Phylogeny of a new gigantic paravian (Theropoda; Coelurosauria; Maniraptora) from the Upper Cretaceous of James Ross Island, Antarctica

Accepted Manuscript Phylogeny of A New Gigantic Paravian (Theropoda; Coelurosauria; Maniraptora) From The Upper Cretaceous Of James Ross Island, Antarctica Ricardo C. Ely, Judd A. Case PII:

S0195-6671(18)30012-0

DOI:

https://doi.org/10.1016/j.cretres.2019.04.003

Reference:

YCRES 4132

To appear in:

Cretaceous Research

Received Date: 6 January 2018 Revised Date:

21 December 2018

Accepted Date: 4 April 2019

Please cite this article as: Ely, R.C., Case, J.A., Phylogeny of A New Gigantic Paravian (Theropoda; Coelurosauria; Maniraptora) From The Upper Cretaceous Of James Ross Island, Antarctica, Cretaceous Research, https://doi.org/10.1016/j.cretres.2019.04.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN PHYLOGENY OF A NEW GIGANTIC PARAVIAN (THEROPODA; COELUROSAURIA;

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MANIRAPTORA) FROM THE UPPER CRETACEOUS OF JAMES ROSS ISLAND,

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ANTARCTICA

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RICARDO C. ELY1 and JUDD A. CASE2

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47408 U.S.A.

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[email protected]

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[email protected]

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Department of Earth and Atmospheric Sciences, Indiana University, Bloomington, Indiana,

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Department of Biology, Eastern Washington University, Cheney, Washington, 99004 U.S.A.

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Abstract

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A description with phylogenetic analyses is provided for Imperobator antarcticus, gen. et sp.

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nov., an early Maastrichtian, basal paravian (Theropoda; Maniraptora) from the Naze Peninsula,

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James Ross Island, Antarctica. In 2003, researchers uncovered the remains of a theropod later

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referred to Dromaeosauridae. Dromaeosaurids are a clade of maniraptorans including well-

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known members such as Velociraptor and Deinonychus. The specimen displays a case of

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gigantism in paravians, a condition best documented in the dromaeosaurids Achillobator,

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Austroraptor, Dakotaraptor, and Utahraptor. In addition to certain morphological traits that

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differ from the dromaeosaurid norm, the smooth surface of the distal metatarsal II prevents

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referral of the ‘Naze Theropod’ to dromaeosaurids (ginglymoidy of the distal surface of

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metatarsal II being considered an unambiguous synapomorphy of dromaeosaurids). The

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specimen also lacks a hypertrophied ungual of the second pedal digit, and is surprisingly small in

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comparison with those of equivalently sized dromaeosaurids such as Utahraptor. A heuristic

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN search and Bayesian phylogenetic analysis were performed, providing the first phylogenetic

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analyses of this enigmatic theropod. Both analyses support a placement of this taxon within

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Paraves, a clade which includes Dromaeosauridae, Troodontidae, and Avialae (birds). Despite

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previous referral to ‘Deinonychosauria,’ placement near or within any of the three major

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paravian subclades could not be retained. We also offer the first biostratigraphic placement of the

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Campanian–Maastrichtian, non-avian Antarctic dinosaurs and can, with confidence, determine

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the contemporaneous nature of the latest Cretaceous, dinosaur fauna in Antarctica.

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Keywords: Paraves; Antarctica; Cape Lamb Member; Maastrichtian; Biostratigraphy

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1. Introduction

Upper Cretaceous deposits in Antarctica are restricted to the James Ross Basin at the

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northeastern tip of the Antarctic Peninsula (Fig. 1), represented by primarily shallow marine

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sedimentary deposits (Crame et al, 2004; Case et al., 2007; Reguero et al, 2013) and where the

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Late Cretaceous dinosaurian paleofauna is located. Lower Jurassic deposits are known from the

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Beardmore Glacier area of the Transantarctic Mountains on the main portion of the continent,

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and have produced the basal sauropodomorph Glacialisaurus (Smith and Pol, 2007) and the

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theropod Cryolophosaurus (Hammer and Hickerson, 1994). The paleoenvironment pertaining to

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a new species of theropod described in this work, based on terrestrial fossil fauna and flora

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examined in deposits from James Ross Island, reveals a surprisingly diverse flora and fauna of a

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cool climate during the Maastrichtian. Based on oxygen-isotope analyses of macrofossils

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(various species of ammonites, nautiloids, belemnites, and bivalves) collected from the Santa

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Marta Formation in northern James Ross Island, the mean annual temperature of this site during

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN the Maastrichtian has been determined as 11.7˚C (Pirrie and Marshall, 1990). Paleoflora of

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James Ross Island collected includes pteridophytes, conifers, Bennettitales, Cycadales, and

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angiosperms, as well as wood attributed to the taxon Antarctoxylon (Kvacek and Sakala, 2011).

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Figure 1 NEAR HERE.

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The dinosaurian fauna of the James Ross Basin includes an ankylosaur (Gasparini et al.,

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1987), three species of ornithopods (a hypsilophont, Hooker et al., 1991; two species of

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elasmarinans, Rodadilla et al., 2016, Coria et al., 2013), a hadrosaurid (Case et al. 2000), a

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titanosaurian (Cerda et al., 2011), and a paravian, the subject of this study. The initial

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identification of the specimen from the Naze Peninsula on James Ross Island described as

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belonging to Dromaeosauridae (Case et al., 2007) seemingly increased the biogeographic range

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of the clade, previously absent from Antarctica. The supposed dromaeosaur resembled North

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American eudromaeosaur taxa such as Deinonychus or Utahraptor (Case et al., 2007). The size

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of the new species, estimated to have been approximately 2 meters in height, introduced a new

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case of gigantism in the Dromaeosauridae (Case et al., 2007).

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Paraves is a clade within Maniraptora (Coelurosauria, Maniraptoriformes) composed of

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the subclades Dromaeosauridae, Troodontidae, and Avialae (birds) (Sereno, 1997). Traditionally,

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dromaeosaurids and troodontids formed a sister-taxon relationship, Deinonychosauria (Gauthier,

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1986; Zheng et al., 2010; Turner et al., 2012), with respect to Avialae. Recent phylogenetic

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analyses have reworked major paravian subclade relationships, establishing Troodontidae and

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Avialae (=Averaptora; Cau, 2018) as sister taxa relative to Dromaeosauridae (Godefroit et al.,

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2013; Lee et al., 2014; Cau et al., 2017; Gianechini et al., 2018; Cau, 2018). Other fairly recent

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phylogenetic analyses have recovered all major paravian subclades as a polytomy (Brusatte et

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al., 2014). The pedal morphology of these clades differ in several respects: dromaeosaurids have

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short metapodia relative to troodontids, having elongate metatarsals (Makovicky and Norell,

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2004); troodontids have a (sub)arctometatarsalian condition of the proximal metatarsals (where

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the proximal end of metatarsal III is compressed between the proximal ends of metatarsals II and

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IV;), among dromaeosaurids, only the unenlagiines display this character (Agnolin and Novas,

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2011); Troodon, as well as other troodontids, have a distal, posterior process of metatarsal III

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shaped like a tongue (Makovicky and Norell, 2004); the penultimate phalanx of digit II in

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troodontids is shorter than the proximal phalanx on the same digit, whereas dromaeosaurids have

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approximately equal lengths of both these phalanges (Makovicky and Norell, 2004: fig. 9.6); the

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anterior, distal face of the metatarsals lacks ginglymoid articulation in troodontids, except for

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Sinovenator (on the third metatarsal) (Makovicky and Norell, 2004: fig. 9.6), dromaeosaurids

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have a well-developed trochlea of metatarsals II and III (Makovicky and Norell, 2004; Turner et

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al., 2012; Gianechini et al., 2018), although Agnolin and Novas (2011) and Gianechini et al.

