Editors’choice A new Arctic hadrosaurid from the Prince …

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Editors’ choice
A new Arctic hadrosaurid from the Prince Creek
Formation (lower Maastrichtian) of northern Alaska

HIROTSUGU MORI, PATRICK S. DRUCKENMILLER, and GREGORY M. ERICKSON

Mori, H., Druckenmiller, P.S., and Erickson, G.M. 2016. A new Arctic hadrosaurid from the Prince Creek Formation
(lower Maastrichtian) of northern Alaska. Acta Palaeontologica Polonica 61 (1): 15–32.

The Liscomb bonebed in the Price Creek Formation of northern Alaska has produced thousands of individual bones of
a saurolophine hadrosaurid similar to Edmontosaurus; however, the specific identity of this taxon has been unclear, in
part because the vast majority of the remains represent immature individuals. In this study, we address the taxonomic
status of the Alaskan material through a comparative and quantitative morphological analysis of juvenile as well several
near adult-sized specimens with particular reference to the two known species of Edmontosaurus, as well as a cladistic
analysis using two different matrices for Hadrosauroidea. In the comparative morphological analysis, we introduce a
quantitative method using bivariate plots to address ontogenetic variation. Our comparative anatomical analysis reveals
that the Alaskan saurolophine possesses a unique suite of characters that distinguishes it from Edmontosaurus, including
a premaxillary circumnarial ridge that projects posterolaterally without a premaxillary vestibular promontory, a shallow
groove lateral to the posterodorsal premaxillary foramen, a relatively narrow jugal process of the postorbital lacking
a postorbital pocket, a relatively tall maxilla, a relatively gracile jugal, a more strongly angled posterior margin of the
anterior process of the jugal, wide lateral exposure of the quadratojugal, and a short symphyseal process of the dentary.
The cladistic analyses consistently recover the Alaskan saurolophine as the sister taxon to Edmontosaurus annectens
+ Edmontosaurus regalis. This phylogenetic assessment is robust even when accounting for ontogenetically variable
characters. Based on these results, we erect a new taxon, Ugrunaaluk kuukpikensis gen. et sp. nov. that contributes to
growing evidence for a distinct, early Maastrichtian Arctic dinosaur community that existed at the northernmost extent
of Laramidia during the Late Cretaceous.

Key words: Dinosauria, Hadrosauridae, Saurolophinae, Edmontosaurini, ontogeny, Cretaceous, Prince Creek For ma-
tion, Arctic, Alaska.

Hirotsugu Mori [hmori@alaska.edu], Department of Geosciences, University of Alaska Fairbanks, 900 Yukon Drive,
Fairbanks, AK 99775-5780, USA; University of Alaska Museum, 907 Yukon Drive, Fairbanks, AK 99775, USA; and
Saikai City Board of Education; Setoitanoura Go, Oseto Cho, Saikai City, Nagasaki Prefecture, 857-2301, Japan.
Patrick S. Druckenmiller [psdruckenmiller@alaska.edu], University of Alaska Museum, 907 Yukon Drive, Fairbanks,
AK 99775, USA; and Department of Geosciences, University of Alaska Fairbanks, 900 Yukon Drive, Fairbanks, AK
99775-5780, USA.
Gregory M. Erickson [gerickson@bio.fsu.edu], Department of Biological Science, Florida State University, 319 Stadi-
um Drive, Tallahassee, FL 32306-4295, USA.

Received 10 January 2015, accepted 7 August 2015, available online 22 September 2015.

Copyright © 2016 H. Mori et al. This is an open-access article distributed under the terms of the Creative Commons
Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original author and source are credited.

