental foramina on the anterolateral surface of the dentary, four are preserved in a diagonal row. The massive coronoid process originates well anterior to the posterior limit of the tooth row. The posteromedial margin of the coronoid descends ventrally before projecting posteriorly as a mediolaterally compressed, dorsoventrally attenuating splenial process that inserts itself on the medial surface of the splenial.

Surangular: A mediolaterally compressed anterolateral process rises approximately vertically from the surangular to contact the posterior margin of the coronoid process, with a conspicuous ridge on its lateral face indicating where the coronoid process overlaps it. The oval mandibular glenoid is rugose and concave. A small foramen is located just anterior to its forward margin.

Articular: The right articular is not preserved in the holotype and the left appears incomplete along its anterior border. It sits between the posterior ends of the splenial and surangular where it contributes to the retroarticular process, leaving only its roughened dorsal surface exposed. The mandibular contribution to the jaw joint appears to be provided entirely by the surangular in the holotype of B. canadensis .

Splenial: Anteriorly, the splenial bears a triangularshaped head that articulates with the posteromedial surface of the dentary, just ventral to the posterior dental foramina ( Fig. 5B, C ). Near the base of the head, where the splenial is tallest, the dorsal edge flares laterally to cradle the dentary posterior to the tooth row. A small, anteroposteriorly directed ridge on the ventrolateral surface of the splenial accommodates the posteriorly directed splenial process of the dentary. The splenial projects posteriorly as a dorsoventrally expanded, mediolaterally thin process that contacts the articular laterally, and forms the medial surface of the retroarticular process.

Angular: The anteroposteriorly elongate angular is mediolaterally compressed and dorsoventrally expanded posteriorly. Posteriorly, a conspicuous splenial facet on the dorsomedial portion of the angular indicates the extent of the dorsal edge of the angular that wedges between the ventrolateral corner of the splenial and the medial surface of the surangular. When viewed in lateral aspect, the ventral rim of the posterolateral surface of the angular is exposed below the surangular. However, the angular appears to have been displaced slightly, as its entire lateral surface is normally obscured by the surangular in other hadrosaurs.

Figures

Figure 1. NMC 8893. Skull in anterior (A) and posterior (B) views; photographs (left) and reconstructions (right). Abbreviations: abs, alar process of basisphenoid; boc, basioccipital; ect, ectopterygoid; ex-op, exoccipital-opisthotic; f, frontal; j, jugal; mx, maxilla; n, nasal; p, parietal; pf, prefrontal; pm, premaxilla; po, postorbital; ppbs, pterygoid process of basisphenoid; pt, pterygoid; q, quadrate; qj, quadratojugal; soc, supraoccipital; sq, squamosal; v, vomer.

Figure 2. NMC 8893. Dorsal (A) and lateral (B) reconstructions of the skull and lower jaw. Abbreviations: dn, dentary; ect, ectopterygoid; ex-op, exoccipital-opisthotic; f, frontal; j, jugal; l, lacrimal; mx, maxilla; n, nasal; pf, prefrontal; pm, premaxilla; po, postorbital; pt, pterygoid; q, quadrate; qj, quadratojugal; s, surangular; sq, squamosal; stf, supratemporal fenestra.

Figure 3. NMC 8893. Lateral (A, right; B, left) and dorsal (C) photographs of the skull.

Figure 4. NMC 8893. Left lateral reconstruction of braincase. Abbreviations: abs, alar process of basisphenoid; boc, basioccipital; exo, exoccipital; ls, laterosphenoid; ops, opisthotic; p, parietal; po, postorbital; ppbs, pterygoid process of basisphenoid; prs, presphenoid; ps, parasphenoid; pvbs, posteroventral process of basisphenoid; sq, squamosal; I–XII, cranial nerve.

Figure 5. NMC 8893. Lateral (A, left; D, right) and medial (B, left; C, right) photographs of the lower jaws.

Figure 8. NMC 8893. Axis/C3 in right lateral (A), left lateral (B) views; reconstruction (C) in left lateral view. Abbreviations: c, centrum; d, diapophysis; ic, intercentrum; ns, neural spine; od, odontoid; poz, postzygapophysis; pozf, postzygapophyseal flange; prz, prezygapophysis.