RAM 14000 is preserved in nearly perfect articulation, with the neck, hip, lower leg and metatarsals strongly flexed (opisthotonic posture, probably resulting from the fresh carcass’s immersion in water; Reisdorf & Wuttke, 2012; Figs. 2 and 3, Fig. S3). The right humerus and pedal digits are gently extended. The specimen was lying on its left side; although more bones are represented on this side, they are much more badly weathered than on the right. Tree roots, freeze-thaw cycles, and recent rodent activity fragmented and displaced many of the elements on the left side. In contrast, the right side is less complete in terms of element representation, but the quality of bone preservation is generally better than on the left side.

Skull and mandible

The skull of RAM 14000 was split in two (parasagittally) by erosion; in order to preserve visibility of internal structures, the two halves have not been reassembled. The skull and mandible are in articulation, with only slight displacement of the quadrate and mandible relative to each other. The left side is more complete, preserving nearly all elements (with the exception of a portion of the premaxilla). The dorsal and rostral portions of the right side are missing, with the exception of some elements (such as the maxilla, parts of the dentary, and braincase) that were separated from the main block by erosion. A digital reconstruction, based on RAM 14000 with missing sections modeled after juvenile lambeosaurins, is presented in Fig. 6. Measurements are included in Tables 3–5.

Figure 6: Reconstruction of the skull of Parasaurolophus sp., RAM 14000. (A) lateral view; (B) dorsal view; (C) rostral view. Missing elements (including sutural relationships that are not visible in RAM 14000) are patterned after other lambeosaurines, and the rhamphotheca is shown in place. Reconstruction copyright Ville Sinkkonen.

In lateral view (Fig. 7), the skull has a profile typical of a juvenile hadrosaur–squared caudally and triangular rostrally. The orbit is proportionately large and slightly longer than tall. The infratemporal fenestra is inclined caudally and quite narrow, with a slight constriction at its midpoint. Because the midline of the skull is missing, the exact shape of the supratemporal fenestra is unknown. However, the preserved portion is roughly trapezoidal. Individual bones and skull regions are described below.

Figure 7: Left half of the skull of Parasaurolophus sp., RAM 14000, in lateral view. (A) interpretive drawing; (B) photograph. Abbreviations: an, angular; cb, first ceratobranchial; d, dentary; en, external naris; exo, exoccipital-opisthotic; f, frontal; itf, infratemporal fenestra; j, jugal; m, maxilla; n, nasal; o, orbit; pd, predentary; pm, premaxilla; pnf, premaxilla-nasal fontanelle; po, postorbital; prf, prefrontal; q, quadrate; ri, extent of impressions of upper rhamphotheca; sa, surangular; sq, squamosal. Scale bar equals 10 cm.

Premaxilla The premaxilla is the most prominent cranial bone in lateral view, extending from the upper “beak” to the dorsum of the skull. The bone is roughly divisible into three portions: a lower portion including the oral margin and external (bony) naris as well as caudodorsal and caudolateral processes that form the remainder of the premaxilla and much of the crest. The rostroventral-most segment of the premaxilla forms the dorsal oral margin. In lateral view (Fig. 7), most of the edge of the beak is straight and only slightly inclined (relative to the maxillary tooth row), contrasting with the more inclined surface seen in most other lambeosaurine specimens (Evans, 2010), including Parasaurolophus walkeri (ROM 768). Furthermore, the caudal corner of the beak is sharply hooked to form a tab-like process below a broadly concave postoral margin. Although this process occurs to varying degrees in many lambeosaurines of all ontogenetic stages (Evans, 2010), the condition in RAM 14000 is unusually prominent and most similar to that in Parasaurolophus walkeri (Parks, 1922; Sullivan & Williamson, 1999), particularly in the combination of the tab-like process and rounded postoral margin. The only major difference is that the concavity in the postoral margin is sharper in ROM 768 (Parasaurolophus walkeri) than in RAM 14000. Measuring from the midline, the mediolateral width of the oral margin is estimated at 26 mm, and the estimated entire width of the free oral margin (perpendicular to the midline) is thus 52 mm. The oral margin is fairly uniform in outline, with no major denticulations. The lower portion of the premaxilla encloses the external (bony) naris. The dorsal margin of the bone is eroded away, but its impression is preserved along the narial margin. The bony naris is roughly lenticular, rounded at its distal (rostroventral) end and pointed at its proximal (caudodorsal) end. The depression in the lateral surface of the premaxilla that houses the naris is delimited from the rest of the skull by a gentle ridge that is most prominent caudodorsally. The caudolateral process of the premaxilla forms the ventral margin of the external (bony) naris and extends caudolaterally. Dorsally, the process contacts the caudodorsal process of the premaxilla. Although much of this suture is extremely fragmented, it appears quite straight along its preserved portions (Fig. 7A). This contrasts with the more sinuous suture seen in juvenile and adult Hypacrosaurus, Corythosaurus, and Lambeosaurus (Evans, 2010; Brink et al., 2011), but more closely matches the fairly straight suture (where it can be discerned) in specimens of Parasaurolophus (Sullivan & Williamson, 1999). Similarly, the sutures with the maxilla, lacrimal, and prefrontal, where they can be discerned, are straight, much closer to the condition in Parasaurolophus than in lambeosaurins. This may reflect the internal absence of an “S-loop” in the narial passages, a feature that occurs in lambeosaurins (e.g., Weishampel, 1981b; Evans, Ridgely & Witmer, 2009). The ventral portions of the process are comparatively narrow, but the process expands dorsally, where it forms part of the crest. The caudolateral process forms the ventral border of the premaxilla-nasal fontanelle and presumably contacts the nasal at the caudal extent of the fontanelle. The caudodorsal process of the premaxilla, which forms much of the rostral profile of the skull, is poorly preserved. Its contact with the nasal cannot be interpreted with confidence due to extensive cracking, so no further comment will be offered here.

