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A New Elasmosaurid from the Early Maastrichtian of Angola and the Implications of Girdle Morphology on Swimming Style in Plesiosaurs

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A New Elasmosaurid from the Early Maastrichtian of Angola and the Implications of Girdle Morphology on Swimming Style in Plesiosaurs Netherlands Journal of Geosciences —– Geologie en Mijnbouw | 94 – 1 | 109-120 | 2015 doi: 10.1017/njg.2014.44 A new elasmosaurid from the early Maastrichtian of Angola and the implications of girdle morphology on swimming style in plesiosaurs R. Araujo´ 1,2,*,M.J.Polcyn1,A.S.Schulp3,O.Mateus2,4,L.L.Jacobs1,A.Ol´ımpio Gonçalves5 & M.-L. Morais5 1 Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas, 75275, USA 2 Museu da Lourinh~a, Rua Jo~ao Lu´ıs de Moura, 2530-157 Lourinh~a, Portugal 3 Naturalis Biodiversity Center, Darwinweg 2, 2333CR Leiden, the Netherlands and Natuurhistorisch Museum Maastricht, Maastricht, the Netherlands and Faculty of Earth and Life Sciences, Amsterdam VU University, Amsterdam, the Netherlands 4 UniversidadeNovadeLisboa,CICEGe,FaculdadedeCiˆencias e Tecnologia, FCT, 2829-516 Caparica, Portugal 5 Departamento de Geologia, Faculdade de Ciencas, Universidade Agostinho Neto, Avenida 4 de Fevereiro 7, Luanda, Angola * Corresponding author. Email: [email protected] Manuscript received: 2 May 2014, accepted: 3 December 2014 Abstract We report here a new elasmosaurid from the early Maastrichtian at Bentiaba, southern Angola. Phylogenetic analysis places the new taxon as the sister taxon to Styxosaurus snowii, and that clade as the sister of a clade composed of (Hydrotherosaurus alexandrae (Libonectes morgani + Elasmosaurus platyurus)). The new taxon has a reduced dorsal blade of the scapula, a feature unique amongst elasmosaurids, but convergent with cryptoclidid plesiosaurs, and indicatesalongi- tudinal protraction-retraction limb cycle rowing style with simple pitch rotation at the glenohumeral articulation. Morphometric phylogenetic analysis of the coracoids of 40 eosauropterygian taxa suggests that there was a broad range of swimming styles within the clade. Keywords: Plesiosauria, locomotion, pectoral girdle, Elasmosauridae, marine reptiles Introduction from the mid-Hauterivian (Evans, 2012) to the end of the Maas- trichtian (Vincent et al., 2011). We report here a new elasmosaurid plesiosaur from the early By the earliest Jurassic, plesiosaurs were fully adapted to Maastrichtian of Angola, and provide a description and a phylo- a pelagic lifestyle and two major Bauplans (plesiosauromorph genetic analysis. The new taxon possesses unusual features of and pliosauromorph) had emerged in multiple phylogenetic lin- the limb and pectoral girdle morphology that suggest a peculiar eages (O’Keefe, 2001; Benson et al., 2012). Plesiosauromorphs mode of locomotion; we therefore also explore the implications have long necks and relatively small, anteriorly abbreviated of girdle morphology on swimming style in a phylogenetic mor- heads, whereas the pliosauromorph Bauplan includes forms phometrics framework. with larger elongate heads and relatively short necks (O’Keefe Plesiosaurs are members of the Eosauropterygia (Rieppel, & Carrano, 2005). However, all plesiosaurs share unique fea- 1994), which include pachypleurosaurs, nothosaurs and pisto- tures of their limbs and girdles amongst secondarily adapted saursbestknownfromtheMiddleTriassic epicontinental shal- Mesozoic marine reptiles. Swimming style based on paraxial low seas of Europe and China (Rieppel, 2000). Elasmosauridae quadrupedal locomotion is largely accepted (e.g. Watson, are regarded as the sister group of Cryptocleididae within 1924; Robinson, 1975), although details of limb motion Plesiosauria (Ketchum & Benson, 2010; Benson & Druckenmiller, are more contentious (e.g. Thewissen & Taylor, 2007; Lingham- 2014). The origin of Elasmosauridae is unclear but its record extends Soliar, 2000). © Netherlands Journal of Geosciences Foundation 2014 109 Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 26 Sep 2021 at 04:19:14, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/njg.2014.44 Netherlands Journal of Geosciences —– Geologie en Mijnbouw 94 – 1 | 2015 The morphological transition between terrestrial forms, pre- Phylogeny sumably in the early Triassic, to fully marine forms known from the Jurassic and Cretaceous involves profound reorganisation Phylogenetic analyses of the new taxon used the data matrix of 177 of the girdle elements along with elaboration of the limbs as characters and 67 taxa modified from Ketchum & Benson (2010), with paddles in a unique body plan without modern analogue. Ple- the nothosaurid Cymatosaurus, as the outgroup. Codings can be found siosaurs likely share a distant relationship with terrestrial in the Appendix. The analysis was run in TNT v1.1 (Goloboff et al., sprawlers (Rieppel, 1997, 2000) and on entry to the marine 2008) with 20 independent hits using the defaults of ‘xmult’ command realm employed paraxial rowing (Schmidt, 1984; Storrs, 1986; and 10 cycles of tree drifting (Goloboff et al., 2008). Tree Fuse was run Lin & Rieppel, 1998; for a different opinion see Sues, 1987). with 22 replicates and over 1 3 109 rearrangements. A single parsimo- Within Diapsida, there are two primary modes of aquatic loco- nious tree was retrieved with a tree length of 1136.78. Resampling motion: limb-based swimming (e.g. turtles, penguins) and scores were calculated using 100 replications of symmetric resampling trunk-and-tail-based lateral undulation (e.g. varanoids, igua- (Goloboff et al., 2003). Each data set was analysed with a single addi- nids,crocodyliforms).Amongextantparaxialswimmersthere tion and the resulting tree collapsed with tree bisection reconnection are two main styles: rowing (e.g. trionychid turtles) and under- (TBR) (Goloboff & Farris, 2001). Group supports were calculated by water flying (e.g. sea turtles). In underwater rowing the main TBR-swapping the trees, and registering of the number of steps needed locomotory vector components are protraction and retraction, to unite a clade. Both absolute (Bremer, 1994) and relative Bremer sup- whereas in underwater flying the main locomotory vector com- ports are presented (Goloboff & Farris, 2001). Continuous characters ponent is adduction and abduction (Carpenter et al., 2010). (both meristic and non-meristic) were analysed as such (Goloboff Within plesiosaurs, both rowing and underwater flying have et al., 2006), i.e. ranges and ratios were plotted in the matrix with been proposed (Watson, 1924; Robinson, 1975; Carpenter the actual values, without the need to create arbitrary groupings. ´ et al., 2010). Araujo & Correia (in press) provide a detailed Vincent et al. (2011) matrix was also coded and is 67 characters 3 analysis of the pectoral myology of plesiosaurs. 22 taxa, focused particularly on elasmosaurid taxa (10 out of 23). In this contribution, we first describe the osteology of the The outgroup included the pachypleurosaur Serpianosaurus and the new taxon and perform a character-based parsimony analysis nothosaur Simosaurus. to determine its phylogenetic position. We then perform an additional analysis employing a continuously variable Phylogenetics morphometrics morphometric character, a quantification of coracoid shape, to develop a testable model of evolution for this bone in In order to develop a testable model of morphological evolution Eosauropterygia. We conclude with a brief discussion of the of the coracoid, we also performed a phylogenetic morphomet- implications of girdle and limb morphology and musculature ric analysis following the methods of Catalano et al. (2010) and variationonswimmingstyleinplesiosaurs. Goloboff & Catalano (2011). Phylogenetic morphometrics employs Farris optimisation by applying parsimony analysis to 2D or 3D spatial continuum (Catalano et al., 2010) using homol- Materials and methods ogous landmarks. A set of landmarks is regarded as a single character by the algorithm. In this case, one character with Institutional abbreviations 14 landmarks was used, forming the character ‘outline shape of the right coracoid in ventral view’. Forty pachypleurosaur, CMN – Canadian Museum of Nature, Ottawa, Canada; IVPP – nothosaur, pistosaur and plesiosaur taxa were scored. For fur- Institute for Vertebrate Paleontology and Paleoanthropology, ther information see Supplementary Material. Beijing, China; KHM – Kaikoura Historical Museum, Kaikoura, – New Zealand; MGUAN MuseudeGeologiadaUniversidade Systematic paleontology Agostinho Neto, Luanda, Angola; SMF – Forschungsinstitut und – Naturmuseum Senckenberg, Frankfurt, Germany; TMM Texas SAUROPTERYGIA Owen, 1860 – Memorial Museum, Texas, USA; YPM Yale Peabody Museum, EOSAUROPTERYGIA Rieppel, 1994 New Haven, USA. PLESIOSAURIA de Blainville, 1835 ELASMOSAURIDAE Cope, 1869 sensu Ketchum & Benson, Materials 2010 Cardiocorax mukulu gen. et sp. nov. MGUAN PA103 (Figs 2 and 3), complete pectoral and pelvic gir- Holotype – MGUAN PA103, complete pectoral and pelvic girdle, dle, cervical and dorsal vertebrae, partial forelimb (humerus, cervical and dorsal vertebrae, partial forelimb (humerus, radius and radius and ulna and isolated phalanges) and several dorsal ribs. ulna, and isolated phalanges) and several dorsal ribs. MGUANPA270(Mateusetal.,2012,Figure11),pubis,ischium, Referred specimen – MGAUNPA270isamoreincomplete femur and completely articulated posterior limb. specimen preserving a pelvic girdle and a single hind limb in 110 Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 26 Sep 2021 at 04:19:14, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/njg.2014.44 Netherlands
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