NORWEGIAN JOURNAL OF GEOLOGY Phylogenetic relationships of Upper (Middle Volgian) plesiosaurians 277

Phylogenetic relationships of Upper Jurassic (Middle Volgian) plesiosaurians (Reptilia: ) from the Agardhfjellet Formation of central Spitsbergen, Norway

Patrick S. Druckenmiller & Espen M. Knutsen

Druckenmiller, P.S. & Knutsen, E.M. Phylogenetic relationships of Upper Jurassic (Middle Volgian) plesiosaurians (Reptilia: Sauropterygia) from the Agardhfjellet Formation of central Spitsbergen, Norway. Norwegian Journal of Geology, Vol 92, pp. 277-284. Trondheim 2012, ISSN 029-196X.

Plesiosaurian relationships have been subject to considerable debate at both higher and lower levels within the clade. Recent fieldwork in the Upper­ most Jurassic of the Agardhfjellet Formation on central Spitsbergen has uncovered numerous ichthyosaurians and plesiosaurian remains, including three new plesiosauroids, one new pliosauroid referrable to , and a previously described, re-classified taxon. The phylogenetic relati­ onships of these five taxa were investigated based on data sets previously constructed for global plesiosaurian relationships. Two specimens from the British Kimmeridge Clay Formation and a Russian Volgian (uppermost Jurassic) taxon referrable to Pliosaurus were added to the data matrix to improve the phylogenetic resolution of this . The results yielded a tree topology closely conforming to the traditional plesiosauroid and pliosauroid dichotomy, nesting Leptocleidia within the latter. Pliosaurus forms a monophyletic clade containing all currently recognised . The three new long-necked taxa form a monophyletic sister group to the . These results should, however, be considered preliminary pending the discovery of more complete cranial material and adult specimens.

Patrick S. Druckenmiller, University of Alaska Museum, 907 Yukon Drive, Fairbanks, AK 99775, United States. E-mail: [email protected]. Espen M. Knutsen, Natural History Museum (Geology), University of Oslo, Pb. 1172 Blindern, 0318 Oslo, Norway. Present address, Haoma Mining NL, Bamboo Creek Mine, P.O. Box 2791, South Headland, 6722 WA, Australia. , E-mail: [email protected].

Introduction of Svalbard (Hurum et al., this volume). The finds were recovered from the dark-grey to black mudstone of the In the past decade, our knowledge of plesiosaurian Slottsmøya Member of the Agardhfjellet Formation­, (Sauro­pterygia: ) relationships has improved which is Volgian (Tithonian) to Valanginian­ in age with the application of cladistic methodologies. How­ (Nagy & Basov, 1998; Collignon & Hammer, this volume;­ ever, a broad consensus regarding plesiosaur relation­ Hammer ­ et al., 2011). Numerous skeletons of plesiosauri­ ships remains elusive. In particular, the first global phylo­ ans and ichthyosaurs have been found and excavated over genetic analyses have called into question long-standing­ the course of seven field seasons. The process of collect­ assumptions of higher-level relationships within the ing and describing these new taxa is ongoing, but work clade, including the validity and definition of the two to date allows the description or redescription of several traditional clades, and plesiosaurian taxa that are unique to this area, including (O’Keefe, 2001; Druckenmiller & Russell, 2008; Ketchum Colymbosaurus svalbardensis (Knutsen et al., this volume & Benson, 2010). Furthermore, there has been consider­ (d)), Spitrasaurus wensaasi (Knutsen et al., this volume able debate regarding species-level relationships within (c)), S. larseni (Knutsen et al., this volume (c)), Djupe­ certain clades, such as Elasmosauridae (Sato, 2002; dalia engeri (Knutsen et al. this volume (a)) and Pliosau­ O’Keefe, 2004; Groβman, 2007; Druckenmiller & Russell, rus funkei (Knutsen et al. this volume (b)). 