Introduction

The Prince Creek Formation (PCF) of northern Alaska pre-
serves one of the most diverse and prolific assemblages of
polar dinosaurs known anywhere in the world. To date, ev-
idence for at least 13 different dinosaurian taxa are known
from early Maastrichtian horizons of the unit, including
five ornithischians, seven non-avian theropods, and an avi-
alan theropod (Gangloff 1994; Druckenmiller et al. 2013).
However, only three of these taxa have been identified tax-

onomically to the species level (Sullivan 2006; Fiorillo and
Tykoski 2012, 2014). The remainder have only been tenta-
tively identified at generic or suprageneric levels (Fiorillo
et al. 2009; Brown and Druckenmiller 2011; Druckenmiller
et al. 2013; Watanabe et al. 2013). Because all three named
dinosaurian species are endemic to the Laramidian Arctic,
Erickson and Druckenmiller (2011) hypothesized that
the Prince Creek Formation supported a distinctive early
Maastrichtian dinosaur polar fauna known as the Paaŋaqtat
Province. Understanding the overall faunal composition of
the PCF is critical in order to test this hypothesis and assess

Acta Palaeontol. Pol. 61 (1): 15–32, 2016

http://dx.doi.org/10.4202/app.00152.2015

16

ACTA PALAEONTOLOGICA POLONICA 61 (1), 2016

Fig. 1. Study area in northern Alaska, USA (A) and location of the Liscomb bonebed (B). C. Paleogeographic reconstruction of North America at 70 Ma
(Blakey .2009); the box indicates the approximate position of Alaska at that time.

larger questions relating to Laramidian biogeography and
dinosaur paleobiology.

Since the 1990s, an abundance of hadrosaurid remains
have been recovered from the Prince Creek Formation
(Fig. 1). The material is primarily derived from a single
well-known horizon known as the Liscomb bonebed (LBB),
from which thousands of disarticulated cranial and postcra-
nial dinosaur remains have been excavated (Brouwers et al.
1987; Davies 1987; Nelms 1989; Clemens and Nelms 1993;
Gangloff 1994, 1998; Fiorillo and Gangloff 2001; Fiorillo
et al. 2007, 2010; Fiorillo 2008a; Flaig 2010; Gangloff and
Fiorillo 2010; Erickson and Druckenmiller 2011; Watanabe
et al. 2013). The Liscomb remains were first identified as a
lambeosaurine hadrosaurid (Brouwers et al. 1987). However,
subsequent researchers have reassigned the remains to
Saurolophinae (Hadrosauria) and tentatively referred them
to the Campanian to Maastrichtian genus Edmontosaurus
Lambe, 1917, or more specifically to E. regalis (Xing et
al. 2014). However, a comprehensive anatomical survey of
this material has not been conducted and the taxonomic
referral formally demonstrated. In part, this stems from the
fact the majority of the LBB remains represent individuals
approximately one-third adult length and it is difficult to
identify the taxonomic status of hadrosaurids from juvenile
remains because most are differentiated by adult features
(Prieto-Márquez 2008, 2010a; Campione and Evans 2011;
Campione et al. 2012).

Here, we provide a description of the hadrosaurid mate-
rial from the Prince Creek Formation. Based on compari-
sons with other saurolophines, particularly Edmontosaurus,
we recognize a new species that can be diagnosed on onto-
genetically invariable characters. The recognition of a new

taxon from the LBB contributes to a broader understanding
of saurolophine diversity, the taxonomic composition of the
PCF and provides important new evidence for testing hy-
potheses of dinosaur provinciality in Laramidia.