Nasal Much of the nasal is poorly preserved in gross external view, with the exception of its suture with the frontal and a portion along the caudal margin of the crest (Fig. 7A). The nasal forms the rostrodorsal margin of the premaxilla-nasal fontanelle, as well as the caudal edge of the crest. The dorsal margin of the nasal is strongly rounded and almost horizontal, unlike the peaked margin seen in juvenile lambeosaurins ROM 758 and 759 (Lambeosaurus sp. and Corythosaurus sp., respectively). The nasal’s suture with the prefrontal is not readily visible, and the contact with the frontal is described with that element. The internasal suture in the crest is flat along the suture’s medial surface.

Maxilla Like other hadrosaurids, the maxilla is triangular in lateral view (Figs. 7 and 12B), apparently with a straight suture with the premaxilla (unlike some lambeosaurins; e.g., Hypacrosaurus altispinus, ROM 702). Fracturing and weathering obscure many additional details. The prominent ectopterygoid ridge extends from the base of the maxilla’s dorsal process to the caudal edge of the maxilla (Fig. 12B). A marked ventral curvature in the ridge from rostral to caudal corresponds with the shape of the ectopterygoid. Figure 12: Disarticulated skull elements of Parasaurolophus sp., RAM 14000. (A) partial right squamosal in lateral view; (B) right maxilla in lateral view; (C–E) right first ceratobranchial in lateral (C, E) and dorsal (D) views. (C) and (D) are reconstructed from CT scan data. (C) includes the caudal portion of the element, and (E) includes the rostral portion, with the relative position of the two parts approximating their original relationship. Abbreviations: ep, ectopterygoid; qc, quadrate cotyle. Scale bar equals 1 cm. Along the flattened medial surface of the maxilla, a series of alveolar foramina, one between each alveolus, forms a dorsally arched sequence (Fig. 10). A subtle ridge, increasing in prominence caudally, occurs immediately dorsal to the foramina and continues at least for the rostral third of the maxilla; the caudal extent is obscured by fracturing. This morphology can only be evaluated on the left maxilla; the medial surface of the right maxilla is too poorly preserved. CT scans indicate approximately 20 tooth positions in the maxillary tooth row, with two (rostrally) to three (at mid-point of tooth row) teeth in each file. The greatest internal height of the tooth file is 20 mm at the middle of the bone, and the smallest height is 8 mm at the rostral margin. As exposed on the left maxilla, there were usually two functional teeth on the wear surface at a time. The wear surfaces on each functional tooth range from 4 to 7 mm tall and 3 to 5 mm wide, and the maximum height of the wear surface as exposed at alveolus 5 is 15 mm. Adult Parasaurolophus have 40 or more tooth positions in the maxilla (NMMNH P-25100, PMU.R1250; Sullivan & Williamson, 1999), twice the number in RAM 14000. This low tooth count is typical of juvenile hadrosaurids (Suzuki, Weishampel & Minoura, 2004).