2008; Ketchum & Benson, 2010), (O’Keefe, 2004; Druckenmiller & Russell, 2008), and Rhomaleo­ The objectives of the present study are to conduct a pre­ sauridae (O’Keefe, 2004; Smith & Dyke, 2008; Ketchum liminary cladistic analysis in order to place the new Sval­ & Benson, 2010). An updated matrix devised to clarify bard OTUs into a preliminary phylogenetic context and aspects of pliosaurid relationships was published recently to test its effect on the topology and stability of broad- by Ketchum & Benson (2011). scale relationships within Plesiosauria. The new material from Svalbard is significant in that it contributes valu­ In 2004, a new locality for Upper Jurassic marine able new information on both long- and short-necked was discovered on the high-arctic Norwegian archipelago morphotypes to an ever-growing data set on plesiosaur 278 P. S. Druckenmiller & E. M. Knutsen NORWEGIAN JOURNAL OF GEOLOGY

morphology. New data on British Pliosaurus are also where xi is the selected datum, and n is the number of incorporated into the analysis, and the first species-level desired states (not including state “0”). xs is rounded up analysis of the genus is presented. Finally, these data help to the nearest integer to give the state. Following Thiele to fill a temporal gap in our knowledge of plesiosaurs (1993), these meristic characters were each given a from the latest Jurassic (Volgian-Tithonian). weight of one, and treated as ordered. Discrete charac­ ters were treated as unordered and given a weight equal Institutional Abbreviations: to number of states available for the meristic characters (Thiele, 1993). BRSMG Bristol City Museum and Art Gallery, Bristol, UK. CAMSM Sedgwick Museum, Cambridge, UK. Analysis of the data matrix NHMUK Natural History Museum, London, UK. PIN Palaeontological Institute, Russian Academy of The data matrix was analysed using PAUP* version Sciences, Moscow, Russia. 4.0b10 (Swofford, 2002). gailardoti, Augusta­ PMO Natural History Museum, University of Oslo, saurus hagdorni and were selected as out­ Norway (Palaeontological collections). group taxa, following Druckenmiller & Russell (2008), and Ketchum & Benson (2010). Tree searches were per­ formed using PAUPRat (Sikes & Lewis, 2001) which Material and methods implements the Parsimony Ratchet strategy described by Nixon (1999). Similar to Ketchum & Benson (2010), Construction of data matrix The data matrix (supplemen­ twenty independent batch files were constructed using tary material) was constructed in Mesquite 2.71 and is a PAUPRat. Each batch file performed 200 heuristic search modified version of Benson et al. (2011), which in turn is iterations, with the random seed number being gener­ largely based on the matrix of Ketchum & Benson (2010). ated by the system clock. ‘WTMODE’ was set to multi­ Five Svalbard taxa were added to the matrix (Supple­ment plicative, with the percentage of characters being per­ 1). Pliosaurus funkei Knutsen et al. (this volume (b)) is turbed to 15%. The best trees from each batch were com­ based on a composite scoring of complementary mate­ bined into one tree-file using PAUP. The twenty inde­ rial from both the holotype (PMO 214.135) and the pendent PAUPRat batch files yielded 313 most parsimo­ referred specimen (PMO 214.136). Three new species of nious trees (MPTs) with a tree length of 18804. These long-necked plesiosaurians (described in this volume) trees were used as starting points for a heuristic search were all scored from the holotype specimens: Djupeda­ in PAUP implementing the ‘TBR’ branch swapping algo­ lia engeri Knutsen et al. (this volume (a); PMO 216.839); rithm, number of repetitions to 200, and ‘maxtrees’ to Spitrasaurus wensaasi Knutsen et al. (this volume ­(c); increase automatically. This resulted in 149679 MPTs PMO 219.718); and S. larseni Knutsen et al. (this vol­ with a tree length of 16484. These MPTs were used to ume (c); SVB 1450). The scores for Colymbo­saurus sval­ calculate the