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(2018) noted that basal dromaeosaurids Microraptor and Sinornithosaurus, as well as

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unenlagiines, have a weakly developed trochlea of metatarsal II. Both troodontids and

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dromaeosaurids display hypertrophy of the digit II pedal ungual, although troodontids tend to

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have smaller digit II unguals than dromaeosaurids (Fowler et al., 2011).

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Case et al. (2007) introduced a description of the ‘Naze Dromaeosaur.’ An unambiguous

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synapomorphy of dromaeosaurids is the presence of ginglymoid articulation of the distal

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metatarsal II (Turner et al., 2012), which is not present in the theropod from James Ross Island.

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Not noted by Case et al. (2007) was the unusually short ungual of the second pedal digit, relative

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN to other equivalently-sized dromaeosaurids such as Achillobator (Perle et al., 1999),

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Austroraptor (Novas et al., 2009), Dakotaraptor (DePalma et al., 2015), and Utahraptor

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(Kirkland et al., 1993). Motivations for the present study include offering a redescription of the

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Naze Theropod and to perform phylogenetic analyses, utilizing both parsimony and Bayesian

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methods, the first performed on the specimen. We choose two different phylogenetic analyses to

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test congruence in topologies produced. Parsimony analyses are more commonly applied to

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morphological datasets in the literature, allowing for comparisons between results in this work

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and previous phylogenetic results (examples of parsimony phylogenetic analyses for Paraves:

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Turner et al., 2012; Godefroit et al., 2013; Brusatte et al., 2014; Lee et al., 2014; Cau et al., 2017;

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Cau 2018; Gianechini et al., 2018). Bayesian phylogenetic analyses serve several advantages

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over parsimony phylogenetic analyses: Bayesian analyses allow for greater model parameter

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flexibility (Brusatte and Carr, 2016) and provide lower error rates and greater accuracy in

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determination of phylogenies compared to parsimony analyses (Wright and Hillis, 2014; albeit at

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the cost of phylogenetic precision, O’Reilly et al., 2018). If any phylogenetic resolution is

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lacking in our parsimony phylogenetic results, we hope by implementing Bayesian phylogenetic

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analyses greater phylogenetic resolution may be obtained.

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2. Material and methods

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The material of the paravian dinosaur described here was collected in the middle of the Comb

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Ridge section at The Naze, between 41-48 m above the local base of the Cape Lamb Member

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(Fig. 2) (di Pasquo and Martin, 2013; Case et al., 2007). The specimen is deposited at the

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University of California Museum of Paleontology (UCMP).

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2.1. Phylogenetic Analyses

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Gianechini et al. (2018) provides the most recent update of the TWiG (Theropod Working

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Group) data matrix, composed of 160 taxa and 905 morphological characters, the character

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matrix utilized for all phylogenetic analyses in this work. Character coding for Imperobator was

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performed in Mesquite 3.10 (Maddison and Maddison, 2015) and added to the character matrix

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for Gianechini et al. (2018) in Mesquite 3.10, for a total of 161 taxa used for the phylogenetic

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analyses. This character matrix is based off Brusatte et al. (2014) with added characters and taxa,

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which in turn is a continuation of the Theropod Working Group Matrix (TWiG; Norell et al.,

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2001).

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TNT 1.5 (Goloboff et al., 2016) identified and excluded 24 uninformative characters (command = ‘xinact’). We utilized TNT 1.5 for parsimony analyses through the traditional

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search option by performing 1,000 replications of Wagner trees with random addition sequences

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(outgroup = Allosaurus fragilis), holding 10 trees at each replication with TBR branch swapping.

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Characters were equally weighted. We used the strict consensus tree for bootstrapping,

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performing 10,000 bootstrap iterations. The consensus tree and bootstrap values for each node

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are reported in Figures 8-9.

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We also performed Bayesian phylogenetic analyses in MrBayes 3.2 (Ronquist et al.,

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2012) using two versions of Lewis’ Mk model, one with and without incorporation of the gamma

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parameter (Lewis, 2001). Datatype was set to standard, allowing for variable numbers of states

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per character (Brusatte and Carr, 2016), with equal substitution rates (nst=1) set for both

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analyses. The first analysis ran for 12,000,000 generations and the second ran for 11,482,000,

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sampling a tree every 1,000 generations. To evaluate Markov Chain Monte Carlo (MCMC)

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN convergence, each analysis ran longer necessary to decrease the average standard deviation of

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the split frequencies below 0.01. By default, the first 25% of samples were treated as burn-in. To

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determine the preferred tree, we collected the harmonic means of the log-likelihoods for both

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analyses. The associated tree with a harmonic mean closest to 0 determines the preferred model

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of evolution, unless the difference of the harmonic means is not significantly different (Kass and

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Raftery, 1995). Significant difference of the two harmonic means is determined by subtracting

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the absolute value of the two harmonic means, with a resulting difference greater than 5

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considered significant (Kass and Raftery, 1995).

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3. Geologic setting

The western flank of Comb Ridge, which is one of two high points at the distal end of the Naze Peninsula (Fig. 1), is represented by a 91 m-thick section (Fig. 2) that has its base at sea

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level and terminates below a Miocene, James Ross Island basalt sill that caps the section. These

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deposits represent an outcrop of the Cape Lamb Member of the Snow Hill Island Formation on

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James Ross Island (Crame et al., 2004). This 91 m section is composed of interbedded, green-

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gray massive and laminated fine-grained quartz sandstones and greenish yellow argillaceous

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mudstones and siltstones, with thin layers of concretions and bentonite clays dispersed through

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the section (di Pasquo and Martin, 2013).

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The Cape Lamb Member on Vega Island (Fig. 1) (Pirrie et al., 1991; Crame et al., 2004)

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contains the lower part of the Maastrichtian Stage in Antarctica, based on an isotopic date of 71.0

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+ 0.2 Ma derived from a mean 87Sr/86Sr value of 0.7077359 from molluscan shells found in the

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section at a stratigraphic level 81m above the base of the Gunnarites antarcticus faunal

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assemblage (Fig. 3). The Campanian–Maastrichtian boundary in Antarctica is defined by the

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN occurrence of this bivalve-nautiloid assemblage at the beginning of the range zone of the

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ammonite Gunnarites antarcticus, as the faunal assemblage extends through some 210 meters of

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the 310-meter reference section on Cape Lamb Peninsula, Vega Island (unit B, Fig. 3) (Crame et

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al., 1999). As indicated in Fig. 3, the boundary is considered to be at ca. 72 Ma.

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The material of the paravian dinosaur described here was collected in the middle of the Comb Ridge section at The Naze, between 41-48 m above the local base of the Cape Lamb

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Member (Fig. 2) (di Pasquo and Martin, 2013; Case et al., 2007).

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Ammonites, pelecypods, and decapods were also found within this 90 m section. The ammonites, Gunnarites antarcticus, Diplomoceras lambi and Kitchinites darwini, the pelecypod

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Pinna, and the decapod Hoploparia antarctica which were found in the middle part of the Comb

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Ridge section are all part of the Gunnarites antarcticus faunal assemblage better known from the

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Cape Lamb Member on Vega Island that crops out in unit B of the 310 m reference section of

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Pirrie et al. (1991) there (Fig. 3). Within that section, the Gunnarites antarcticus faunal

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assemblage ranges through about 210 m of section with the ammonites, Gunnarites antarcticus

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and Kitchinites darwini, present through the entirety of the assemblage range. However, the

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stratigraphic range of the heteromorphic ammonite, Diplomoceras lambi, is restricted to about 50

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m of section (approximately from 150 m to 200 m level in the Cape Lamb section; Pirrie et al.,

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1991) within the lower half of the Gunnarites antarcticus faunal range. The 71.0 +0.2 Ma datum

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was determined from 87Sr/86Sr ratios from molluscan shell material (at the 191 m level) is near the

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top of the Diplomoceras lambi range in the Cape Lamb reference sequence (Crame et al., 1999).

