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José Manuel Padilla-Gutiérrez P. 87‒134 VOL. 69NO. 1 BOL. SOC.GEOL.MEX.2017 Maravillas, 25022Saltillo, Mexico. 3745, Centro Metropolitano, Parque Las Museo delDesierto, Carlos Abedrop Dávila Arturo Homero González-González José Manuel Padilla-Gutiérrez Héctor E.Rivera-Sylva 69120 Heidelberg, . senschaften, ImNeuenheimerFeld 234-236, Universität Heidelberg, InstitutfürGeowis Wolfgang Stinnesbeck the Netherlands. Oldenzaalsestraat 39,7591GLDenekamp, Museum Natura DocetWonderryck Twente, Eric W. A.Mulder prinzenstraße 13,76133Karlsruhe, Germany. sruhe, Geowissenschaftliche Abteilung, Erb- Staatliches MuseumfürNaturkunde Karl- [email protected] Eberhard Frey Eberhard Frey from theearlyLateCretaceousofnortheastMexico A newpolycotylidplesiosaurwithextensivesofttissuepreservation Manuscript December 31,2016 accepted: Corrected manuscript received: December29,2016 Manuscript received: December4,2016 , EricW.A. Mulder,Wolfgang Stinnesbeck - , Arturo Homero González-González tion, palaeoecology. Mexico, soft tissue preserva dae, Late , northeast tology, , Polycotyli Keywords: palaeon gen. etsp. nov. cotylidae, Poly in anew and of the new specimenisplaced gastralia, als aswell as the medially converging the girdles andpropodi- of phology and according tothe unique mor palate, between which isintermediate the of Based on the unique osteology similar to extant leatherback . speed a swimming tissues suggests from the preserveddetermined soft body shape unit. The ing asingle contour, withthe body andtail form the hydrodynamicdrop-shaped body the tail base.responsible Itwas for mal tissueispresent, especially along subder trailing edge. Athicklayer of and scalerows to the perpendicular preservestrailing flap edge skin fibers in longitudinal rows.arranged The ezoid millimetric scale-like structures versely elongate rectangular to trap well preserved areas there are trans- preservation. Insomeexceedingly Mexico. Itshowsextensive softtissue ed limestonesat Vallecillo, northeast the early laminat- cotylid plesiosaur is described from apoly nearlyA complete skeleton of ABSTRACT fernandezi Mauriciosaurus Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín and , , Héctor E.Rivera-Sylva, ------partes blandas,partes paleoecología. este de México, preservación de cotylidae, Cretácico Tardío, nor- vertebrados, Plesiosauria, Poly- Palabras clave: Paleontología de gen.etsp. fernandezi Mauriciosaurus nov. género yespecie de los Polycotilidae,nuevo espécimen a un asignar el nuevo permiten vértebras gastrales medialmente convergentes, de los cinturones ypropodiales, igual que las chops del paladar, entre Dolichorhyn intermedio una tortuga laúd. La enigmática osteología debe dehaberse aproximada a la de dos blandos, sepresume del quela velocidad ylos teji cola. acuerdoDe conelcontorno una entidad entre elcuerpo yla formándose degota del animal, drodinámico forma en hi cola y debehaber contribuido al contorno la base en de la gruesa es particularmente la que de tejido subdermal, tificó una capa perpendiculares al borde de salida. Se iden fibra yescamas,serva ordenadas filas en y elbordela solapa, posterior de la piel pre- a trapezoidal, y conorden longitudinal. En rectangular das transversalmente de forma milimétricas,tificaron estructuras alarga de las partes blandaspreservadas se iden- Cretácico Tardío. En las porciones mejor a la parte temprana estratigráficamente del cillo del noreste deMéxicoyfueasignada procede delas calizas laminares deValle plesiosaurio polycotílido.nuevo El ejemplar Se describe el esqueleto casi completo de un RESUMEN y Trinacromerum, la morfología única /2017 87 ------