strict consensus tree (Figure 1A). bardensis (Persson, 1962) Knutsen et al. (this volume (d)) are based on the holotype specimen (PMO A 27745) col­ Following the method implemented by Ketchum & Ben­ lected in 1931. son (2010), and described by Wilkinson (2003), ‘wild­ card’ taxa were identified based on comparisons of the As a result of a broader review of the Upper Jurassic plio­ strict Adams consensus trees (Figure 1) constructed saurids (Knutsen, this volume), additional data on Plio­ from the 14976 MPTs and found in the analysis of the saurus species was also added into the analysis (Supple­ un-pruned data matrix. This resulted in the removal of ment 1). Pliosaurus macromerus (NHMUK 39362, sensu Colymbosaurus svalbardensis and Pliosaurus sp. (BRSMG Knutsen, this volume), and P. rossicus (PIN 304/1, holo­ Cc332) from the data matrix and then reanalysing the type) were newly incorporated into the matrix, and the matrix as described above. This strict reduced consensus scores for P. brachydeirus were modified from Benson tree is presented in Figure 2. et al. (2011; Supple­ment 2). In the original analysis by Ketchum­ & Benson (2010), BRSMG Cc332 was scored Bootstrap support was calculated using 2000 replicates to represent P. brachyspondylus; however, recent work and the heuristic search options described above. Max­ indicates that this specimen cannot with certainty be Trees were set to 100 to reduce computation time. Fol­ referred to any existing species and is listed in this matrix lowing Ketchum & Benson (2010), calculation of Bremer as Pliosaurus sp. (Knutsen, this volume). In this analysis support was not performed due to the large size of the P. brachyspondylus (sensu Knutsen, this volume) is repre­ data sets (Müller, 2004, 2005), and because it is computa­ sented by CAMSM J.35991 (Supplement­ 2). tionally expensive. Character reconstructions were per­ formed using both ACCTRAN and DELTRAN character Meristic characters were divided into twenty-six states by optimisation, and unambiguous character definitions of using the formula provided by Thiele (1993): nodes were found by comparison of the two.

xs=[(xi–xmin)⁄(xmax–xmin )]n NORWEGIAN JOURNAL OF GEOLOGY Phylogenetic relationships of Upper Jurassic (Middle Volgian) plesiosaurians 279

Augustasaurus hagdorni (46%) hagdorni A Cymatosaurus (56%) B Cymatosaurus Simosaurus gaillardoti (23%) Simosaurus hgaillardoti NHMUK 49202 (45%) NHMUK 49202 Attenborosaurus conybeari (75%) Attenborosaurus conybeari Strateosaurus taylori (55%) Strateosaurus taylori hawkinsi (39%) Thalassiodracon hawkinsi dolichodeirus (23%) Plesiosaurus dolichodeirus Microcleidus homalospondylus (38%) Microcleidus homalospondylus OUMNH J.28585 (85%) OUMNH J.28585 Seeleyosaurus guilelmiimperatoris (25%) Seeleyosaurus guilelmiimperatoris Hydrorion brachypterygius (49%) Hydrorion brachypterygius Occitanosaurus tournemirensis (41%) Occitanosaurus tournemirensis parvidens (73%) Colymbosaurus svalbardensis Eromangasaurus australis (83%) leedsii Colymbosaurus svalbardensis (96%) seeleyi Spitrasaurus wensaasi (80%) eurymerus Spitrasaurus larseni (72%) Kimmerosaurus langhami Djupedalia engeri (77%) Spitrasaurus wensaasi Muraenosaurus leedsii (17%) Spitrasaurus larseni Tricleidus seeleyi (41%) Djupedalia engeri Cryptoclidus eurymerus (31%) Aristonectes parvidens Kimmerosaurus langhami (78%) Eromangasaurus australis snowii (50%) Styxosaurus snowii haningtoni (61%) Thalassomedon haningtoni colombiensis (39%) Callawayasaurus colombiensis platyurus (87%) Elasmosaurus platyurus morgani (41%) Libonectes morgani alexandrae (63%) Hydrotherosaurus alexandrae pontiexensis (56%) Terminonatator pontiexensis Eurycleidus arcuatus (70%) Maresaurus coccai Maresaurus coccai (67%) zetlandicus Rhomaleosaurus victor (56%) Eurycleidus arcuatus Rhomaleosaurus zetlandicus (56%) Rhomaleosaurus victor Rhomaleosaurus megacephalus (46%) Rhomaleosaurus