Jugal Although the left jugal is more complete, crushing obscures the sutures along the rostral margin (Fig. 7). The right side preserves the impressions of these sutures (Figs. 13B and 13D), and the following description is thus a composite of both sides. The jugal forms part of the rostral margin and the entire caudal margin of both the orbit and infratemporal fenestra. The rostral process, along its contact with the maxilla and lacrimal, is triangular and sharply pointed (Fig. 13B). The ventral edge of this rostral process is longer than the dorsal edge, unlike most lambeosaurins of various ontogenetic stages (in which the ventral edge is equal to or shorter in length to the dorsal edge) but similar to the condition in Parasaurolophus walkeri (ROM 768; Fig. 14D) as well as a larger juvenile Parasaurolophus sp. (SMP VP-1090). A distinct, slightly constricted extension occurs at the rostral end of this rostral process, visible as an impression on the right side, which creates a hooked ventral margin on the process. The ventral and dorsal margins of this rostral process are more acutely angled than seen in adult P. walkeri (Figs. 14C and 14D). These shape differences may due, at least in part, to the relatively larger orbit in juveniles. The postorbital process is inclined parallel to the quadratojugal process and tapers along the infratemporal fenestra towards an articulation with the descending process of the postorbital. The quadrate process is tapered and caudodorsally inclined at a 40° angle. Its caudodorsal edge is exceptionally pointed compared to other lambeosaurines, and is not expanded relative to the rest of the process as in Kazaklambia convincens. The jugal is dorsoventrally constricted ventral to the orbit (19 mm tall) and on the quadrate process ventral to the infratemporal fenestra (22 mm tall). Similar constrictions are also seen in Corythosaurus, Lambeosaurus, and other Parasaurolophus (Evans, 2010). The angle between the postorbital and quadrate processes is quite tight, similar to the condition in Hypacrosaurus, Parasaurolophus, and Kazaklambia convincens (Bell & Brink, in press; Rozhdestvensky, 1968). As preserved, the jugal forms only the ventral third and quarter of the rostral and caudal margins of the infratemporal fenestra, respectively (Figs. 7 and 13). Figure 13: Skull and neck of Parasaurolophus sp., RAM 14000. (A) and (C) are in right lateral view; (B) and (D) are a medial view of the same block. (A), (B), interpretive drawings; (C), (D), photographs. Abbreviations: bo, basioccipital; cb, first ceratobranchial; cc, centrum of cervical vertebra; cr, cervical rib; cv, cervical vertebra; d, dentary; dr, dorsal rib; ex, exoccipital; j, jugal; la, lacrimal; m, maxilla; nat, neural arch of atlas; nax, neural spine of axis; nc, neural canal; ns, neural spine; pd, predentary; po, postorbital; prs, presphenoid; ps, parasphenoid; q, quadrate; sa, surangular; sq, squamosal; tp, transverse process; V, foramen for CN V; V 2,3 , sulcus for CN V 2 and V 3 . Bone is shown in white, impressions of bone are shown in green, and rock without bone impressions is shown in gray. Scale bar equals 10 cm.