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico ABSTRACT A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico INTRODUCTION 1. Introduction 88 88 fof saurs with a tail are based on a single specimen al. Lingham-Soliar, 2000; Robinson, 1975; Sanders 1989; Halstead, Godfrey,1984; 1982; Riess, and the tail (Frey tion remains debated as the role of opera of mode the locomotion, of mode themain as accepted generally is flight aqueous McHenry and Everhart, 2001; Cope, 1872;Martill, 1992; Cicimurri 1904; (Brown, debated still is which of some specimensalsocontainsgastroliths, the role rare fossilstomach contents andthebody cavity of elasmosauroidsand pliosauroids evidencedis by and Chiappe, 2011;Taylor, diet of 1986). The (Noé, 1999; O’Keefe and Carrano, 2005; O’Keefe but little about their reproduction andontogeny imens, andmuchknownis about their style, known from numerous excellently preserved spec these predatory marine is tal anatomy of skele- The to 1992). Hampe, 2003; (Ellis, respect size body with varies size flipper Plesiosauria, . Among of unique pattern a bones, limb flattened dorsoventrally with size with four hydrofoil-shaped almostflippers equal of characterize swam all Plesiosauria. Plesiosaurs shorter than the body, are the main features that lar or oval cross-section andatail, whose length is O’Keefe, 2001).Abodywith arounded triangu- and Russell, 2008;Ketchumand Benson,2010; (Carpenter, 1997;Druckenmiller andtheexclusively short-necked al systematics, the either long- orshort-necked age, twoare ‘suborders’ tradition in distinguished Middle to late anditsallies of marine reptiles. Besides the enigmatic the dominant groups of Plesiosauria are one of of the specimen that this tail fin is likely to have to likely is fin tail this that specimen the of (Großmann, 2006) states that after a detailed study posterior . However, Großmann the to the posterior quarter of ed substancedorsal specimenshowsa black This expandGermany). (South from the Early Jurassicof / , 2004; Taylor, plesio- 1981). Reconstructions of Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Seeleyosaurus et al. 20; alr 19) Wie sub- While Taylor, 1993). 2005; , guilelmiimperatoris Dms 1895) (Dames, et - - - - /2017 95.87.01, comes from the Clearwater ForClearwater Albian the from comes 95.87.01, earliest polycotylid from , TMP (Kear, 2006), have named.The not been formally from both orAlbianBulldog of the P36356, SAM and 6206-6298 AM 2007; Schumacher III many authors, liesoutside (Albright the which, according to Shale of oscyllus saurus and Russell,true same is for 2009).The to Polycotylidae by(Druckenmiller authors most representatives, the Australian the currently oldest and Russell, 2009).One of to the Late MaastrichtianAptian (Druckenmiller with atemporal range extending from the Early Polycotylid are plesiosaurs a cosmopolitan taxon remains amystery. their skin andthe surface structureplesiosaurs of onthe bodyin plesiosaurs.shape of Information softtissuepreservation resents the only record of - rep this 1895) (Dames, fin tail the Besides 1975). flexible trailing edge (Großmann, 2006; skinnyRobinson, a suggesting preserved is front the of theposterior margin of trailing the proximal half substance black a (GPIT/RE/3185), Germany ologisch-Paläontologisches Institut at Tübingen, Hydrorion Holzmaden specimenof plesiosaurs. Inonesingle softtissuefor thereunequivocalno is record of knownfrom other inthe assemblage in localities where soft tissue preservation is well Plesiosauria. Even tissues inthe fossilrecord of soft skeletons being available, thereof a lack is Despite numerous complete and fullyarticulated laying (O’Keefe andChiappe, 2011). egg not need of to emerge on land for the purpose idence that Plesiosauria were viviparousand did Late Cretaceous plesiosaurs, providesev group of apolycotylid plesiosauroid, alongirostrine male of (Taylor, apregnant fe- discovery 1986).The of and pinnipeds,how andon fast they could swim could crawlplesiosaurs on land, as do sea turtles been fabricated.on whether There is discussion et al. (Kear muddi , 2007a;Benson