megacephalus Archaeonectrus rostratus (69%) Archaeonectrus rostratus tenuiceps (54%) Macroplata tenuiceps Hauffiosaurus longirostris (77%) Hauffiosaurus longirostris Hauffiosaurus tomistomimus (39%) Hauffiosaurus tomistomimus Hauffiosaurus zanoni (58%) Hauffiosaurus zanoni Plesiosaurus macrocephalus (73%) Plesiosaurus macrocephalus Marmornectes candrewi (64%) Marmornectes candrewi Pliosaurus andrewsi (60%) Pliosaurus andrewsi OUMNH J.02247 (64%) OUMNH J.02247 philarchus (7%) Peloneustes philarchus vorax (27%) Simolestes vorax ferox (18%) Liopleurodon ferox NHMUK R2439 (84%) Pliosaurus sp. (BRSMG Cc332) Pliosaurus brachydeirus (84%) Pliosaurus brachyspondylus Pliosaurus sp. (BRSMG Cc332; 53%) NHMUK R2439 Pliosaurus brachyspondylus (85%) Pliosaurus brachydeirus FHSMVP321 (69%) FHSMVP321 lucasi (62%) Brachauchenius lucasi queenslandicus (68%) Kronosaurus queenslandicus Pliosaurus funkei (composite; 79%) Pliosaurus funkei (composite) Pliosaurus macromerus (84%) Pliosaurus macromerus Pliosaurus rossicus (86%) Pliosaurus rossicus Umoonasaurus demoscyllus (64%) Umoonasaurus demoscyllus Brancasaurus_brancai (48%) brancai Kaiwhekea katiki (73%) Kaiwhekea katiki capensis (48%) Leptocleidus capensis Leptocleidus superstes (72%) Leptocleidus superstes Nichollssaura borealis (36%) Nichollssaura borealis Thililua longicollis (75%) Thililua longicollis latipinnis (84%) Polycotylus latipinnis QMF 18041 (43%) QMF 18041 muddi (37%) Edgarosaurus muddi bentonianum (54%) Trinacromerum bentonianum Plesiopleurodon wellesi (73%) Plesiopleurodon wellesi herschelensis (41%) Dolichorhynchops herschelensis Eopolycotylus rankini (71%) Eopolycotylus rankini Dolichorhynchops osborni (15%) Dolichorhynchops osborni Manemergus anguirostris (76%) Manemergus anguirostris Palmulasaurus quadratus (83%) Palmulasaurus quadratus

Figure 1. Strict (A; tree length=16886, CI=0.32, HI=0.68, RI=0.61) and Adams (B) consensus trees of 14976 most parsimonious trees resulting from the analysis of the un-pruned data matrix. ‘Wildcard’ taxa are marked in red. Percentages give the proportion of missing data for each operational taxonomical unit (OTU). 280 P. S. Druckenmiller & E. M. Knutsen NORWEGIAN JOURNAL OF GEOLOGY

Augustasaurus hagdorni 46% Cymatosaurus 56% 99 Simosaurus gaillardoti 23% NHMUK 49202 45% Attenborosaurus conybeari 75% Strateosaurus taylori 55% 3 Thalassiodracon hawkinsi 39% 23% 1 Plesiosaurus dolichodeirus Microcleidus homalospondylus 38% 90 66 OUMNH J.28585 85% Seeleyosaurus guilelmiimperatoris 25% Hydrorion brachypterygius 49% Occitanosaurus tournemirensis 41% Muraenosaurus leedsii 17% 5 Tricleidus seeleyi 41% Cryptoclidus eurymerus 31% Kimmerosaurus langhami 78% Spitrasaurus wensaasi 80% 7 Spitrasaurus larseni 72% 77% 6 Djupedalia engeri 2 Aristonectes parvidens 73% 8 Eromangasaurus australis 83% Styxosaurus snowii 50% Thalassomedon haningtoni 61% Callawayasaurus colombiensis 39% Elasmosaurus platyurus 87% Libonectes morgani 41% Hydrotherosaurus alexandrae 63% Terminonatator pontiexensis 56% Eurycleidus arcuatus 70% Maresaurus coccai 67% Rhomaleosaurus victor 56% Rhomaleosaurus zetlandicus 56% Rhomaleosaurus megacephalus 46% 4 Archaeonectrus rostratus 69% Macroplata tenuiceps 54% Hauffiosaurus longirostris 77% Hauffiosaurus tomistomimus 39% 66 Hauffiosaurus zanoni 58% Plesiosaurus macrocephalus 73% Marmornectes candrewi 64% NHMUK R2439 84% Pliosaurus brachydeirus 84% 9 Pliosaurus funkei (composite) 79% 11 51 Pliosaurus brachyspondylus 85% Pliosaurus macromerus 84% Pliosaurus rossicus 86% OUMNH J.02247 64% Peloneustes philarchus 07% Simolestes vorax 27% Liopleurodon ferox 18% Brachauchenius lucasi 62% 51 Kronosaurus queenslandicus 68% FHSMVP321 69% Pliosaurus andrewsi 60% Brancasaurus brancai 48% Kaiwhekea katiki 73% 12 Umoonasaurus demoscyllus 64% Leptocleidus capensis 48% 10 66 Leptocleidus superstes 72% 1 - Plesiosauria Plesiopleurodon wellesi 73% 2 - Neoplesiosauria 13 QMF 18041 43% 3- Plesiosauroidea Nichollssaura borealis 36% 4- Pliosauroidea Edgarosaurus muddi 37% 54% 8- Elasmosauridae Trinacromerum bentonianum Dolichorhynchops herschelensis 41% 9- Pliosauridae Dolichorhynchops osborni 15% 10- Leptocleidida Eopolycotylus rankini 71% 11- Pliosaurus Manemergus anguirostris 76% 12- Lepticleididae Palmulasaurus quadratus 83% 13- Polycotylus latipinnis 84% Thililua longicollis 75%