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In the Comb Ridge section at The Naze, Gunnarites antarcticus, was recovered from the

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bottom part of the section (<20 m) below the Naze Theropod remains, while the other

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ammonites, Diplomoceras lambi and Kitchinites darwini, were found above Imperobator at

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN approximately 73 m (Fig. 2). These theropod remains are clearly associated with the early

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Maastrichtian, Gunnarites antarcticus faunal assemblage and within (and possibly ranging

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slightly below) the more restricted stratigraphic range of Diplomoceras lambi. The resulting age

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assignment for the specimen described in this work from The Naze based on the

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palynoassemblages as proposed by di Pasquo and Martin (2013), the stratigraphic range of the

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ammonite Diplomoceras lambi (Pirrie et al., 1991), and the 71.0 Ma datum (Crame et al., 1999)

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is earliest Maastrichtian.

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Figure 2 NEAR HERE

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Figure 3 NEAR HERE

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3. Systematic Paleontology

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Dinosauria Owen, 1842 Theropoda Marsh, 1881 Maniraptora Gauthier, 1986 Paraves Sereno, 1997

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antarcticus for its location of discovery.

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Holotype. UCMP 276000, Imperobator antarcticus is incompletely preserved, with only a

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fragmented left pes and other smaller fragments from the right pes. Pedal material preserved

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includes: the distal portion of the tibia; an incomplete astragalus; calcaneum-fibula (fusion of

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calcaneum and fibula); fragments of metatarsals II-IV; material from metatarsal I, and even

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Imperobator antarcticus gen. et sp. nov. Figs. 4-7 Etymology. Impero (Latin), meaning commanding or powerful; bator (Mongolian) warrior;

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN metatarsal V may be preserved; pedal digit material from all digits, including the ungual phalanx

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of the second pedal digit.

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Type locality. This specimen was collected from the western flank of Comb Ridge on the Naze

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Peninsula of James Ross Island, Antarctic Peninsula (Case et al. 2007) designated as UCMP

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(University of California Museum of Paleontology) Locality RV-9502. This locality pertains to

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the lower Maastrichtian Cape Lamb Member (di Pasquo, M. and J.E. Martin. 2013; Martin et al.,

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2009) of the Snow Hill Island Formation, at western flank of Comb Ridge on the Naze Peninsula

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of James Ross Island, Antarctic Peninsula (Case et al. 2007).

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Stratigraphic position. The specimens of the theropod described here, were collected (Fig. 2) in

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the middle of the Comb Ridge section at The Naze between 41 m to 48 m above the local base of

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the Cape Lamb Mbr. (Fig. 2) (di Pasquo and Martin, 2013; Case et al., 2007).

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Age. The specimen is within the stratigraphic range of the ammonite Diplomoceras lambi, which

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has the upper part of its range dated to ca. 71.0 + 0.2 Ma on Vega Island, James Ross Basin

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(Crame et al., 1999) and is thus earliest Maastrichtian.

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Diagnosis. The flowing traits are unique to Imperobator: fusion of the fibula and calcaneum;

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parallelogram-outline of metatarsal II cross section; metatarsal II medial slanting where the

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diaphysis terminates (pathological?). Following traits are non-diagnostic, but represent unusual

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traits important for referral of the described taxon as non-dromaeosaurid: distal articular surface

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of metatarsal II non-ginglymoid; ungual phalanx of second pedal digit small and without strong

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curvature, contrary to the condition seen in eudromaeosaurs (likely a plesiomorphy of more basal

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coelurosaurs).

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4. Description

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN Figure 4 displays a reconstruction of the left pes of Imperobator antarcticus and

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recovered material associated. Only the distal left tibia is preserved (Fig. 5A), and little

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anatomical information can be described, especially after freeze-thaw processes have

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deteriorated many details. Approximately half of the astragalus, the lateral portion in articulation

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with the calcaneum, is missing (Fig. 5B). Only basal portions of the astragalur ascending process

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is preserved. Laterally (non-medial view) the astragalus is semicircular ventrally and semi-planar

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dorsally.

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Calcanea are present from both left and right pes, with the right being more complete.

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The calcanea are fused to their respective fibulae (Fig. 5C, 5D). The internal calcaneal surface

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forms a fossa (Fig. 5D) for articulation with the astragalus, with the external surface convex (Fig.

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5C). The semi-circular outline of the distal portion of the calcaneum is matched with a dorsal,

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posterior groove on metatarsal IV, best seen in lateral view. The external surface of the

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calcaneum possesses a circular pattern that reaches the limits of the calcaneum, but is separated

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by a shallow groove.

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Figure 5 NEAR HERE

The distal tarsals are almost entirely missing except for one either fused to the proximal

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articular surface of metatarsal III or attached by sediment. It is anteroposteriorly longer than

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wide, with a narrow, sub-triangular outline anteriorly and a pseudo-hexagonal outline

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posteriorly, and contains a slight anterior groove (Fig. 6D).

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN The metatarsus is heavily fragmented. The left pes is more complete, with only a few

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fragments from the right pes. Metatarsal II is divided into three fragments. The proximal

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fragment contains the articular surface with the distal tarsus. Distally this fragment terminates

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approximately where the diaphysis originates (=metaphysis). In anterior view, the proximal

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surface slopes downward laterally, which is due to the distal expansion of the tarsal elements

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(Fig. 6A). In lateral view, the proximal surface is formed by protrusions, or ‘horns’, anteriorly

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and posteriorly (Fig. 6A). The posterior horn is expanded more than the anterior horn. The

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diaphysis attached to this fragment is broken, revealing a semi-circular cross-section.

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The inner cavity of the diaphysis is filled with a hardened, resinous material. Metatarsal

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II is further broken into a medial element, which deviates from the semi-circular cross-section of

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the diaphysis and forms a semi-parallelogram cross-section (Fig. 6B). In anterolateral view, the

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lateral face forms a sharp angle to the anterior face, forming a rectangular outline. The medial

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face is deteriorated, and exposed is a resinous interior which can also be seen in the proximal

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fragment.

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The distal fragment of metatarsal II proximally preserves the distal diaphysis down to the

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distal articular surface with digit II. The diaphysis shows a slight medial protrusion as a result of

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being slightly displaced so the shaft is not oriented vertically, but slants medially where the

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diaphysis terminates (Fig. 6C). The distal articular surface of metatarsal II is non-ginglymoid. Its

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surface is narrowed anteriorly and smooth (Fig. 6C). Posterior epicondyles forming a midline

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fossa indicate a strong ligament associated with the second pedal digit.

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The material preserved for metatarsal III includes a proximal articular head, as well as a

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distal fragment preserving the articular aspect with digit III. The proximal articular surface of

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metatarsal III has a preserved tarsal element adhering to it. Anteriorly, the proximal head of the

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN metatarsal shows a subtriangular face pointing distally. Laterally, the articular surface seems to

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be roughly planar, with a gently sloping downward anterior face, and a posterior protrusion (Fig.

