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Journal of Systematic Palaeontology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tjsp20 Skeletal morphology of Kritosaurus navajovius (Dinosauria: Hadrosauridae) from the Late Cretaceous of the North American south-west, with an evaluation of the phylogenetic systematics and biogeography of Kritosaurini Albert Prieto-Márquez a a Bayerische Staatssammlung für Paläontologie und Geologie , Richard-Wagner-Straße 10 , D-80333 Munich , Germany Published online: 08 May 2013.

To cite this article: Albert Prieto-Márquez (2013): Skeletal morphology of Kritosaurus navajovius (Dinosauria: Hadrosauridae) from the Late Cretaceous of the North American south-west, with an evaluation of the phylogenetic systematics and biogeography of Kritosaurini, Journal of Systematic Palaeontology, DOI:10.1080/14772019.2013.770417 To link to this article: http://dx.doi.org/10.1080/14772019.2013.770417

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Skeletal morphology of Kritosaurus navajovius (Dinosauria: Hadrosauridae) from the Late Cretaceous of the North American south-west, with an evaluation of the phylogenetic systematics and biogeography of Kritosaurini Albert Prieto-Marquez´ ∗ Bayerische Staatssammlung fur¨ Palaontologie¨ und Geologie, Richard-Wagner-Straße 10, D-80333 Munich, Germany (Received 26 March 2012; accepted 3 July 2012)

The osteology of the hadrosaurid dinosaur Kritosaurus navajovius (late Campanian of southern North America) is documented in detail, and the taxonomy and phylogenetic relationships of the genus are revised. Kritosaurus is rediagnosed based on the extensive length of the dorsolateral margin of the maxilla and a unique combination of characters that includes a jugal with orbital constriction deeper than infratemporal one, infratemporal fenestra greater than orbit and with dorsal margin greatly elevated above dorsal orbital margin in adults, frontal participating in orbital margin, and paired caudal parasagittal processes of nasals resting over frontals. The taxonomy of numerous hadrosaurid specimens previously referred to Kritosaurus is reassessed; the vast majority of these cannot be positively referred to Kritosaurus. One exception is a specimen collected from the Cerro del Pueblo Formation that extends the geographical range of K. navajovius further south in Laramidia, to present-day northern Mexico. Anasazisaurus is regarded a junior synonym of Kritosaurus; their holotypes are indistinguishable from each other when considering the overlapping elements. However, many characters support distinction of Naashoibitosaurus ostromi as a valid taxon. Kritosaurus, consisting of the sister species K. navajovius and K. horneri, is deeply nested within Saurolophinae as a member of Kritosaurini. The latter clade includes also Naashoibitosaurus, Gryposaurus, and the South American Secernosaurus. Kritosaurini is characterized by a rostral nasal dorsal process not reaching the rostral margin of the narial foramen, frontal with triangular rostrolateral projection ending in a narrow apex (convergent in Brachylophosaurini), and a subrectangular dorsal region of infratemporal fenestra, among other characters. Kritosaurin hadrosaurids are hypothesized to have originated in southern Laramidia no later than the early Campanian. Subsequently, members of the clade reached northern Laramidia and South America via dispersal no later than the early and late Campanian, respectively. Keywords: Dinosauria; Hadrosauridae; Saurolophinae; phylogeny; biogeography; evolution

Introduction ery and naming of Gryposaurus notabilis, a ‘hook-nosed’ hadrosaurid from the late Campanian Dinosaur Park Forma- Hadrosaurids are a Late Cretaceous radiation of large tion of southern Canada (Lambe 1914), Brown regarded (7–14 m long) ornithopod dinosaurs widespread in the Kritosaurus as congeneric with Gryposaurus. In a note Americas, Eurasia and Antarctica (Lull & Wright 1942; reproduced by Sinclair & Granger (1914, p. 303), Brown, Prieto-Marquez´ 2010a). These herbivores are remarkable in comparing the holotype skulls of K. navajovius (AMNH for their well-developed dental batteries, hypertrophied 5799) and G. notabilis (CMN 2278), stated: “In all

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 nasal passages, and often, the possession of supracranial respects, including the remarkable development of the ornamentation (Hopson 1975). nasals, premaxillaries and predentary and reduction of One of the first hadrosaurid dinosaurs discovered, albeit the orbital portion of the frontal, this skull agrees with among the less understood, is Kritosaurus navajovius the type of Kritosaurus and there is no doubt of its generic Brown, 1910. The genus has one of the longer and more identity”. Consequently, Gryposaurus was widely accepted debated taxonomic histories in hadrosaurid systematics. as a junior synonym of Kritosaurus for many decades Brown (1910) originally erected the binomen K. navajovius (e.g. Gilmore 1916; Parks 1919, 1920; Lull & Wright on the basis of AMNH 5799, the partial skull of a 1942; Lapparent & Lavocat 1955; von Huene 1956; Young large hadrosaurid dinosaur (Figs 1–4). This specimen 1958; Langston 1960; Vialli 1960; Ostrom 1961; Waldman was collected in 1904 from late Campanian strata of 1969; Galton 1970; Hopson 1975; Taquet 1976; Baird & the upper Kirtland Formation near Ojo Alamo, San Juan Horner 1977, 1979; Horner 1979; Pinna 1979; Maryanska County, New Mexico (Brown 1910; Lull & Wright 1942; &Osmolska´ 1979; Davies 1983; Bonaparte et al. 1984; Williamson 2000) (Fig. 5). However, soon after the discov- Brett-Surman 1989; Weishampel & Horner 1990; Wagner

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Figure 1. Partial holotype skull of Kritosaurus navajovius, AMNH 5799. A, left lateral view; B, interpretative drawing of the same; white areas indicate restored elements, which were reconstructed after acceptance of the synonymy of Kritosaurus with Gryposaurus and based on the latter (Lull & Wright 1942). Skeletal morphology of Kritosaurus navajovius 3 Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 2. Partial holotype skull of Kritosaurus navajovius, AMNH 5799. A, right lateral view; photograph reproduced from Brown (1910, pl. 28), courtesy of the American Museum of Natural History; B, interpretative drawing of the same; white areas indicate reconstructed elements at the time of Brown’s (1910) original work on K. navajovius.

2001), despite a few dissenting voices (Lambe 1920; been refuted (Prieto-Marquez´ et al. 2006; Prieto-Marquez´ Morris 1973). Some authors went even further by consid- 2011). ering Kritosaurus a junior synonym of Hadrosaurus Leidy, In 1992, however, Horner resurrected Gryposaurus and 1858 (Baird & Horner 1977; Horner 1979; Brett-Surman revised the taxonomic status of Kritosaurus, pointing out 1979; Lehman 1981), although this synonymy has recently important differences in the morphology of the nasofrontal 4 A. Prieto-Marquez´

(holotype BYU 12950) and Naashoibitosaurus ostromi (holotype NMMNH P-16106). Additional hadrosaurid materials recovered within the USA in regions other than the type locality of Kritosaurus navajovius have been referred to the genus (see Online Supplementary Material Table 1). These include the Kimbe- toh Wash of the late Campanian Kirtland Formation (Gilmore 1919, 1935; Lehman 1981; Lucas et al. 1987; Brett-Surman 1989; Horner 1992; Williamson 2000), the late Campanian Fruitland Formation of New Mexico (Lucas et al. 1987; Wagner 2001), the late Campanian–early Maastrichtian Aguja (Davies 1983; Lehman 2001; Sankey 2001) and middle–late Maastrichtian Javelina (Wagner 2001) formations cropping out in Big Bend National Park, Texas and, tentatively, the marine Bearpaw Shale of south- central Montana (Horner 1992). Likewise, two hadrosaurid exemplars from the late Campanian Olmos and Cerro del Pueblo formations in the Sabinas and Parras basins, respectively, of Coahuila, northern Mexico, have also been referred to Kritosaurus (Hernandez´ et al. 2003; Serrano- Branas˜ 2006; Kirkland et al. 2006). Finally, Bonaparte et al. (1984) erected a new species of Kritosaurus, K. australis, based on partial cranial and postcranial remains from the late Campanian–early Maastrichtian Los Alamitos Forma- tion, in south-western R´ıo Negro Province, Argentina (see also Bonaparte & Rougier 1987; Bonaparte 1996). This species, however, has been recently revised and removed from Kritosaurus, and shown to be probably a junior Figure 3. Partial holotype skull of Kritosaurus navajovius, AMNH 5799. A, dorsal view; B, interpretative drawing of the synonym of Secernosaurus koerneri (Prieto-Marquez´ & same; white areas indicate reconstructed elements. Salinas 2010). Given this complex taxonomic background, the present study aims to re-evaluate and clarify the anatomy, taxon- suture between these two taxa: “The junction where the omy, phylogenetic relationships and historical biogeogra- nasals meet the frontals appear to show that the nasals phy of Kritosaurus. Such a goal needs to build upon a more bifurcated [in Kritosaurus], so that the rostral end of the complete understanding of the anatomy and systematics of frontal at mid-line extended between the nasals. (...)In its type specimen. Since Brown’s (1910) original cursory all species of Gryposaurus, it is the rostral end of the description, and despite the plethora of referrals in the frontals that bifurcate so that the nasals extend between literature summarized above, the holotype of Kritosaurus the frontals, as correctly pointed out by Waldman (1969)” has never been described in detail. This specimen is here (Horner 1992, p. 13). In addition, Horner (1992) referred documented in detail, with emphasis on those characters

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 two partial skulls (BYU 12950 and NMMNH P-16106) that contain diagnostic and phylogenetic information. The from the Kirtland Formation to K. navajovius and redi- latter is then used as a frame of reference for reassessing agnosed this species based on the caudally folded nasal the diagnosis of this hadrosaurid and evaluating the taxo- crest of BYU 12950. Although various authors concurred nomic status of hadrosaurid specimens and taxa previously with Horner in considering Gryposaurus distinct from assigned to Kritosaurus. Finally, a maximum parsimony Kritosaurus (Hunt & Lucas 1992, 1993; Williamson 2000; analysis is conducted for re-evaluating the phylogenetic Horner et al. 2004; Kirkland et al. 2006; Prieto-Marquez´ position of this taxon. et al. 2006; Lucas et al. 2006; Gates & Sampson 2007; Prieto-Marquez´ 2010a, b), some remained unconvinced of the diagnostic value of the holotype skull of K. navajovius Institutional abbreviations and regarded this taxon as a nomen dubium (Hunt & Lucas 1993; Horner et al. 2004). In relation to the latter, Hunt & AMNH: American Museum of Natural History, New Lucas (1993) erected two new hadrosaurid taxa based on the York, NY, USA; ANSP: Academy of Natural Sciences two skulls from the Kirtland Formation that Horner (1992) of Philadelphia, Philadelphia, PA, USA; CM: Carnegie had referred to K. navajovius, Anasazisaurus horneri Museum of Natural History, Pittsburgh, PA, USA; CMN: Skeletal morphology of Kritosaurus navajovius 5

Figure 4. Partial holotype skull of Kritosaurus navajovius, AMNH 5799. A, caudal view; B, interpretative drawing of the same; white areas indicate reconstructed elements.

Canadian Museum of Nature, Ottawa, Ontario, Canada; Geolog´ıa, UNAM, Mexico D.F., Mexico; IPS: Institut BYU: Brigham Young University, Provo, UT, USA; Catala` de Paleontologia, Sabadell, Spain; IVPP: Institute GSC: Geological Survey of Canada, Ottawa, Ontario, of Vertebrate Paleontology and Paleoanthropology, Beijing, Canada; IGM: Museo de Paleontolog´ıa, Instituto de China; LSUMG: Louisiana State University Museum of Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 5. Geographical location of the fossil localities that have yielded specimens of Kritosaurus. The paleogeographical reconstruction of North America during the late Campanian shown in the middle image is modified from Blakey (2009). 6 A. Prieto-Marquez´

Geology, Baton Rouge, LA, USA; MACN: Museo Remarks. The name Kritosaurini was coined by Argentino de Ciencias Naturales Bernardino Rivadavia, Lapparent & Lavocat (1955, p. 849; literally Buenos Aires, Argentina; MNA: Museum of Northern ‘Kritosaurines’)´ as a subgroup within hadrosaurids Arizona, Flagstaff, AZ, USA; MOR: Museum of the that included solely the genus Kritosaurus (which they Rockies, Bozeman, MT, USA; MSNM: Museo Civico considered to be a senior synonym of Gryposaurus). Subse- di Storia Naturale di Milano, Milano, Italy; NMMNH: quently, Brett-Surman (1989) used Kritosaurini to name one New Mexico Museum of Natural History and Science, of the tribes in which he divided the subfamily Hadrosauri- Albuquerque, NM, USA; OMNH: Sam Noble Oklahoma nae (i.e. unadorned and solid-crested hadrosaurids). In Museum of Natural History, Norman, OK, USA; PASAC: Brett-Surman’s systematics of Hadrosaurinae, Kritosaurini Paleontological Association of Sabinas, Coahuila, Sabinas, included the genera Aralosaurus (currently regarded Mexico; PMU: Museum of Evolution, Uppsala University, a lambeosaurine; see Godefroit et al. 2004a), Brachy- Uppsala, Sweden; RAM: Raymond M. Alf Museum, Clare- lophosaurus, Hadrosaurus (a basal form excluded from mont, CA, USA; ROM: Royal Ontario Museum, Toronto, the two major subclades of Hadrosauridae according to Ontario, Canada; SM: Senckenberg Museum, Frankfurt Prieto-Marquez´ 2010a, 2011) and Kritosaurus (again am Main, Germany; TCMI: The Children’s Museum of synonymized with Gryposaurus). Kritosaurini is thus Indianapolis, Indianapolis, IN, USA; TMP: Royal Tyrrell defined and diagnosed here for the first time. Museum of Paleontology, Drumheller, Alberta, Canada; Kritosaurus Brown, 1910 TMM: Texas Memorial Museum, Austin, TX, USA; UMNHVP: Natural History Museum of Utah, Salt Lake 1993 Anasazisaurus Hunt & Lucas: 80, fig. 7. City, UT, USA; UM: University of Montana, Missoula, 2006 Anasazisaurus Hunt & Lucas; Lucas et al.: figs 1–4. MT, USA; UNM: University of New Mexico, Albuquerque, Type species. Kritosaurus navajovius Brown, 1910. NM, USA; USNM: National Museum of Natural History, Washington, DC, USA; UTEP: Centennial Museum at the Emended diagnosis. Hadrosaurid dinosaur with dorsolat- University of Texas, El Paso, TX, USA; YPM-PU:Yale eral margin of maxilla (rostral and adjacent to jugal artic- Peabody Museum of Paleontology (Princeton collection), ular surface) that is 40% or more of distance between New Haven, CT, USA; ZPAL: Institute of Paleobiology, rostral end of maxilla and caudoventral corner of orbital Polish Academy of Sciences, Warsaw, Poland. margin of jugal. In addition, Kritosaurus is character- ized by the following unique combination of charac- ters: jugal with orbital constriction being deeper than Systematic palaeontology infratemporal constriction; infratemporal fenestra greater than orbit and with dorsal margin greatly elevated above Dinosauria Owen, 1842 dorsal orbital margin in adults, so as to produce steep Ornithischia Seeley, 1887 rostroventral slope of caudal skull roof (angle between Ornithopoda Marsh, 1881 squamosal ramus of postorbital and maxillary tooth row Iguanodontia Dollo, 1888 greater than 20◦ in adults); frontal participating in orbital Hadrosauria von Huene, 1956 (sensu Wagner & Lehman margin by means of intervening apex between prefrontal 2009) and postorbital (convergent in Brachylophosaurini); and Hadrosauridae Cope, 1870 paired caudal parasagittal processes of nasals resting over Saurolophinae Brown, 1914 (sensu Prieto-Marquez´ frontals, so that rostromedial margin of frontals inserts 2010a) in between nasal processes. Characters of infratempo-

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 Kritosaurini Lapparent & Lavocat, 1955 ral fenestra and frontal allow distinction of Kritosaurus from other known saurolophines except Gryposaurus Definition. The most exclusive clade of hadrosaurids notabilis. Likewise, possession of caudal paired nasal containing Kritosaurus navajovius Brown, processes over frontals allows distinction of Kritosaurus 1910, Gryposaurus notabilis Lambe, 1914, and from all other saurolophines except Prosaurolophus and Naashoibitosaurus ostromi Hunt & Lucas, 1993. Naashoibitosaurus (diagnosis revised from Brown 1910). Diagnosis. Saurolophine hadrosaurids with rostral end of Two characters, observable only in Kritosaurus nava- dorsal process of nasal not reaching rostral margin of narial jovius, might be added to the above character combina- foramen; ventral spur of rostral process of jugal being as tion if proven to be also present in the other species deep as or slightly deeper than it is wide proximally; wide of the genus: deep skull (ratio of dorsoventral height and strongly concave margin of jugal between caudoventral along caudal margin of quadrate/rostrocaudal length from and quadratojugal flanges; frontal with triangular rostro- caudal quadrate margin to predentary oral margin of 0.70 lateral projection ending in narrow apex (convergent in or greater); and dentary tooth crowns with diminutive Brachylophosaurini); and subrectangular dorsal region of marginal denticles composed of tubercles arranged in infratemporal fenestra. quincunx-like fashion. Skeletal morphology of Kritosaurus navajovius 7 Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 Figure 6. Fragmentary premaxillae of Kritosaurus navajovius, holotype, AMNH 5799. A, laterodorsal view of right premaxilla; B, detail of laterodorsal view of maxillary articular facet; C, dorsal view of the same; D, medial view of right premaxilla; E, detail of medial view of maxillary articular facet; F, ventromedial view of right premaxilla; G, laterodorsal view of left premaxillary fragment; H, ventromedial view of the same; I, idealized model of saurolophine rostrum showing the hypothetical position of the right premaxillary fragment of AMNH 5799.

