Gryposaurus monumentensis, Gates & Sampson, 2007

Gates, Terry A. & Sampson, Scott D., 2007, A new species of Gryposaurus (Dinosauria: Hadrosauridae) from the late Campanian Kaiparowits Formation, southern Utah, USA, Zoological Journal of the Linnean Society 151 (2), pp. 351-376 : 353

GRYPOSAURUS MONUMENTENSIS SP. NOV.

Etymology: In reference to the Grand Staircase- Escalante National Monument in southern Utah, where all referred materials of this species have been recovered.

Diagnosis: Hadrosaurids of the genus Gryposaurus possessing: anterodorsal process of maxilla seen through the external nares; subparallel anterior and posterior margins of the infratemporal fenestra; anteroposterior width of the infratemporal fenestra approximately half of the width of the orbit; predentary with large, pronged denticles; anterior portion of the dentary sharply downturned; surangular with distinct dorsal process on the median ridge of surangular; and ovoid mandibular foramen. The following suite of characters is also present: sigmoidal lateroventral margin of the maxilla; large nasal arch located near the orbits rising above the level of the frontals; narrow ‘U’-shaped posterior margin of the external naris; and squamosal raised well above the level of the skull roof. Gryposaurus monumentensis is significantly more robust than any other species of Gryposaurus . It is most similar to G. notabilis , but differs in having more steeply angled premaxillae, mediolaterally wider dentary, and generally more prominent jugal tubercle.

Holotype: RAM 6797, largely articulated skull lacking most of the right side of the skull ( Figs 1 , 3 , 5A , 7A, B , 9 , 11 , 12 , 13A , 14 , 15 ).

Figures

Figure 1. Lateral view of type specimen of Gryposaurus monumentensis gen. et sp. nov. skull, RAM 6797: A, photograph of left side of skull; B, line drawing of skull based on photograph in (A) and showing slight reconstruction. Ar, articular; D, dentary; F, frontal; J, jugal; La, lacrimal; Mx, maxilla; Na, nasal; Pd, predentary; Pf, prefrontal; Pm, premaxilla; Po, postorbital; Qj, quadratojugal; Qu, quadrate; Sq, squamosal; Su, surangular. Scale bar, 10 cm.

Figure 3. Lateral view of Gryposaurus monumentensis gen. et sp. nov. left premaxilla, RAM 6797. en, external nares; MX, maxilla; or, oral margin rugosities; pmd, dorsal process; pmf, premaxillary foramen; pml, lateral process; pmlf, premaxilla lateral process flare; pmlp, premaxillary lip; pms, premaxillary shelf. Scale bar, 5 cm.

Figure 5. Line drawings of the four Gryposaurus species in lateral view, showing synapomorphies of the genus and other comparative features: A, G. monumentensis gen. et sp. nov. (RAM 6797); B, G. notabilis (ROM 873); C, G. incurvimanus (TMP 80.22.1); D, G. latidens (after Horner, 1992; no scale included). itf, infratemporal fenestra; mf, mandibular foramen; na, nasal arch; pmlf, lateral process flare. Scale bar, 10 cm.

Figure 7. Maxillae from Gryposaurus monumentensis gen. et sp. nov., specimens RAM 6797 and UMNH VP 13970: A, left maxilla in lateral view with surrounding elements from RAM 6797; B, posterior region of right maxilla from UMNH VP 13970; C, right maxilla from RAM 6797 in lateral view; D, anterior region of left maxilla from UMNH VP 13970. D, dentary; ecr, ectopterygoid ridge; ecs, ectopterygoid shelf; J, jugal; jp, jugal process; La, lacrimal; madp, anterodorsal process; mavp, anteroventral process; mdp, maxilla dorsal process; mf, maxillary foramen; Mx, maxilla; nf, nutrient foramen; palp, palatine process; Pm, premaxilla; ptp, pterygoid process. Scale bar, 5 cm.

Figure 9. Posterior view of left lacrimal–jugal contact in Gryposaurus monumentensis gen. et sp. nov. (RAM 6797). The left side of the figure is lateral and the right side is medial. Note the interlocking relationship between these elements. J, jugal; La, lacrimal; lf, lacrimal foramen.

Figure 11. Gryposaurus monumentensis gen. et sp. nov. (RAM 6797) braincase: A, ventral view; B, anterior region in lateral view. bpt, basipterygoid process; Bs, basioccipital; bsmm, basioccipital median mound; Bsp, basisphenoid; bst, basitubera; btr, basisphenoid transverse ridge; CN, cranial nerve; Exo, exoccipital; Ls, laterosphenoid; mvp, median ventral process; Pr, pro-otic; psp, parasphenoid process; Qu, quadrate. Scale bar, 5 cm.

Figure 12. Gryposaurus monumentensis gen. et sp. nov. (RAM 6797) right quadrate: A, lateral view; B, medial view. mc, mandibular condyle; ptw, pterygoid wing; qb, quadrate buttress; qh, quadrate head; qjn, quadratojugal notch; qs, quadrate shaft. Scale bar, 5 cm.

Figure 13. Right vomer of Gryposaurus monumentensis gen. et sp. nov. in lateral view: A, RAM 6797; B, UMNH VP 13970. The broken line marks the estimated position of the dorsal margin of the anteroventral excavation. ave, anteroventral excavation; mxa, maxillary articulation; pma, premaxillary articulation; pvl, posteroventral lobe. Scale bar, 5 cm.

Figure 14. Predentary of RAM 6797 in left anterolateral view. D, dentary; nf, nutrient foramen; pdd, predentary denticles; pdlp, predentary lateral process; pdvp, predentary ventral process. Scale bar, 5 cm.

Figure 15. Right surangular of Gryposaurus monumentensis gen. et sp. nov. (RAM 6797): A, lateral view; B, dorsal view. ap, articular process; asn, anterior surangular notch; mc, medial concavity; mr, median ridge; msp, median surangular process; qas, quadrate articular surface; scp, surangular coronoid process. Scale bar, 5 cm.