brachypterygius from the Late Albian Thermopolis from the Late Albian Thermopolis et al. , 2006), is nolonger referred et al. i h olcino theGe the collectionof in et al. , 2016)Two specimens, , 2013; Schumacher,2013; , Umoonasaurus Edgaro- dem- - - - Vallecillo. The exact quarry of provenanceVallecillo. Theexact cannotbe reconstructed,because theslabswere alreadyloaded on atruck. Figure 1 Fuente, 2000). (Gasparini and trichtianof boundary erraini geologically youngest named species, Sulcusuchus (Kear, 2006: p. 847, Figure 2E). The mal name or collection number and comesfrom geologically youngestThe polycotylid hasnofor [Thililua b), ica [ NorthAmer reported from theCenomanianof Thus, theearliest named polycotylids are those also unnamed. Alberta, is , and mation of Palmulasaurus Geographicalposition of thetownofVallecillo. Thenew polycotylidcomesfrom the quarry field intheclosevicinity of Pahasapasaurus Eopolycotylus comesfrom near the /Maas- quadratus

rankini, (Albright III

haasi longicollis , (Albright IIIetal. , (Schumacher, 2007)] and , (Bardet et al. et al. , 2007a), , 2003)]. , , 2007a, Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - -

iiiyo Vallecillo. vicinity of workmen inanactive inthe quarry of discoveredimen was insummer2011bya group spec- The detail. fine in structures surface dermal preserving plesiosaur first representsthe latedand (Figure skeleton is complete, 1). The fully articu Monterrey, theCityof Nuevo León north of km 100 about 99°59’W), Vallecillo(26°39’N of town laminated cropping outaround the northeast Mexico.from specimencomes The of Cretaceous P.F.1)Late 2544 the RFG from CPC polycotylid plesiosaur(collection number INAH report describes anewgenusThis and speciesof /2017 89 89 -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico INTRODUCTION MATERIAL AND METHOD / GEOLOGICAL A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico SETTING 3. Geologicalsetting 2. Materialandmethod 90 90 artificial low illumination. angle investigated specimenwas The under natural and drawings were designed using the same program. weretographs traced with CorelDraw X6.The Pho- 36R. FL Flash Electronic Olympus trolled with aninfrared con- photography wasperformed light angle Low 1:3.5. lens, mm 35 Macro Digital Zuiko a and 5.6 – 1:3.5 lens, mm 42 – 14 Digital (“Tough”)E 620withaZuiko andanOlympus limestone. micritic were Photographs TG takenwithanOlympus 1 laminated, finely in served materialspecimen preThe a single - comprises 2007; Blanco and Alvarado-Ortega, 2006; Blanco Alvarado-Ortega, and Blanco-Piñón 2005; et al. , ria are represented by tooth (Blanco-Piñón a single al. the exhibit soft tissuepreservation (Buchy reptiles (Mosasauroidea and Chelonia). Many of aspidorhynchiforms,tiforms, ) and marine pycnodon