Remarks. Brown (1910) originally diagnosed the genus teeth. The narrow snout is not retained in the revised Kritosaurus as having a deep skull with a narrow snout; diagnosis because, given the partial preservation of the short frontal with reduced orbital region at the orbital type K. navajovius and other specimens referred to the rim; elongate nasal, premaxilla and quadrate; rostrocau- genus, this condition cannot be properly quantified and dally short quadratojugal entirely separating the quadrate compared with that in other hadrosaurid species known and jugal; massive mandibular rami; ventrally deflected from more complete crania. In the loosely qualitative usage edentulous portion of the dentary; and spatulate dentary of Brown (1910), elongate nasals and premaxillae are 8 A. Prieto-Marquez´

prevalent among saurolophine taxa (Prieto-Marquez´ 2008). The massive nature of the dentary ramus may reflect indi- vidual size rather than, or as well as, taxonomic affinities; regardless, it is a qualitatively generic description of the dentary that lacks diagnostic value pending a more compre- hensive understanding of the ontogenetic and taxonomic variation of this mandibular element. Finally, the quadrato- jugal being (presumably rostrocaudally) short and separat- ing the quadrate and jugal bones is a condition found in all hadrosaurids (Lull & Wright 1942). Characters from Brown’s (1910) diagnosis retained here (albeit modified) as taxonomically informative for Kritosaurus when considered in combination include: the depth of the skull, reduced frontal contribution to the orbital rim, and, tentatively, pattern and structure of marginal denti- cles of dentary teeth. The deep predentary, and the strong deflection and short proximal edentulous margin of the dentary are retained as diagnostic of K. navajovius (see below) because the predentary is missing and the dentary is too incompletely preserved in other species of the genus. Kritosaurus navajovius Brown, 1910 (Figs1–4,6,7,9–18A–C,E) Holotype. AMNH 5799, an incomplete skull consisting of partial predentary, nearly complete dentaries, partial left and nearly complete right surangular, right splenial, angular and articular, fragmentary premaxillae, caudalmost region of the nasals, fragment of left and most of the right maxilla, fragmentary left and nearly complete right jugal, right quadratojugal, partial left and complete right quadrate, caudal region of both prefrontals, partial postorbitals, partial squamosals, frontals, nearly complete parietal, braincase including partial orbitosphenoid, laterosphenoid, prootic, basisphenoid, fused opisthotic–exoccipital, basioc- cipital and supraoccipital, and palatal complex consisting of nearly complete pterygoids and possibly (obscured in skull mount) ectopterygoids and palatines, as well as postcrania solely represented by the atlas (intercentrum and partial neural arch) (Figs 1–4, 6–15). Referred material. USNM 8629, a partial cranium includ- Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 ing caudal skull roof (consisting of partial prefrontals, postorbitals, squamosals, partial right quadrate, frontals, parietal and braincase), disarticulated left jugal, partial left quadrate, partial right quadratojugal, left dentary, partial right surangular, and axial skeleton composed of axis and third and fourth cervical vertebrae (Figs 16, 17). IGM 6685, rostral region of skull consisting of predentary, symphy- Figure 7. Cranial elements of the holotype skull of Kritosaurus seal processes and rostral portion of dental battery of both navajovius, AMNH 5799. A, dorsolateral view of the left orbital dentaries, rostral region of both premaxillae, and fragments region and skull table, with white arrows pointing to the caudal of maxilla (Fig. 18). nasal processes; B, dorsal view of the nasofrontal articular region, showing the V-shaped caudal nasal processes; the upper margin Emended diagnosis. Saurolophine hadrosaurid of the of the photograph corresponds to the rostral side of the skull; C, genus Kritosaurus possessing a predentary with autapo- dorsal view of the right orbital margin; D, ventral view of the left morphic dorsoventral depth of rostral surface being at orbital margin. least half of mediolateral breadth of oral margin and Skeletal morphology of Kritosaurus navajovius 9

Figure 8. Cranial fragment of uncertain archosaurian affinity found among disarticulated bone fragments of AMNH 5799. A, probable external view; B, orthogonal view of the left margin of A; C, probable internal view; D, oblique view of the right margin of C.

steeply inclined forming at least 65◦ angle with long axis Formation (Williamson 2000) (Fig. 5); the De-Na-Zin of lateral rami. In addition, K. navajovius possesses the Member (and its associated Willow Wash local fauna of following unique character combination: dentary ramus the Kirtlandian land vertebrate ‘age’) has an estimated age combining short proximal edentulous margin (that is less of 73.4 ± 0.28 to 73.04 ± 0.25 Ma (Sullivan & Lucas than 20% of distance between first tooth position and 2006). USNM 8629 was collected in 1916 by J. B. Reeside, caudal margin of coronoid process; convergent in the Jr from strata corresponding also to the upper Kirtland saurolophine Secernosaurus koerneri and lambeosaurines Formation, four miles south-west of Kimbetoh Wash, San Arenysaurus ardevoli and Charonosaurus jiayinensis), Juan County, north-western New Mexico, USA (Gilmore straight articular predentary articular margin (convergent in 1935) (Fig. 5). IGM 6685 came from late Campanian strata Shantungosaurus giganteus, P. maximus, and species of (approximately 72.5 Ma, Eberth et al. 2004) of the Cerro del Saurolophus and Edmontosaurus), and at least 35◦ of Pueblo Formation cropping out in the Presa de San Antonio ventral deflection (convergent in G. monumentensis and ‘ejido’ (communal land) of the town of Parras de la Fuente, some lambeosaurines) originating near rostral end of central Parras Basin, southern Coahuila, Mexico (Kirkland dentary (convergent in Saurolophus spp., P. maximus, and et al. 2000, 2006) (Fig. 5). some specimens of G. notabilis and Edmontosaurus spp.) Remarks. Brown (1910) provided the following characters (diagnosis modified from Brown 1910). for diagnosing Kritosaurus navajovius: smooth margins on Additionally, Kritosaurus navajovius may be poten- maxillary teeth, papillate marginal denticles on dentary tially distinguished from other hadrosaurids, except teeth, low median carina of tooth crowns, deep and massive Gryposaurus, on the basis of rostrocaudally narrow and predentary, and short edentulous portion of the dentary that subrectangular premaxilla that has prominent subsquared is not overlapped by the predentary. The dentary teeth of rostromedial margin and autapomorphic dorsoventral deep- K. navajovius are best described as lanceolate rather than ening of reflected rostromedial oral margin (only preserved ‘spatulate’ and in this regard, as well as in the possession

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 in IGM 6685; Fig. 18E). Likewise, complete osseous lateral of a median carina and smooth margina, these teeth do not closure of ophthalmic sulcus on laterosphenoid contribu- differ from those of many other saurolophine hadrosaurids tion to rostral margin of trigeminal foramen (convergent (Prieto-Marquez´ 2010a). Only the short edentulous portion in Lambeosaurus spp. and saurolophine PASAC-1), only of the dentary is retained here as diagnostic, albeit in combi- preserved in USNM 8629 (Fig. 16C), might also contribute nation with other mandibular characters. to the diagnostic character combination of K. navajovius. Later, Horner diagnosed Kritosaurus navajovius based Occurrence. AMNH 5799 was recovered near Ojo Alamo, on the possession of a “caudally folded nasal crest with a a former trading post located near the homonymous lateral ridge extending out toward the prefrontal” (Horner spring, within the Bisti/De-Na-Zin Wilderness Area (a 1992, p. 14). However, this character is an autapomorphy of Federal Wilderness Area of the USA managed by the Anasazisaurus (= Kritosaurus) horneri (see below). There Bureau of Land Management), in San Juan County, north- is yet no unambiguous evidence of nasal crest in K. nava- western New Mexico, USA (Brown 1910). The sedimen- jovius. tary deposits that yielded the holotype belong to the late More recently, Williamson (2000) emended the diagnosis Campanian De-Na-Zin Member of the upper Kirtland of Kritosaurus navajovius as the only hadrosaurid showing 10 A. Prieto-Marquez´ Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 9. Cranial elements of the holotype skull of Kritosaurus navajovius, AMNH 5799. A, dorsal view of the supratemporal region of the skull (see Fig. 3 for an interpretative line drawing of the articular bone relationships); B, occipital view of the skull (see Fig. 4 for an interpretative line drawing of the articular bone relationships). Abbreviation: R, reconstructed areas. Skeletal morphology of Kritosaurus navajovius 11 Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 10. Cranial elements of the holotype skull of Kritosaurus navajovius, AMNH 5799. A, lateral view of the left caudodorsal region of the skull; B, lateral view of the left rostral half of the braincase. Abbreviations: R, reconstructed areas; V,foramen for trigeminal nerve; V3, grooved surface for mandibular ramus of trigeminal nerve. 12 A. Prieto-Marquez´

Figure 12. Palatal elements of the holotype skull of Kritosaurus navajovius, AMNH 5799. A, left pterygoid in lateral view; B, Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 medial view of the same; C, medial view of the right pterygoid and surrounding elements.

a nasal arch extending dorsal, and caudally (in adults), to between the orbits; nasals bifurcated caudally to articulate with a median tongue of the frontals and being overlapped by extensive medial wings of the prefrontals (narrowing Figure 11. Caudal half of the braincase of the holotype skull the mediolateral width of the frontals exposed in dorsal of Kritosaurus navajovius, AMNH 5799. A, lateral view of the view); and caudal region of the circumnarial depression metotic foramen; B, left lateral view; C, ventrolateral, and slightly extending laterally from near the dorsal margin of the nasals caudal, view; D, caudoventral, and slightly lateral, view. onto the prefrontals and lacrimals. However, the charac- ters of the nasal arch and circumnarial fossa are autapo- morphies of Anasazisaurus [= Kritosaurus] horneri (see below). Finally, the caudal bifurcation of the frontals is Skeletal morphology of Kritosaurus navajovius 13

Holotype. BYU 12950, a poorly preserved skull includ- ing part of the premaxillae, nasals, right maxilla, lacrimal, jugal, prefrontal, postorbital, squamosal, frontal, parietal, and fragment of dentary with teeth (Fig. 19).

Revised diagnosis. Saurolophine hadrosaurid of the genus Kritosaurus possessing the following autapomorphies: short, mediolaterally compressed and dorsally rugose nasal crest folding caudally to end medial and dorsal to mid- length of orbit, with lateral surface of nasal crest gently depressed by invasion of caudodorsal region of circumnar- ial fossa; lateral process of premaxilla being mediolaterally wider than the ellipsoidal (not slit-like; unlike Prosaurolo- phus and Saurolophus) narial foramen; and thin, elongate, and rostrally wedging dorsal process of nasal that is shorter than in Gryposaurus, distal tip of process barely project- ing below level of ventral margin of lacrimal (diagnosis modified from Horner 1992; Lucas et al. 2006).

Occurrence. BYU 12950 was collected in 1977 from the Farmington Member of the Kirtland Formation at Betonnie Tsosie Wash, south of Farmington, New Mexico (Lucas et al. 2006) (Fig. 5). The age of the Farmington Member has been estimated as approximately 73.4–74 Ma (Sullivan & Lucas 2006). This would indicate an older age for the Farmington Member relative to the De-Na-Zin Member of the Kirtland Formation. However, it is worth noting that the Farmington Member ranges from being very thick in the north-west of the San Juan Basin, near Farmington where it was originally defined (Bauer 1916), to relatively thin in the southern region of the basin, so that these strata are probably time-transgressive (Thomas Williamson, personal communication).