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6D). The articular surface is much thicker anteroposteriorly than where the diaphysis begins,

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which is reduced in diameter. Proximally, metatarsal III displays a sub-rectangular outline and is

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not pinched anteriorly (Fig. 6D). Metatarsal III bears equal exposure as the proximal heads of

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metatarsals II and IV. The distal half of metatarsal III is preserved, with a heavily damaged distal

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metaphysis and distal articular facet. A ginglymoid articulation is present in the articular facet,

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with a deep fossa running anteroposteriorly (Fig. 6E). The left condyle of the ginglymus is

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slightly larger than the right (Fig. 6E). The ginglymoid nature of the articular surface contrasts

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with the articular surface of metatarsal II, which is non-ginglymoid. The lateral fossa of the distal

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head is preserved.

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The fourth metatarsal is fragmented into proximal, medial, and distal fragments. The

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proximal fragment shows a similar shape to the other metatarsal heads, with an anteroposteriorly

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wider head and a shaft (diaphysis) reduced in size. The ventral surface of this fragment is planar

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(Fig. 6G), whereas the dorsal surface has a robust protrusion proximally (Fig. 6G). In medial

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view, the proximal posterior side of this fragment has a slight semi-circular arch where the

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calcaneum articulates with this articular surface (Fig. 6F). The medial fragment of metatarsal IV

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bears the posterior, longitudinal ridge (Fig. 6H). The distal end of metatarsal IV is also preserved

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(Fig. 6I). It bears a narrow articular area proximally, expanding distally in anterior view. The

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articular surface is slanted medially, and is non-ginglymoid. The medial edge of the articular

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surface is distally expanded more than the lateral edge. In distal view, the articular end is

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narrower anteriorly than posteriorly. Most of the diaphysis above the articular surface is missing,

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only the metaphysis is preserved.

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ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN 304

Figure 6 NEAR HERE

305 306

The preserved elements of the second pedal digit of Imperobator include the proximal

308

half of the second phalanx and the proximal half of the ungual phalanx. The proximal portion of

309

pedal phalanx II shows a semi-circular fossa of the articular surface (Fig. 7A). The

310

proximoventral heel is weakly developed, with a flattened ventral surface and transversely wide

311

(Fig. 7A). Without the whole fragment intact, it is impossible to determine the presence mid-

312

length constriction because the distal half of this fragment is missing, but there is a reduction in

313

size distally.

M AN U

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307

As mentioned before, only the proximal half of the ungual is preserved, along with a

315

small distal fragment. Proximally, the articular surface in lateral view is concave in outline (Fig.

316

7B) as opposed to the strong semi-circular outline generally of most dromaeosaurids and

317

troodontids. In proximal view, the articular surface has a weak ridge subdividing it medially. A

318

proximoventral heel is present, but not nearly the same size of other dromaeosaurids or

319

troodontids. The overall curvature of the ungual is weak, but not as straight as in the troodontid,

320

Borogovia (Osmalska, 1987). In cross-section, the ungual is asymmetrical, best seen from

321

proximal view, and lacks a sub-rectangular outline. Instead, the outline curves medially, and

322

reduces in size dorsoventrally. The lateral grooves are asymmetrical, a trait seen in most paravian

323

second pedal digit unguals. The medial groove begins more proximally than the lateral groove.

324

The distal fragment is small and very thin mediolaterally; a lateral groove is present which

325

indicates it belongs to this ungual.

AC C

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314

326

Phalangeal elements of the third and fourth pedal digits are also preserved. The trochlea

327

of a proximal phalanx pertaining to digit III (?) indicates ginglymoid articulation (Fig. 7E). The 14

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN 328

condyles of the trochlea are symmetrical. A lateral fossa is present on each condyle. The

329

phalangeal shaft would have been quadrangular in cross section, as seen from proximal view of

330

this fragment, which is broken where the shaft terminates. A complete proximal-most phalanx of the fourth pedal digit in association with the distal

332

end of metatarsal IV is also preserved as the most complete phalanx in the pes (Fig. 7C). The

333

proximal phalanx of pedal digit IV bears a ginglymoid distal articular surface. From lateral and

334

medial views the phalanx is constricted at its midpoint with both articular surfaces more

335

dorsoventrally expanded. The distal the articular surface is less dorsoventrally expanded than the

336

proximal articular surface. Fossae are present on the lateral and medial surfaces of the distal

337

portion of this phalanx. In proximal view, there is a dorsal extension expanding greater than the

338

ventral portion of the articular surface.

M AN U

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331

A small portion of the ungual is also present. Potential material from digit I may be

340

present (Fig. 7D). It is distinguished by what may be a prominent flexor heel on the

341

proximoventral surface, morphologically similar to that of the dromaeosaurid (avialan?) Balaur

342

bondoc (Csiki et al. 2010).

Figure 7 NEAR HERE

344

347 348

AC C

346

6. Results

EP

343

345

TE D

339

6.1 Phylogenetic Analyses

349

Initial parsimony analyses recovered 340 most parsimonious trees of length 3,548

350

(10,910,497,001 rearrangements tried), with the best score retrieved 34 out of 1,000 times.

15

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN Imperobator is placed within a monophyletic Paraves, but subclade resolution is low.

352

Troodontidae and Avialae are recovered as monophyletic groups, while dromaeosaurids and

353

other basal paravians are placed in a polytomy along with Imperobator. Bootstrap values for

354

Paraves is 3%, while for the clades Troodontidae and Avialae is both 11%. Coelurosauria

355

displays the highest bootstrap value among all nodes in the analysis performed (93%). These

356

results bear similarity to those of Brusatte et al. (2014), where analyses recovered a trichotomy

357

among the three major paravian subclades. However, the present analysis recovers a non-

358

monophyletic Dromaeosauridae. These clades are recovered in a polytomy with several basal

359

ornithomimosaurs and two basal oviraptorosaurs.

M AN U

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351

The following character states are synapomorphies of Paraves according to the heuristic

361

search performed (numeric character.state): 198.1: ginglymoid distal articular surface of

362

metatarsal II; 199.1: ginglymoid distal articular surface of metatarsal III; 201.1: hypertrophied

363

ungual phalanx of the second pedal digit; 226.1: a posterolateral flange on metatarsal IV. See

364

Brusatte et al. (2014) and Gianechini et al. (2018) for list of characters used in the analysis.

TE D

360

We performed another set of maximum parsimony analyses utilizing the same character

366

matrix and settings used in the previous analysis, but excluding three taxa identified by

367

Gianechini et al. (2018) as wildcards: Kinnareemimus, Pyroraptor, and Pamparaptor. 590 most

368

parsimonious trees of length 3557 were retained, best score hit 59 times out of 1000. Basal

369

ornithomimosaurs are resolved within Ornithomimosauria, and the two oviraptorosaur taxa are

370

placed within Oviraptorosauria (Fig. 8; Fig. S2). Other coelurosaurian clades are recovered as

371

monophyletic in the present analysis (with nodal bootstrap values): Alvarezsauridae,

372

Therizinosauridae

373

Scansoriopterygidae, Compsognathidae, Tyrannosauroidea (64%), and Coelurus fragilis +

AC C

EP

365

(97%),

Oviraptorosauria

16

(57%),

Ornithomimosauria

(64%),

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN Tanycolagreus; (Fig. 8; Figs. S1-S3). These clades are recovered in a polytomy with several

375

basal ornithomimosaurs and two basal oviraptorosaurs (Fig. 8; Figs. S1-S3). Paraves is still

376

recovered as monophyletic, with a monophyletic Troodontidae and Avialae (Fig. 9; Fig. S3).

377

Anchiornithidae is present as a polytomy. Most dromaeosaurid taxa are still recovered as

378

polytomous, except for the following clades: Velociraptor + Adasaurus, Utahraptor +

379

Achillobator, Mahakala + Unenlagiinae, and (Tianyuraptor + Zhenyuanlong) + Microraptoria

380

(Fig. 9; Fig. S3). With the exception of a few avian subclades, no major clades within Paraves

381

retrieve bootstrap values higher than 50%. Imperobator is present in a polytomy of

382

dromaeosaurid and anchiornithid taxa, as in the previous set of analyses without wildcard

383

excluded (Fig. 9; Fig. S3).

