Prieto-Márquez and Gutarra—Hadrosaurid dinosaurs from Careless Creek Quarry (Montana)
maximum length ratio of the iliac plate is 0.58. Relatively shallow (depth-to-width ratio less than 0.8) iliac plates are widespread among saurolophines except known brachylopho- saurin ilia (Prieto-Márquez, 2007). The preacetabular process of the ilium projects rostroventrally beyond the level of the pubic process, forming an angle of 147° with a line uniting the pubic and ischiadic processes. The dorsal margin of the preacetabular process is straight, whereas the ventral border displays a wide convexity. Two longitudinal ridges are present on the lateral side of the process: one ridge extends obliquely from mid-depth of the proximal region to merge with ventral margin at mid- length of the process; the other ridge occurs near the distal end of the process. The supraacetabular crest of ANSP 17729 shows an asymmetrical, caudally skewed V-shaped lateral profile. It greatly extends lateroventrally to overlap part of the ischiadic process. As in Gryposaurus notablis, G. latidens, Secernosaurus koerneri, and Willinaqake salitralensis Juárez Valieri, Haro, Fiorelli, and Calvo, 2010 (Juárez Valieri et al., 2010; Prieto-Márquez and Salinas, 2010), the length of the crest of ANSP 17729 is approximately three-fourths of the length of the iliac plate. The caudodorsal margin of the supraacetabular crest is continuous with the proximolateral surface of the postacetabular process, lacking a well-defined ridge. The post- acetabular process of ANSP 17729 is subrectangular (slightly wider distally than proximally, as in G. latidens AMNH FABR 5465), medially inclined, and caudodorsally oriented. As preserved, the postacetabular process is 10% longer than the iliac plate. However, the process was probably slightly longer given that its caudal margin is incomplete. Such long post- acetabular processes characterize species of Gryposaurus (Prieto-Márquez, 2012) and Saurolophini (Prieto-Márquez et al., 2015).
Kritosaurin indeterminate Figure 6.1, 6.2
Referred material.—ANSP 17730 and 17731, right and left ilia, respectively (Table 2).
Remarks.—Because these elements show similar size and morphology, and correspond to the left and right side of the pelvic girdle, we interpret them as coming from a single indi- vidual. These ilia are treated separately from the kritosaurin taxon mentioned previously because they differ from the ANSP 17729 ilium in possessing a more slender preacetabular process, a slightly deeper iliac plate, a less lateroventrally expanded supraacetabular crest, and a shorter and more medially inclined postacetabular process. Given that the morphology of ANSP 17730 and 17731 is less markedly saurolophine (and kritosaurin) when compared to that of ANSP 17729, we tested phylogenetically the affinities of this material by including it in the analysis as a separate operational taxonomic unit (see the following for a detailed account of supporting characters).
Lambeosaurine Parks, 1923 Lambeosaurine indeterminate Figure 6.3
141
Figure 6. CCQ saurolophid pelvic elements. (1) Saurolophine left ilium (ANSP 17731) in lateral view. (2) Saurolophine right ilium (ANSP 17730) in lateral view. (3) Lambeosaurine left ischium (ANSP 17727) in lateral view.
Referred Material.—ANSP 17727, a left ischium.
Ischium.—The only recovered ischium, ANSP 17727, lacks the pubic process and the ventral margin of the proximal region (Table 2). The iliac process extends craniodorsally, forming a 140º angle with the proximal-most dorsal margin of the ischia- dic shaft. This process is relatively long, with a ratio between its proximodistal length and the width of its distal margin of 2.1; typically, this ratio ranges from 1.5 to 2 in lambeosaurines dino- saurs (Prieto-Márquez, 2010b). The caudodorsal margin of the process is recurved, as in all lambeosaurines (Brett-Surman and Wagner, 2007). The articular surface of the iliac process is abra- ded. Ventrally from the iliac process, the proximal region of the ischium becomes thinner and laterally concave. The ischiadic shaft displays a gently sinusoidal lateral profile, and it is remark- ably short and robust. Specifically, the shaft accounts for 65% of the total length of the ischium. Its minimumdorsoventral diameter is 10%of the total length of the shaft. Other lambeosaurines with relatively thick ischiadic shafts (i.e., ratio of minimumthickness to total length greater than 7.5%) include Corythosaurus spp., Lambeosaurus magnicristatus Sternberg, 1935, Magnapaulia laticaudus Morris, 1981, and Parasaurolophus cyrtocristatus Ostrom, 1961 (Prieto-Márquez, 2008; Prieto-Márquez et al., 2012). The distal half of the shaft is postdepositionally compressed mediolaterally. ANSP 17727 partially preserves a foot-like distal process, as expected in a lambeosaurine specimen
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