Remarks. Lucas et al. (2006, p. 294) revised the diagno- sis of Kritosaurus horneri as “a hadrosaurine most simi- lar to Kritosaurus navajovius but distinguished from it by possessing a short, rugose dorsal crest of the nasals that extends caudally to a position above the middle of the orbit”. These authors emphasized that both K. navajovius and K. horneri shared morphologically similar maxilla

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 Figure 13. Predentary of the holotype skull of Kritosaurus nava- and exclusion of the frontal from the orbital rim. The jovius, AMNH 5799. A, rostroventral and left lateral view; B, maxillae of the two species are certainly similar, partic- left lateral view; C, left laterodorsal view. Abbreviation: R, ularly in possessing a deep rostral region and a rostrocau- reconstructed areas. dally extensive rostrodorsal margin underlying the lacrimal rostrally and the jugal caudally. However, the frontal of K. a condition shared by Prosaurolophus, Naashoibitosaurus navajovius does participate in the orbital rim and it is and Kritosaurus; it is only diagnostic of Kritosaurus as part uncertain whether this condition occurs in BYU 12950. of the aforementioned combination of cranial characters. In K. horneri, the frontal extends rostrolaterally forming a wedged-shaped projection like in AMNH 5799, as illus- Kritosaurus horneri Hunt & Lucas, 1993 trated in Lucas et al. (2006, fig. 1B). Yet, the lateral margin (Fig. 19) of the skull roof at the orbit is heavily abraded and frag- mented, which obscures the articular relationships among 1993 Anasazisaurus horneri Hunt & Lucas: 80, fig. 7. the prefrontal, frontal and postorbital (Fig. 19D). 2006 Anasazisaurus horneri Hunt & Lucas; Lucas et al.: Williamson (2000, fig. 7J, K) figured a predentary that figs 1–4. he referred to BYU 12950, the same predentary that Lucas 14 A. Prieto-Marquez´ Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 Figure 14. Mandibular elements and dentition of the holotype skull of Kritosaurus navajovius, AMNH 5799. A, medial view of the right dentary; photograph reproduced from Brown (1910, pl. 29), courtesy of the American Museum of Natural History; B, interpretative drawing of the same; C, right post-dentary elements in medial view; D, left surangular in lateral view; E, caudal extent of the right maxilla and dentary in lingual view; F, detail of the right dentary dental battery in lingual view.

et al. (2006) listed as the available material for Kritosaurus I refrained from referring this predentary to K. horneri. horneri. Of this element, Lucas et al. (2006, p. 294) only In the photographs in Williamson (2000; reproduced here pointed out that its morphology “is identical to that of other in Fig. 20), the bone shows an arcuate oral margin as in, hadrosaurines”. However, no mention of such a preden- for example, K. navajovius, species of Gryposaurus and tary exists in the database of the BYU collections nor any Saurolophus (Prieto-Marquez´ 2008). The oral margin is indication of its association with the holotype skull BYU heavily eroded, missing all the denticles, and the caudal 12950, and, furthermore, the bone seems to be uncatalogued ends of the lateral rami are incompletely preserved, so that (Rodney D. Scheetz, personal communication). Therefore, any estimation of the width/length proportions of this bone Skeletal morphology of Kritosaurus navajovius 15

would be too inaccurate. The ventral median process is also partially preserved but prominent. More importantly, the rostral surface appears to be substantially shallower than that of K. navajovius. The combination of arcuate oral margin with moderate depth of the rostral surface suggests that this predentary belongs to an indeterminate taxon within the Kritosaurini–Saurolophus clade. The numerous character states shared by Kritosaurus horneri and K. Navajovius are summarized in Online Supplementary Material Table 2. Indeed, if one only consid- ers the overlapping elements preserved in these two taxa, BYU 12950 cannot be distinguished from AMNH 5799. This fact led to consideration of Anasazisaurus as junior synonym of Kritosaurus at the generic level. However, because the nasal crest (if present in K. navajovius) and the caudal extent of the lateral premaxillary process and narial foramen (which, along with the nasal crest, are autapomor- phic in K. horneri) are not preserved in K. navajovius,itwas deemed more cautious to maintain for the time being the taxonomic separation of these two taxa at the specific level in recognition of the unique premaxillonasal morphology of K. horneri. The alternative taxonomic choice, i.e. consider- ing K. horneri as a junior synonym of K. navajovius, would assume that the later taxon showed the same nasal crest and other autapomorphies seen in BYU 12950, an assump- tion that cannot be demonstrated with the available fossil material.

Osteology of Kritosaurus navajovius

Recently, Lucas et al. (2006) provided a detailed redescrip- tion of Kritosaurus horneri and figured much of the holotype BYU 12950. Thus, the following description is concerned with K. navajovius, with a particular focus on the holotype specimen AMNH 5799. Reconstructed areas were identified after visual inspection of differences in texture and tonality between these and the actual fossilized bone of the specimen. Access to the holotype skull of K. navajovius was limited to close-range observation of the rostral, left

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 lateral, caudal and dorsal sides of the specimen while on display, beneath a tightly secured glass enclosure, in the Hall of the Ornithischian Dinosaurs at the AMNH. In addition to AMNH 5799, all other specimens described and figured in this contribution were studied from first-hand examina- tion of actual fossil material, with exception of a predentary previously referred to K. horneri (Williamson 2000), which was studied in digital photographs. Selected measurements Figure 15. Atlas of Kritosaurus navajovius, AMNH 5799. A, of the specimens are provided in Online Supplementary cranial view; B, left lateral view of same; C, caudal view of the Material Table 3. same. Skull Premaxilla. Brown (1910) indicated that the rostral region of the skull of AMNH 5799 was found in a very frag- mentary state of preservation and that several of the bone 16 A. Prieto-Marquez´ Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 16. Partial cranium of Kritosaurus navajovius, USNM 8629. A, caudal skull roof in dorsal view; B, interpretative drawing of the same; white areas indicate plaster reconstruction and the asterisk signals the articular region on the frontal surface for the left caudal process of the missing nasal; C, caudal skull roof and braincase in right lateral view; D, interpretive drawing of the same; white areas indicate plaster reconstruction; E, occipital view of the skull; F, left jugal in lateral view; G, partial right surangular in dorsal view; H, partial left quadrate in lateral view. Abbreviations: V,foramen for trigeminal nerve; VII, foramen for facial nerve; VIII, fenestra vestibuli. Photographs courtesy of Thomas E. Williamson. Skeletal morphology of Kritosaurus navajovius 17

the elongate portion of the J-shaped right fragment shows a lateral surface that is gently concave mediolaterally, as typically occurs in the lateral processes of the premaxil- lae of saurolophines, such as Gryposaurus notabilis (e.g. ROM 873), G. monumentensis (e.g. RAM 6797), Edmon- tosaurus annectens (e.g. SM R4036) and Prosaurolophus maximus (e.g. AMNH 5386). The lateral process of AMNH 5799 is mediolaterally broad. However, given the frag- mentary nature of the bone, it is uncertain whether the process would be wider than the narial foramen, as occurs in Kritosaurus horneri (BYU 12950; Fig. 19A). The lateral and medial margins of the lateral process of AMNH 5799 are incomplete, except for a short segment along the rostral region of the medial margin. The latter contains a dorsoven- trally narrow articular facet for reception of the mediodorsal rostral process of the maxilla and, aside from the laterodor- sal side of the lateral process, it is the only complete surface present in this bone fragment (Fig. 6B, C, E). A simi- lar facet is observable in the premaxilla of G. latidens (Prieto-Marquez´ 2012, fig. 1E). Rostral to this articular surface in AMNH 5799, the incomplete lateral margin of the lateral process curves rostromedially and the rostral fossa of the circumnarial depression is entirely missing. The preserved rostrolateral margin of the premaxilla is gently arcuate. However, because it is unknown how much of the actual rostrolateral margin is missing, it is uncertain whether this corner of the premaxilla had a more subsquared profile as in IGM 6685 (Fig. 18E) and some species of Gryposaurus (e.g. G. notabilis, CMN 2278), or a smoother Figure 17. Dentary and dentition of Kritosaurus navajovius, and more in arcuate profile as in, for example, some spec- USNM 8629. A, tooth rows of the left dentary in lingual view; B, imens of Prosaurolophus maximus (e.g. CMN 2870) and left dentary in lingual view; C, labial view of the same. species of Saurolophus (e.g. S. osborni, AMNH 5220). The preserved rostrolateral region is tentatively interpreted as being near the oral margin of the premaxilla. Alternatively, fragments collected from that area were left out of the mount given the relatively short distance separating the medial because they were too incomplete for articulation. Sinclair articular facet for the maxilla from the curved rostrolat- & Granger (1914) quoted Brown recognizing the recov- eral segment, it is also possible that the latter represents ery of a partial left nasal; because this putative nasal frag- the transverse convexity that separates the rostral fossa ment was excluded from the skull mount due to the lack of from the more caudal circumnarial fossa proper of the contacting surfaces, it is likely to represent part of the frag- circumnarial depression, all of which are typically present

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 ments collected from the heavily weathered rostral region in saurolophines (e.g. Gryposaurus latidens Horner, 1992, of the skull of AMNH 5799. Williamson (2000, fig. 6D, AMNH 5465). E) figured for the first time the largest of these fragments (Fig. 6A–F) and identified it as the partial medial region of Nasal. The only bones in AMNH 5799 that can be unam- the left nasal. Subsequently, Hernandez´ et al. (2003) recog- biguously identified as nasals constitute the median portion nized an additional fragment (Fig. 6G, H) as the rostral of the interorbital region of the skull roof (Fig. 3). Rostrally, portion of the element figured by Williamson (2000) and most of this nasal region is probably restored, continu- agreed with the latter in interpreting the bone as a nasal. ous with the reconstruction of the rostrum inspired on However, Kirkland et al. (2006) recognized the ‘nasal’ frag- that of Gryposaurus notabilis (Gilmore 1916). The interor- ment as the ventral part of the lateral process of the right bital region of the nasal is gently concave rostrocaudally. premaxilla and another of the ‘float’ pieces as an even more Horner (1992) described the morphology of the nasofrontal incomplete portion of the left premaxillary lateral process. suture in Kritosaurus navajovius, in which a narrow median Several attributes of these elements, particularly in the ‘tongue’ of the rostral margin of the frontals containing more complete right fragment, support the interpretation the sagittal plane of the skull in between a pair of caudal of Kirkland et al. (2006) of this bone (Fig. 6). Specifically, processes of the nasals (Fig. 7A, B). These processes, 18 A. Prieto-Marquez´ Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 18. Presa de San Antonio (Mexico) Kritosaurus navajovius specimen (IGM 6685) and comparison with selected saurolophine premaxillae. A–C, E, IGM 6685; A, lateral view of rostral right premaxilla and dentary, and right lateral view of predentary; B, rostral view; C, lateral view of rostral left premaxilla and dentary, and left lateral view of predentary; E, left premaxilla in lateral view. D, right premaxilla of Gryposaurus notabilis (ROM 873) in lateral view (reversed). F, right premaxilla of Brchylophosaurus canadensis (MOR 794) in lateral view (reversed). G, left premaxilla of Edmontosaurus regalis (CMN 2288) in lateral view. H, right premaxilla of Prosaurolophus maximus (CMN 2277) in lateral view (reversed). Skeletal morphology of Kritosaurus navajovius 19 Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 19. Partial holotype skull of Kritosaurus horneri, BYU 12950. A, right lateral view; B, dorsal view; C, dentary tooth crowns; D, dorsal view of the nasal crest and right orbital region. Photographs in A, B, and D courtesy of Terry A. Gates. 20 A. Prieto-Marquez´

Hernandez´ et al. (2003) and Kirkland et al. (2006) tenta- tively regarded one of the ‘float’ fragments recovered with the articulated AMNH 5799 skull as the caudal extent of the nasal, containing part of the caudodorsal circumnarial region (Fig. 8). This bone is mediolaterally compressed and shows two morphologically distinct sides. One side is rela- tively smooth and contains a gently concave to convex relief followed by a deeply depressed area. The other side has a large ridge that extends obliquely from the bone surface. The ridge and one of the margins of the bone are broken off, leaving an X-shaped cross section. Only the gently arcuate margin, adjacent to the area where the ridge origi- nates, appears to be complete; the remaining edges are the result of breakage. The morphology of this fragment does not conform to that of any known saurolophine nasal. In all saurolophines, the nasals meet at the sagittal plane of the rostrum and the rostral region of the skull roof. Throughout most of its length, the internasal articular surface forms a more or less flattened and subvertical facet adjacent to the dorsal margin of the medial side of each nasal (e.g. Maiasaura peeblesorum, OTM F138; Gryposaurus lati- dens, AMNH 5465). Such an internasal facet is not seen in the AMNH 5799 fragment and it is difficult to envision how this element would meet its counterpart at the sagit- tal plane of the skull. Furthermore, the prominent ridge present in that bone fragment is nowhere to be seen in the available disarticulated saurolophine nasals. Thus, this fragment is provisionally referred to Archosauria indeter- Figure 20. Uncatalogued hadrosaurid predentary previously minate, barring unambiguous evidence in support of its referred to Kritosaurus horneri by Williamson (2000) and proba- hadrosaurian or even non-hadrosaurid dinosaurian nature. bly the same bone that Lucas et al. (2006) considered as the preden- tary of this taxon. A, dorsal view; B, ventral view. Photographs Maxilla. This element is more completely preserved on the courtesy of Thomas E. Williamson. right side of the skull (hidden from sight in the mount of the skull), being almost entirely reconstructed on the left side; therefore, the following osteological remarks are based on first figured by Williamson (2000, fig. 6B, C), protrude the photograph in Brown (1910, pl. 28) (Figs 1, 2). The over the flatter surface of the skull roof and show a V- rostrodorsal margin of the maxilla of AMNH 5799 appears shaped dorsal profile, particularly the more complete right to be steeply inclined, much like in Kritosaurus horneri (e.g. process. Paired caudal nasal processes, along with a similar BYU 12950), species of Gryposaurus (Prieto-Marquez´ configuration of the nasofrontal suture, are also present in 2010b), and Secernosaurus koerneri (Prieto-Marquez´ &

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 Prosaurolophus maximus (e.g. CMN 2870), and in the other Salinas 2010), where the rostrodorsal margin is oriented two saurolophine taxa erected from the Kirtland Forma- more than 40◦ relative to the tooth row.However, this margin tion, Kritosaurus horneri and Naashoibitosaurus ostromi is only partially preserved on the right side of AMNH 5799 (Horner 1992; Hunt & Lucas 1993; Williamson 2000). and, judging only from Brown’sphotographs, it is uncertain Subtle variations are observable in the morphology of how much of the margin is preserved but covered with plas- these processes within taxa. For example, in P. maximus ter, or reconstructed (Fig. 2A). Therefore, a steep inclination the processes range from being tulip-shaped, asymmetri- of the rostrodorsal margin of the maxilla in K. navajovius cal, and widely separated in CMN 2870 to V-shaped (as in can only be regarded as tentative at this juncture. The dorsal K. navajovius) in the larger TMP 84.1.1. The caudal end process of the maxilla does not appear to be preserved and of the nasals in Edmontosaurus annectens (e.g. AMNH that region of the skull is filled with plaster. However, the 5730) and E. regalis (e.g. CMN 2288) also show a pair of position of the maxillary dorsal process may be assessed median processes; however, in contrast to the taxa listed from the location of the rostral process of the jugal. This is above (contra Prieto-Marquez´ 2010a) these processes are because the dorsal region of the rostral process of the jugal rectangular and strip-like in morphology, and form a nearly contacts the ventral region of the dorsal maxillary process straight transversal suture with the frontal. in hadrosaurids (e.g. Brachylophosaurus canadensis,MOR Skeletal morphology of Kritosaurus navajovius 21