Institutional abbreviations.—AENM, Amur Natural History
Museum, Blagoveschensk, Russia; AMNH, American
Museum of Natural History, New York City, USA; BHI,
Black Hills Institute of Geological Research, Hill City, USA;
BMNH, The Natural History Museum, London, UK; CM,
Carnegie Museum of Natural History, Pittsburgh, USA;
CMN, Canadian Museum of Nature, Ottawa, Canada (for-
merly NMC, National Museums of Canada); DMNH, Denver
Museum of Nature and Science, Denver, USA; FMNH, The
Field Museum, Chicago, USA; GMV, National Geological
Museum of China, Beijing, China; MACN, Museo Argentino
de Ciencias Naturales Bernardino Rivadavia, Buenos Aires,
Argentina; RAM, Raymond M. Alf Museum of Paleontology,
Claremont, USA; ROM, Royal Ontario Museum, Toronto,
Canada; SM, Senckenberg Museum, Frankfurt, Germany;
TMNH, Toyohashi Museum of Natural History, Toyohashi,
Aichi, Japan; UMMP, University of Michigan Museum of
Paleontology, Ann Arbor, USA; UAMES, University of
Alaska Museum, Fairbanks, USA; USNM, Smithsonian
National Museum of Natural History, Washington DC,
USA; YPM, Yale Peabody Museum of Natural History, New
Haven, USA.

Other abbreviations.—LBB, Liscomb bonebed; PCF, Prince
Creek Formation.

Nomenclatural acts.—The electronic edition of this article
conforms to the requirements of the amended International

MORI ET AL.—ARCTIC HADROSAURID FROM MAASTRICHTIAN OF ALASKA

17

Code of Zoological Nomenclature, and hence the new
names contained herein are available under that Code from
the electronic edition of this article. This published work
and the nomenclatural acts it contains have been registered
in ZooBank, the online registration system for the ICZN.
The ZooBank LSIDs (Life Science Identifiers) can be re-
solved and the associated information viewed through any
standard web browser by appending the LSID to the pre-
fix “http://zoobank.org/”. The LSID for this publication
is: urn:lsid:zoobank.org:pub:84BD5626-4F09-4246-9D86-
E831E9465D69.

The electronic edition of this work was published in a
journal with an eISSN 1732-2421, and has been archived
and is available from the following digital repository: http://
www.app.pan.pl/article/item/app001522015.html

Geological setting and taxonomic
composition

The Prince Creek Formation (formerly referred to as the
Kogosukuruk Tongue of the PCF; Gryc et al. 1951) is com-
posed of non-marine sandstone, conglomerate, coal, and
mudstone layers representing interbedded fluvial (mean-
dering channels and floodplains) and marginal marine
sediments that were deposited on a low gradient coastal
plain (Mull et al. 2003; Flaig et al. 2011). Palynological
(Frederiksen et al. 1988, 2002; Frederiksen 1991) and bio-
stratigraphic data (Brouwers and Deckker 1993) suggest the
entire PCF ranges from the Upper Cretaceous to Eocene in
age. The numerical age of the dinosaur-bearing section of
the formation, where it is exposed along the lower Colville
River and including the LBB, has been dated at 71–68 Ma
using 40Ar/39Ar methods (McKee et al. 1989; Besse and
Courtillot 1991). The age of LBB is further constrained by
an 40Ar/39Ar age of 69.2±0.5 Ma from a stratigraphically
underlying tuff at a locality known as Sling Point (approxi-
mately 1 km from the LBB) and from palynological analyses
(Flores et al. 2007) consistent with an early Maastrichtian
age (Flaig 2010). This age estimate is within the known
stratigraphic range of Edmontosaurus, notably falling be-
tween the last appearance date of E. regalis Lambe, 1917
(late Campanian; Campione and Evans 2011; Eberth et al.
2013) and the first appearance of E. annectens Marsh, 1892
(late Maastrichtian; Campione and Evans 2011).