Figure 2. Strict consensus tree of 3718 most parsimonious trees (tree length=16582, CI=0.32, HI=0.68, RI=0.61). Circled numbers label nodes, numbers below lines are bootstrap values, percentages give the proportion of missing data for each operational taxonomical unit (OTU). The Svalbard taxa are in bold. NORWEGIAN JOURNAL OF GEOLOGY Phylogenetic relationships of Upper Jurassic (Middle Volgian) plesiosaurians 281

Results and Discussion analysis. Benson et al. (2012) did not recover a sister group relationship between Pliosauridae and Rhomaleo­ The pruning of two ‘wildcard’ taxa (Colymbosaurus­ sauridae. The addition of new OTUs and modified scores svalbard­ensis and Pliosaurus sp. (BRSMG Cc332)) for some taxa resulted in several topological differences reduced the number of MPTs from 14976 to 3718, and in Pliosauridae compared to that of Ketchum & Benson reduced tree length by 304 fewer steps (Figure 2). The (2010). In the current analysis Marmornectes candrewi is strict reduced tree fully resolves the three new Svalbard recovered (Figure 2) as the most basal pliosaurid, and not plesiosauroid taxa into a single clade and recovers Plio­ NHMUK R2439, which nests with Pliosaurus. The other saurus funkei within a monophyletic, but unresolved significant difference is in the sister group relationships Pliosaurus (except ‘P’. andrewsi). of Brachaucheninae (Brachauchenius+Kronosaurus) FHSM VP321); al­though it is consistently the most Similar to the analysis of Ketchum & Benson (2010), derived clade within Pliosauridae, it was recovered as the the monophyly of Plesiosauria (node 1) is well sup­ sister taxon to Pliosaurus (P. brachydeirus+P. brachyspon­ ported, with a bootstrap value of 90. Two plesiosaurians, dylus) in Ketchum & Benson (2010) but is the sister Attenboro­saurus and NHMUK 49202, are successive sis­ taxon of Liopleurodon in this study. Brachaucheninae ter taxa to Neoplesiosauria (node 2). Two major clades also differs here by its inclusion of ‘Pliosaurus’ andrewsi. are recovered in Neoplesiosauria; Plesiosauroidea (node As discussed elsewhere (Knutsen, 2012), ‘P.’ andrewsi is 3) and Pliosauroidea (node 4). However, the composi­ not referrable­ to Pliosaurus (it lacks teeth with a subtri­ tion of these two clades most closely corresponds to the hedral cross-­section, among other features) and awaits traditional definition of Plesiosauroidea and Pliosauroi­ formal taxonomic revision. dea (Welles, 1943; Brown, 1981; Druckenmiller & Rus­ sell, 2008; Smith & Dyke, 2008), in marked contrast to The present study is the first species-level analysis of the analysis of O’Keefe (2001) and Ketchum & Benson all valid Pliosaurus taxa including P. brachydeirus, P. (2010). Specifically, this difference is due to the position brachyspondylus, P. rossicus, P. macromerus and the new of Leptocleidida (Polycotylidae+Leptocleididae), which Svalbard taxon, P. funkei (Knutsen et al., 2012a). Plio­ is recovered here within Pliosauroidea, but is nested saurus is recovered as a monophyletic, but un­resolved within Plesiosauroidea in Ketchum & Benson (2010). clade, along with NHMUK R2439. Pliosaurus­ (exluding Leptocleidia was similarly recovered in Pliosauro­idea NHMUK R2439) is unambiguously supported by four in Benson et al. (2011), despite minor alterations to the synapomorphies including the absence of a notochordal matrix of Ketchum & Benson (2010). Given the low pit in the occipital condyle (81:0), teeth with a