794). Accordingly, the dorsal process of Kritosaurus nava- latidens (e.g. MOR 478-6-10-87-2) and K. horneri (e.g. jovius was located rostral to the mid-length of the maxilla. A BYU 12950). row of three widely spaced foramina rostrodorsally oriented Prefrontal. This element is represented by the caudal is present below the rostral process of the jugal. A fourth region of the medial wing and the caudal extent of the foramen appears to be present adjacent to the ventral jugal element at the orbital margin on both sides of the skull tubercle. Only the rostral third of the ectopterygoid ridge (Figs 7, 10). The prefrontal contacts extensively the nasal is visible and this is parallel to the tooth row. Because the medially and the frontal caudomedially. In Kritosaurus caudal end of the maxilla is also visible, caudal to the ventral navajovius (e.g. AMNH 5799) and K. horneri (Lucas et al. flange of the jugal, the relative length of the ectopterygoid 2006, fig. 4) the medial wing is as wide as each nasal shelf may be estimated. The latter comprises approximately process and occupies approximately half of the interorbital 45% of the length of the maxilla. width of the skull at each side of the sagittal plane. A similar condition is present in other saurolophines, albeit Jugal. The jugal of Kritosaurus navajovius is relatively with slight variation in the relative width of the nasal gracile in the context of Saurolophinae (Figs 1, 2); the ratio process and prefrontal wing. Thus, within Gryposaurus between the minimum depth of the infratemporal constric- notabilis, the nasal process is substantially broader in tion and the distance between the maximum curvature of the CMN 2278 and almost as wide as the prefrontal wing in infratemporal border and the caudal margin of the lacrimal AMNH 5350 (Prieto-Marquez´ 2010b, fig. 3); in Maiasaura process is 0.56 (taxa with relatively robust jugals like peeblesorum (e.g. ROM 44770), Edmontosaurus regalis species of Edmontosaurus show ratios of 0.60 or greater; (e.g. CMN 2288) and E. annectens (e.g. SM R4036) the Prieto-Marquez´ 2008). The rostral apex of the triangular prefrontal wing is slightly broader caudally but subequally rostral process was probably located within the dorsal half wide with the nasal more rostrally; and in Prosaurolophus of the process, a condition shared with all saurolophines maximus (e.g. CMN 2870) the nasal is only slightly broader except Brachylophosaurini Gates et al., 2011 (Prieto- than the prefrontal. A remarkable condition is found in Marquez´ 2010a). The rostroventral margin of the rostral Naashoibitosaurus ostromi (NMMNH P-16016), in which process forms a ventrally projected apex that is approx- at the narrowest point of the nasal the prefrontal is approxi- imately as deep as it is rostrocaudally broad proximally. mately twice as broad as the caudal nasal processes and the The ventral embayment of the jugal, between the rostral prefrontal forms more than half of the interorbital breadth process and the caudoventral flange, is relatively wide, as of the skull; a similarly broad prefrontal may be also present in Gryposaurus notabilis and G. latidens (Prieto-Marquez´ in Acristavus gagslarsoni (Gates et al. 2011, fig. 5). The 2012), Secernosaurus koerneri, Prosaurolophus maximus, photograph provided by Brown (1910, pl. 28) of the right species of Saurolophus, Kerberosaurus manakini Bolot- side of AMNH 5799 shows an upturned (‘flared’) orbital sky & Godefroit, 2004 and Wulagasaurus dongi Godefroit margin of the prefrontal (corresponding to the supraorbital et al., 2008 (Prieto-Marquez´ 2010a). The orbital constric- II identified in Saurolophus angustirostris by Maryanska tion of Kritosaurus navajovius is slightly deeper than the & Osmolska 1979; Bell 2011b), just rostral to the contact infratemporal constriction (orbital constriction minimum with the frontal. This condition is present in at least some depth/infratemporal constriction minimum depth ratio of specimens of Brachylophosaurus canadensis (e.g. MOR 1.02), as in K. horneri (e.g. BYU 12950, ratio of 1.01), G. 794) and Maiasaura peeblesorum (e.g. TCMI 2001.89.2), latidens (Prieto-Marquez´ 2012), Prosaurolophus maximus and species of Saurolophus (S. osborni, Bell 2011a; S. and species of Saurolophus (Prieto-Marquez´ 2010a). The angustirostris, Bell 2011b). caudoventral flange of the jugal is greatly expanded: the

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 ratio between the maximum dorsoventral depth of the Postorbital. Most of the rostral region of the central body caudoventral flange and the minimum depth of the infratem- of the postorbital, including the caudal corner of the orbit, poral constriction of the jugal is 1.67. Within Saurolophi- is not preserved (Figs 7, 9, 10). The jugal ramus appears nae, greatly expanded caudoventral flanges (i.e. ratio greater to be long and slender in overall proportions; however, it than 1.55 according to character 110 of Prieto-Marquez´ is missing in the right postorbital and is heavily abraded 2010a) are found in Brachylophosaurini and Gryposaurus rostrally and laterally in the left postorbital. Rostromedially, monumentensis (e.g. RAM 6797, ratio of 1.69). The auric- the postorbital articulates along an oblique and rostrolater- ular quadratojugal flange extends caudodorsally into a rela- ally oriented sutural margin with the parietal caudally and, tively long and conical end. The concave caudoventral for the most part, with the frontal medially. Ventrally and margin of the jugal located between the quadratojugal and medial to the orbital rim, the postorbital forms an enarthro- caudoventral flanges is remarkably wide. The infratempo- sis with the laterosphenoid. The squamosal ramus projects ral margin is substantially wider than the orbital margin, caudodorsally to meet the homonymous element, contribut- which is related to the infratemporal fenestra being greater ing to the pronounced rostroventral slope of the caudodorsal than the orbit (Lull & Wright 1942), a condition occurring region of the skull and becoming gradually wider medio- in G. notabilis (e.g. CMN 2278) and probably also in G. laterally. Although the morphology of the left ramus is 22 A. Prieto-Marquez´

partially obscured by abrasion and dorsoventral crushing fig. 2) and USNM 8629 (Fig. 16H). It lies within the ventral (the dorsal surface of the right one is masked with paint), half of the quadrate, as in all known saurolophines (Prieto- the caudal extent of the squamosal ramus appears to display Marquez´ 2010a). The dorsal segment of the caudal margin a bifid configuration. The caudal tip of the left squamosal of the notch forms a 30◦ angle with the caudal border of the ramus is missing and the preserved end abuts the recon- quadrate. Relatively low angles (up to 45◦) are characteris- structed dorsolateral region of the squamosal including the tic of saurolophines (Prieto-Marquez´ 2008, fig. D78). quadrate cotylus. Thus, the complete caudal extent of the squamosal ramus of the postorbital would probably end Quadratojugal. Approximately the caudal half of this somewhere above the quadrate cotylus. element is visible on the right side of AMNH 5799, whereas its rostral region is overlapped by the caudal quadratoju- Squamosal. The postorbital ramus of the squamosal gal flange of the jugal (Figs 1, 2). The caudal region of projects rostroventrally to underlie the squamosal ramus of the quadratojugal forms a fan-shaped lamina that mirrors the postorbital (Figs 9, 10). The infratemporal margin of the the arcuate lateral profile of the homonymous notch in the squamosal lies well above the level of the orbital margin, quadrate. The caudoventral and caudodorsal corners of the as in Gryposaurus notabilis (e.g. ROM 873), G. monu- quadratojugal end in acute apices. mentensis (e.g. RAM 6797) and Kritosaurus horneri (e.g. BYU 12950). Only the proximal region of the precotyloid Frontal. The ectocranial surface of each frontal (Figs 3, process is present in both squamosals, bounding rostrally 7) is depressed caudolateral to the caudal process of the the quadrate head. That segment of the process is rostro- nasal. Caudomedially, adjacent to the suture with the pari- caudally compressed. Rostrally, the precotyloid process is etal, the frontal gently slopes rostroventrally (its high- continuous with the caudal surface of a shallow precoty- est point being at the frontoparietal suture) while being loid fossa, which constitutes the caudodorsal corner of the slightly convex mediolaterally. The frontal is wider than infratemporal fenestra and the ventral surface of the postor- long, with a maximum length (along the sagittal plane of bital ramus of the squamosal. The supracotylar regions of the skull)/maximum width (perpendicular to the sagittal both squamosals are reconstructed in AMNH 5799. The skull plane) ratio of 0.84. The element extends rostro- postcotyloid process is missing in the left squamosal; obser- ventrally forming a triangular projection. The apex of vation of Brown’s (1910) photograph of the right side of this projection reaches the orbital rim and inserts in AMNH 5799 suggests that it may be also absent in the right between the prefrontal and postorbital. This rostrolat- squamosal. The medial rami of the squamosals appear to eral triangular projection of the frontal occurs also in be reconstructed. Gryposaurus notabilis (Prieto-Marquez´ 2010b), G. monu- mentensis (Gates & Sampson 2007), Brachylophosaurus Quadrate. The quadrate of Kritosaurus navajovius is canadensis (Prieto-Marquez´ 2005), Maiasaura peebleso- elongate and slender in overall proportions (see Brown rum (Horner 1983), and Acristavus gagslarsoni (Gates et al. 1910, fig. 3), as well as straight in both AMNH 5799 (Figs 1, 2011), Naashoibitosaurus ostromi (e.g. NMMNH P-16106) 2) and USNM 8629 (Fig. 16H). Typically, the quadrate and possibly in Kritosaurus horneri (e.g. BYU 12950; see of saurolophines is gently curved caudally, although the Lucas et al. 2006, fig. 1B). In addition, the rostrolateral apex extent of this curvature is variable intraspecifically (Prieto- of the frontal reaches the orbital margin in these taxa, except Marquez´ 2008, fig. D76). Given the range of intraspe- N. ostromi (Hunt & Lucas, 1993). It is uncertain whether cific variation of this character and the fact that in forms the frontal contributes to the orbital margin in K. horneri such as Prosaurolophus maximus (e.g. CMN 2777, ROM (contra Lucas et al. 2006, who concluded that it does not) 1928, TMM 41262-1), Gryposaurus notabilis (e.g. CMN because that margin and adjacent area are heavily abraded Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 2278), and to a lesser extent G. monumentensis (RAM and critical portions of bone are missing (Fig. 19D). 6797) the quadrate is practically as straight as in K. nava- jovius, it seems more cautious to refrain from considering Parietal. The parietal forms the median section of the the lack of quadrate curvature as an autapomorphy for K. caudodorsal region of the skull roof, including most of navajovius. Near the articular head, the caudodorsal margin the medial and a large part of the rostral margin of the of the quadrate displays a prominent buttress (Fig. 10A); supratemporal fenestra (Figs 9, 10). In dorsal view, the this condition is also found in some saurolophines such parietal roughly displays an hourglass-shaped profile, with as Naashoibitosaurus ostromi (e.g. NMMNH P-16106), lateral margins that are subparallel throughout most its Gryposaurus notabilis (e.g. MSNM V345), G. monu- length. Rostrally, however, the parietal expands mediolat- mentensis (Gates & Sampson 2007), and to a slightly lesser erally by means of two processes that curve rostrolaterally. extent in Brachylophosaurus canadensis (Prieto-Marquez´ Most of the rostral margin of these processes and the median 2005) and Maiasaura peeblesorum (e.g. YPM-PU 22405). section of the parietal suture with the frontals; the lateral The quadratojugal notch is widely arcuate and symmetri- end of each rostrolateral process contacts the postorbital. cal (i.e. its dorsal and ventral segments are approximately The sagittal crest has been entirely reconstructed in AMNH equal in length), as seen both in AMNH 5799 (Brown 1910, 5799. The ventrolateral margin of the parietal overlies the Skeletal morphology of Kritosaurus navajovius 23

laterosphenoid, prootic, fused opisthotic-exoccipital, and rostral portion of the sphenooccipital tubera and includes probably also the supraoccipital. the contact with the basioccipital. This contact is seen later- ally as an oblique and coarsely crenulated suture. The inter- Orbitosphenoid. Patches of the ventrolateral surface of tuberal region is deeply depressed; this depression deep- the orbitosphenoid are observable on the rostrolateral wall ens rostrally within the basisphenoid. A transverse ridge of the braincase (Fig. 10). This element contacts the frontal extends between the basipterygoid processes, present also rostrolaterally, the other orbitosphenoid medially at the in various hadrosaurids such as Gryposaurus monumenten- sagittal plane of the skull, the laterosphenoid caudally, sis (e.g. RAM 6797), Hypacrosaurus stebingeri (e.g. MOR and the basisphenoid ventrally. The median, caudoventral 553S-7-27-2-93), Edmontosaurus regalis (e.g. CMN 2289) margin of the orbitosphenoid forms the dorsal border of the and Brachylophosaurus canadensis (e.g. UCMP 130139); foramen for the optic nerve, which is mostly reconstructed there is no sign, however, of a median ventral process. in AMNH 5799. More dorsally, on the lateral side of the basisphenoid near Laterosphenoid. Caudal to the orbitosphenoid, on the the lateral surfaces of the sphenooccipital tubera and the dorsolateral wall of the braincase, lies the triradiate proximal region of the basispterygoid process, a large fora- laterosphenoid (Fig. 10B). The caudodorsal region is deeply men may represent the exit of the internal carotid artery. concave rostrodorsally and sutures dorsally with the parietal Dorsal to the latter, the alar process is almost entirely and caudally with the prootic. Its ventral margin forms most missing, retaining only its base. Rostral and adjacent to of the dorsal edge of the trigeminal foramen. In AMNH the alar process, a ventrally elongate and irregular excava- 5799, the caudal and rostral margins, as well as the rostral tion corresponds to the mandibular ramus of the trigeminal area where the ophthalmic trigeminal ramus would be nerve. located, have been filled with plaster. However, this region Prootic. The prootic occupies a median position in the of the braincase is well preserved in USNM 8629, display- lateral wall of the braincase below the parietal (Figs 10, 11). ing a complete lateral osseous closure of the ophthalmic Its rostroventral region fuses rostrally with the laterosphe- sulcus for the ophthalmic ramus of the trigeminal fora- noid and contributes to the caudal half of the trigeminal men (Fig. 16C). This is an uncommon condition among foramen. The suture between the prootic and the basisphe- hadrosaurids, being observed in species of Lambeosaurus noid is obscured by plaster reconstruction. Caudal and adja- (Ostrom 1961; Evans & Reisz 2007) and a saurolophine cent to the trigeminal foramen, the area typically contain- specimen (PASAC-1) from the Parras Basin of the Mexican ing the foramen for the facial nerve in hadrosaurids (e.g. state of Coahuila (Kirkland et al. 2006, fig. 8A; see discus- Godefroit et al. 2004b, fig. 8) is filled with plaster. Caudal sion below). The postorbital process of the laterosphe- to this area, a large subtriangular foramen corresponds to noid is mediolaterally compressed and projects laterodor- the fenestra vestibuli. The edges of the fenestra appear to sally, separating the orbital cavity from the temporal region be partially eroded and contain minor plaster restoration. of the skull. Caudal to the contact with the frontal, the process is slightly expanded rostrally and sutures with the Opisthotic–exoccipital complex. These elements contri- orbitosphenoid. Rostroventral to the trigeminal foramen, bute to the caudolateral wall of the braincase and a rugose surface is slightly offset laterally from the more most of the occipital region that surrounds the fora- concave lateral surface of the underlying basisphenoid. A men magnum (Figs 3, 9, 11). The rostral region of the similar subrectangular surface occurs in Gryposaurus nota- opisthotic–exoccipital complex forms an rostrocaudally bilis (e.g. AMNH 5350; see Prieto-Marquez´ 2010b, fig. 7) narrow, obliquely (caudodorsally) oriented, and mediolat- and G. monumentensis (e.g. RAM 6797). Rostromedial erally convex surface. Caudal to the latter and caudoventral Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 to this surface, a large reconstructed subcircular opening to the fenestra vestibuli lies the metotic foramen. This fora- probably constitutes the rostral exit of the abducens nerve, men is heart-shaped and is subdivided into two smaller following the identification of this nerve in the endocast of cavities that are separated ventrally by a mediolaterally AMNH 5350 (G. notabilis) by Ostrom (1961) and Hopson oriented ridge. One of the subdivisions is located rostrodor- (1979). Adjacent to the ventral margin of the optic foramen, sally and likely transmitted the vagus nerve, perhaps along a rostrally bifurcated bridge-like structure made of plas- with the glossopharyngeal nerve, according to the endo- ter connects with the dorsal surface of the rostral region cast morphology interpreted by Ostrom (1961) and Hopson of the basisphenoid. Among hadrosaurids, only the G. (1979). Likewise, the caudoventral subdivision possibly notabilis specimen AMNH 5350 displays a similar ‘bridge’. transmitted branches of the hypoglossal nerve, congruent However, this structure is made of plaster in both AMNH with the position of these nerves indicated in the AMNH 5799 and AMNH 5350 (Prieto-Marquez´ 2010b). 5350 endocast by Hopson (1979) and in hadrosaurids in general (Evans 2005). Ventral to the metotic foramen, the Basisphenoid. The basisphenoid contributes to the rostro- opisthotic–exoccipital complex fuses with the basioccipi- ventral and lateroventral regions of the braincase (Figs 10, tal. Caudally, on the occipital region of the skull, the fused 11). The caudal region of its ventral surface forms the opisthotic–exoccipital forms the lateral and dorsal margins 24 A. Prieto-Marquez´