Quadrate The quadrate is complete on both sides, but the right quadrate is slightly displaced ventrally and both quadrates are slightly displaced laterally. The quadrate forms the caudal margins of the infratemporal fenestra and the skull (Figs. 7 and 13). The dorsal condyle of the quadrate articulates with the squamosal cotyle, as is typical of hadrosaurids. Dorsal to its contact with the jugal, the quadrate is slightly concave caudally and is inclined caudodorsally at 30° relative to vertical. The ventral third of the quadrate is straight. The surface for articulation with the caudal process of the jugal is rostrally bifurcated, resulting in an S-shaped sutural surface (Fig. 7); the dorsal half of the quadrate tapers along the infratemporal fenestra towards this articulation. The dorsal condyle of the quadrate is triangular (with a rounded and medially directed apex) in dorsal view, whereas it is rounded in lateral view. The ventral end is rounded in lateral view and trapezoidal with a saddle-shaped articular surface in ventral view. The ventral condyle of the quadrate is 21.4 mm wide and 18.2 mm long on its lateral edge and 8.7 mm long on its medial edge, respectively. In caudal view, the quadrate is straight but slightly bowed medially (Figs. 8F and 8G). The quadrate articulates with the pterygoid wing rostromedially along a V-shaped suture, extending from the quadratojugal to the dorsal margin of the infratemporal fenestra (Fig. 10). The pterygoid flange of the quadrate is only partially preserved, forming a plate-like and slightly concave (in medial view) region of bone (Fig. 10). At its ventral third, the caudal edge of the quadrate is flattened; dorsally, the element’s caudal edge tapers to a rounded ridge. The quadrate in RAM 14000 is more gracile than seen in adult Parasaurolophus (Figs. 14G and 14H). Figure 14: Ontogenetic changes in selected cranial elements of Parasaurolophus. P. walkeri (ROM 768). All elements are in left lateral view. (A) and (B) postorbital; (C) and (D) jugal; (E) and (F) lower jaw; (G) and (H) quadrate. The jugal in (C) is a composite of the bone preserved on the left side and the impressions of the sutural regions on the right side. Parasaurolophus walkeri elements are redrawn and modified after Juvenile elements (A, C, E, G) are from RAM 14000; adult elements (B, D, F, H) are from the holotype of(ROM 768). All elements are in left lateral view. (A) and (B) postorbital; (C) and (D) jugal; (E) and (F) lower jaw; (G) and (H) quadrate. The jugal in (C) is a composite of the bone preserved on the left side and the impressions of the sutural regions on the right side.elements are redrawn and modified after Evans, Reisz & Dupuis (2007) . Scale bars equal 5 cm.

Quadratojugal The quadratojugal is not visible on the left side, but CT scans indicate that the rest of the element is displaced rostromedially relative to the jugal. The quadratojugal is a thin, sinuous and rostrally inclined element that rostrodorsally tapers to a point and buttresses the quadrate caudoventrally.

Squamosal The squamosal is thin and arched dorsally, with a concave quadrate cotyle on its ventrolateral surface (Fig. 12A). The prequadratic process is sharply pointed rostrodorsally. The postquadratic process has a straight rostral border and a convex caudal border that abuts the paroccipital process (Fig. 7). The squamosal forms the caudolateral margin of the supratemporal fenestra and the dorsal margin of the infratemporal fenestra. Measuring from its edge on the base of the paroccipital process to the dorsal margin of the squamosal, the element is 67 mm tall. The caudomedial corner of the squamosal hooks upward in lateral view, and the dorsal surface of the squamosal is entirely convex. The medial extents of the squamosals are not preserved, so we cannot determine if they contacted each other as in most lambeosaurins, Kazaklambia convincens and adult Parasaurolophus, or were separated by the parietals as in Velafrons (Bell & Brink, in press; Gates et al., 2007; Brink et al., 2011).

Lacrimal The lacrimal forms the mid-rostral margin of the orbit. Sutures with the prefrontal are difficult to interpret, as are those with the premaxilla. Impressions on the right side (Fig. 13B) show that the lacrimal articulates ventrally with the jugal along a caudoventrally inclined, slightly ventrally convex suture.

Postorbital The postorbital is T-shaped in lateral view (Figs. 7 and 14A), bounding part of the dorsal margin of the orbit and nearly the entire caudal margin as well. The postorbital articulates with the prefrontal rostromedially along a straight suture and the frontal medially along a more sinuous suture (Fig. 8D). The jugal process is slightly curved rostrally and forms most of the rostrodorsal margin of the infratemporal fenestra, tapering alongside the caudal towards articulation with the ascending process of the jugal. The caudal process of the postorbital measures 13 mm wide at its narrowest point, but broadens caudally. The caudal-most portion of the caudal process thins and splits into dorsal and ventral prongs (Fig. 7A), as in Parasaurolophus and lambeosaurins except for Hypacrosaurus altispinus (Evans, 2010); the ventral prong is more extensive. This process overlaps the dorsal surface of the squamosal, and forms a small part of the rostrolateral margin of the supratemporal fenestra. In lateral view, the dorsal edge of the postorbital is slightly concave, unlike the convex margin in P. walkeri (ROM 768). The maximum length of the jugal and caudal processes are roughly equal, similar to lambeosaurins of various sizes, but unlike adult Parasaurolophus (where the jugal process is longer; NMMNH P-25100, ROM 768) or Charonosaurus (where the caudal process is longer). Similarly, the rostral process of the postorbital is much shorter in adult Parasaurolophus (e.g., ROM 768, Fig. 14B) than in RAM 14000. Consequently, the proportion of the skull roof in RAM 14000 formed by the postorbital is much greater than that formed by the squamosal in lateral view (Fig. 7A), unlike adult Parasaurolophus. Unlike Kazaklambia convincens or Charonosaurus jiayinensis (Bell & Brink, in press), the postorbital lacks a dome on its rostral process in RAM 14000.