crossopterygians, (selachians, of age.nian faunaincludesadiverse assemblage The latest to earliest Turovertebrates of tenkalk) withabundant andexquisitely preserved thin-bedded laminated limestone and marl (plat of macrofossils(Sohl AguaNuevaThe Formationgenerally is poor in 2001; Ifrim,2006;Muir, 1936;Sohl Mexico Basin(Goldhammer and Johnson, of Gulf America and the United States of Interior of ern Mexico extending as far as the West of the Gulf which were developed coast of along the western low relief, of a moderately in shelf deposited deep Mexico. stratauted in northeastern These were cyclic limestone and shale that are widely distrib- ly carbonate thick sequencesof unit comprising to Agua Nueva Formation, a dominant- fromcomes newspecimen The the Cenomanian / , 2007;Ifrimetal. Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín et al. , 2005). Until now,Until Plesiosau 2005). , , 1991),but it includes aunit et al. , 1991). et - - - - - /2017 - the only abundant benthic element in the macro- scavengers, andinfaunal benthos. Inoceramids are carnivores, substrate resultingthe absenceof in combined withdysoxic toanoxicon the conditions traction currents and wavesstorm on the sea floor, vertebrate fossilsexplainedis bythe absence of Mexico (Figure excellent 2). The preservation of of into to the Paleogulf the ican coastline, opening of near the southern several hundred kilometres from theNorthAmer inanopen marine environmentstätte deposited VallecilloThe plattenkalk is a Konservat-Lager theVallecilloEarly Turonian section. interval of mites scribed hereassociated is of with aspecimen slabcontainingthe polycotylidThe plesiosaurde havedetail beendescribedin byIfrim (2006). stratigraphy, aswell as sedimentological aspects, invertebrate2008). The beck, assemblage, thebio- Early Turonian ( Cenomanian zonationdetailed biostratigraphic from the latest taceans ( ifera, inoceramid bivalves, ammonitesandcrus and containsabundantm thick plankticforamin ded and millimetrically laminated platy marl is 7.7 thin-bed At Vallecillo, the plattenkalk section of cotylid from Mexico. poly- complete first Vallecillo,the and of taceous the Late Cre virtually complete plesiosaur of first kyns, polycotylid 1976). The presented here is the Ifrim andStinnesbeck, 2008;Schlanger and Jen Anoxic Event 2 OAE 2(Ifrim under anoxiccaused by conditions Oceanic global environment onanopenshelf meters. Itformed at least 10000 square kilo and covers anarea of Vallecillo-typeThe ria (Ifrimetal. including Monterrey, and Ciudad Victo Arteaga knownfrom Mexico, other areas innortheastern ilar coeval lithologies and fossiliferous horizons are Vallecillo,from around but the small town of sim- assemblageIfrim, 2006). This is known mainly and Cavin, 2003; Buchy Mytiloides