subtrihe­ bootstrap support (less than 50 percent) for Pliosauroi­ dral cross-section (109:2), dorsal neural spines that are dea and Plesiosauroidea in the present analysis, and the less or equal in height to the centrum (137:0), and the high degree of plasticity in the systematic position of radius is proximodistally shorter than its anteroposte­ Leptocleidia (O’Keefe, 2001; Druckenmiller & Russell, rior width (162:4). The inclusion of NHMUK R2439 in 2008; Ketchum & Benson, 2010), the status and composi­ this clade is likely erroneous. This Oxford Clay specimen tion of these major clades must remain uncertain. (Callovian) is missing data for characters 81, 109 and 137, and is the only OTU in the clade scored for charac­ Pliosauroidea (node 4) is supported unambiguously by ter 162 (scored 4) except for P. funkei, which is scored 2. ten synapomorphies (3:G-H, 60:0, 63:1, 91:1, 95:C, 99:1, 112:A, 118:C, 140:1, 146:1). A paraphyletic assemblage of The breaking apart of a monophyletic Pliosaurus by Early to Middle Jurassic pliosauroids is recovered basal to inclusion of BRSMG Cc332 may indicate paraphyletic Leptocleidia (Node 10) and its sister group Pliosauridae relationships within the genus, or be a result of lacking (Node 9). Leptocleidia (node 10) is unambiguously sup­ completeness of character scorings for other members of ported by nine synapomorphies (54:1, 67:1, 68:1, 78:1, the genus. 83:0, 125:2, 153:B-C, 167:1, 174:1) and is composed of Polycotylidae and Leptocleididae (Druckenmiller & Rus­ The new Svalbard taxon Pliosaurus funkei clearly nests sell, 2008; Ketchum & Benson, 2010). A certain degree with other Pliosaurus taxa in this analysis, but based on of incongruity in the topology and resolution in Lepto­ the strict pruned tree alone, the exact nature of relation­ cleidia exists between this analysis and that of Ketchum ships among the different species of the genus requires & Benson, (2010), but are not discussed further here. further study. A putative relationship between P. funkei and P. macromerus and P. rossicus is indicated in the Pliosauridae is supported by nine unambiguous synapo­ strict reduced and Adams trees. The similarity between morphies: (95:H, 97:1, 98:0, 102:0, 107:0, 123:0, 124:1, these two taxa and P. funkei was also noted in the com­ 153:6, 168:2). State 98:0 (surangular is mediolaterally parative analysis of cranial material in the description thick and broadly rounded in dorsal view) is unique to of P. funkei (Knutsen et al., 2012). Resolving species- Pliosauridae. Four synapomorphies supported Pliosau­ level relationships within Pliosaurus remains problem­ ridae in Ketchum & Benson (2010), of which only one atic; the scorings for all of the specimens in this ana­ state, 123:0 (ventral surface of cervical centra is flat or lysis are highly incomplete (ranging from 53-86%), and only slightly convex) was shared in common with this one of the more cranially complete specimens, BRSMG 282 P. S. Druckenmiller & E. M. Knutsen NORWEGIAN JOURNAL OF GEOLOGY

Cc332, was identified as a wildcard taxon in the pres­ wide (162:4-5). Because of the small amount of cranial ent analysis. Furthermore, none of the characters recog­ material, state 75:0 was only scored for Djupedalia and nised as diagnostic for the different Pliosaurus species 109:1 for Spitrasaurus larseni. Thus, the shared presence by Knutsen (2012) were considered here, as it would of a greatly elongate neck and short but wide epipodials require extensive revisions of the data matrix beyond appears to have had a large influence on this grouping. the scope of this study. Ongoing work to describe new However, both of these postcranial characters exhibit material­, taxonomic clarifications of existing specimens, high degrees of homoplasy (ci = 0.34) and bootstrap sup­ and a reanalysis ­of phylogenetically important characters port for this grouping