The Late Cretaceous paleolatitude of northern Alaska
is estimated to range between 67–82° N (Witte et al. 1987;
Besse and Courtillot 1991; Lawver et al. 2002), thus the
LBB was well within the paleo-Arctic (above approximately
66° N). Although considerably milder than today, paleobo-
tanical evidence indicates a mean annual temperature for
the Maastrichtian of northern Alaska at around 5–6°C, with
a cold month mean warmer than 2.0±3.9°C (Parrish and
Spicer 1988; Spicer and Parrish 1990; Spicer et al. 1992;
Spicer and Herman 2010). From pedogenic and paleobotan-

ical evidence Flaig et al. (2013) concluded that the Arctic
coastal plain had polar woodlands with an angiosperm un-
derstory, and that it experienced both strong dry and wet
seasons. In addition to hadrosaurid remains, the PCF pre-
serves a modestly diverse assemblage of ornithischian and
saurischian dinosaurs and mammals (Brouwers et al. 1987;
Nelms 1989; Clemens and Nelms 1993; Gangloff 1994;
Gangloff et al. 2005; Fiorillo 2008a; Fiorillo et al. 2009;
Gangloff and Fiorillo 2010; Brown and Druckenmiller 2011;
Fiorillo and Tykoski 2012, 2014; Watanabe et al. 2013).
However, to date, no unequivocally ectothermic terrestrial
vertebrates have been recovered from the formation. This
faunal distribution led Clemens and Nelms (1993) to sug-
gest that the climate was too cold for most terrestrial and
amphibious ectotherms, including crocodilians, champso-
saurs, choristodires, squamates, and turtles that were more
common contemporaneously at lower latitudes.

Taphonomically the dinosaur remains from the LBB
are dominated by juvenile specimens of hadrosaurids that
have been previously assigned to Edmontosaurus (Gangloff
and Fiorillo 2010). Other rare elements represented in the
bonebed included isolated hadrosaurid material and shed
thescelosaurid, tyrannosaurid, and troodontid teeth. The
hadrosaurid remains are almost entirely disarticulated,
show little evidence of weathering, predation, or trampling,
and are typically uncrushed and unpermineralized (Fiorillo
et al. 2010; Gangloff and Fiorillo 2010). The LBB occurs in
a trunk channel on a distributary channel splay complex and
flood plain (Fiorillo et al. 2010; Flaig 2010). The bonebed
is posited to reflect a mass mortality event associated with
overbank flood deposits (Gangloff and Fiorillo 2010), which
could have resulted from rapid snowmelt from the then-ris-
ing Brooks Range to the south (Fiorillo et al. 2010).

Material and methods

Material.—More than 6000 hadrosaurid bones from the
LBB that form the basis for this study have been collected
during expeditions led by the University of Alaska Museum
and the University of California Museum of Paleontology
(this material is now housed at UAMES). The majority
of this material consists of individuals from an immature
growth stage (size class 1; humeral length = ~22 cm; SOM 1,
Supplementary Online Material available at http://app.pan.
pl/SOM/app61-Mori_etal_SOM.pdf), approximately one-
third the adult humerus length of Edmontosaurus (approx-
imately 60–70 cm). The remaining material represents
size class 2 juvenile individuals (SOM 1) (~29 cm humeral
length), and size class 3 subadult individuals (SOM 1)
(~43 cm humeral length). The three size classes may rep-
resent a mass mortality event of a herd or herds containing
yearly cohorts (Gangloff and Fiorillo 2010).

393 specimens bearing phylogenetically informative
characters, including cranial and postcranial elements were
examined in detail during the course of this study (SOM 1).

18

ACTA PALAEONTOLOGICA POLONICA 61 (1), 2016

Because of the abundance of material, most elements are
known from multiple specimens making it possible to ac-
count for variation in both size and morphology.