Frontal The left frontal is nearly completely preserved with visible sutures, except for its extreme caudomedial portion (Figs. 8C and 8D). In dorsal view, the frontal articulates with the prefrontal rostrolaterally along a linear suture that trends laterally along its caudal extent. The suture with the postorbital is comparatively linear also, with a slight medial trend from rostral to caudal. The contact with the parietal is obscured, but a small portion of the frontal’s contribution to the supratemporal fenestra is visible. The paired nasals form a triangular prong that laps onto the rostral end of the dorsal surface of the frontals (Fig. 8D). This morphology is unique relative to the rounded or squared contact in lambeosaurins and adult Parasaurolophus, where the sutures can be determined (Evans, Reisz & Dupuis, 2007; Brink et al., 2011). It also differs from Kazaklambia convincens, where a prong of the paired frontals inserts between the nasals on the midline (Bell & Brink, in press). Adult and subadult Parasaurolophus have a nasofrontal suture that is expanded caudodorsally and sharply angled relative to the rest of the skull roof (Evans & Reisz, 2007); there is no evidence in CT scan or direct visual observation of such a feature in RAM 14000. Thus, the condition here is comparable to the non-angled and unexpanded state in lambeosaurin juveniles and adults, as well as the condition in K. convincens. Similarly, the individual frontal in RAM 14000 is approximately as long at the midline (measuring from the caudal extent of the nasal suture to the rostral extent of the parietal suture) as it is wide (34.2 mm vs. 31.7 mm, a ratio of 1.08; doubling to approximate the width across both frontals produces a ratio of 0.54). The median frontal dome is thus fairly elongate (Fig. 7). This too contrasts with the condition in adult and subadult Parasaurolophus (where the frontal is wider than long) and is more similar to the state in lambeosaurins of various growth stages (Evans, Reisz & Dupuis, 2007). Similar to other lambeosaurines, the frontal does not reach the orbital rim.

Prefrontal Only the sutures on the caudal edge of the left prefrontal are clearly visible (Figs. 7, 8C and 8D). Here, the bone forms a triangular point interposed between the medial margin of the postorbital and the lateral margin of the frontal, as in other lambeosaurines. The bone forms the rostrodorsal margin of the orbit and contacts the lacrimal ventrally. Based on the extent of the premaxilla, it is unlikely that the prefrontal formed any significant portion of the crest in RAM 14000 (unlike adult lambeosaurines but similar to many subadult specimens; Evans, Forster & Reisz, 2005).

Ectopterygoid The ectopterygoid sits atop the caudodorsal margin of the caudal process of the maxilla, extending medial to the coronoid as viewed on CT scans. The element is best-preserved on the right side (Fig. 12B), showing that the ectopterygoid is a thin and broad element with a prominent ventral bend at its caudal third. The mediolateral width of the ectopterygoid and its relationship to structures such as the pterygoid cannot be visualized because of weathering.

Pterygoid The pterygoid is visible only on the left side (Fig. 10), with just its caudal quadrate wing preserved. The wing is thin (<1 mm) and gently concave medially, paralleling the corresponding medial surface of the quadrate ramus. As viewed in CT scan, the nearly complete pterygoid on the right side is typical of the condition expected for hadrosaurids (Ostrom, 1961; Heaton, 1972).

Palatine The palatine is not sufficiently preserved or exposed to comment upon its morphology.

Vomer The caudodorsal portion of the vomer is exposed on the left half of the skull (Fig. 10). The preserved dorsal edge is acutely angled, and the rostral edge of the element tapers rostrolaterally towards its (inferred) insertion between the premaxillae. The apex of the vomer is located just rostral to the rostral end of the orbit, at approximately the same height (dorso-ventral level). The vomer is not sufficiently preserved for detailed comparison with the element in other hadrosaurids.