nodosoides Stramentum) which provide aprecise and kossmati , 2008; Stinnesbeck and Frey,and Stinnesbeck 2008; , 2014). , indicating that it is from the late Inoceramus Mammites assemblage) (Ifrim andStinnes- plattenkalk

et al. pictus

nodosoides , 2005; Giersch, 2014; isthuswidespread

pictus et al. Zoneto late Vascoceratid , 2011,2008; Mam------Paleogulf ofMexico(modified from Bhattacharya and MacEachern, 2009). 4. Preservation Figure 2 (Figure 3). The specimen has a length of 1.9 me- 1.9 of length a has specimen The 3). (Figure together closely fit that slabs 28 on preserved is P.F.1.2544 RFG CPC number collection It toria) INAH (Instituto Nacional de Antropología e His del Desierto, Saltillo, Coahuila Mexico underthe plesiosauroid, isaccessible through the Museo complete and fullyarticulatedThe polycotylid Hoppe, 1992). and Bottjer, 1995; Ifrim moautotrophic microbes(e.g. assymbionts hostile low-oxygen conditions by sheltering che- and microfauna andmayhave adapted to the Geographical position of Vallecillo N.L. during the Turonian. Note that the Western Interior Seaway is connected with the with connected is Seaway Western Interior the that duringTuronian.NoteN.L. the Vallecillo position of Geographical et al. , 2011;MacLeodand , Fischer Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - straight, butstronglyis the curved tothe postcervical vertebralThe nearlyis column compaction. als andphalangesare due to somewhat deformed vertebrae,The , epipodials, metapodi cracks.showslight impactionand/ordeformation propodialsThe the specimen. andallgirdle bones were workmen lost when the quarry excavated the tail (Figure elements 3A). These and the tip of flipper hind right the of part mid the of segment a flipper, hind theleft of third distal the flipper, therightfore of the left plate,pubic thedistalhalf are aslabimmediately missing: craniomedially to the skeleton left of , onlysmallsections the in ventral aspect. Besides asubstantial part of exposed is and meters 1.15 of span flipper a ters, /2017 91 91 -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico GEOLOGICAL SETTING / PRESERVATION A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico PRESERVATION Figure 3 drawing. Note themassivetailbaseand thedorsal skinpreserved betweentheribs. 92 92 h nmlo all preserved teeth as well as some enamel of The B). A, 4 (Figure mandible the of margin left the medially adjacent totheleft splenial andlateral to the left are visible Only a few fragments of exposed. fully is which of flange alveolar the illa, max- right the on positivelyidentified be only can belong to the premaxilla. However, tooth positions which two teeth are preserved on the left side, of which likelybelong to the premaxilla. Nine two of the , teeth are visible on the right side of the articulations remaining incontact.Fifteen with but cranium the of long the against 5° by the mandible was sheared to the left by about and mandible are slightlytwisted sinistrally where- only minorcompactionfractures. cranium The exposed between the mandibular rami and shows ramusshows its ventrolateral palate aspect. The is with only itsventral edge visible, while the right distorted because the left is positioned vertically been have rami mandibular The B). A, 4 3, ures tral aspect with the mandible inarticulation (Fig ven- in exposed is The 3). (Figure skeleton tail and trunk the of axis long the to 85° about of right such that the skull isorientated at an angle / : Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. A) Photograph of the specimen after preparation, B) interpretative line interpretative B) preparation,specimen after the Photograph of A) P.F.1. 2544 RFG CPC INAH - /2017 odteltrlmri fthe preservedon skin yond the lateral margin of now extend beyond the ribcage and protrude be- the gastralia of thatpaction so the ventral termini com- by flattened been has basket gastral entire slightly disarticulatedonly in afewplacesbut the must was maintained on burial. are gastralia The the ribs,that implying vertebrocostal articulation of movement lateral a of trace no is There 8). 3, the ribs overlie each other (Figures of tral termini ribcage has collapsed posteriorlyThe andthe ven- theneck. cervicothoracic transitionat thebaseof dyle (Figures 3, 4 A, B). This torsion persists to the ulated butstill incontactwiththe occipital con is posterior to the -axis, whichslightly disartic is the cervical seriesbeginsimmediately of torsion dextrally at their bases due to compression. The curvature. neural havespines The been distorted neck the define and other each contact spines ral theneu- anterior posterior and marginsThe of 6). 