The Alaskan material is compared in detail to Edmonto-
saurus, which has two recognized species, E. regalis
(late Campanian) and E. annectens (late Maastrichtian;
Campione and Evans 2011) represented by abundant mate-
rial from the United States of America and Canada (SOM
2). Edmontosaurus was chosen as the primary compara-
tor, particularly for the regression analyses (see below), for
four reasons. First, the Alaskan taxon at a coarse anatom-
ical level appears to be Edmontosaurus and has been re-
ferred to as such (Clemens and Nelms 1993; Gangloff 1998;
Fiorillo and Gangloff 2001; Prieto-Márquez 2008; Gangloff
and Fiorillo 2010; Campione and Evans 2011; Xing et al.
2014). Specifically, the Alaskan material possesses two of
the diagnostic characters of the genus, proposed by Xing
et al. (2014); (i) the premaxillary margin is strongly folded
dorsoventrally, and (ii) the dorsolateral process of the lat-
erosphenoid is truncated. Also, the PCF material has two
premaxillary foramina in the prenarial region of the cir-
cumnarial fossa as in Edmontosaurus, although we dis-
agree with Xing et al. (2014) in regarding this character as
unique to Edmontosaurus, as such a structure is also seen
in Maiasaura (Horner 1983). Further, the PCF taxon bears
numerous other general anatomical similarities to these taxa
such as a nasal lacking ornamentation, as seen in some gen-
era of Saurolophinae (Brown 1913; Lambe 1914; Sternberg
1953; Maryańska and Osmólska 1981; Horner 1983, 1992;
Gates and Sampson 2007; Prieto-Márquez 2010b, 2012;
Prieto-Márquez et al. 2014), the tooth form bears closest sim-
ilarity to Edmontosaurus (Prieto-Márquez 2008; Erickson
and Druckenmiller 2011), and the frontal is widely exposed
laterally. Second, the Alaskan material occurs within the
temporal range of the genus Edmontosaurus, although it
lies stratigraphically intermediate to both species (Fig. 2).
Third, it occurs within the same landmass as Edmontosaurus
(Laramidia), although north of the known geographic ranges
for both species (Colorado, USA to Alberta, Canada). Finally,
the Prince Creek Formation taxon and Edmontosaurus are
also clearly distinct from three closely related Asian taxa
(Godefroit et al. 2012; Prieto-Márquez 2013, 2014; Xing et
al. 2014). Specifically, the PCF taxon and Edmontosaurus
differ from Shantungosaurus Hu, 1972 in that the dorsal
surface of the postorbital is nearly straight, in possessing
a smaller anterior portion of the scapula, a less developed
suprailiac crest of the ilium and the absence of well devel-
oped boss in the proximal region of the ischiadic peduncle.
Both differ from Kerberosaurus Bolotsky and Godefroit,
2004 in lacking a pocket on the basisphenoid process of
the prootic, a wide groove for ophthalmic nerve on the lat-
erosphenoid, a prominent palatine process on the maxilla,
and a markedly depressed dorsal surface of the postorbital.
Finally, the PCF taxon and Edmontosaurus differ from
“Kundurosaurus” Godefroit, Bolotsky, and Lauters, 2012
in possessing a ventrally-projecting posterior buttress of the

Fig. 2. Temporal distribution of Edmontosaurus species and Ugrunaaluk
kuukpikensis gen. et sp. nov. from the Prince Creek Formation in the Late
Cretaceous.

