144


Journal of Paleontology 90(1):133–146


Figure 8. Biostratigraphical and geographical distribution of species of the North American kritosaurin genera Gryposaurus and Rhinorex. Literature sources for each taxon’s distribution and geochronological range are as follows: G. latidens (Prieto-Márquez, 2012); G. notabilis (Evans, 2007; Farke and Herrero, 2014 Gates et al., 2014); G. monumentensis (Gates and Sampson, 2007); and R. condrupus (Gates and Scheetz, 2015). Depicted skulls are redrawn and/or modified based on the following: G. latidens (Horner, 1992); G. notabilis (photographs of CMN 2278 by APM); G. monumentensis (Gates and Sampson, 2007); R. condrupus (Gates and Scheetz, 2015).


Table 3. Selected mandibular measurements (in millimeters) of CCQ juvenile hadrosaurid elements.


Element Dentary (ANSP 16242), preserved length


Dentary (ANSP 16242), distance from base of mandibular ramus to apex of coronoid process


Scapula (ANSP 15979), preserved length


Scapula (ANSP 15979), maximum width across deltoid fossa Humerus (ANSP 15979), length


Humerus (ANSP 15979), maximum width across deltopectoral crest


Tibia (ANSP 15979), length Tibia (ANSP 15979), width of proximal margin


Measurement (mm)


95 47


180 64


169 41


282 80


Gilmore, 1933, the coronoid process remains subvertically oriented throughout ontogeny (Prieto-Márquez, 2011b). The apex of the coronoid process of ANSP 16242 is not rostrocaudally expanded, unlike those of adult hadrosaurid individuals (Fig. 3.4, 3.5). The scapula (ANSP 15979) is nearly complete, missing


that would allow intrageneric or intraspecific ontogenetic comparisons forced us to arbitrarily choose adult specimens from selected hadrosaurid taxa for such purposes. The dentary (ANSP 16242) preserves the coronoid process


and a ventrally eroded caudal region of the mandibular ramus (Fig. 3.1, 3.2). Eight alveoli are preserved lacking all teeth. The coronoid process is nearly vertically oriented, in contrast to the strong rostral inclination typically seen in adult forms. Similarly, Maryanska and Osmólska (1981) noted that in the saurolophine Saurolophus angustirostris Rozhdestvensky, 1952, coronoid process is also less rostrally inclined in juveniles. While this may be a trend in hadrosaurids, at least in some hadrosaurid outgroups such as Bactrosaurus johnsoni


only the distal extent of the blade (Fig. 3.3). The proximal constriction is 63% of the width of the articular margin of the scapula, wider than typically seen in adult hadrosaurids (e.g., in G. latidens AMNH FABR 5465, it is 54% the width of the proximal articular margin; Fig. 3.6). Narrower juvenile scapular ‘necks’ have been also previously noted in the saurolophine Edmontosaurus annectens Marsh, 1892 (Prieto- Márquez, 2010b), the lambeosaurine Hypacrosaurus stebingeri Horner and Currie, 1994, and some nonhadrosaurid hadrosaur- oids (Prieto-Márquez, 2011b). Brett-Surman and Wagner (2007) and Prieto-Márquez (2011b, 2014b) reported an increase in the robustness and caudoventral elongation of the deltoid ridge in adult hadrosaurids and the basal hadrosauroid Bactrosaurus johnsoni, respectively. Such trend is not oberved here: the CCQ juvenile displays a relatively robust, long, and well-defined deltoid ridge (Fig. 3.3), more so than in some large adult specimens such G. latidens AMNH FABR 5465 (Fig. 3.6). Differences between the CCQ juvenile humeri (best


exemplified by the complete element ANSP 15979; Fig. 3.7, 3.8) and typical adult hadrosaurid humeri follow previous trends


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