of the foramen magnum. Further ventrally, the caudolateral site side of the pterygoid, a vaulted palatine flange projects wall of the opisthotic–exoccipital curves caudally, expand- rostrodorsally to meet the dorsal edge of the palatine. Only ing mediolaterally and dorsoventrally form a condyloid. the proximal region of this flange is preserved in the disar- This condyloid is triangular in occipital view and has a ticulated and partial left pterygoid. Ventral to the palatine bulbous surface, contributing to the laterodorsal corner of flange is the ectopterygoid process. This process, the short- the occipital condyle. The ventral surface of this expansion est of the radial rami of the pterygoid, is dorsoventrally articulates with the basioccipital contribution to the occip- compressed and wider proximally than distally. Its rostro- ital condyle. Dorsal to the occipital condyle, the caudolat- medial surface contacts the caudal surface of the maxilla, eral wall of the opisthotic–exoccipital complex extends whereas rostrolaterally it articulates with the caudomedial dorsolaterally to form the horn-shaped paroccipital process. region of the ectopterygoid. On the medial side of the Distally, these large processes curve lateroventrally and pterygoid, three prominent and large ridges converge at rostrally. In AMNH 5799, the lateral margins of their prox- the centre of the element. The convergence of these ridges imal halves have been heavily eroded. forms a thick and dorsoventrally compressed buttress that contacts the basipterygoid process of the basisphenoid. One Supraoccipital. The supraoccipital occupies a median of the three ridges extends rostrodorsally and is continu- position inset on the caudodorsal region of the occiput, ous with the dorsal edge of the palatine flange. A second between the proximodorsal corners of the paroccipi- ridge extends caudoventrally from the central buttress and tal processes and resting on the dorsal surface of the is obliquely aligned with the long axis of the rostrodorsal opisthotic–exoccipital shelf (Figs 3, 9). Only the eroded ridge. The third ridge extends ventrally and slightly rostrally caudal surface of the supraoccipital is visible in AMNH from the central buttress, merging with the medial edge 5799; its dorsal surface, as well as its contact with the of the ectopterygoid process. These ridges are completely parietal, is not preserved. The caudoventral surface of the eroded in the left pterygoid of AMNH 5799. As seen in the supraoccipital is caudally offset relative to the dorsal half right pterygoid, the rostroventral and caudoventral ridges of the element and faces caudodorsally. define an A-shaped profile, the apex of which constitutes Basioccipital. The basioccipital forms the caudoventral the central buttress that meets the basisphenoid. The space region of the braincase (Figs 9, 11). It contacts the basisphe- bounded by those two ridges is bounded laterally by a bony noid rostrally, the fused opisthotic–exoccipital caudodor- lamina that is part of the ventral region of the lateral surface sally, and the prootic dorsally. The caudal half of the of the pterygoid. A dorsoventrally short process is present basioccipital is smooth and bulbous. This caudal region above and lateral to the central buttress, between the prox- forms most of the occipital condyle, as well as the ventral imal regions of the alar quadrate and the vaulted palatine margin and part of the laterodorsal border of the foramen flanges. This process typically has a peg-like morphology magnum at the joint with the opisthotic–exoccipital condy- in hadrosaurids (Prieto-Marquez´ 2005). However, in the loids. Likewise, the basioccipital contributes to the floor of articulated right pterygoid of AMNH 5799 this process is the foramen magnum rostral to its ventral margin. Rostral obscured by the skull mount; only the base of the process to the bulbous caudal half of the basioccipital, separated is preserved in the disarticulated left pterygoid of AMNH from the latter by a dorsally recessed area, lies the oval and 5799. ventrally protruding sphenooccipital tubera. Most of the caudal region of the tubera corresponds to the basioccipi- Mandible tal, whereas the remaining more rostral area is basisphenoid Predentary. The predentary of AMNH 5799 is missing the in nature. The area between the tubera is deeply depressed ventral median process and most of the left lateral ramus Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 and extends rostrally into the basisphenoid. (Fig. 13). This element displays a horseshoe dorsal profile, with rounded and widely arcuate rostrolateral corners Pterygoid. This tetraradiate bone consists of a medially (Brown 1910, fig. 4). The lateral rami extend caudally and buttressed central region from which two large flanges are nearly parallel to each other. As preserved, the length extend rostrodorsally and caudodorsally, and two shorter of the predentary along the right lateral ramus is 1.6 times but robust processes project rostroventrally and caudoven- the maximum mediolateral width of the bone just caudal trally (Fig. 12). The pterygoid contacts the quadrate to the oral margin. As noted by Brown (1910), the rostral caudally via the dorsal alar flange and the caudoventral surface of the predentary is remarkably deep. Indeed, the process. The alar flange is only preserved in the articulated bone is unique among hadrosaurids in that the depth of its right pterygoid. It is a thin and triangular bony sheet, the rostral surface (not including the median ventral process) is sharp apex of which projects caudodorsally, and contacts half of the mediolateral breadth of the oral margin. In other the medial surface of the pterygoid flange of the quadrate. saurolophines, the rostral predentary surface is substantially Ventrally, a shorter and thick process projects caudoven- shallower, ranging from 30% to 40% of the width of the trally to abut a depressed area of the quadrate, adjacent oral margin (e.g. 30% in Brachylophosaurus canadensis, to the medial margin of the latter element. On the oppo- MOR 1071-7-28-98-299; 40% in Gryposaurus notabilis, Skeletal morphology of Kritosaurus navajovius 25

CMN 2278; 34% in Prosaurolophus maximus, MOR 447- ing or exceeding 35◦ are present in the lambeosaurines 7-27-7-5; 33% in Edmontosaurus regalis CM 26258). The Amurosaurus riabinini (Godefroit et al. 2004b), Pararhab- rostral surface of the predentary forms a 65◦ angle with dodon isonensis (Prieto-Marquez´ & Wagner 2009), Tsin- the dorsal margin of the right lateral rami. Four foramina taosaurus spinorhinus (Young 1958), and some specimens oriented rostroventrally are present on the right rostrolateral of Corythosaurus casuarius (e.g. AMNH 5240) and C. surface of the predentary (two foramina are partially recon- intermedius (e.g. ROM 777), as well as the saurolophine structed on the left side). Although no denticle is preserved Gryposaurus monumentensis (Gates & Sampson 2007) and in the predentary oral margin of AMNH 5799, the spots the basal hadrosauroid Protohadros byrdi (Head 1998). The where these structures were located are still recognizable origin of the ventral deflection in Kritosaurus navajovius on the right half of the element. A ventrally recessed and originates near the rostral end of the dentary. In particular, narrow surface lies caudal and adjacent to the oral margin. the ratio between the distance from the caudal margin of This surface is carved with large foramina, the distribution the coronoid process to the origin of the deflection and the of some of which follows the arrangement of the denti- distance from the caudal margin of the coronoid process cles. There were a minimum of five denticles on each to the first tooth position is 0.87. Although the mounted side of the oral margin, as well as probably an additional position of the skull of AMNH 5799 prevents accurate median one, although the exact number is uncertain due to measurement of the lingual extension of the symphyseal erosion of the oral margin. As in other hadrosaurids (Prieto- process, it can be observed that this is relatively moderate: Marquez´ 2010a), the denticles did not extend onto the lateral the ratio between the labiolingual projection of the symphy- rami. The lateral rami are mediolaterally compressed and seal process and the maximum labiolingual breadth of the wedge-shaped in lateral view. The dorsal shelf of each dentary probably lies between 1.65 and 2.85 (state 1 of lateral ramus, for occlusion with the oral margin of the character 38 of Prieto-Marquez´ 2010a). premaxilla, is elongate and mediolaterally narrow, slightly Along the caudal half of the dentary, the ventral margin is widening distally and sloping lateroventrally. The distal end nearly straight, only slightly bowed immediately rostral to of each lateral ramus is bifid, having a short mediodor- the long axis of the coronoid process. The latter in AMNH sal process and an elongate ventrolateral finger-like 5799 is unusual among hadrosaurids in being perpendicu- projection. lar relative to the alveolar margin of the dental battery in both dentaries. Subvertical to caudally inclined coronoid Dentary. The dentary of Kritosaurus navajovius has a processes (angle with the alveolar margin of the tooth row relatively short edentulous margin (Fig. 14A, B). Specif- greater than 82◦; character 42 of Prieto-Marquez´ 2010a) ically, the ratio between the length of the proximal edentu- are typically found basally among hadrosaurid outgroup lous slope (i.e. the edentulous margin excluding the steep taxa. In all hadrosaurids, apparently except K. navajovius, deflected portion that contains the predentary articular the long axis of the coronoid process is rostrally inclined border) and the distance between the first tooth position (Horner et al. 2004) and forms an angle of 82◦ or less with and the caudal margin of the coronoid process is 0.15. the alveolar margin of the tooth row. It must be noted, Adult or large subadult specimens with ratios lower than however, that most of the coronoid process of the left 0.2 are typically present in basal hadrosauroids; among dentary is reconstructed, whereas the base of the coronoid hadrosaurids, a similarly short proximal edentulous margin process of the right dentary in hidden from sight in the is found in Secernosaurus koerneri (e.g. MACN-RN 142; mount of the skull in exhibit at the AMNH. The observa- Prieto-Marquez´ & Salinas 2010). The articular preden- tions presented here of the right coronoid process of AMNH tary margin of the edentulous region of the dentary is 5799 are based on Brown (1910, pls 28, 29). Thus, a vertical

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 straight in lateral and medial views. Among hadrosaurids, orientation of the coronoid process in K. navajovius is here taxa with straight to nearly straight predentary margins regarded as tentative and therefore is not included in the include the saurolophines Edmontosaurus spp. (e.g. MOR diagnosis. The apex of the coronoid process has a rhom- 003), Prosaurolophus maximus (e.g. MOR 447), Saurolo- boidal medial profile, comprising the dorsal half of the phus spp. (e.g. ZPAL MgD-I 162), Shantungosaurus gigan- segment of the process that rises above the occlusal plane teus (Zhao et al. 2007), and the lambeosaurines Tsin- of the dental battery. The apex appears to be only rostrally taosaurus spinorhinus (e.g. IVPP V723) and Pararhab- expanded, as seen in plate 29 of Brown (1910). It is possi- dodon isonensis (e.g. IPS-SRA 27); all other hadrosaurids ble, however, that the apparent lack of caudal expansion is display concave lateral and medial profiles of their preden- a preservational artefact, a possibility that, again, cannot tary articular margins (Prieto-Marquez´ 2010a). This margin be verified because the mounted position of the specimen slopes rostroventrally forming a 125◦ angle with the long prevents direct observation of the right side of the skull. axis of the tooth row. The ventral margin of the rostral As in all hadrosaurids (Horner et al. 2004; Prieto-Marquez´ region of the dentary is strongly deflected ventrally, form- 2010a), the coronoid process is laterally offset relative to ing an angle of 37◦ with the long axis of the dental the tooth row and a concave platform separates the base battery. Among hadrosauroids, deflection angles approach- of the process from the dental battery, the occlusal plane 26 A. Prieto-Marquez´

is straight and oriented parallel to the lateral surface of spaced tubercles distributed in alternating oblique rows, the dentary ramus, and the tooth row ends caudal to the producing a quincunx-like arrangement (i.e. alternating coronoid process. positions in alternating rows like the five dots of a six-sided dice) (Brown 1910, fig. 7). Similar sized denticles with the Surangular. The mediolaterally compressed rostral same arrangement pattern have been described by Wagner ascending flange arches rostrodorsally to contact the (2001, fig. 81) in TMM 42876, a tooth collected from the dentary (Fig. 14D). The ventrolateral surface of the flange upper shale member of the Aguja Formation in Big Bend overlies the medial surface of the large Meckelian opening National Park, Texas (see Online Supplementary Material of the dentary. The D-shaped lateral lip of the surangular Table 1). The apparent absence or extreme reduction of is dorsoventrally thick and its caudal slope is continuous marginal denticulation is a condition widespread among with the glenoid facet for the quadrate. The retroartic- hadrosaurids, in both saurolophines (e.g. Gryposaurus ular process is mediolaterally compressed and gradually notabilis, G. monumentensis, Naashoibitosaurus ostromi, narrows caudally. Edmontosaurus spp., Brachylophosaurus canadensis and Splenial. The splenial is a mediolaterally compressed bony Shantungosaurus giganteus; Prieto-Marquez´ 2010a) and lamina that forms the majority of the dorsal two-thirds of the lambeosaurines (Amurosaurus riabinini, Hypacrosaurus medial side of the postdentary region of the mandible, being altispinus, Sahaliyania elunchunorum and Nipponosaurus twice as deep as the underlying angular (Fig. 14C). The sachalinensis; Prieto-Marquez´ 2010a). The structure of dorsal and ventral margins are subparallel throughout most each individual denticle for most hadrosaurid species, of its length. The splenial is slightly expanded dorsoven- particularly those showing reduction of marginal dentic- trally near the articulation with the caudoventral margin ulation, is known to the author only in a handful of the dentary by means of two wedge-shaped process, of taxa. For example, the greatly reduced denticles in one forming the rostrodorsal and the other the rostroventral Edmontosaurus, barely visible with the naked eye, are corner of the bone. composed of densely appressed clusters of tubercles, whereas the small papillae of the basal hadrosauroid Angular. The angular is a long and mediolaterally Lophorhothon atopus are composed of mesiolabially compressed strip of bone that forms the ventral third of the arranged triads of knob-like tubercles (Prieto-Marquez´ medial surface of the postdentary region of the mandible 2008, fig. B16). Thus, it is uncertain whether the quincunx- (Fig. 14A–C). Rostrally, it extends beyond the level of the like arrangement of denticles seen in AMNH 5799 splenial–dentary articulation ending ventral to the caudal and TMM 42876 is also present in other hadrosaurid third of the dental battery. Caudally, the angular wedges specimens. forming a gently curved and sharp apex underlying the The maxilla (Fig. 13E) contains 47 tooth positions, as slightly arcuate caudoventral border of the splenial. noted by Brown (1910). None of the labial enamelled Articular. This is the smallest element in the mandible, sides of the maxillary tooth crowns were observable in a saddle-shaped bone that contributes to the retroarticular the mounted AMNH 5799. However, Brown (1910, p. 274) process with the caudal process of the surangular (Fig. 14C). described the margins of those teeth as being “smooth”, The articular is mediolaterally compressed, more so which suggests either the absence or extreme miniaturiza- ventrally than dorsally, and is ‘sandwiched’ between the tion of denticles. surangular and the splenial. Specifically, the concave lateral surface of the articular contacts the medial surface of the Axial skeleton caudal process of the surangular, whereas the convex medial Atlas. The atlas is a ring-shaped structure composed of an Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 surface of the articular meets the lateral surface of the arcuate intercentrum and a neural arch (Fig. 15). The inter- splenial. centrum wedges cranioventrally and its craniodorsal surface Dentition. The dental battery of the dentary contains 42 is strongly concave. The caudal surface is nearly vertically tooth positions and at least four teeth per alveolus arranged oriented and dorsoventrally convex. The two lateral halves dorsoventrally. The occlusal surface shows a maximum of the neural arch are strongly compressed mediolaterally. of three functional teeth arranged mediolaterally. Tooth Each half is craniocaudally expanded at mid height. Adja- crowns are lanceolate and, on average, have a height/width cent and above the maximum craniocaudal width, the neural ratio of 2.9 (Fig. 14E, F). The enamelled surface of each arch is craniocaudally constricted. The craniodorsal border tooth crown in AMNH 5799 contains a prominent single of this constriction is crescentic. The dorsal region of each median ridge. This ridge always occupies a central position, half of the neural arch extends both cranially and caudally but it is variably sinuous or straight among dentary crowns. forming wedge-shaped projections. The posterior projec- Denticles are diminutive and present in both the mesial and tion is also mediolaterally expanded toward the caudodorsal distal margins of dentary crowns. They consist of widely margin of the neural arch. Skeletal morphology of Kritosaurus navajovius 27