Fig. 3. Histogram of hadrosaurid bones from the Liscomb bonebed (Prince
Creek Formation) for which at least 10 specimens are known. Size is stan-
dardized by the mean of size classes 1 and 2 for each bone. The relative
size is adjusted so that the mean size of the size class 1 specimens be-
comes 1. The hypothesis of normal distribution for all samples, and sam-
ples whose relative sizes range 0.88–1.52, are both rejected (p << 0.001). The hypothesis of normal distribution for specimens whose relative size range 0.88–1.12 was not rejected (p = 0.25). Relative sizes of juvenile E. annectens specimens are also shown at the bottom. Note that due to insufficient numbers of corresponding bone types, size class 3 individuals of E. annectens are not shown in the histogram. For raw data, see SOM 3. scapula, straight anterior process of the nasal, and a ventrally - -curved preacetabular process of the ilium, although Xing et al. (2014) consider Kundurosaurus to be a junior synonym of Kerberosaurus, with which we concur. For these reasons, we assume the PCF taxon is either referable to, or closely related to Edmontosaurus. Size classes in the Liscomb bonebed.—We characterized the size distribution of the individuals in the LBB and a his- togram showing size versus specimen counts was prepared depicting size versus the number of specimens (Fig. 3). First, MORI ET AL.—ARCTIC HADROSAURID FROM MAASTRICHTIAN OF ALASKA 19 A elements for which at least 10 specimens are known were se- lected (dentary, frontal, humerus, ulna, radius, tibia, meta- tarsal II–IV; SOM 3) for size standardization. The length of each bone was divided by the mean length of each element in order to compare the lengths of different bone types. When calculating the mean length, specimens that are more than twice as long as the smallest specimens were removed. Distribution of the sizes were tested for normality using the Shapiro-Wilk test in PAST 3.0 (Harper and Ryan 2001). The PCF elements can be classified into three ontoge- netic stages, all of which are interpreted to represent three different developmental stages (Fig. 3). Approximately 85% of the specimens examined are categorized into size class 1. A three-dimensional composite skull (Fig. 4) was recon- structed from casts of size class 1 individuals and found to measure approximately 33 cm long (measured from the ante- rior end of the premaxilla to the mid-point of the quadrate). This is 36% of the length of the adult paratype specimen of E. annectens, YPM 2182 (91 cm). Size class 2 accounts for about 10% of the examined specimens and the isolated cra- nial elements are approximately 30% longer than size class 1 specimens, which is equivalent to ~40% of the skull length of YPM 2182. Size class 3 represents less than 5% of the total specimens, and the cranial elements are approximately 80–100% longer than the size class 1 specimens. These cor- respond to individuals ~60% of the size of YPM 2182. Fortuitously, Edmontosaurus is represented by material spanning a broad ontogenetic range, including specimens of E. annectens that overlap in size with the Prince Creek Formation that permit some direct size-standardized ana- tomical comparisons. Comparative material of E. annectens (SOM 3) was also categorized by size class after standardi- zation to mean lengths of the PCF material (Fig. 3). While overlapping material of size class 1 for E. annectens and the Alaskan material is not known, there is overlap in size classes 2 and 3 (size class 3 is not included in Fig. 3 because fewer than 10 specimens of a corresponding bone type of the PCF material were available). Among the ontogenetic spectrum of E. annectens available for comparison are in- dividuals approximately equivalent to size class 2 (LACM 23504, skull length = estimated 47 cm), size class 3 (e.g., ROM 53530, disarticulated), to subadult (CMN 8509, skull length = 75 cm), and adult (ROM 57100, skull length = 101 cm; MOR 003, skull length = 118 cm) specimens. It should be noted, however, that there is a limited number of PCF specimens that overlap in absolute size with E. annectens, thus direct comparisons are not possible for some bones. E. regalis specimens are all larger than size class 3 specimens of the PCF taxon and range from subadult (CMN 8399, skull length = 78 cm; BMNH 8937, skull length = 75 cm) to adult (ROM 801, skull length = 107 cm; USNM 12711, skull length = 105 cm). Regression analysis.