5, 3, (Figures aspect lateral in visibleare spines ventrolateralseen in suchview that theneural All vertebrae posterior to the atlas-axisare system away duringpreparation. the crownsbeen largelyhas scratched apices of - - drawing, C)reconstructionof theskullinventralaspect. Figure 4 ly separated,ly but theischia maintaintheir is intight contact, the pubic symphysishas slight- thecoracoids,preserved,far as as dian suture of me- the While 8). 3, (Figures plane one in flat lie both girdles the ventralLike the gastralia, bones of thetrunk(Figure 6). the leftsideof : Mauriciosaurus fernandezi INAH CPCRFG2544P.F.1.A)skull aspreservedinventrolateralaspect, B)interpretative line in situ Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín enlfc fwhich isexposed, have symmetrical face of ternal underlying bones(Figure 6). Both scapulae, the ex both girdles have around the been deformed of situ disarticulated but stilllie close totheir original bothgirdles are elements of dorsal contact. The oiin Fgrs , ) Te eta elements ventral The 8). 3, (Figures position /2017 93 93 in - -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico PRESERVATION PRESERVATION / SYSTEMATIC A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico 94 94 the reddish-brownsubstance. softtissue at The the by surrounded are flippers front both of podials flipper (Figures 3, 16).The and proximal the along preserved also is tissue Soft 14). (Figure the gastralia the ribs and the central elements of surface orthe peritoneum, skin is visible between dark coating, which likelyrepresents the visceral thetail. Wrinkled thebodyand at of both sides of the soft tissue, are preserved along the right side a grey matter, whichof are apparently related to thetail. Patches ally converges towardsthe endof terior to the ischiadic plates andfrom there gradu immediately 170mm pos maximumof thickness a reaches tissue soft the Here, 8). 3, (Figures base pelvic girdle without any onto the constriction tail the along continues It mm. 70 and mm 50 tween be of width a with flanks the and girdle shoulder preservedsoft tissueis thetrunk, at the of sides both On 15). (Figure transition cervicothoracic the neck the soft tissue is restricted to the side of left the On 3). (Figure neck the of side right the the skull, and from there it continues along part of the postorbital preserved along the right side of a reddish-brown softtissuehas The color and is 9). theinterclavicles(Figure bones, possiblyparts of the left humerus there are two disk-shaped ner of cor posterodistal the to Adjacent 3). (Figure four all of curvature strongest the shows flipper right front incomplete The flippers. hind the in than posteriorly. curvature The stronger is the front in metapodial and digital elements are slightly curved The 3). (Figure 60° ~ of angle an at dolaterally the trunk,the femora are orientated cau- axis of ~90° to the long meri face laterally at of an angle hu- both laterally. While extend flippers four All medial faceexposed (Figures 3,8). theischia withtheir lie along thelateral margin of teriorly at the posterior acetabular contact. They scapulae facelaterally. Bothiliahave rotated pos both vical vertebrae. scapularprocesses The of bothscapulae lie adjacent to the cer of corners anteromedial The 8). 3, (Figures fossa glenoid the the withtheir anteroproximal at corner ly rotated anterolaterally but retain contact with / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------/2017 5. Systematicpaleontology 2. 1. h it ftheflipper(Figures 3,12). the widthof the IVth right digit hind of flipper, and is one third the soft tissue preserved that extendsto the tip of the . There is at about in the mid-length of terminates and flipper the of width the of fourth one about to posteriorly expands flipper front left Family: features: ing tothefollowing combination of specimenisreferredThe to Polycotylidae accord - Cretaceous). Aguas Nuevas Formation (Early Turonian, Late Type the horizon: Vallecillo Member of field(Figure 1) quarry western 99°59’W), (26°39’N Vallecillo Type locality: display intheMuseoPapalote Verde, Monterrey. on P.F.1.and 2544 housed RFG is specimen The Antropología e Historia)registration number CPC de Nacional (Instituto INAH the with 3) (Figure skeleton with extensive soft tissuepreservation : Anearly complete and articulated Nuevo León. the state of in Earth- and biological sciences predominantly in area atry Vallecillo andsupportspublic education search, but alsosecures all future workthe quar in only made the specimen accessible for scientific re- MauricioFernández Garza,who not in honorof name:Genus andspeciesname Derivation of Benson al.