M AN U

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374

384

Figure 8 NEAR HERE

386

Figure 9 NEAR HERE

TE D

385

387

Bayesian analyses provided greater resolution and higher nodal values (posterior

389

probabilities) for many Coelurosaurian clades (Fig. 10; Figs. S4-S6). The harmonic mean of the

390

Mkv model without the gamma parameter is -15616.96, and the Mkv model with the gamma

391

parameter is -15412.56. As the harmonic mean of the Mkv + gamma parameter model is closest

392

to zero, this suggests the tree associated with this model best fits the data. The difference

393

between the harmonic means of the two Mkv models is 204.4, greater than 5, and thus

394

significantly greater than the harmonic mean of the Mkv model without the gamma parameter

395

(Kass and Raftery, 1995).

AC C

EP

388

17

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN 396

Imperobator is placed within a monophyletic Paraves (posterior probability = 65%). Paraves is presented in a polytomy with Troodontidae, Avialae, Dromaeosauridae, and a

398

polytomy of the basal paravian clade Anchiornithidae (Fig. 10; Fig. S6). Dromaeosauridae is

399

recovered as a monophyletic clade, contrary to the topology produced via parsimony analyses.

400

Posterior probabilities for Dromaeosauridae, Troodontidae, and Avialae are 50%, 98%, and 91%,

401

respectively. Non-paravian coelurosaurian clade resolution is improved compared to our

402

parsimony analyses. Oviraptorosauria (63%), Scansoriopterygidae (95%), Therizinosauridae

403

(100%), Alvarezsauroidea (91%), Ornithomimosauria (73%), Compsognathidae (99%),

404

Tyrannosauroidea (99%), and Coelurus fragilis + Tanycolagreus (100%) are recovered a

405

monophyletic (Fig. 8-10; Figs. S4-S6), and in non-polytomous relationships among these clades,

406

unlike results from the parsimony analyses.

M AN U

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397

407

Figure 10 NEAR HERE

409

412 413

EP

411

7. Discussion

7.1 Anatomical comparisons

Among paravians alone, Imperobator displays traits common both to troodontids and

AC C

410

TE D

408

414

dromaeosaurids. Imperobator does not display any degree of arctometatarsaly, such as in

415

dromaeosaurids (excluding unenlagiines; Agnolin and Novas, 2011), lacks a tongue-like process

416

posterodistally on metatarsal III (the presence of which has previously been considered a

417

synapomorphy of Troodontidae; Godefroit et al., 2013), and has a well-developed ginglymus of

418

metatarsal III. Imperobator has troodontid-like features, such as a non-ginglymoid anterior

18

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN articulation of distal metatarsal II and pedal ungual morphology of digit II similar to that of

420

troodontids. However, the lack of these characters in Imperobator otherwise present in

421

troodontids or dromaeosaurids suggest plesiomorphic traits in Imperobator relative to Paraves,

422

such as: a smooth distal articular surface of metatarsal II, non-arctometatarsaly of the proximal

423

metapodium, and the tongue-like process of the posterodistal articular surface of metataral III.

424

The latter character has previously been considered a synapomorphy of Troodontidae (Godefroit

425

et al., 2013), although the distribution of this trait is perhaps more widespread (see Section 7.4

426

7.5; “Distal, posterior tongue-like process of metatarsal III”).

SC

RI PT

419

Fusion of the proximal aspect of the calcaneum to the distal aspect of the fibula known in

428

the coelurosaurs Buitreraptor, Graciliraptor, and Balaur, which bear fusion of the distal tibia

429

and fibula with the proximal tarsals (Brusatte et al., 2013). Variation in fusion among the

430

proximal tarsals, tibia, and the fibula exists. In Imperobator, only the fibula and the calcaneum

431

are fused.

TE D

M AN U

427

The head of metatarsal III, in caudal view, has a semi-rectangular outline, as opposed to

433

the condition in (sub)arctometatarsaly as seen in troodontids, unenlagiines, and tyrannosaurids,

434

where the proximal head forms a sub-triangular outline because of the buttressing metatarsals II

435

and IV (Holtz, Jr., 1995; White, 2009). In paravians, the subarctometatarsus is displayed in

436

unenlagiine dromaeosaurids (Agnolin and Novas, 2011), troodontids (Norell and Makovicky,

437

2004), and some basal avialans (Agnolin and Novas, 2011). In proximal view, the third

438

metatarsal is unconstrained and inconsistent with (sub)arctometatarsaly, such as the condition in

439

non-unenlagiine dromaeosaurids.

AC C

EP

432

440

Although the previous publication on the specimen described in this work (Case et al.,

441

2007) argued a placement within Dromaeosauridae, re-examination of the Naze specimen

19

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN revealed certain anatomical deviations from dromaeosaurid pedal anatomy. The ungual phalanx

443

of digit II, although enlarged relative to the other unguals of the foot, is not nearly as long or

444

robust as in Deinonychus or Utahraptor. For a gigantic dromaeosaurid, the ungual is not nearly

445

as large as in Velociraptor mongoliensis, or Deinonychus antirrhopus, though these two

446

dromaeosaurids are smaller in overall body size than the Naze theropod. Its aberrant features cast

447

doubt on a dromaeosaurid placement by some authors. Turner et al. (2012) examined the

448

anatomy of the Naze Raptor and concluded due to a lack of ginglymoid distal articulation of

449

metatarsal II in this new taxon (a highly diagnostic character of Dromaeosauridae) that a

450

placement at least within Deinonychosauria (Troodontidae + Dromaeosauridae) may be justified,

451

but a dromaeosaurid diagnosis is not.

M AN U

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442

A weakly-ginglymoid surface of the anterodistal metatarsal II is observed in the

453

dromaeosaurid subclade of South American unenlagiines Unenlagia, Rahonavis, and

454

Buitreraptor (Agnolin and Novas, 2011). Most phylogenetic analyses by other authors (Turner et

455

al., 2012; Godefroit et al., 2013; Brusatte et al., 2014; Lee et al., 2014; Cau et al., 2017; Cau

456

2018; Gianechini et al., 2018) have placed the Unenlagiinae within Dromaeosauridae, though

457

Agnolin and Novas (2011, 2013) placed the Unenlagiinae as a sister taxon to Avialae.

458

Sinornithosaurus and Microraptor are basal dromaeosaurids without a well-developed

459

ginglymus (Agnolin and Novas, 2011), like in Imperobator. Most troodontids lack distal

460

ginglymoid articulation of all metatarsals (excluding Sinovenator changii whose distal articular

461

surface of metatarsal III is ginglymoid) (Norell and Makovicky, 2004), and basal avialans such

462

as Archaeopteryx, Jeholornis, and Zhongornis also lack this ginglymus of metatarsal II (Agnolin

463

and Novas, 2011), so it is probable that the ancestral state for the basal-most paravian was a lack

464

of a ginglymoid, distal articular surface of metatarsal II.

AC C

EP

TE D

452

20

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN The atypical characteristics of Imperobator compared with dromaeosaurids are limited to

466

the second pedal digit. Pedal phalanx II-2 lacks a strong proximoventral heel. Typically,

467

dromaeosaurids have a robust proximoventral heel ventral to the proximal, articular surface, such

468

as in Deinonychus (Ostrom, 1969). The raptorial second pedal digit in paravians such as

469

dromaeosaurids and troodontids was typically elevated from the ground (Makovicky and Norell,

470

2004), allowing for the robust process of the proximoventral heel. The ungual is unusually small,

471

in comparison with typical dromaeosaurids such as Deinonychus antirrhopus (Ostrom, 1969),

472

and Velociraptor mongoliensis (Norell and Makovicky, 1999). Imperobator is of comparable

473

size to Utahraptor, and is estimated to have been about 2 meters in height by Case et al. (2007).

