The cladistic analysis was conducted using the matrix by Xing et al. (2014). In the second matrix, those characters determined to be ontogenetically variable, based on a larger analysis of the Alaskan material and Edmontosaurus (Mori 2014; Mori et al. in prep; Matrix 2), were scored as missing for U. kuukpikensis. Here we summarize which characters are considered variable and provide a short explanation for each.
Character 2. Estimated from the dentary teeth enamel and the tooth sulcus lengths. Average 1.13 cm.
Character 40. The angle between the slope of the dentary anterioral region with the horizontal is about 135° in a size class 1 specimens and 127° in size class 2 specimen (UAMES 4946). The angle between the edentulous process and horizontal changes as Edmontosaurus grew (Mori, 2014); thus this traits would change as well.
Character 40-43.The edentulous process straightens during growth. See Mori (2014, fig. 1-26A).
Character 51. SomeEdmontosaurus specimens have this projection (i.e. ROM 53530, ROM 64083, see also Lambe 1920, fig. 21).
Character 66. In the size class 3 specimen (UAMES 14132), this angle is 147°, more curved than the size class 1 specimen (UAMES 4457, 151°), and marginally more than those of Edmontosaurus.
Character 81. Modified as: Premaxillary additional accessory fossa located lateral to the premaxillary accessory narial fossa and anterioral to the circumnarial fossa, separated from the premaxillary anterioral fossa by a well developed vestibular promontory (corresponding with Prieto-Marquez and Wagner, 2009 character 73, modified): (0) absent; (1) present.
Character 95. Exposure of the anterodorsal process of the maxilla through the external naris is rather exceptional in Edmontosaurus. Such condition is only seen in UMCP 20000 (Edmontosaurus annectens).
Character 96. See the main text.
Character 119. As Campione (2015, personal com.) noted, a strongly inclined palatine articular surface is also seen in a juvenile Edmontosaurus annectens (Campione, personal communication). However, we assume this is a unique condition seen in Ugrunaaluk, as discussed in the main text.
Character 162.Ugrunaaluk materials have an invaginated posterodorsal margin of the circumnarial fossa, but not “strongly” invaginated. Comparisons with subadult and adult Edmontosaurus suggest this is an ontogenetically variable character (Mori, 2014).
Character 181. Size class 1 U. kuukpikensis specimens have a narrow jugal process, but an incomplete size class 3 specimen (UAMES 33308) has relatively wider, but still slender jugal process. Regression analysis shows this narrow jugal process can be regarded as similar to the hypothetical juvenile condition of Edmontosaurus (status 2) (Mori, 2014).
Character 183. The size class 3 postorbital (UAMES 33308) lacks the posterior process. The length of the posterior process is known to become relatively smaller (Mori, 2014), and this character is related to the character 181, the width of the jugal process. For these reasons, the length the posterior process is considered an ontogenetically variable character.
Character 187. Size class 2 Edmontosaurus annectens (ROM 53510) also has a short precotyloid process. This suggests the length of the precotyloid process is ontogenetically variable.
Character 209. This character is related to the ontogenetic change in the quadrate and exoccipital-opisthotic. As Edmontosaurus and Ugrunaaluk grow (on assumption that juvenile Ugrunaaluk was similar to juvenile Edmontosaurus), the exoccipital rotates posteroventrally, and the quadrate curves posteriorly (Mori 2014). These changes would also bring the supraoccipital-exoccipital shelf posteriorly.
Character 210. As the exoccipital rotates posteroventrally (see above), the orientation of the paroccipital process would also change.
Character 213. This constriction is weak in the size class 1 specimens, but the size class 2 specimen (UAMES 35030) has a stronger constriction.
Character 214. Juvenile Edmontosaurus annectens (ROM 53492) has a shorter basipterygoid process than those of subadults (YPM 618 and ROM 59786), thus this is an ontogenetically variable character.
Character 216. Possibly an ontogenetic variable. The size class 2 specimen (UAMES 35030) is as less strongly constricted as in the size class 1 specimens.
Character 223. The lamina between the ectopterygoid process and ventral quadrate process in size class 1 Ugrunaaluk kuukpikensis is less extensive than in a specimen of size class 2 of Edmontosaurus annectens (ROM 53539). In subadult E. annectens (CMN 8509) and adult E. regalis (CMN 2289), this bony lamina is more extensive than in these juvenile specimens (Mori, 2014). Therefore, less extensive lamina can be an ontogenetic feature.
Character 224. The orbit changes dramatically as the animal grows. However, the orbital shape of AMNH 5046 (size class 2 Edmontosaurus annectens) and CMN 8509 (subadult E. annectens) do not differ much.
Character 227. Shape of the infratemporal fenestra is related to the width of the postorbital jugal process, which is an ontogenetically variable.
Character 231. The skull, as well as the premaxilla, would elongate as they grow (Campione and Evens, 2011).
Character 258. This character is related to the degree of the scapular neck constriction, which is ontogenetically variable.
Character 293. Contra to Xing et al. (2014), some Edmontosaurus specimens (DMNH 1493, CMN 289) have a supraacetabular process which expands lateroventrally at around 25% of the depth of the ilium body.
Character 297. The dorsal margin of the ilium above the supraacetabular process is slightly convex in Ugrunaaluk kuukpikensis specimens. Such a condition is also seen in other juvenile to subadult hadrosaurids (i.e., CMN 8399, Edmontosaurus regalis; AENM 2/922-7L , Kerbosaurus; TMP 98.50.01, Prosaurolophus), suggesting this curve is ontogenetically variable.
Campione, N. E. and Evans, D. C. 2011. Cranial growth and variation in edmontosaurs (Dinosauria: Hadrosauridae): Implications for Latest Cretaceous megaherbivore diversity in North America. PLoS ONE 6: e25186.
Lambe, M. L. 1920. The hadrosaur Edmontosaurus from the Upper Cretaceous of Alberta. Canada Geological Survey Memoir 120: 1-79.
Mori, H. 2014. Osteology, relationships and paleoecology of a new Arctic hadrosaurid (Dinosauria: Ornithopoda) from the Prince Creek Formation of northern Alaska. unpublished Ph.D. thesis, Fairbanks, AK.
Xing, H., Zhao, X., K., W., Li, D., Chen, S., Jordan, C. M., Zhang, Y. and Xu, X. 2014. Comparative Osteology and Phylogenetic Relationship of Edmontosaurus and Shantungosaurus (Dinosauria: Hadrosauridae) from the Upper Cretaceous of North America and East Asia. Acta Geologica Sinica-English Edition 88: 1623-1652.