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Cranial Variation in Gryposaurus and Biostratigraphy of Hadrosaurines (Ornithischia: Hadrosauridae) from the Dinosaur Park Formation of Alberta, Canada

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Cranial Variation in Gryposaurus and Biostratigraphy of Hadrosaurines (Ornithischia: Hadrosauridae) from the Dinosaur Park Formation of Alberta, Canada Canadian Journal of Earth Sciences Cranial variation in Gryposaurus and biostratigraphy of hadrosaurines (Ornithischia: Hadrosauridae) from the Dinosaur Park Formation of Alberta, Canada Journal: Canadian Journal of Earth Sciences Manuscript ID cjes-2019-0073.R1 Manuscript Type: Article Date Submitted by the 17-Aug-2019 Author: Complete List of Authors: Lowi-Merri, Talia; Royal Ontario Museum, Department of Natural History; University of Toronto, Ecology & Evolutionary Biology Evans, David C.; Royal Ontario Museum, Department of Natural History; University Draftof Toronto, Ecology & Evolutionary Biology dinosaur, geometric morphometrics, biostratigraphy, allometry, Keyword: Hadrosauridae Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? : https://mc06.manuscriptcentral.com/cjes-pubs Page 1 of 48 Canadian Journal of Earth Sciences 1 Cranial variation in Gryposaurus and biostratigraphy of hadrosaurines (Ornithischia: 2 Hadrosauridae) from the Dinosaur Park Formation of Alberta, Canada 3 4 Talia M. Lowi-Merria,b* and David C. Evansa,b 5 6 Affiliations 7 a. Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks St. Rm 8 3055, Toronto, ON M5S 3B2, Canada 9 b. Department of Natural History, Royal Ontario Museum, 100 Queens Park, Toronto, ON M5S 10 2C6, Canada 11 Draft 12 *Corresponding Author 13 Talia M. Lowi-Merri 14 E-mail Address: [email protected] 15 Mailing Address: Department of Natural History, Royal Ontario Museum, 100 Queens Park, Toronto, 16 ON M5S 2C6, Canada 17 Telephone number: +1 416-300-3757 18 19 20 21 22 23 24 1 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 2 of 48 25 26 ABSTRACT 27 The Dinosaur Park Formation (Campanian) of Alberta documents one of the most diverse 28 assemblages of hadrosaurine dinosaurs. Historically, two species of the genus Gryposaurus have 29 been recognized in the Dinosaur Park Formation, G. notabilis and G. incurvimanus, which are 30 differentiated primarily on their nasal arch morphology. These two species have recently been 31 suggested to represent either variable morphs within G. notabilis (e.g., ontogeny) or two distinct 32 taxa within an evolving Gryposaurus lineage (e.g., anagenesis). These alternative hypotheses 33 have never been adequately tested via detailed morphological comparisons, morphometrics, or 34 biostratigraphy. A geometric morphometric analysis of hadrosaurine skulls from the Dinosaur 35 Park Formation was performed to assessDraft the influence of ontogeny on skull morphology. G. 36 incurvimanus skulls were found to be distinctly smaller, and morphologically divergent from 37 those of G. notabilis, with larger G. notabilis skulls having higher nasal arches set farther back 38 on the skull, a feature commonly seen in adult individuals of other hadrosaurids, such as 39 Brachylophosaurus and lambeosaurines. Stratigraphic data were used to map this morphology 40 through time, to evaluate the anagenesis hypothesis. The stratigraphic distributions of the two 41 species showed considerable overlap, indicating that the sampled individuals lived over a short 42 period of time (< 0.5 mya). Overall, our results suggest that the hypothesis that G. incurvimanus 43 and G. notabilis represent different ontogenetic stages within a single species cannot be rejected. 44 This study improves our understanding of the extent of potential individual variation within a 45 single Gryposaurus species, which can be useful in assessing the validity of other hadrosaurines. 46 KEYWORDS: dinosaur, Hadrosauridae, biostratigraphy, geometric morphometrics, allometry 47 2 https://mc06.manuscriptcentral.com/cjes-pubs Page 3 of 48 Canadian Journal of Earth Sciences 48 49 INTRODUCTION 50 Hadrosauridae are among the most common and diverse late Cretaceous ornithischian 51 dinosaurs in the Northern Hemisphere. In terms of relative abundance, the family dominates 52 many Campanian-Maastrichtian dinosaur faunas of western North America. Notably, 53 hadrosaurids are particularly abundant and diverse in the middle to upper Campanian Dinosaur 54 Park Formation (DPF) of southern Alberta, Canada (Dodson 1971; Brinkman 1990; Brinkman et 55 al. 1998; Ryan and Evans 2005). The hadrosaurid fauna of the DPF includes at least six species, 56 with multiple taxa assignable to the each of the two classically recognized subfamilies, 57 Hadrosaurinae and Lambeosaurinae (Ryan and Evans 2005; Mallon et al. 2012). Most recent 58 taxonomic assessments recognize the lambeosaurineDraft genera Corythosaurus Brown, 1914, 59 Lambeosaurus Parks, 1923, and the rare Parasaurolophus Parks, 1922 (Ryan and Evans 2005; 60 Mallon et al. 2012). Lambeosaurines are numerically more common than hadrosaurines in the 61 assemblage, and due to the large sample of skulls preserved at different growth stages, have been 62 the focus of considerable ontogenetic and taxonomic research (Dodson 1975; Ryan and Evans 63 2005; Evans and Reisz 2007; Evans 2007; Evans 2010). 