474

The approximate length of the pedal ungual of digit II in Utahraptor is 10 cm (approximate

475

measurement made by one of the authors based on illustrations provided by Kirkland et al.,

476

1993), and although the distal half of the pedal ungual in Imperobator is missing, an estimate for

477

its total length would be 4-5 cm. A supposed dromaeosaurid of comparable size to

478

dromaeosaurids displaying gigantism would be expected to bear an ungual of approximate length

479

to taxa such as Utahraptor, Achillobator, or Austroraptor. Imperobator lacks a digit II ungual of

480

comparable size to these gigantic dromaeosaurids. This feature was not noted by the original

481

authors of the ‘Naze dromaeosaur’ (Case et al. 2007), even though the digit II ungual is still

482

technically hypertrophied. Dromaeosaurids tend to display strong curvature of the digit II ungual,

483

which Imperobator does not display.

485 486 487

SC

M AN U

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AC C

484

RI PT

465

7.2 Phylogeny

Our parsimony phylogenetic analysis provides synapomorphies supporting the Paravians as a clade. The posterolateral flange of metatarsal IV has been considered an unambiguous

21

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN synapomorphy by previous works of paravian phylogeny (Agnolin and Novas, 2012; Cau 2018).

489

This character is present in the taxon described here. Hypertrophy of the second pedal ungual is

490

considered extreme in eudromaeosaurs, while variation in this condition exists in other paravians

491

(Gianechini et al., 2018). In addition to our phylogenetic analyses supporting a paravian affinity

492

for the taxon described in this work, the Paravian synapomorphies recovered in this work are

493

also identified in previous studies as paravian synapomorphies. With the exclusion of character

494

198.1, all these characters have been considered Paravian synapomorphies in previous

495

phylogenetic analyses of Paraves, and are present in Imperobator.

SC

RI PT

488

In our analyses, three of the four paravian synapomorphies are present in Imperobator.

497

Distal ginglymoidy of metatarsal II has previously been considered a dromaeosaurid

498

synapomorphy rather than one of Paraves (Gianechini et al., 2018; Turner et al., 2012). In our

499

parsimony analysis, most dromaeosaurid taxa collapse into a polytomy with Troodontidae and

500

Avialae, while our Bayesian analysis support the monophyletic dromaeosaurid subclades

501

eudromaeosaurids, microraptoriines, and unenlagiines. Phylogenetic analyses performed by

502

Gianechini et al. (2018) display similar resolution to our parsimony analyses. The distal

503

ginglymoid metatarsal II as a paravian synapomorphy in our analysis is likely due to the collapse

504

of dromaeosaurids into these polytomies in both phylogenetic analyses. Character mapping

505

performed in TNT 1.5 shows only dromaeosaurid taxa displaying this character. Another

506

interpretation for character 198.1 as a paravian synapomorphy is as a synapomorphy for a less

507

inclusive clade of Paravians, in which Imperobator is the sister taxon to the clade

508

Dromaeosauridae + (Troodontidae + Avialae), while maintaining its paravian affinity given the

509

presence of three paravian synapomorphies.

AC C

EP

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M AN U

496

510

22

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN 7.3 Gigantism in Imperobator

512

Gigantism has been reported in the dromaeosaurid taxa Austroraptor (Novas et al., 2009),

513

Achillobator (Perle et al., 1999), Dakotaraptor (DePalma et al., 2015), and Utahraptor (Kirkland

514

et al., 1993). Basal members of the three major paravian clades, Dromaeosauridae, Troodontidae,

515

and Avialae, are small-bodied theropods, implicating a small body size for the ancestral

516

paravian, estimated by Turner et al. (2007) to be 600-700 g and approximately 65 cm in length.

517

The causes for gigantism in Imperobator may be similar to those hypothesized for Austroraptor.

518

Leanza et al. (2004) suggested the body size increase in coelurosaurians in the South American

519

continent are due to the extinction of larger bodied carcharodontosaurid theropods. Imperobator

520

may represent a response to similar conditions, although very few theropods from the upper

521

Campanian or Maastrichtian deposits have been found in Antarctica, or prior to the

522

Maastrichtian, and no evidence exists that can support this claim.

M AN U

SC

RI PT

511

524

TE D

523

7.4 Distal, posterior tongue-like process of metatarsal III The presence of a tongue-like distal, posterior process is a feature present in the basal

526

dromaeosaurid Sinornithosaurus millenii (Xu and Wang, 2000), as well as some troodontids such

527

as Troodon formosus, Sinornithoides youngi, Saurornithoides (Currie and Zhiming, 2001), and

528

Borogovia gracilicrus (Osmalska, 1987). Early in our evaluation of morphological characters of

529

Imperobator, this process seemed to exist in metatarsal III of Imperobator. Early phylogenetic

530

tests as part of our study attempted placement of Imperobator within Troodontidae. This feature

531

seemed an appropriate justification for its placement; upon further inspection, this process is

532

absent in Imperobator. Due to freeze-thaw processes, the surrounding condyles have

533

deteriorated, and preserved is the flexor canal on the distal, posterior portion of metatarsal III,

AC C

EP

525

23

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN which appears as if it is the tongue-like process present in some troodontids. We have come to

535

define this feature with more clarity for future referrals of this character to certain taxa. In taxa

536

with this character, the proximal portion of the ‘tongue’ must not be continuous with the ventral

537

surface of metatarsal III, but must be elevated slightly to form a pronounced limit to the tongue.

538

In Imperobator, the flexor canal is a continuous surface with the ventral surface of metatarsal III,

539

so the ‘tongue’ not present in this taxon.

RI PT

534

Although beyond the scope of this study, we found that this tongue-like process is far

541

more widespread than in the troodontids listed above (and Sinornithosaurus), but seems to be

542

present in several avialans, and is especially prominent in neornithine taxa that we have

543

analyzed. The process is also present in theropods outside of Paraves, such as Tyrannosaurus rex

544

(Brochu, 2003). We noted the presence of this process in phorusrhacids (Degrange et al., 2015),

545

ratites (Tambussi et al., 1994), and penguins (Ksepka et al., 2012). This process may be

546

widespread in the Pelecanidae (Stidham et al., 2014). The early avialan Evgenavis nobilis, which

547

is described as having a confuciusorniform-like tarsometatarsus, displays this feature in plantar

548

view (O’Connor et al., 2014).

M AN U

TE D

EP

549

SC

540

8. Biostratigraphy of latest Cretaceous dinosaur fauna

551

The stratigraphic location, biostratigraphic associations and the age assessment for Imperobator,

552

indicates (Fig. 3) that it is a contemporary of the hypsilophodont recovered from the top of the

553

Diplomoceras lambi range on the eastern slope of Cape Lamb (Hooker et al., 1991). A medium-

554

sized ornithopod, Morrosaurus antarcticus (Rozadilla et al., 2016) was collected from the “El

555

Morro” locality at the base of the Naze Peninsula also from deposits of the Cape Lamb Mbr.,

556

some 30 m down section from the locality where Imperobator was collected. The Morrosaurus

AC C

550

24

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN specimen is also associated with the early Maastrichtian, Gunnarites antarcticus faunal

558

assemblage and occurs within the Diplomoceras lambi range, as this species of ammonite was

559

found in association with the ornithopod specimen. Thus, the 30 m of section of the Cape Lamb

560

Mbr. on the Naze, which contain Imperobator and Morrosaurus, would be contained within the

561

50 m of stratigraphic range of Diplomoceras lambi in the reference section on Cape Lamb for

562

that Member. This results in all three, dinosaur taxa recovered from the Cape Lamb Member

563

deposits, the paravian Imperobator, the hypsilophodont and Morrosaurus, being recovered from

564

the Diplomoceras lambi stratigraphic range within the Cape Lamb Member of the Snow Hill

565

Island Formation, with an age of approximately 71.0 Ma.