—Because the PCF material is gen- erally much smaller than material for E. annectens and E. regalis, quantitative methods were used to compare many 10 cm frontal postorbital squamosal B nasal prefrontal lacrimal maxilla jugal premaxilla predentary dentary exoccipital -opisthotic quadrate quadratojugal surangular Fig. 4. Cranial reconstruction of Ugrunaaluk kuukpikensis gen. et sp. nov. from the early Maastrichtian Prince Creek Formation, Alaska, in left lateral view. Photograph (A) and bone interpretation (B). elements. Quantitative data on specimens not personally measured were taken from the literature (Lull and Wright 1942; Brett-Surman 1989) or from photographs provided by colleagues. A regression analysis was employed to test if a given feature observed in the PCF material is potentially a juvenile condition of a feature seen in adult E. annectens or E. regalis. Dodson (1975a–c) demonstrated that among the same species of reptiles, log-transformed lengths of various parts show high correlations against body size. However, because the correlation coefficient is not reliable when the data include outliers (specimens which are much smaller than the others), in this case the PCF specimens themselves (Schuyler 2004), testing whether the relatively small speci- mens represent juveniles requires a different approach. In order to address this problem, a new approach was employed in this study. The method is based on the assump- tion that the growth trend line of Edmontosaurus, from ju- venile to adult, can be expressed by the following equation: Length = A × (body length) B A and B are constants. This assumption is based on the observations by Dodson (1975c), who reported linear rela- tionships between the skull length and various parts of the (1) 20 ACTA PALAEONTOLOGICA POLONICA 61 (1), 2016 skull in species of lambeosaurines. By logarithmic transfor- mation, the equation above can be transformed as: Log (length) = B × Log (body length) +log (A) (2) If a log-transformed length of any body part correlates with the log-transformed body length, any sets of log-trans- formed body lengths would also correlate to each other. Using this assumption, we null-hypothesized that the char- acter condition of the PCF taxon is similar to an extrapolated juvenile of E. regalis or E. annectens. From this null-hy- pothesis, growth trend lines of other Edmontosaurus species + PCF materials combined were prepared. If these hypothet- ical growth lines are significantly different (p < 0.05) from the growth trend lines of other Edmontosaurus specimens alone, or PCF materials alone, we concluded the PCF mate- rials represent a different ontogenetic trajectory for that fea- ture. For the postorbital and quadratojugal, the length of the dentary was used as a proxy for body size. Because nearly all specimens excavated from the LBB are disarticulated, only size class 1 material of the PCF taxon were compared against the mean size of the dentary of size class 1. Because size class 1 specimens represent the majority of the PCF material, other size class 1 material also likely belongs to individuals of the same size. When statistically significant results were discovered, either maximum or minimum lim- its of the confidence interval of the dentary length (mean length +/– two standard deviations) is adopted as the proxy of the body size, and the regression analysis was conducted again. When a given element length is too short (or long) relative to dentary length, we used the minimum (or maxi- mum) length of the dentary. This alleviates the problem of using disarticulated bones in the regression analysis, and is more conservative. A reduced major axis (RMA) regression line was chosen to calculate the growth trend line, because it minimizes the errors in the both variables (Pearson 1901; Warton et al. 2006; Smith 2009). SMATR ver. 2.0 (Falster et al. 2006) was used to prepare the RMA regression lines, R2 and P values, and to assess whether two regression lines are statistically different by Wald statistics. Systematic paleontology Ornithischia Seeley, 1887 Ornithopoda Marsh, 1881 Hadrosauridae Cope, 1869 Saurolophinae Brown, 1914 sensu Prieto-Márquez, 2010a Edmontosaurini Brett-Surman, 1989 Genus Ugrunaaluk nov. ZooBank LSID: urn:lsid:zoobank.org:act:8B8256BA-F280-4460-B0F0- 31762267586E Etymology: Transliterated from the Alaskan Iñupiaq noun ugruŋnaq, referring to a grazing animal with a long set of grinding teeth, and the adjective -aluk, old. Literally, “ancient grazer”. Intended pronun- ciation: “oo-GREW-nah-luk”. The name honors the Alaskan Native Iñupiaq culture from the area where the type material was discovered. Type species: Ugrunaaluk kuukpikensis sp. nov., monotypic Diagnosis.