Re-evaluation of hadrosaurid specimens and than the infratemporal constriction, and the infratemporal taxa previously referred to Kritosaurus margin is wider than the orbital margin. The medial wing of the prefrontal in species of Kritosaurus does not reach Is Naashoibitosaurus distinct from the great width seen in N. ostromi; the prefrontal wing is Kritosaurus? as wide as the caudal nasal process in Kritosaurus (e.g. Horner (1992) referred to Kritosaurus navajovius two BYU 12950), whereas in NMMNH P-16106 it is twice partial skulls collected from late Campanian strata of the as wide as the nasal at its narrowest point. Likewise, the Kirtland Formation in San Juan County, north-western quadrate of Kritosaurus (e.g. K. navajovius AMNH 5799 New Mexico. Soon after Horner’s referral, Hunt & Lucas and USNM 8629) is straight, whereas that of NMMNH P- (1993) removed those skulls from K. navajovius and made 161606 displays a caudal curvature along the proximal third them the holotype specimens of two new hadrosaurids, of the element. Notably, the frontal does not reach the orbital Anasazisaurus [= Kritosaurus] horneri (BYU 12950; margin in N. ostromi due to the articulation between the Fig. 19) and Naashoibitosaurus ostromi (NMMNH P- prefrontal and postorbital, in contrast to the frontal contri- 16106; Fig. 21). Since then, the taxonomic status of these bution to the orbit present in K. navajovius. The rostral two taxa has seen little consensus, with some authors edge of the trigeminal foramen is continuous in K. nava- regarding them as junior synonyms of K. navajovius jovius USNM 8629, whereas it opens onto an ophthalmic sulcus in N. ostromi. The dorsal region of the infratempo- (Williamson 2000; Wagner 2001; Prieto-Marquez´ 2010a) and others as valid distinct species (Horner et al. 2004; ral fenestra is rostrocaudally narrower than the orbit in N. Lucas et al. 2006; Sullivan & Lucas 2006). ostromi, but it is wider than the orbit in Kritosaurus (e.g. NMMNH P-16106 is the holotype and the only known K. navajovius, AMNH 5799). Finally, the dorsal margin of example of Naashoibitosaurus ostromi. It consists of a the infratemporal fenestra lies approximately at the same well-preserved skull lacking the premaxillae and mandible, level than the dorsal margin of the orbit and the squamosal ramus of the postorbital gently slopes rostroventrally form- and includes a partial left humerus and various cervical ◦ and dorsal vertebrae (Fig. 21). Hunt & Lucas (1993, pp. inga5 angle with the long axis of the maxillary tooth row. 82–83) provided the following differential diagnosis of N. In contrast, in species of Kritosaurus (e.g. AMNH 5799 and ostromi: “Differs from other members of the family, except BYU 12950) the dorsal margin of the infratemporal fenes- Gryposaurus, in possessing a nasal arch that rises above tra lies well above the dorsal margin of the orbit and the rostroventral slope of the squamosal ramus of the postor- the rostral end of the orbits; differs from Gryposaurus in ◦ possessing nasals that bifurcate caudally so that the frontals bital is substantially greater, forming an angle of 21 with extend rostrally between the nasals along the midline; and in the maxillary tooth row. possessing nasals whose caudal processes are overlapped by In referring NMMNH P-16106 to Kritosaurus nava- extensive medial wings of the prefrontals so that it appears jovius, Horner (1992) suggested that the nasal arch in the in dorsal view that the transverse width of the nasals is former represents a subadult condition, thus opening the narrower than the transverse width of the prefrontals”. possibility that later in ontogeny the nasal could change Naashoibitosaurus ostromi differs from species of into the morphology seen in BYU 12950. However, such Kritosaurus in numerous characters of the skull (Online a possibility is not testable given the material available for Supplementary Material Table 2). In NMMNH P-16106, Kritosaurus spp. and Naashoibitosaurus. Still, comparative the angle between the rostrodorsal margin of the maxilla and osteology of the relative position of the dorsal margin of the the tooth row is 32◦; the base of the dorsal process is centred infratemporal fenestra supports consideration of NMMNH on the mid-length of the maxilla. In contrast, the maxilla P-16106 as a subadult individual. At least in Gryposaurus Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 of Kritosaurus (e.g. K. horneri BYU 12950 and tenta- notabilis, the rostroventral slope of the squamosal ramus of tively also in AMNH 5799) has a substantially more steeply the postorbital increases during ontogeny, so that the dorsal oriented rostrodorsal margin, forming a angle greater than margin of the infratemporal fenestra becomes gradually 40◦ with the tooth row; also unlike N. ostromi, the base of the more dorsally positioned relative to the dorsal margin of the dorsal process in Kritosaurus lies rostral to the mid-length orbit (Fig. 22). Farke & Herrero (in press) recovered this of the element. Furthermore, the jugal of N. ostromi differs trend by showing negative correlation between skull width from that of Kritosaurus in having a moderately expanded and the angle of postorbital flexion (lower angles indicating caudoventral flange (i.e. flange depth/infratemporal depth increased relative elevation of the caudodorsal region of ratio less than 1.55), an infratemporal constriction that the skull) in Gryposaurus spp. The rostral jugal to caudal is deeper than the orbital constriction, and orbital and quadrate length of NMMNH P-16106 is comparable to that infratemporal margins subequally wide. In contrast, the of the subadult G. notabilis specimen TMP 80.22.1 (Fig. 22; jugal of Kritosaurus (e.g. K. navajovius AMNH 5799) Online Supplementary Material Table 4); thus, both indi- displays a caudoventral flange depth/infratemporal depth viduals might correspond to similar ontogenetic stages. It ratio greater than 1.55, the orbital constriction is deeper is therefore conceivable that adults of N. ostromi could display steeply inclined caudodorsal regions of the skull 28 A. Prieto-Marquez´ Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 21. Partial holotype skull of Naashoibitosaurus ostromi, NMMNH P-16106. A, dorsal view; B, left lateral view.

roof similar to K. navajovius, K. horneri and G. notabilis. the infratemporal fenestra in N. ostromi is likely to remain Less variable through ontogeny is the size of the infratem- narrower than the orbit in adulthood and represents a useful poral fenestra relative to that of the orbit. In TMP 80.22.1 character for distinguishing this taxon from Kritosaurus, the infratemporal fenestra already has a greater area than the as are the other aforementioned characters of the skull, orbit, a condition that is also present in the larger G. nota- which have been shown to be phylogenetically informa- bilis specimens (e.g. ROM 764 and CMN 2278). Therefore, tive (Prieto-Marquez´ 2008, 2010a). Considered together, Skeletal morphology of Kritosaurus navajovius 29

Figure 22. Bivariate plot showing positive correlation in Gryposaurus notabilis between the rostroventral slope of the squamosal ramus of the postorbital and skull length (using the distance between the rostral process of the jugal and the caudal margin of the quadrate as proxy for skull length). Naashoibitosaurus ostromi (NMMNH P-16106) is added to the plot for comparison with TMP 80.22.1 but was not included in the calculation of the correlation coefficient.

the morphological differences existing between NMMNH P-16106 and species of Kritosaurus support the validity of Naashoibitosaurus ostromi as a distinct taxon.

Other specimens previously referred to Figure 23. Partial elements of AMNH 5797. A, left maxilla in Kritosaurus lateral view; B, medial view of the same; C, fragmentary coronoid process of right dentary in lateral view; D, caudal view of the same; For many decades, Kritosaurus has become a dustbin E, medial view of the same. genus to which numerous hadrosaurid specimens have been assigned, particularly those collected in Late Cretaceous strata of southern North America. A list of such exem- gular proportions (e.g. Gryposaurus monumentensis,RAM plars, with a revision of their taxonomic status in relation 6797; Prosaurolophus maximus, TMP 84.1.1) and, consid- to the revised diagnosis of Kritosaurus presented above, ering that most of the rostral third of the maxilla (rostral to is provided in Table 1 of the Online Supplementary Mate- the jugal articular surface) is missing in AMNH 5797, when rial. Some of these materials are discussed below due to Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 complete this element would have an estimated length of their more complete skeletal representation and/or impli- 650 mm. Such dimensions closely approach the length of cations for a more complete understanding of the anatomy the maxilla of the largest recorded saurolophine, Shantun- and distribution of Kritosaurus. gosaurus giganteus (Hu et al. 2001). AMNH 5797. This fragmentary specimen was collected The maxilla of AMNH 5797 (Fig. 23A, B) preserves in 1913 from strata corresponding to the Maastrichtian a minimum of 43 tooth positions and a maximum of two Naashoibito Member of the Kirtland Formation near teeth arranged mediolaterally on the occlusal surface. The Kimbetoh Wash, San Juan County, north-western New bone displays a relatively shallow lateral profile, so that the Mexico (Sinclair & Granger 1914; Lehman 1981; height from the dorsal edge of the partial dorsal process Williamson 2000; Kirkland et al. 2006). It consists of to the alveolar margin is about 40% of the total rostrocau- a partial left maxilla, the coronoid process of a left dal length of the bone. The articular surface for the jugal dentary, and various unidentified bone and dental fragments occupies a large portion of the lateral maxillary surface and (Fig. 23). The preserved regions of the maxilla measure the ventral jugal tubercle is very prominent, located at a 437 mm in length; based on comparisons with complete and short distance from the alveolar margin of the maxilla. The disarticulated maxillae with similar elongate and subrectan- ectopterygoid shelf is proportionately long, comprising half 30 A. Prieto-Marquez´

of the preserved length of the maxilla, and curves caudoven- and the proximal edentulous margin is notably short, being trally near the caudal end of the element. In occlusal view, less than 20% of the dental battery length (Fig. 17B, C). the maxilla shows a sigmoid profile. Because the rostrodor- Furthermore, USNM 8629 shares additional characters sal region of the AMNH 5797 maxilla is missing, it is with AMNH 5799, such as a prominent squamosal buttress not possible to ascertain whether the rostrodorsal margin in the quadrate; a jugal with deeper orbital constriction, formed a steep angle (i.e. 40◦ or more) with the tooth row wide embayment of the ventral margin, very prominent and whether the dorsal process was located rostral to the caudoventral flange, greatly elongate quadratojugal flange, mid-length of the maxilla, as in Kritosaurus horneri (BYU and greatly broadened infratemporal margin; and dentary 12950). The other regions observable both in Kritosaurus tooth crowns with a height/width ratio near 2.9. and AMNH 5797 do not contain taxonomically informa- Gilmore (1935) pointed out that the margins of the tive characters that would allow evaluation of whether these dentary teeth in USNM 8629 are ‘smooth’. However, exam- specimens belong to the same taxon. The coronoid process ination of the gross morphology of the AMNH 5799 dentary of AMNH 5797 only informs of the hadrosaurid affinities teeth also results in a smooth appearance of their margins. of this specimen (Fig. 23C–E). Consequently, neither the Yet, USNM 8629 exhibits marginal denticulation, albeit coronoid process nor the partial maxilla display diagnostic notably reduced as in K. navajovius and consisting of characters allowing referral of AMNH 5797 to Kritosaurus diminutive denticles that are barely visible with the naked or any other known hadrosaurid. The specimen is here eye (Fig. 17A). referred to Saurolophinae indeterminate, concurring with YPM-PU 16970. Horner (1979) briefly described two Williamson (2000). partial skeletons (YPM-PU 16969 and 16970) collected USNM 8629. In 1916, J. B. Reeside collected a frag- in 1901 from the late Campanian marine Bearpaw Shale of mentary saurolophine specimen also from the Kirtland south-central Montana and referred them to Gryposaurus Formation near Kimbetoh Wash, San Juan County, north- notabilis (as Hadrosaurus [Kritosaurus] notabilis). One western New Mexico (Gilmore 1935). The fossil includes of the specimens, YPM-PU 16970, was later referred by the caudal skull roof with the braincase, postorbitals, Horner (1992) to cf. Kritosaurus sp. It consists of a partial jugal, quadrates and partial occiput, as well as mandibu- cranium with fragmentary articulated skull roof and nearly lar elements and cranialmost cervical vertebrae (Figs 16, complete braincase, maxillae, left lacrimal, partial ptery- 17). This specimen has been referred to Kritosaurus (Lucas goid, left palatine, vomers, and partial postcrania includ- et al. 1987), K. navajovius (Gilmore 1935; Brett-Surman ing several cervical vertebrae, scapulae, left pubis, right 1989; Horner 1992), and Hadrosaurinae indeterminate ilium and several manual and hindlimb elements (Fig. 24). (Williamson 2000). However, only Gilmore (1935) and According to Horner (1992), YPM-PU 16970 has a slight Williamson (2000) briefly provided justification for their lateral ridge extending from a crest that lies dorsal to the referrals. rostral margin of the orbit, and the nasals are mediolater- Gilmore (1935, p. 161) pointed out that USNM 8629 ally wide over the crest and bifurcate caudally, attributes “agrees closely” morphologically with Kritosaurus nava- that presumably supported referral of the specimen to jovius, except in the marginal denticulation of dentary teeth. Kritosaurus. In contrast, Williamson (2000) deemed the specimen devoid The nasals preserve most of the medial processes and of sufficient diagnostic characters at a lower level than the caudal regions that contribute to the skull roof. The ‘Hadrosaurinae’. Yet, examination of USNM 8629 reveals elevated area rostromedial and dorsal to the orbit proba- that this specimen possesses many of the characters that bly represents a nasal crest, as correctly noted by Horner confirm the diagnostic combination of Kritosaurus and K. (1992). The crest is mediolaterally compressed and prob- Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 navajovius presented above. These characters support refer- ably was morphologically similar to the nasal protuber- ral of USNM 8629 to K. navajovius. ance (commonly arcuate) present in species of Gryposaurus Specifically, the rostral border of the left frontal of USNM (Prieto-Marquez´ 2010b). However, the summit of the nasal 8629 shows a shallow V-shaped excavation that probably crest has been truncated and eroded away (Fig. 24A). There served as contact surface for a caudal process of the nasal is no evidence of the caudal folding of the nasal crest (Fig. 16A, B); the frontal likely extends onto the orbital that characterizes Kritosaurus horneri (BYU 12950). As rim between the prefrontal and postorbital, as evidenced in Gryposaurus spp. (e.g. G. notabilis, ROM 873) and K. in the more complete triangular lateral projection of the horneri, there is a smooth and shallow concavity ventral right frontal (the apex of which is not preserved); the dorsal and slightly rostral to the crest, on the lateral surface of margin of the infratemporal fenestra lies well above the the nasals. Such a concavity constitutes the caudodorsal dorsal orbital rim and, consequently, the caudal region of the extent of the circumnarial fossa. The dorsal surface of the skull roof is steeply inclined rostroventrally (Fig. 16C); the caudal region of the nasals, as well as the ectocranial surface quadrate is straight; and in the dentary, the ventral deflec- of the frontals, is broken in several fragments that have tion originates near the rostral end of the dental battery, been reassembled and small pieces of bone are missing. Skeletal morphology of Kritosaurus navajovius 31 Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 24. Selected cranial and appendicular elements of the Gryposaurus sp. specimen YPM-PU 19670. A, partial skull roof and braincase in dorsal view; B, left lateral view of the braincase; C, partial skull roof and braincase in right lateral view; D, ventral view of the same; E, left lacrimal in lateral view; F, right maxilla, rostral process of the jugal and partial premaxillay lateral process in lateral view; G, medial view of the same; H, right ilium in lateral view; I, left pubis in lateral view. Abbreviations: ob, orbitosphenoid; op-ex, opisthotic–exoccipital complex; ls, laterosphenoid; mf, metotic foramen; pr, prootic; V, foramen for trigeminal nerve; V1, ophthalmic sulcus; V3, mandibular ramus of trigeminal foramen; VII, foramen for facial nerve; VIII, fenestra vestibuli. 32 A. Prieto-Marquez´