SC

M AN U

566

RI PT

557

Morrosaurus antarcticus is similar in form, especially pedally, to Trinisaura santamartaensis (Coria et al., 2013) from Santa Marta Cove area of James Ross Island and both

568

species are classified as elasmarian iguanodontians, which are considered to be basal ornithopods

569

by Rozadilla et al. (2016). Trinisaura was recovered from the uppermost Campanian, Herbert

570

Sound Member (Pirrie et al., 1991) or Gamma Mbr. (Olivero, 2012), of the Snow Hill Island

571

Formation from the Santa Marta Cove area at the southeast base of the Ulu Peninsula, which is

572

only twelve kilometers to the east of the Naze. The Herbert Sound or Gamma Member, underlies

573

the Cape Lamb Member (Fig. 3) within the Snow Hill Island Formation on both James Ross

574

Island (the Naze/El Morro) and Vega Island (Cape Lamb) and on Humps Island as well. The

575

ankylosaur Antarctopelta oliveroi Salgado and Gasparini (2006) was also recovered from the

576

Gamma Mbr. of the Snow Hill Formation in the Santa Marta Cove area only some 10 meters

577

stratigraphically below the level where Trinisaura was discovered. A third dinosaur taxon, a

578

lithostrotian titanosaur, was recovered in the upper third of Gamma Mbr. deposits at Santa Marta

579

Cove (Cerda et al., 2011). The titanosaur specimen was approximately 40 meters up section

AC C

EP

TE D

567

25

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN 580

from the Trinisaura locality where ammonites once again become abundant (see Coria et al.,

581

2013 for stratigraphic data).

582

Olivero (2012a,b) places the first occurrence of Gunnarites antarcticus at the very top of the Gamma Mbr. section at Santa Marta Cove and overlaps the uppermost portion of the 70-

584

meter total stratigraphic range of Neograhamites cf. kiliani illustrated by Olivero (2012b) in his

585

stratigraphic section No. 2 near his site QF (Olivero et al., 1991). This same biostratigraphic

586

Neograhamites/Gunnarites ammonite sequence is repeated in the Gamma Mbr. (=Herbert Sound

587

Member of Crame et al., 2004) equivalent sequence of the Cape Lamb Peninsula on Vega Island,

588

except that the stratigraphic range for G. antarcticus extends for some 200 meters higher in the

589

deposits of the Cape Lamb Mbr. The Neograhamites cf. kiliani and Gunnarites antarcticus

590

ammonite biostratigraphic zonations (Fig. 3) allow for correlation between the dinosaur bearing

591

sequence in the Gamma Mbr. in Santa Marta Cove area with those from the Cape Lamb Mbr. on

592

the Naze and Cape Lamb peninsulas.

TE D

M AN U

SC

RI PT

583

Based on the sections of Olivero (2012a,b) and Coria et al. (2013) and the reference

594

section for the Cape Lamb Mbr. (Pirrie et al., 1991; Crame et al. 2004) on Vega Island, this

595

places the three dinosaurs (Antarctopelta, Trinisaura and the titanosaur) from the Santa Marta

596

Cove area within 150 meters of the Campanian–Maastrichtian boundary and thus, they would be

597

of latest Campanian age, most likely between ca. 73 and 72.1 Ma. The three dinosaur species

598

(Imperobator, Morrosaurus and the hypsilophodontid) from the Cape Lamb Mbr. of the Snow

599

Hill Island Fm. on the Naze and Cape Lamb peninsulas, all of which are associated with the

600

Diplomoceras lambi range zone at ca. 71.0 Ma are of earliest Maastrichtian age and only 50 to

601

100 meters above the Campanian–Maastrichtian boundary. Given the limited spread of section

602

and age between all six dinosaur species we consider all the dinosaur species discussed here as

AC C

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593

26

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN 603

contemporaries of each other and as a single dinosaur fauna in a time span from ca. 71.0 to 73.0

604

Ma.

605

9. Conclusions

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Imperobator antarcticus is introduced as a non-dromaeosaurid paravian taxon from the

608

lower Maastrichtian of James Ross Island, Antarctica. Case et al. (2007) previously referred to

609

this specimen as a dromaeosaurid. Turner et al. (2012) suggested a non-dromaeosaurid affinity

610

due to the non-ginglymoid nature of the anterodistal surface of metatarsal II. Imperobator also

611

displays a shortening and lack of robust features of the second pedal ungual relative to most

612

dromaeosaurids. Autopomorphies of Imperobator antarcticus include the fusion between the

613

distal fibula and proximal calcaneum, and the parallelogram outline of the metatarsal II

614

diaphysis. Proximal tarsal and distal tibia-fibula articulations/fusions exist among paravian taxa,

615

this is the only known case of fusion between the calcaneum and fibula exclusively. In this

616

present work, the taxon is identified as a paravian based on our phylogenetic results. Support for

617

a paravian placement is further given support via Bayesian phylogenetic analyses.

618

Synapomorphies of Paraves recovered in our analyses, include a ginglymoid articular surface of

619

metatarsal III, hypertrophy of the second pedal ungual, and presence of a posterolateral flange on

620

metatarsal IV. Ginglymoidy of anterodistal surface of metatarsal II is recovered as a paravian

621

synapomorphy in our analysis, previously only a dromaeosaurid synapomorphy (Turner et al.,

622

2012), not present in Imperobator. This is likely due to nearly every member of

623

Dromaeosauridae collapsed into a polytomy at the base of Paraves. Alternatively, due to a lack

624

of resolution of paravian subclade relationships in our analyses, ginglymoidy of anterodistal

625

metatarsal II may be a synapomorphy of the clade Dromaeosauridae + Troodontidae + Avialae,

AC C

EP

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M AN U

SC

607

27

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN while Imperobator exists as a sister taxon to all other paravians in future phylogenetic analyses.

627

With the congruence of parsimony and Bayesian phylogenetic results placing Imperobator

628

antarcticus within Paraves, and the presence of three paravian synapomorphies in this taxon, we

629

can confidently place I. antarcticus within Paraves. Future phylogenetic analysis, with recovery

630

of more material pertaining to this specimen, will hopefully resolve relationships to other

631

paravian subclades. Biostratigraphic data indicates that the six dinosaur taxa from the Herbert

632

Sound and Cape Lamb Members of the the Snow Hill Island Formation are contemporaries of

633

each other and represent a single dinosaur fauna in a time span from ca. 71.0 to 73.0 Ma.

SC

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626

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634

Acknowledgements

636

We wish to thank the National Science Foundation, Division of Polar Programs for support to

637

JAC from NSF OPP-0003844 when the specimen discussed here was found. We thank Eric

638

Galey and Larry Conboy for photography of the specimen; We would like to thank Dr. Matthew

639

Lamanna for his general assistance on the manuscript and we especially want to thank Andrew

640

McAfee, Scientific Illustrator for Vertebrate Paleontology, for his wonderful work on several of

641

the illustrations in this paper, both gentlemen are from the Carnegie Museum of Natural History;

642

Additional thanks goes to Paul Upchurch for discussions pertaining to phylogenetic methods;

643

James Clark, Michael Woodburne, Jonah Choiniere, Stephen Brusatte, two anonymous

644

reviewers, and Eduardo Koutsoukos (editor for Cretaceous Research) for reviews, comments,

645

and feedback.