Braincase Most of the braincase was partially disarticulated from the rest of the skull by weathering, and the right side was prepared out to show relevant details (Fig. 15). Additional features are seen as impressions on the right skull block (Figs. 13B and 13D). This section describes only visible features. Additional internal details were reconstructed from CT scans and are described in the section on the endocast. With the exception of the sutures between the exoccipital and basioccipital on the occipital condyle, sutures within the braincase are not visible due to crushing, weathering, and fusion. Figure 15: Partial braincase of Parasaurolophus sp., RAM 14000, in right lateral view. (A) interpretive drawing; (B) photograph. Abbreviations: atc, atlas centrum (odontoid); ati, atlas intercentrum; axc, axis centrum; bo, basioccipital; ex, exoccipital; fv, foramen vestibuli; nat, neural arch of atlas; XII?, foramen tentatively identified as that for CN XII; V, foramen for CN V; V 2,3 , sulcus for CN V 2 and V 3 . Bone is shown in white, broken bone surface is shown in light gray, and matrix is shown in dark gray. Unlabeled bones are not confidently identified, but may represent vertebral fragments. Scale bar equals 1 cm. The parasphenoid, represented by an impression, is 28 mm long, gently arched along its length, and tapered to a point at its rostral end (Figs. 13B and 13D). It terminates just caudal to the midpoint of the orbit. A shallow sulcus occupies the lateral surface of the bone. Faint impressions tentatively identified as presphenoid occur dorsal to the parasphenoid, but no notable details are visible. The form is generally similar to that seen in P. tubicen (NMMNH P-25100, PMU.R1250). A foramen interpreted as that for cranial nerve XII (hypoglossal nerve) is small (1.9 by 2.2 mm) and located roughly midway between the caudal extent of the occipital condyle and a ridge of bone that slants caudodorsally along the braincase (Fig. 15). Additional foramina may have occurred also, as in Hypacrosaurus altispinus (Evans, 2010), but cannot be confirmed in the specimen’s current state of preparation and preservation. A portion of the trigeminal foramen is exposed at the front of the right side of the isolated braincase (Fig. 15), and the remainder of the impression is seen on the right skull block (Figs. 13B and 13D). This impression is triangular, measuring 11 mm long and 9 mm tall. Two distinct grooves (ridges on the natural mold) extend from the foramen; one trends directly rostrally from the rostral edge of the foramen (probably representing the path for CN V 1 ), and the other trends rostroventrally from the ventral edge (representing the path for CN V 2,3 ). The left caudal semicircular canal is exposed through a fortuitous break (Fig. 10). The maximum diameter of its lumen is 1.8 mm. The occipital condyle is roughly cardoid in caudal view, composed of the basioccipital at the ventral and ventrolateral edges and the exoccipitals at the dorsolateral edges (Fig. 15). All three elements are bulbous on their caudal edges. The rounded basal tuberosity has its maximum lateral extent slightly lateral to the extreme edge of the occipital condyle. In lateral view, the exoccipitals rise to bound the exposed portion of the foramen magnum, sweeping dorsally. The exoccipital and opisthotic are fused both in gross examination and CT scans. The most prominent and best-preserved aspect of these elements is the paroccipital process, which curves rostrally and tapers dorsoventrally along the caudal margin of the paroccipital process and upper squamosal (Figs. 7, 8F and 8G). The caudal surface of the bones is remarkably flat, with only a slight concavity at its distal extent (Figs. 8F and 8G). The fenestra vestibuli (fenestra ovalis) measures approximately 5 mm tall by 2.6 mm long. The auditory recess is deepest and narrowest by the fenestra vestibuli, becoming broader and shallower dorsocaudally (Fig. 15).

Dentary The ramus of the left dentary has an average height of 27 mm. The edentulous process is roughly 25 percent of the dentary’s length, and the rostral border of the process is rostroventrally inclined (Fig. 7). The ventral border of the dentary is relatively straight, with comparatively little declination at its rostral portion. This is comparable to the morphology in Parasaurolophus walkeri (Fig. 14F, ROM 768; Evans, 2010), but different from the more inclined morphology in P. tubicen (NMMNH P-25100), a dentary from the Fruitland Formation tentatively identified as juvenile Parasaurolophus sp. (SMP VP-1090; Sullivan & Bennett, 2000), and other lambeosaurines. The condition in P. cyrtocristatus is unknown. The lateral surface of the body of the dentary is strongly convex (Fig. 7). The coronoid process is perpendicular to the ventral margin of the dentary, and, based on CT scans and the incomplete dentary on the right half of the skull (Figs. 13B and 13D), reaches the ventral margin of the orbit when in articulation, roughly 72 mm above the ventral margin of the dentary. The rostral margin of the coronoid process is more prominently extended than the caudal process. Rostrally, the dentary tapers to articulate with the caudal margin of the predentary. Caudally, the dentary articulates with the surangular along a sinuous suture (Fig. 7). The number of dentary teeth cannot be determined.