—As for type species, by monotypy. Ugrunaaluk kuukpikensis sp. nov. ZooBank LSID: urn:lsid:zoobank.org:act:1CAF186F-11A2-4A9E-A8F9- C3789B97459F Figs. 4–10. Etymology: The specific name is derived from the Iñupiaq word kuuk- pik, which refers to the Colville River, Alaska, USA along which the type material was found. Type material: Holotype: UAMES 12995, anterior portion of a size class 1 right premaxilla. Paratypes: All paratypes are of size class 1, unless otherwise specified. UAMES 4271, posterior portion of the right nasal; UAMES 13250, left prefrontal; UAMES 4245, left lac- rimal; UAMES 4189, right jugal; UAMES 4272, left quadratojugal; UAMES 4286, right quadrate; UAMES 33308, right postorbital of size class 3; UAMES 4361, right squamosal of size class 2; UAMES 4327, right maxilla; UAMES 15284, left laterosphenoid; UAMES 4357, right prootic; UAMES 4301, basisphenoid; UAMES 4276, basioccip- ital; UAMES 4309, parietal; UAMES 4291, supraoccipital; UAMES 4095, right exoccipital-opisthotic; UAMES 4240, right ectopterygoid; UAMES 4331, left palatine; UAMES 4215, left pterygoid; UAMES 4437, predentary; UAMES 4946, left dentary of size class 2; UAMES 4457, right surangular; UAMES 6646, dorsal vertebra of size class 3; UAMES 23071, sacrum of size class 3; UAMES 4873, right coracoid; UAMES 12711, right scapula; UAMES 21596, right humerus; UA- MES 12525, right ulna; UAMES 6272, left radius; UAMES 6637, left ilium; UAMES 22058, pubis; UAMES 12955, left ischium; UAMES 12515, femur; UAMES 12715, left tibia; UAMES 15553, left fibula; UAMES 21950, astragalus; UAMES 21884, right calcaneum; UAMES 12545, right metatarsal IV of size class 3. Type locality: Liscomb bonebed, along the Colville River, northern Alaska, USA. The exact location is on file with the Bureau of Land Management Arctic Field Office. Type horizon: Upper portion of the Prince Creek Formation, lower Maastrichtian (Upper Cretaceous). Referred specimens.—See SOM 1. Diagnosis.—Saurolophine hadrosaurid that differs from Edmontosaurus in possessing the following unique combina- tion of characters: a circumnarial ridge of the premaxilla that projects posterolaterally without a premaxillary vestibular promontory (Edmontosaurus has anteroposteriorly expanded circumnarial ridge with vestibular promontory); groove lat- eral to the posterodorsal premaxillary foramen is shallow (deep in Edmontosaurus annectens); absence of a shallow postorbital fossa (Edmontosaurus has a distinct, deep postor- bital pocket); dorsoventrally short maxilla (relatively taller in E. annectens); relatively gracile jugal (relatively robust in E. annectens); the posterior margin of the anterior process of the jugal is strongly angled (less angled in Edmontosaurus); wide lateral exposure of the quadratojugal (relatively narrow in E. regalis); short symphyseal process of the dentary that is 30% dental battery length (relatively longer in E. annectens). Description.—In this section, only taxonomically informa- tive characters that distinguish Ugrunaaluk kuukpikensis MORI ET AL.—ARCTIC HADROSAURID FROM MAASTRICHTIAN OF ALASKA 21 A1 B1 C1 gen. et sp. nov. from Edmontosaurus annectens and E. re- galis are described, along with a description of ontogenetic trajectories for these features. Characters that are ontogenet- ically variable were excluded. A more comprehensive and detailed description of all skeletal elements of Ugrunaaluk kuukpikensis gen. et sp. nov., along with an analysis of onto- genetic variation in the taxon, will be presented elsewhere. Premaxilla: In size class 1 specimens of Ugrunaaluk kuukpikensis gen. et sp. nov., the circumnarial ridge of the premaxilla is narrowly triangular in the parasagittal plane and projects posterolaterally, extending nearly to the lateral margin of the premaxilla. As a result, the circum- narial ridge divides the anterior region of the circumnarial fossa into anterior and posterior premaxillary depressions. In Edmontosaurus regalis and E. annectens, the circum- narial ridge diverges laterally to form an anteroposteriorly expanded vestibular promontory, giving this structure an