This fragmentary preservation, along with abrasion of some both premaxillae and probably the rostralmost portions of areas, prevented the unambiguous determination of whether the maxillae (Fig. 18A–C). The latter, however, are mostly the frontals intervene sagitally between the paired nasal obscured by matrix and only the mediodorsal process of processes, as in Kritosaurus navajovius and as suggested the left maxilla can be seen through the narial fenestra. by Horner (1992), or whether the nasals formed two narrow It is uncertain whether this process would be exposed median processes that insert between the frontals at the through the narial foramen in life, since the dorsal margin sagittal plane of the skull, as occurs in Gryposaurus (Gates of the lateral process of the premaxilla shows signs of abra- & Sampson 2007). The mediolateral width of the nasals sion; a complete dorsal margin might have concealed the is comparable to that in both Gryposaurus (e.g. G. nota- mediodorsal maxillary process from lateral exposure. The bilis, CMN 2278) and K. navajovius (AMNH 5799). The mandible consists of an almost complete predentary and postorbital, particularly the left one, projects rostrolater- the symphyseal region and rostral dentigerous regions of ally forming an apex that probably contributed to the both dentaries, with the dentition still partially embedded orbital rim, as in K. navajovius, Gryposaurus spp. and in matrix. Brachylophosaurini (Fig. 24A). Notably, the braincase of Kirkland et al. (2006) and Serrano-Branas˜ (2006) YPM-PU 16970 shows that the trigeminal foramen opens referred IGM 6685 to Kritosaurus sp. on the basis of the rostrally onto a wide ophthalmic sulcus (Fig. 24B). The following characters: reflected premaxillary oral margin, basisphenoid has a median process projecting from the massive and deep dentary that is strongly deflected ventrally transversal ridge that extends between the basipterygoid and shows a short edentulous portion, and remarkably processes. The latter two braincase characters are present deep predentary being mediolaterally narrower than in in Gryposaurus (Gates & Sampson 2007; Prieto-Marquez´ Gryposaurus. The reflected (i.e. caudodorsally folded) 2010b) and other saurolophines (Prieto-Marquez,´ 2010a), morphology of the premaxillary oral margin is a condition but not in K. navajovius (AMNH 5799, USNM 8629). shared with species of Gryposaurus (Fig. 18D), Prosaurolo- The right maxilla shares with both Gryposaurus (Prieto- phus (Fig. 18H) and Saurolophus (Brown 1912). It is Marquez´ 2010b, 2012) and K. navajovius (e.g. AMNH not known whether this condition is also present in the 5799) a tall and steeply rostroventrally inclined rostrodor- type specimen of Kritosaurus navajovius, given the frag- sal margin (Fig. 24F). Another character shared among mentary preservation of its premaxillae. Among those YPM-PU 16970, Gryposaurus and K. navajovius is a hadrosaurid taxa with reflected premaxillary oral margins, rostral convexity on the ventral margin of the lacrimal the premaxilla of IGM 6685 (Fig. 18E) is most similar (Prieto-Marquez´ 2008). to that of Gryposaurus spp. (e.g. ROM 873; Fig. 18D). The pubis of YPM-PU 16970 displays a subrectangu- In IGM 6685 and all known species of Gryposaurus the lar and ventrally deflected distal blade of the prepubic premaxilla is rostrocaudally narrower than in Prosaurolo- process (Fig. 24I). This morphology is typically present phus and Saurolophus, with nearly parallel lateral and in members of the Gryposaurus–Prosaurolophus clade of medial processes that do not diverge substantially towards Prieto-Marquez´ (2010a), such as G. notabilis (e.g. ROM the oral margin. Unlike the broad and arcuate rostrolat- 764), G. latidens (e.g. AMNH 5465), P. maximus (e.g. eral corner of the oral margin present in Prosaurolophus ROM 787) and Secernosaurus koerneri (MACN-RN 2). and Saurolophus, those of Gryposaurus and IGM 6685 It is, however, unknown in Kritosaurus navajovius because are subsquared (a condition that is further accentuated no pubis is preserved for this taxon. in the Mexican specimen). As noted by Kirkland et al. In conclusion, YPM-PU 16970 is here referred to (2006), the reflected portion of the premaxillary oral margin Gryposaurus sp. based on the combination of a medio- in IGM 6685 becomes gradually deeper dorsoventrally

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 laterally narrow and unfolded nasal protuberance, lightly towards the sagittal plane of the snout. In this regard, it is incised caudal extent of the circumnarial fossa adjacent to deeper and distinct from the premaxillae of Gryposaurus, the base of the crest, rostrolateral apex of the frontal form- Saurolophus and Prosaurolophus. Although it appears that ing part of the orbital margin, open ophthalmic sulcus of the oral margin of AMNH 5799 is also deeper rostrome- the laterosphenoid, median process on the transverse ridge dially than in Gryposaurus, Saurolophus and Prosaurolo- of the basisphenoid, and subrectangular distal blade of the phus, the fragmentary and abraded state of preservation of prepubic process of the pubis. AMNH 5799 prevents an unambiguous conclusion as to whether the same morphology occurring in IGM 6685 was IGM 6685. This material consists of a sandstone block present in K. navajovius. containing the rostral region of the cranium of a large Serrano-Branas˜ (2006) and Kirkland et al. (2006) were hadrosaurid (Fig. 18). The specimen was collected in 1987 correct in comparing the strong deflection and short from late Campanian strata of the Cerro del Pueblo Forma- proximal edentulous margin of IGM 6685 with that of tion, in Presa de San Antonio, Parras de la Fuente, central Kritosaurus navajovius (Fig. 18A, C). Specifically, the Parras Basin, Coahuila, Mexico (Kirkland et al. 2000, ventral margin of the rostral region of the IGM 6685 2006). The skull is represented by the rostral regions of dentary forms a 35◦ angle with the alveolar margin of the Skeletal morphology of Kritosaurus navajovius 33

tooth row. This value is nearly identical to that of AMNH tary of AMNH 5799 is likely to be a preservational 5799 (see description above). The length of the proximal artefact. edentulous border in IGM 6685 equals approximately the Notwithstanding the non-overlapping premaxillary char- combined breadth of 4–5 tooth crowns, as in AMNH 5799 acters between AMNH 5799 and IGM 6685, the combi- and USNM 8629. Among saurolophine species, high angles nation of the predentary and dentary characters shared of ventral deflection of the dentary similar to those occur- by these specimens suffice to distinguish the Coahuila ring in K. navajovius and IGM 6685 are only present in specimen from all hadrosaurids, except Kritosaurus nava- Gryposaurus monumentensis (e.g. 35◦ in RAM 6797) and jovius. Because, in combination, such mandibular charac- approached by G. notabilis (29◦ in ROM 873, but only 23◦ ters conform to the diagnosis of this taxon presented above, in CMN 2278) (Prieto-Marquez´ 2008). However, unlike in IGM 6685 is referable to Kritosaurus navajovius. K. navajovius and IGM 6685, in species of Gryposaurus the proximal edentulous margin is substantially longer, being PASAC-1. This specimen (Fig. 25) represents the most between 27% (e.g. G. notabilis, CMN 873) and 35% (e.g. G. complete hadrosaurid skeleton found in Mexico. It was latidens, AMNH 5465) of the dental battery length (as collected in 2001 from a site south-west of the town of defined in Prieto-Marquez´ 2008, fig. C12). Secernosaurus Sabinas, Coahuila, from strata belonging to the latest koerneri possesses a proximal edentulous margin of the Campanian Olmos Formation (Kirkland et al. 2006). dentary as short as in K. navajovius; however, the ventral PASAC-1 consists of a partial skull including the brain- deflection in S. koerneri is less prominent (Prieto-Marquez´ case, partial pterygoid and ectopterygoid, left maxilla, right & Salinas 2010). Two additional characters shared by K. postorbital, quadratojugal, quadrates and both dentaries, navajovius and IGM 6685 are the straight dorsal margin of and postcrania composed of over 20 presacral vertebrae, the deflected symphyseal process of the dentary and the fact sacrum, numerous caudal vertebrae, ribs, left scapula and that the ventral deflection originates near the rostral end of coracoid, partial ilium, ischium and pubis, and various limb the dental battery. elements (Kirkland et al. 2006). The specimen was referred The predentary of IGM 6685 (Fig. 18A–C) shares several to Kritosaurus sp. by Serrano-Branas˜ (2006) and Kirkland characters with that of AMNH 5799. The rostral surface of et al. (2006) based on the elongate, slender quadrate, and the IGM 6685 predentary forms a 67◦ angle with the long the strong ventral flexion of the dentary near the rostral end axis of the lateral rami, a value that is very similar to the of the tooth row. angle measured in AMNH 5799. As in K. navajovius,the The subrectangular lateral profile of the maxilla noted depth of the rostral surface of the predentary (excluding by Kirkland et al. (2006) and Serrano-Branas˜ (2006) is the ventral median process) is approximately 50% of the likely enhanced by lack of preservation of the rostral third mediolateral width of the oral margin. The right lateral of the element (a greater portion missing than noted by ramus of the predentary of IGM 6685 is 1.5 times longer Kirkland et al. 2006, fig. 8Q) and the fact that the entire than the maximum mediolateral width of the bone, thus dorsal process and dorsal margin of the maxilla rostral to indicating a length/width ratio nearly identical to that of the palatine ridge are not preserved (Fig. 25G, H). In the AMNH 5799. absence of these maxillary regions, there are insufficient Serrano-Branas˜ (2006) noted that IGM 6685 displays a informative characters in the maxilla of PASAC-1 for eluci- concave lateral oral margin of the predentary. In lateral view, dating its taxonomic affinities, particularly in relation to K. the rostrolateral border of the predentary forms a 150◦ angle navajovius. The left quadrate of PASAC-1 is gently curved with the caudal extent of the more complete lateral rami. caudally near its proximal articular end, thus lacking the Similar curvatures are common among hadrosaurid preden- straight lateral profile seen in AMNH 5799 (Fig. 25L). In

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 taries; examples are the predentary of Brachylophosaurus the braincase, however, the rostral margin of the trigemi- canadensis (e.g. CMN 8893 and MOR 1071-7-28-98-299), nal foramen of PASAC-1 does not open into an ophthalmic Maiasaura peeblesorum (e.g. ROM 44770), Gryposaurus sulcus (Fig. 25C), hitherto a condition only seen among notabilis (e.g. MSNM V345) and Prosaurolophus maximus hadrosaurids in K. navajovius (USNM 8629, Fig. 16C) and (e.g. CMN 2870). Likewise, a wide variation exists in the Lambeosaurus spp. (Evans & Reisz 2007). The exoccipital development of this curvature, ranging from the extremely shelf above the foramen magnum is remarkably extensive concave lateral oral margin of the predentary of ROM in PASAC-1, approximately longer rostrocaudally than the 44770 to the gentle curvature present in CMN 2870. This diameter of the foramen magnum (Fig. 25E). This condi- condition, however, contrasts with the horizontal rostro- tion is present in those saurolophines for which this region lateral margin seen in the holotype of Kritosaurus nava- of the occiput is known, except Brachylophosaurini. jovius. Yet, the entire left lateral predentary oral margin In the mandible, the ventral deflection of the dentary of that specimen is reconstructed, whereas the rostro- certainly occurs near the rostral end of the tooth row lateral border of the right margin is abraded and bone (Fig. 25I), as in AMNH 5799 and the Mexican IGM 6685. is missing (Fig. 13). Therefore, the apparently horizon- However, the angle of deflection in PASAC-1 is not as great tal orientation of the rostrolateral margin of the preden- as in AMNH 5799 and IGM 6685. In the more complete left 34 A. Prieto-Marquez´ Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013

Figure 25. Selected cranial and appendicular elements of PASAC-1. A, partial braincase in rostral view; B, left lateral view of the same; C, left lateral view of neurocranial foramina; D, caudal view of occiput; E, partial braincase in ventral view; F, partial right squamosal in lateral view; G, partial right maxilla in lateral view; H, medial view of the same; I, left dentary in lingual view; J, partial right dentary in lingual view; K, partial left pubis in lateral view; L, left quadrate missing its distal end in lateral view. Abbreviations: ex, exoccipital; ls, laterosphenoid; mf, metotic foramen; pr, prootic; V,foramen for trigeminal nerve; VII, foramen for facial nerve; VIII, fenestra vestibuli. Skeletal morphology of Kritosaurus navajovius 35

dentary of PASAC-1, the ventral border of the symphyseal group from which other hadrosaurids with more deeply process forms a 28◦ angle with the long axis of the dental excavated circumnarial fossae and elaborate supracranial battery. This angle falls within the range of Gryposaurus structures evolved. Horner (1992) presented yet another notabilis (Prieto-Marquez´ 2008, fig. C17) and is substan- hypothesis in which Kritosaurus shared a most recent tially less than the minimum of 35◦ of deflection reached in common ancestor with Saurolophus, these two genera K. navajovius. The dorsal margin of the edentulous region of then forming a clade with Prosaurolophus. According to the dentary is heavily eroded in the left dentary and incom- Horner (1992), Kritosaurus shares with Saurolophus a nasal pletely preserved in the right one, so that the relative length crest that extends caudodorsal to the rostral end of the of the proximal endentulous border and the medial profile frontal, whereas these two genera share with Prosaurolo- of the predentary margin cannot be established. Thus, it phus a caudal end of the circumnarial fossa located is not possible to ascertain whether the predentary margin dorsal or caudal to the rostral orbital margin, caudal nasal was straight, as in AMNH 5799, or whether the proximal processes, nasal crest, and V-shaped caudal end of the border was as short as in K. navajovius. narial foramen. More recently, Hu et al. (2001) allied The pubis of PASAC-1 is informative in the possession of Kritosaurus to a clade of solid-crested forms like Saurolo- a subrectangular and ventrally deflected distal blade of the phus, Prosaurolophus, Lophorhothon and Tsintaosaurus. prepubic process (Fig. 25K). As noted above, this morphol- Wagner (2001) positioned Kritosaurus as the sister taxon ogy characterizes species of Gryposaurus (e.g. G. latidens, to Hadrosaurus, the two genera forming a clade of basal AMNH 5465), Prosaurolophus maximus (e.g. ROM 787), hadrosaurids. and Secernosaurus koerneri (MACN-RN 2). Yet, no pelvic Many of the more recent cladistic studies dealing elements are known for the type and referred specimens of with the interrelationships of unadorned and solid-crested Kritosaurus navajovius. hadrosaurids have excluded Kritosaurus from their anal- In summary, the morphological differences existing yses (Weishampel & Horner 1990; Horner et al. 2004; between PASAC-1 and Kritosaurus navajovius outnum- Gates & Sampson 2007; Cuthbertson & Holmes 2010; ber the similarities between these animals. The Sabinas Bell 2011a, b). Exceptions to this trend are the analyses hadrosaurid is not referable to Kritosaurus because it lacks of Prieto-Marquez´ (2010a) and Gates et al. (2011). On most of the characters integrating the diagnostic unique one hand, the analysis of Prieto-Marquez´ (2010a) showed combination of this taxon. Consequently, it is referred to Kritosaurus navajovius (synonymized with Anasazisaurus Saurolophinae indeterminate. horneri and Naashoibitosaurus ostromi)asamember of a speciose clade including Prosaurolophus, Saurolo- phus and Gryposaurus, as the sister taxon to the Phylogenetic affinities of Kritosaurus and the Gryposaurus–Secernosaurus clade. On the other hand, the interrelationships of kritosaurin study of Gates et al. (2011) supported a closer relation- saurolophines ship of the genus Kritosaurus with Brachylophosaurini Soon after its discovery, Kritosaurus was featured in numer- and Gryposaurus than with forms such as Prosaurolophus, ous phylogenetic hypotheses of Hadrosauridae, either as Saurolophus and Edmontosaurus. a distinct taxon or as senior synonym of Gryposaurus. In order to test the above hypotheses, the phylogenetic However, only a few of these hypotheses were derived from position of Kritosaurus navajovius was reassessed using numerical cladistic analyses. Thus, in early pre-cladistic maximum parsimony analysis. The character dataset times, authors agreed in including Kritosaurus among crest- consisted of 265 equally weighted and unordered morpho- less or solid-crested hadrosaurids (Brown 1914; Lambe logical characters (179 cranial and 86 postcranial; see