Predentary Only the left side of the predentary is preserved (Figs. 7, 8A, 8B and 14E), but the element can be mirrored to reconstruct the overall shape. In dorsal view, the element would have been roughly horseshoe-shaped, with a moderately convex rostral margin. As exposed at the midline, the cross-section of the rostral portion is approximately triangular (Fig. 10). The dorsal triturating surface is approximately 14 mm long and only slightly rostrally inclined. This inclination becomes more extreme towards the lateral and caudal wings of the predentary, so that the triturating surface is nearly vertical and laterally facing (14 mm tall) at its caudal end. Thus, the surface only changes its orientation and not its width. The ventral surface of the predentary is gently convex. The caudal edge of the lateral wing of the predentary is forked; the ventral process of this fork is slightly longer and more sharply pointed (Fig. 7). This is in contrast to the unforked lateral wing in the holotype of P. walkeri, ROM 768 (Fig. 14F), but similar to the condition in other lambeosaurines. The morphology is not known in other species of Parasaurolophus. The median process of the predentary is not definitively preserved in RAM 14000.

Surangular The surangular (Figs. 7, 13A, 13C and 14E) buttresses the caudal margin of the coronoid process, with a smoothly continuous lateral surface at this point. A ridge at the base of the contribution to the coronoid process continues onto the lateral edge of the articular surface for the quadrate. This coronoid process is also relatively broader than in ROM 768 or NMMNH P-25100. The surangular’s ventral margin is slightly convex, with a strong curvature caudally on the articular process. The surangular receives the ventral condyle of the quadrate and articulates with the angular caudomedially. The retroarticular process of the surangular is thinner and more horizontal than in P. walkeri (ROM 768, Fig. 14F).

Angular The angular is a flattened bone that curves caudodorsally and articulates medially with the surangular. On both sides, the element has been displaced downward so that its ventral margins are visible beyond that of the surangular (Figs. 7, 13A and 13C). It is inferred to receive the distal end of the quadrate. In ventral view, the element is long and narrow.

Hyoid A bone interpreted as the caudal end of the first ceratobranchial is positioned immediately ventral to the surangular (Figs. 7, 13A and 13C); the right first ceratobranchial is slightly better preserved than the left. The element is partially exposed, and described from gross examination as well as CT scan reconstructions (Figs. 12C–12E). Although the ceratobranchials of hadrosaurids (including Hypacrosaurus sternbergii, adults of Saurolophus osborni, Lambeosaurus lambei, and Corythosaurus casuarius, as well as juveniles of Hypacrosaurus altispinus and H. stebingeri) previously have been described as generally uniform (Ostrom, 1961; Gates et al., 2007; Brink et al., 2011), the morphology of these elements in RAM 14000 has some unique aspects. These differences may be taxonomic or perhaps ontogenetic. However, the hyoids of embryonic H. stebingeri (RTMP 89.79.52) are quite similar to those of Corythosaurus in major details, so we posit that taxonomic differences are most influential here. The articulated preserved portion of each ceratobranchial in RAM 14000 is gently arched ventrally, with a slight dorsoventral curvature. The caudal portion is dorsoventrally flattened (rather than cylindrical, as described for other hadrosaurids; Ostrom, 1961). Rostrally, the bone twists so that it is mediolaterally compressed at the rostral-most preserved portion. This caudal portion is approximately 43 mm long, as preserved. The rostral end of the right first ceratobranchial is within a disarticulated block of matrix; impressions of surrounding elements permit confident placement of the bone. The part that connects with the rest of the ceratobranchial is missing, but the preserved portion in this separate block (including a partial impression) is 37 mm long. The impression is 8 mm tall at narrowest, 14 mm tall at its rostral end, and only 3.5 mm thick mediolaterally. Such extremely expanded rostral ends are typical of known hadrosaurid ceratobranchials (Ostrom, 1961). Including both portions, the total ceratobranchial length was at least 80 mm. The rostral end of the left first ceratobranchial was displaced by erosion (Fig. 10), and is similar in overall morphology to the element on the right.