Prieto-Márquez and Gutarra—Hadrosaurid dinosaurs from Careless Creek Quarry (Montana)
Table 1. Selected measurements (in millimeters) of CCQ indeterminate hadrosaurid elements.
Element
Basisphenoid (ANSP 18325), length from pterygoid process to cultriform process, parallel to sagital plane
Opisthotic-exoccipital (ANSP 17690), preserved length Pterygoid (ANSP 17689), width across ventral lamina Dentary (ANSP 17671), preserved length
Surangular (ANSP 18322), preserved length Surangular (ANSP 18322), width across lateral lip Sacrum (ANSP 17728), preserved length
Dentary (ANSP 17671), distance from base of mandibular ramus to apex of coronoid process
Sacrum(ANSP 17728), length of longest preserved neural spine
Measurement (mm)
118 116 220
61
147 135
65
1070 420
widely opens caudally and the coronoid process is rostrally inclined, as expected from a hadrosaurid (Prieto-Marquez, 2010b). The medial surface of the apex of the process bears an array of fine striations arranged radially, and its dorsal margin is incompletely preserved. The ventral border of the dentary shows only a very minor convex lateral profile. The surangular ANSP 18322 is missing most of the rostral ascending flange and the entire retroarticular processes (Fig. 2.9,
2.10). The mediodorsal surface of the base of the ascending flange shows a large concavity that ends caudally into the rostral region of the central body of the surangular. The ventrolateral surface of this region of the ascending flange is occupied by an extensive V-shaped facet that would underlie the caudal region of the dentary by means of a scarf joint. On the medial side of the surangular, the mediodorsal edge of the ascending flange is caudally continuous with a prominent ridge. This ridge constitutes the dorsal border of the long and shallow articular facet for the angular and separates this facet from the articular surface for the splenial above. The thick D-shaped lateral lip of the surangular is caudally continuous with the glenoid facet for the quadrate.
Postcranial elements.—The sacrum ANSP 17728 consists of eight fused vertebrae (Fig. 2.11). It is relatively complete, missing the distal region of most of the neural spines. The stout transverse processes show triangular distal facets. An extensive sacral rib fuses to the ventral margin of each transverse process and, ventrally, to the iliac bar. The latter extends parallel and slightly ventral to the sacral centra. Like the entire series of sacral vertebrae, the thick iliac bar is strongly curved, showing a maximum point of inflexion at the level of the third centrum. The neural spines are subrectangular laminae. Progressing along the vertebral series, these structures become slightly more inclined caudally. Distally, they become gradually wider and gently curved craniodorsally. The five preserved pedal phalanges (not shown) possess the
usual hadrosaurid morphology in being broad wedge-shaped, dorsoventrally compressed, and spade-shaped bones. The dorsal and plantar surfaces are gently convex and concave, respectively. No ridges are present on the plantar side of each phalanx. The proximal articular surfaces are elliptical and mediolaterally convex.
Remarks.—The juvenile indeterminate hadrosaurid material (Fig. 3) is treated in the ‘Discussion’ section of this study, where we focus on those morphological attributes that are
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ontogenetically variable in a comparative context with adult hadrosaurid specimens. Saurolophinae Brown, 1914 (sensu Prieto-Márquez, 2010b) Kritosaurini Lapparent and Lavocat, 1955 (sensu Prieto- Márquez, 2014a) ?Gryposaurus sp. Figures 4, 5; Table 2
Referred material.—ANSP 15981, right humerus; ANSP 17692, partial left prefrontal; ANSP 18320, right postorbital; ANSP 18323, left squamosal; ANSP 18324, fragmentary right squamosal; ANSP 18328, right lacrimal; ANSP 17723, 17724, 17726, and 17725, three right and one left pubes, respectively; and ANSP 17729, a right ilium. Although it could be argued that each individual bone in the saurolophine sample may corre- spond to a different species, we opted for choosing a most par- simonious hypothesis here, that is, that all saurolophine material belongs to the same taxon. As shown below, the anatomy of these elements is congruent with this hypothesis.
Prefrontal.—The incomplete prefrontal ANSP 17692 preserves the main body that forms the rostrodorsal corner of the orbit. It lacks the ventral margin of the rostroventral process and part of the caudomedial process (Fig. 4.1–4.3). The orbital margin exhibits a subsquared profile, as in saurolophine hadrosaurids (Prieto-Márquez, 2010b), and becomes gradually thicker caudally. Medial to the orbit, the dorsal surface of the prefrontal is greatly flattened and subtly concave mediolaterally. Rostrally, the prefrontal is abruptly deflected ventrally to form a broad rostroventral process that is extensively exposed laterally, another condition commonly present in saurolophines (Prieto- Márquez, 2010b). This process faces both laterally and slightly rostrally. The medial side of the prefrontal is deeply excavated, containing a few irregularly shaped and poorly defined ridges (Fig. 4.3). The caudomedial process preserves part of the medial apex that would insert into the lateral margin of the frontal.
Lacrimal.—The lacrimal, ANSP 18328, consists of a triangular bony lamina (Fig. 4.7–4.9). The wedge-shaped rostral process is missing the distal apex, as well as a few fragments of the proximodorsal border. The jugal notch occupies 40% of the preserved ventral margin of the lacrimal, adjacent to the cau- doventral corner of the element. The notch becomes deeper caudally; its shallower rostral half shows a medially recessed surface in lateral view. The caudoventral corner of the lacrimal forms a prominent subtrihedral process. The ventral margin of the lacrimal displays a wide convexity just rostral to the jugal notch, as in Kritosaurus navajovius Brown, 1910, Gryposaurus spp., Saurolophus spp., and Prosaurolophus maximus Brown, 1916 (Bell, 2011; McGarrity et al., 2013; Prieto-Márquez, 2014a; Prieto-Márquez et al., 2015). The caudodorsal region of the lacrimal forms a tall and subtriangular lamina. This caudo- dorsal process is gently deflected medially. Laterally, the pro- cess displays an extensive surface that would underlie the rostroventral process of the prefrontal. The medial side of the lacrimal is concave. Its caudal half is longitudinally excavated by a wide lacrimal canal. This broad groove gradually becomes
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