64 The hadrosaurines from the DPF have been less intensively studied than the 65 lambeosaurines, likely due to the smaller available sample sizes and less complete ontogenetic 66 representation. The hadrosaurines from the DPF are typically assigned to two genera, 67 Prosaurolophus Brown, 1916 and Gryposaurus Lambe, 1914 (Ryan and Evans 2005). Only one 68 species of Prosaurolophus has been recognized from the DPF, P. maximus (McGarrity et al. 69 2013). However, the taxonomic history and diversity within Gryposaurus has been controversial 70 since Lambe (1914) first described the genus based on the type specimen (CMN 2278 from the 3 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 4 of 48 71 DPF). The holotype was assigned the species name G. notabilis and was described based on a 72 few characteristic cranial features: a dorsally arched nasal crest anterior to the orbits, a 73 circumnarial depression near the anterior end of the lacrimal, broad posterior nasal processes, 74 and frontals that bifurcate at the midline of the skull (Horner 1992). Shortly after the initial 75 description of CMN 2278, a field crew from the Royal Ontario Museum collected a nearly 76 complete hadrosaurine skeleton (ROM 764) that was designated as the type specimen of 77 Kritosaurus incurvimanus Parks, 1920, based on several cranial characters, most notably, a more 78 anterior projection of nasal prominence, as well as generally smaller size (Parks 1920; Fig. 1). 79 The genus Gryposaurus was later recognized as a junior subjective synonym of Kritosaurus by 80 Lull and Wright (1942), which was followed by Ostrom (1961) and most subsequent authors 81 over the course of the next several decades.Draft Horner (1992) argued that Gryposaurus was distinct 82 from Kritosaurus at the generic level, and revised the genus to include three species: G. 83 notabilis, G. incurvimanus, and G. latidens Horner, 1992. Subsequent phylogenetic analyses and 84 systematic revisions of Hadrosauridae have supported this generic division (e.g., Gates and 85 Sampson 2007; Prieto-Márquez 2010a, 2012). 86 Despite an adequate sample, the systematics of Gryposaurus species from the DPF are still 87 unresolved. Although the holoype of G. incurvimanus, ROM 764, includes an articulated 88 skeleton and skull, the skull is incompletely preserved, and lacks the majority of its rostrum, 89 including the nasal crest, which is a diagnostic feature for the genus (Parks 1920; Prieto-Márquez 90 2010b). Hopson (1975) was the first to hint that G. incurvimanus might be better considered a 91 junior synonym of G. notabilis when he suggested the two were sexual dimorphs of a single 92 species. However, Horner (1992) recognized G. incurvimanus as a distinct species, as did Gates 93 and Sampson (2007). Most recently, Prieto-Márquez (2010b) argued that G. incurvimanus may 4 https://mc06.manuscriptcentral.com/cjes-pubs Page 5 of 48 Canadian Journal of Earth Sciences 94 in fact be a junior synonym of G. notabilis, and that their morphological differences can be 95 attributed to ontogenetic and intraspecific variation. This opinion was followed by Bertozzo et al. 96 (2017), but with no additional insights into the issues. Several morphological characters have 97 been used to distinguish G. notabilis and G. incurvimanus as two separate species, including the 98 shape of the orbit relative to the infratemporal fenestra (ITF), the height and anteroposterior 99 position of the nasal arch, and posterior breadth of the narial fenestra (Parks 1920; Horner 1992; 100 Gates and Sampson 2007). G. notabilis specimens have a strikingly taller nasal arch, which sits 101 much farther posteriorly on the skull, closer to the nasofrontal suture, than those of G. 102 incurvimanus. G. notabilis also possesses a tightly “U”-shaped posterior margin of the narial 103 fenestra, which is broader in G. incurvimanus. The only specimens unequivocally referred to G. 104 incurvimanus, ROM 764 and TMP 1980.022.0001,Draft are of smaller overall size than those of G. 105 notabilis and display similar nasal arch morphologies to one another (Ryan and Evans 2005). A 106 greater number of specimens have been definitively assigned to G. notabilis (CMN 2278, ROM 107 873, AMNH 5350), compared with the G. incurvimanus morphotype (ROM 764, TMP 108 1980.022.0001), whereas MSNM v345 has been ambiguously referred to as either G. 109 incurvimanus or G. notabilis by different researchers (e.g., Pinna 1979; Currie and Russell 2005; 110 Prieto-Márquez
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