was less than 50 percent. within the genus are needed. Node 5, including four British plesiosauroid taxa, is sup­ Plesiosauroidea is unambiguously supported by three ported by nine unambiguous synapomorphies: presence synapomorphies (82:1, 83:0, 115:1). At the base of the of bone surface ornamentation around the orbit margin clade is a paraphyletic assemblage of several Early Juras­ (34:1); the presence of an anterior interpterygoid vacu­ sic plesiosauroids, including Plesiosaurus dolichodei­ ity (59:1); the parasphenoid is wide and blunt posteri­ rus. Three derived plesiosauroid clades are recovered. orly in ventral view between the posterior interpterygoid The newly described taxa from Svalbard, Spitrasau­ (68:2); basisphenoid contributes to the articulation sur­ rus wensaasi,­ S. larseni and Djupedalia engeri (node 7; face of the basioccipital tuberosities for contact with the Knutsen­ et al., 2012a and 2012c), form a monophyletic pterygoids (71:0); 4-5 teeth in the mandibular symphysis group that is the sister taxon to Elasmosauridae (node (112:9); atlas centrum participates in the rim of the rim 8). This unnamed clade, in turn, is the sister taxon to of the atlantal cup (114:1); axis rib articulates partly with four taxa (Muraeonosaurus (Tricleidus (Cryptoclidus the atlantal centrum (117:1); ventral plates of the scapu­ + Kimmerosaurus­ ))) (node 5). Support for all of these lae meet along the midline (145:1); and the posterolat­ nodes is low (bootstrap values less than 50 percent). eral margin of the coracoid forms an angled cornu that extends lateral to the glenoid fossa (151:1). Most of the In general terms, the topology among derived plesio­ synapomorphies of node 5 are unknown in the Svalbard sauroids in congruent with stratigraphic distribution; taxa. The first four of these are cranial features that are Node 5 includes Middle to Late Jurassic forms, and the unknown in any of the Svalbard taxa, in only one taxon relatively derived Svalbard and elasmosaurid taxa are (Spitrasaurus larseni) is the number of symphyseal teeth Late Jurassic and Cretaceous, respectively. However, the known, and in only Djupedalia engeri is the contribution clade Cryptoclidia, sensu Ketchum & Benson (2010) was of the atlantal centrum to the atlantal cup known. Like­ not recovered by exclusion of Leptocleidia (see above). wise, the early ontogenetic state of the Svalbard mate­ Although a re-evaluation of global relationships among rial makes it impossible to score for features of the pec­ plesiosaurians is beyond the scope of this study, it is toral girdle. In the light of these observations, it is appar­ likely that ongoing morphological work to better under­ ent that missing data plays an influential role in the cur­ stand Middle to Late Jurassic long-necked taxa, includ­ rent topology. For these reasons, we view these results as ing putative basal cryptoclidians and the new Svalbard preliminary pending discovery of new specimens from taxa, will play a pivotal role in resolving the systematic later ontogenetic stages and with key cranial material. The relationships of Leptocleidia and Cryptoclidia (Ketchum future inclusion of the British Late Jurassic taxon Colym­ & Benson, 2010) with either plesiosauroids or pliosau­ bosaurus trochanterius (which has been shown to exhibit roids (Benson et al., 2011). similarities to C. svalbardensis; Knutsen et al., 2012 (d)) in the data matrix might also aid in understanding the affini­ The definition of Elasmosauridae has long been a con­ ties of the Svalbard taxa as well as other Jurassic plesio­ tentious issue (O’Keefe, 2001; Druckenmiller & Rus­ sauroids. sell, 2008; Ketchum & Benson, 2010). In this analysis, it is supported by a single synapomorphy (presence of a Node 7 forms an unnamed clade consisting of the three ventral notch in the articular face of the cervical centra Svalbard plesiosauroid taxa Spitrasaurus wensaasi, S. in anterior view; 122:1), but is otherwise composed of larseni and Djupedalia engeri. The other currently recog­ the same taxa (although in a somewhat different topol­ nised Svalbard plesiosauroid, Colymbosaurus svalbard­ ogy) as that recovered in Ketchum & Benson (2010). ensis, is known only from a small amount of material Putative members of the clade, Muraenosaurus (Druck­ from the pelvic girdle and hind limb and was removed enmiller & Russell, 2008) and Brancasaurus (O’Keefe, as a wildcard taxon in this reduced analysis (Figure 2). 