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823

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Appendix A

826

Character coding

827

Imperobator antarcticus

828

???????????????????????????????????????????????????????????????????????????????????????

36

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN ???????????????????????????????????????????????????????????????????????????????????????

830

?????????????0??0???0000101???0????????????????????1??????????????????????????????????

831

???????????????????????????????????????????????????????????????????????????????????????

832

???????????????????????????????????????????????????????????????????????????0000?0?0?00

833

?????????????????????????????????????00????????????????????????????????????????????????

834

???????????????????????????????????????????????????????????????????????????????????????

835

???????????????????????????????????????????????????????????????????????????????????????

836

????????????????????????????000000?????????????????0??????????????????????????????????

837

???????????????????????????????????????????1???????????0???????????????????????????????

838

??????????????????????????????????????

M AN U

SC

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829

839 840

FIGURE CAPTIONS

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841 842

Fig. 1 - Locality map of latest Cretaceous dinosaur taxa collected in the James Ross Basin. Solid

844

square is the Naze Peninsula which has produced the paravian Imperobator and the elasmarian

845

ornithopod, Morrosaurus. The dashed square is the Cape Lamb Peninsula which has produced a

846

hypsilophodontid from the lower Maastrichtian Cape Lamb Mbr. and a hadrosaurine hadrosaur

847

from the mid-Maastrichtian Sandwich Bluff Mbr. The dotted square is Santa Marta Cove area

848

where three dinosaur species have be collected from the uppermost Campanian Gamma Member,

849

which includes the elasmarian ornithopod, Trinisauria, the ankylosaur, Antarctopelta and a

850

lithostrotian titanosaur.

AC C

EP

843

851

37

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN Fig. 2 – Stratigraphic section of the Cape Lamb Member of the Snow Hill Island Formation

853

measured at Comb Ridge on the Naze Peninsula, James Ross Island, northeastern Antarctic

854

Peninsula. The location of the paravian theropod, Imperobator antarcticus gen. et. sp. nov.

855

within the stratigraphic section is indicated from 41 m to 48 m with the initial fossils recovered

856

at 45 m. Ammonites Diplomoceras lambi and Kitchinites darwini were found in the upper part

857

of the section whereas the ammonite Gunnerites antarcticus is found low in the section. The

858

unit is capped by Miocene basalt. Modified from di Pasquo and Martin (2013) and Martin et al.

859

(2009).

M AN U

SC

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852

860

Fig. 3 - Summary and correlation of the stratigraphy of dinosaur sites and taxa, plus the pertinent

862

ammonite biostratigraphy in the Herbert Sound region, Antarctic Peninsula. The Cape Lamb

863

sequence is summarized from after Pirrie et al. (1991) and the radiometric datum is from Crame

864

et al. (1999) with the hadrosaur location from Case et al. (2000) and hypsilophodontid location

865

from Pirrie et al. (1991) and Hooker et al. (1991). The Naze sequence is summarized from di

866

Pasquo and Martin (2013) with dinosaur stratigraphic locations from di Pasquo and Martin

867

(2013; Imperobator) and Rozadilla et al.,(2016; Morrosaurus). The Santa Marta Cove sequence

868

and dinosaur locations are summarized from Coria et al. (2013). Ammonite biostratigraphy

869

illustrated here is from Pirrie et al. (1991) and Olivero (2012a,b). The location of the

870

Campanian–Maastrictian boundary within the reference section on Cape Lamb Peninsula, Vega

871

Island, Antarctica is from Crame et al. (1999; 2004).

AC C

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861

872

873

Fig. 4 - Recovered material from Imperobator antarcticus gen. et sp. nov. Scale bar = 3 cm. 38

ACCEPTED MANUSCRIPT ELY AND CASE—ANTARCTIC PARAVIAN 874

Fig. 5 - Imperobator antarcticus gen. et sp. nov. A. Anterior (or posterior?) view of distal tibia.

876

Scale bar = 3 cm. B. Anterodistal view of astragalus, medial fragment. Scale bar = 1 cm. C, D.

877

Calcaneum and distal fibular shaft fusion from left pes in lateral view (C) and right pes in medial

878

view (D). Scale bar = 3 cm.

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875

SC

879

Fig. 6 - Imperobator antarcticus gen. et sp. nov. A. Metatarsal II, proximal fragment in medial

881

view. B. Metatarsal II, diaphyseal fragment in proximal (distal?) view. C. Metatarsal II, distal

882

fragment in anterior view. dia: diaphysis; ng: non-ginglymoid articular surface. D. Metatarsal III

883

in lateral view, with fused (?) distal tarsal dorsally. E. Metatarsal III, distal aspects in anterior

884

view. F. Metatarsal III in posterior view. G. Metatarsal IV, proximal fragment in medial view.

885

H. Metatarsal IV, posterolateral surface with longitudinal flange (plf: posterolateral flange). I.

886

Distal end of the fourth metatarsal in anterior view. Scale bar = 3 cm.

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Fig. 7 - Imperobator antarcticus gen. et sp. nov. A. DII-2 proximal phalanx. pvh: proximoventral

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heel. B. Pedal digit II ungual phalanx in lateral view. C. Distal articular surface of a phalanx

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possibly pertaining to digit III (?). D. Proximal phalanx of pedal digit IV in dorsal view. E.

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Phalanx of digit I (?); assignment to specific pedal digits cannot be determined. Scale bar = 3

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Kinnareemimus, Pyroraptor, and Pamparaptor pruned from analysis. See Fig. S1 for bootstrap

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values below each node.

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Fig. 9 - Strict consensus of traditional search performed in TNT 1.5, displaying only Paravian

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groups. I. antarcticus is presented in red. Kinnareemimus, Pyroraptor, and Pamparaptor pruned

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from analysis. See Fig. S2 for bootstrap values below each node.

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Fig. 10 - Results of Bayesian phylogenetic tree (Mkv, with gamma parameter) performed in

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MrBayes. I. antarcticus is presented in red. Posterior probability values are indicated below each

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Fig. S1. Strict consensus tree based on a parsimony analysis run in TNT 1.5 with Kinnareemimus, Pyroraptor, and Pamparaptor pruned from analysis. Based on 570 most

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parsimonious trees of length 3,557. Only basal Coelurosaurians are shown, continued in Figures S2, S3.

Fig. S2. Strict consensus tree based on a parsimony analysis run in TNT 1.5 with Kinnareemimus, Pyroraptor, and Pamparaptor pruned from analysis. Based on 570 most

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parsimonious trees of length 3,557. Basal and more derived are shown, continued in

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Figures S3.

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Fig. S3. Strict consensus tree based on a parsimony analysis run in TNT 1.5 with

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Kinnareemimus, Pyroraptor, and Pamparaptor pruned from analysis. Based on 570 most

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parsimonious trees of length 3,557. Oviraptorosauria, Scansoriopterygidae, and Paraves

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are shown.

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Fig. S4. Bayesian topology utilizing Lewis’ Mkv model with the gamma parameter. Only basal

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Coelurosaurians are shown, continued in Figures S5, S6.

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more derived are shown, continued in Figures S3.

Fig. S6. Bayesian topology utilizing Lewis’ Mkv model with the gamma parameter. Oviraptorosauria, Scansoriopterygidae, and Paraves are shown.

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Fig. S5. Bayesian topology utilizing Lewis’ Mkv model with the gamma parameter. Basal and

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Imperobator recovered as non-dromaeosaurid (contra Case et al., 2007). Phylogenetic analyses (parsimony and Bayesian) suggest possible basal paravian. First comprehensive biostratigraphy of latest Cretaceous Antarctic dinosaur faunas. Presents first time of occurrence of dinosaur taxa from the Antarctic Peninsula.

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