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 1920; Nopcsa 1928; von Huene 1956; Young1958). Lull & Online Supplementary Material appendices 1, 2). The Wright (1942) included Kritosaurus navajovius in one of character dataset presented in Appendix 1 is a revision their three lineages of ‘flat-headed’ hadrosaurids. Accord- of that of Prieto-Marquez´ (2010a). Counting Kritosaurus ing to these authors, Gryposaurus notabilis would have navajovius, the analysis included 34 hadrosaur species: evolved into K. navajovius (apparently via anagenesis), and 23 Saurolophinae (sensu Prieto-Marquez´ 2010a), three these two taxa would have been morphologically interme- Lambeosaurinae and eight non-hadrosaurid Hadrosauria diate between crestless and lambeosaurine hadrosaurids. (sensu Wagner & Lehman 2009) constituting the outgroup Ostrom (1961) and Morris (1973) considered Kritosaurus taxa to Hadrosauridae. The search for the optimal tree as more closely related to Edmontosaurus than to any was conducted in TNT version 1.0 (Goloboff et al. 2008). other hadrosaurid. In contrast, Hopson (1975) and Brett- A heuristic search of 10 000 replicates using random Surman (1979, 1989) grouped Kritosaurus (inclusive of additional sequences was performed, followed by branch Gryposaurus) with Brachylophosaurus and Aralosaurus swapping by tree-bisection-reconnection saving up to to form one of the lineages in which they subdivided 10 trees per replicate. Bremer support (Bremer 1988) the non-hollow crested hadrosaurids (‘Hadrosaurinae’); was assessed by computing decay indices (Donoghue for Hopson (1975) ‘kritosaurs’ represented the ancestral et al. 1992) using MacClade version 4.0 (Maddison & 36 A. Prieto-Marquez´

Figure 26. The single most parsimonious tree resulting from the maximum parsimony analysis, showing the phylogenetic position of Kritosaurus and Kritosaurini within saurolophine hadrosaurids. Numbers above the branches indicate bootstrap frequencies, numbers below are decay indices.

Maddison 2003) and PAUP∗ version 4.0b10 (Swofford Kritosaurini (Lapparent & Lavocat 1955; Brett-Surman 2002). Bootstrap proportions (Felsenstein 1985) were also 1989), which constitutes the most speciose clade within calculated with PAUP∗, using 5000-replicate heuristic Saurolophinae, is unambiguously supported by: the rostral searches, where each search was conducted using random end of the dorsal process of the nasal not reaching the rostral additional sequences with branch-swapping by subtree margin of the narial foramen; ventral spur of the rostral

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 pruning and regrafting at 25 replicates. process of the jugal being as deep as or slightly deeper than it The analysis resulted in a single most parsimonious tree is wide proximally; wide and strongly concave margin of the of 614 steps (Consistency Index (CI) = 0.61; Retention jugal between the caudoventral and quadratojugal flanges; Index (RI) = 0.75), a score reached in 5476 of the 10, frontal with triangular rostrolateral projection ending in 000 random sequences (Fig. 26). The genus Kritosaurus a narrow apex (convergent in Brachylophosaurini); and is deeply nested within Saurolophinae and is more subrectangular dorsal region of infratemporal fenestra. closely related to the Gryposaurus–Secernosaurus clade Naashoibitosaurus ostromi was positioned as the sister than to other hadrosaurids. Unambiguous synapomorphies taxon to all other kritosaurins. The clade including all supporting inclusion of Kritosaurus within saurolophines kritosaurins except N. ostromi was supported by three include: a circumnarial depression with a premaxillary unambiguous synapomorphies: rostrodorsal margin of rostral fossa set rostral to the circumnarial fossa proper; maxilla dipping steeply ventrally, forming an angle of 40◦ the presence of premaxillary foramen located rostral and or greater with the tooth row; base of dorsal process and ventrolateral to the rostral margin of the narial foramen; and dorsolateral margin of maxilla located rostral to the mid- rostromedially broad prefrontal with subsquared rostrodor- length of the bone; and dorsal margin of the infratemporal sal orbital margin. fenestra positioned well above the dorsal margin of the Skeletal morphology of Kritosaurus navajovius 37

orbit, so that the caudal region of the skull roof is steeply Kritosaurin hadrosaurids lived in Laramidia during the inclined rostroventrally relative to the frontal plane. early Campanian (Prieto-Marquez´ 2010a, 2012) through Within Kritosaurus, the two species K. navajovius and probably the early Maastrichtian (Wagner 2001; Prieto- K. horneri are unambiguously united by the possession of Marquez´ & Salinas 2010). Although the area of Laramidia a wide dorsolateral margin of the maxilla that is as long represented less than 20% of that of the present-day as at least 40% of distance between the rostral end of the North America, dinosaurian diversity appears to have maxilla, and the caudoventral corner of orbital margin of been relatively high and palaeogeographical reconstruc- jugal. The two species also share a unique combination of tions of Late Cretaceous North America do not prevent characters in the jugal, frontal and infratemporal fenestra the following inferred biogeographical scenarios, with (see generic diagnosis above). north–south trending variations in kritosaurin geograph- Finally, the clade consisting of the three species of ical ranges. Thus, according to DIVA results, the most Gryposaurus and a subclade composed of the Big Bend recent common ancestor of Kritosaurini was present in UTEP OTU and the South American genera Secernosaurus southern Laramidia no later than the early Campanian and Willinaqake is united by the possession of a concave (Fig. 27). The subsequent evolutionary history of the medial profile of the dorsal margin of the symphyseal clade, that is, the split of the Naashoibitosaurus and process of the dentary and the caudal end of nasals insert- Kritosaurus lineages and the appearance (no later than the ing between the frontals at the sagittal plane of the skull early Campanian) of the most recent common ancestor of roof. the Gryposaurus–Secernosaurus clade, are also hypothe- sized to have occurred in southern Laramidia. Not later than the early Campanian, a dispersal event from southern Kritosaurin biogeography to northern Laramidia can explain the widespread distribu- tion throughout the continent of the most recent common Dispersal-vicariance analysis (DIVA; Ronquist 1997) was ancestor of the species of Gryposaurus (Fig. 27). Subse- implemented to infer the ancestral areas of the internal quently, a vicariant event taking place no later than the nodes of the phylogeny resulting from the parsimony anal- early Campanian would have resulted in the split of G. ysis. DIVA assumes allopatric speciation (resulting from latidens in northern Laramidia from the most recent vicariance) as a null hypothesis, and dispersal, extinction common ancestor of G. notabilis and G. monumentensis in and duplication as alternative hypotheses to explain the southern Laramidia; the occurrence in northern Laramidia observed distribution of taxa. It uses a model in which of G. notabilis was explained by a dispersal event from the vicariance, sympatric speciation, dispersal and extinction southern region of the continent. are given costs that are related to the likelihood of occur- In agreement with previous studies (Weishampel & rence of these events (Sanmart´ın & Ronquist 2004). Thus, Weishampel 1983; Bonaparte et al. 1984; Horner et al. vicariance and sympatric speciation receive a cost of zero, 2004; Prieto-Marquez´ 2010c), DIVA posited a disper- whereas dispersal and extinction have a cost of one per sal event from southern Laramidia to South America area unit added or deleted from the distribution (Ronquist during Campanian times, giving rise to a widespread 1997). The method was implemented in the program DIVA common ancestor for the Big Bend National Park (Texas) 1.1 (Ronquist 1996) using the optimization algorithm of saurolophine–Secernosaurus clade. Subsequently, a vicari- Ronquist (1997). It uses parsimony as the optimality crite- ant event occurring no later than the late Campa- rion, searching for the reconstruction that minimizes the nian would have given rise to the split of the Big number of dispersal and extinction events required to Bend kritosaurin in southern Laramidia from the South

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 explain the geographical distribution of terminal taxa. American genera Secernosaurus and Willinaqake.Theexis- For most of the Turonian through most of the Maas- tence of a land connection between the Americas during trichtian stages of the Late Cretaceous, an intercontinental the Late Cretaceous has been supported by several stud- seaway (the Cretaceous Western Interior Seaway) split the ies (Pough et al. 2004). Subduction of the southern part North American continent into two landmasses: Appalachia of the North American plate under the eastward-moving to the east and Laramidia to the west, a narrow strip of land Caribbean plate may have given rise to a Proto-Antillean that stretched from present-day Alaska to Mexico (Samp- volcanic arc (Duellman 2001; Pindell & Kennan 2001; son et al. 2010). Laramidia was further bounded on the west Hedges 2006). This chain of islands would have been by the Sevier Orogenic belt, a north–south trending moun- located between North and South America in the position tain range that extended from northern Canada through the currently occupied by Central America, thereby provid- south-western USA (Lawton 2008). For the DIVA, four ing a dispersal route for hadrosaurids and other vertebrates large continental areas were considered: the northern and during at least the Late Campanian (Hedges 2006). The southern regions of Laramidia, Asia and South America. connection may have been interrupted during the latest These areas contain the fossil record of all taxa under Campanian or Maastrichtian (Pindell & Kennan 2001), consideration. which is congruent with vicariance being involved in the 38 A. Prieto-Marquez´

Figure 27. Phylogram showing the ancestral area reconstruction for the various clades of the single most parsimonious tree resulting from parsimony analysis of 23 saurolophine species.

∗

Downloaded by [Mount Allison University 0Libraries] at 00:07 10 May 2013 evolution of the Secernosaurus–Salitral Moreno clade in Supplementary Material Table 6). The resulting MSM South America (Fig. 27). A similar scenario, whereby coefficient of 0.84 suggests the existence of a substantial the Caribbean plate carried ancient Mesozoic biota east- fit between the stratigraphy and phylogeny of kritosaurin wards, has been posited to explain the evolution of vari- saurolophines. Yet the p-value of 0.05 derived from a ous endemic terrestrial vertebrates in the Antilles (Hedges permutation test indicates that such fit is barely significant. 2006). The lack of a strongly significant stratigraphical fit is more The fit between the chronostratigraphical occurrence of congruent with the presence of several relatively long ghost hadrosaurid taxa and the order of branching events for lineages in kritosaurin phylogeny. In particular, the lineages the phylogenetic hypothesis presented here was evaluated leading to Naashoibitosaurus ostromi, Kritosaurus spp., using the Manhattan Stratigraphic Measure (Siddall 1998) and the Secernosaurus–Willinaqake clade imply missing as modified by Pol & Norell (2001; MSM∗). Conceptually, fossil records that span large portions of the Campanian. the MSM∗ is analogous to the consistency index (Kluge Such ghost lineages are mainly caused by the topology & Farris 1969) and is based on the optimization of an age and late Campanian record of those taxa in relation to the character (Online Supplementary Material Table 5) using a position and early Campanian occurrence of Gryposaurus symmetrical Sankoff step matrix of age differences (Online latidens (Fig. 27). Skeletal morphology of Kritosaurus navajovius 39

Conclusions Sampson, and particularly T. A. Gates and A. A. Farke provided insightful comments during the preparation of The type specimen of the hadrosaurid Kritosaurus nava- the manuscript. J. Alicea skilfully prepared AMNH 5797. jovius, AMNH 5799, contains sufficient taxonomic infor- This study was supported by an Alexander von Humboldt mation for rediagnosing this species on the basis of Fellowship for Postdoctoral Researchers and the American a unique combination of mostly mandibular characters. Museum of Natural History through a Kalbfelisch Post- Anasazisaurus horneri is regarded as congeneric with doctoral Fellowship. Additional funds for the acquisition Kritosaurus navajovius. Therefore, Kritosaurus consists of of comparative anatomical data on other hadrosaurids was two species, K. navajovius and K. horneri, and the genus is provided by the Charlotte and Walter Kohler Charitable rediagnosed based on a unique combination of characters of Trust, the National Science Foundation (EAR 0207744 and the maxilla, infratemporal fenestra and frontal. K. horneri is DBI 0446224 grants to G. M. Erickson), and the Ministry of regarded as a separate species conditional upon the lack of Education and Science of Spain (CGL2005-07878-C02-01 overlapping autapomorphies in both species of Kritosaurus. grant to A. Galobart). Naashobitosaurus ostromi is a valid taxon and distinct from species of Kritosaurus in numerous characters of the skull. Supplementary material IGM 6685, a partial skull collected from the Cerro del Pueblo Formation in the Mexican state of Coahuia, is refer- Supplementary material is available online DOI: 10.1080/ able to K. navajovius, and extends the geographical range 14772019.2013.770417 of this species to northern Mexico. Kritosaurus is phylogenetically positioned within Saurolophinae as the sister taxon to a clade that References contains Gryposaurus and the Argentinian Secernosaurus– Willinaqake subclade. The latter three genera, together with Agnolin,F.L.& Martinelli, A. G. 2009. Fossil birds from Kritosaurus and Naashoibitosaurus, are included within the Late Cretaceous Los Alamitos Formation, R´ıo Negro the clade Kritosaurini. This clade is here defined and Province, Argentina. Journal of South American Earth diagnosed for the first time, and has a sister relationship Sciences, 27, 42–49. with the Prosaurolophus–Saurolophus clade. Kritosaurin Armstrong-Ziegler, J. G. 1980. Amphibia and Reptilia from the Campanian of New Mexico. Fieldiana, 4, 1–39. hadrosaurids are hypothesized to have originated in south- Baird, D. & Horner, J. R. 1977. A fresh look at the dinosaurs of ern Laramidia no later than the early Campanian. Subse- New Jersey and Delaware. Bulletin of the New Jersey Academy quently, members of the clade reached northern Laramidia of Sciences, 22, 50. and South America via dispersal no later than early and late Baird, D. & Horner, J. R. 1979. Cretaceous dinosaurs of North Campanian times, respectively. Carolina. Brimleyana, 2, 1–28. Bauer, C. M. 1916. Contributions to the geology and paleontology of the San Juan County, New Mexico. 1. Stratigraphy of a part of the Chaco River Valley. US Geological Survey, Professional Paper, 98P, 271–278. Acknowledgements Bell, P. R. 2011a. Redescription of the skull of Saurolophus osborni Brown 1912 (Ornithischia: Hadrosauridae). Creta- ceous Research, 32, 30–44. I thank M. A. Norell for allowing access to the holotype Bell, P. R. 2011b. Cranial osteology and ontogeny of Saurolo- of Kritosaurus navajovius and other hadrosaurid material phus angustirostris from the Late Cretaceous of Mongolia under his care. Thanks also to T. E. Williamson and T. with comments on Saurolophus osborni from Canada. Acta

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