2004), were not identified as elasmosaurids here. The sis­ Spitrasaurus and Djupedalia are supported unambigu­ ter group relationship between Elasmosauridae and the ously by two characters: dorsal neural spines are less or new Svalbard taxa (node 6) is supported by four unam­ equal in height to the dorsal centrum (137:0), and the biguous synapomorphies: absence of a distinct notch in radius is relatively proximodistally even shorter than for the suspensorium for articulation with the paraoccipi­ node 6 (162:2). In the present analysis S. larseni and D. tal process (75:0), teeth with oval cross-section (109:1), engeri are recovered as sister taxa, to the exclusion of S. a high number of (118:P) and a radius wensaasi, suggesting that Spitrasaurus is paraphyletic. that is proximodistally shorter than anteroposteriorly However, this result must be viewed with caution. S. NORWEGIAN JOURNAL OF GEOLOGY Phylogenetic relationships of Upper Jurassic (Middle Volgian) plesiosaurians 283 larseni and D. engeri unambiguously cluster on the basis Acknowledgements – We thank R.B.J. Benson for sharing his data of the relative length of the cervical centra (120:0), which matrix and helpful discussions on plesiosaurian phylogeny; Tommy Wensås, Stig Larsen, Magne Høyberget, Øyvind Enger and Lena Kris­ has been argued to vary ontogenetically in elasmosaurids tiansen for spending their summer holidays excavating marine repti­ (O’Keefe & Hiller, 2006; Brown, 1981), and one quanti­ les on Svalbard every summer over the last seven years, and May-Liss tative character: the relative length to width dimensions Knudsen Funke for preparing the specimens; H.T. and R. Schassberger of the radius (162:1). This topology is somewhat a prod­ and H.S. and J.K. Druckenmiller; our financial sponsors ExxonMobil, uct of the gap weighting method employed here (Thiele, Fugro, OMW, Spitsbergen Travel, Powershop, Hydro, StatoilHydro, National Geographic, and Brian Snyder for funding our annual Arctic 1993) in which different scores may be derived from very fieldwork. Constructive reviews were provided by R.B.J. Benson and R. slight differences in the actual dimensions of features. For Forrest. This work is part of a Ph.D. study funded by the University of example, the actual values for character 162 in S. larseni Oslo, Norway. and S. wensaasi are 0.714 and 0.711, respectively, but they are assigned two different scores (0 and 1). Additionally, all three specimens are juvenile specimens and the val­ Supplementary material: ues recorded for the radius are only approximate and are The following supplementary material accompanies the intended to show that this element is wider than long. online version of this paper: http://www.geologi.no/njg/ Finally, most of the features used to diagnose both genera, Supplement 1 - Character scores for added taxa. such as the posterior displacement of the cervical neural Supplement 2 - Modified character scores for Pliosaurus spines, the medial contact of the postzygapophyses and (in bold). the presence of preaxial accessory ossicles, are not charac­ ters used in this phylogenetic analysis. We feel that subse­ quent analyses that incorporate new characters will more References faithfully resolve the relationships between these taxa. 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