, 2016;Williston, 1908) (“dished” according(“dished” to O’Keefe, 2001) lateral Pterygoid body with ashallow oval depression body (Figure 4). the anterior pterygoid from the middle of Pterygoids with anterior processesemerging Leptocleidia KetchumLeptocleidia andBenson,2010 et al. Polycotylidae (Albright III Plesiosauria deBlainville, 1835 sp. fernandezi nov.Mauriciosaurus Polycotylidae Williston, 1908 Plesiosauroidea Welles, 1943 , 2013; O’Keefe, 2001; Schumacher gen.novMauriciosaurus et al. , 2007a; et - 5.1. DIAGNOSIS FORTHEGENUSAND SPECIES 1. 9. 8. 7. 6. 5. 4. 3. 6. 5. 4. 3. 2.

. Mauriciosaurus acher and itresembles that of isperfectly preserved in three dimensions lief re (Figure - This 4). pterygoidealthe corpus of half posterior the covering W-configuration prominent ridgesthat are in a arranged of posteriorlyis sion open,merging witharelief the pterygoideal plates. depres- The of half Dish-like depressionrestricted to the anterior (Figure 4). vacuities ing the posterior interpterygoideal Pterygoids meet atop the clos (Figures 10–12). Phalange digits one through four interlocking (Figures 10–12). Supernumerary inepipodial rows ture (Figure 12). curva humeruswithsubtle sigmoid - Shaft of more expanded thanfemur (Figures 10,12). Humerus shorterbut posterodistally slightly compared withotherLeptocleidia). cervicalvertebrae reduced (when Number of length; Table 1;Figure 4). the entire mandibular least one fourth of Mandibular symphysislong (measuring at cuities (Figure 4). va - posterior to the posterior interpterygoidal vacuities meeting to posterior interpterygoid No posterior or medial perforations inthe upper jaw. At least 42 tooth positions on the either side of pansion (Figure 4). longitudinally oval withaslightanterior ex - Posterior vacuities narrow, interpterygoidal protuberance. median a of trace any without 4) (Figure ed the bone;anterior processbifurcat dle part of face and concave lateral margins inthe mid - Parasphenoid concave withadeeply ventral theprocesses (Figure 4). third of the the vomers to three times the width of Anterior pterygoid rods expand at union with et al. , 2016),butmore is complex in (Schum Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - measurements oftheskullinmm. Table 1.Mauriciosaurus 5.2. NOMENCLATURAL ACTS ai adblrsmhsa eghapprox.45% Ratio mandibular/symphyseallength symphysis Mandibular widthatcaudalendof Length ofsymphysis Length ofrightmandibularramus Length ofleftmandibularramus Measurements oftheskullinmm 7. E19F-F78E63 o te species.. the for genus 4E81-98F8-AFE7086E7693 urn:lsid:zoobank.org:act:8D331E82-25B5- the and for 4BEC-8723-A9B7B4A888B9 urn:lsid:zoobank.org:act:DF54BB6D-73DE- is: ture, ICZN, LSIDfor 2017).The thispublication on Zoological Nomencla- Commission ternational the LSID to the prefix “http://zoobank.org/” (In- through any standard web browser by appending resolved viewed and the associated information be can Identifiers) Science (Life LSIDs ZooBank the online registration for system the ICZN. The acts it contains have been registered in ZooBank, ticle.published work This andthe nomenclatural thisar that Code from the electronic edition of new names contained herein are available under Zoological Nomenclature, andhencethe Code of the amended International the requirements of to this article conforms electronicThe edition of 8.

es oteataeo such perforations. least totheatraceof anadult, one shouldexpect at the length of fact that this animal probably had at least half the specimen, but given the juvenile stage of could beduetothe (Figure coracoids 8).This ol b 15 Tbe ; lrgt III Albright 2007a). 5; (Table 1.5 be would polycotylid1.77. The digit III is standard phalangesof Average length/width ratio of (Brown, 1981),but notfor any polycotylid. structurebeen described for has dian plate-like structure (Figure 9).Asimilar Gastralia converging medially, ame- forming fernandezi INAH CPCRFG2544P.F.1; /2017 et al. 175 425 420 95 95 70 - ,

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico SYSTEMATIC PALEONTOLOGY SYSTEMATIC PALEONTOLOGY / A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY MANDIBLE (FIGURE4;TABLE 1) SKULL (FIGURE4) 6. Osteology 96 96 4DF3-8149-77217E598238. urn:lsid:zoobank.org:pub:2B15EAB5-9688- ital repositories: PubMed Central, LOCKSS archivedavailable andis from thefollowing dig- with anISSN,lished ina journal andhasbeen this work waspub- electronicThe edition of otro emnso the maxilla. Ultimately, it of posterior terminus slightly concave, the boneis andlevels withthe of symphysis terior to thedentary the lateral margin an acute inanterior tip.teriorly terminating Pos isslightly convex the dentary an lateral margin of length. At the symphysis the dentary the sixth of the symphysismeasures one part of dentary The minates at the twelfth tooth position. maxillary the mandibular symphysisthat posteriorly ter of % 50 about forms which symphysis, dentary the ~10°towards dentaries converge at of anangle the pterygoideal The corpus. posterior margin of the at the level terminates right dentary of The preserved. length, while the left half one is only minus,preservedis therightdentary for itsentire itsanterior ter With the exceptionDentary: of or impossible. difficult outline their of reconstruction the makes the bones are crushed, which compaction many of the rostrummissing. is Dueto visible. tipof The the alveolar margin are the mid part of ments of frag only maxilla left the Of A). 4 (Figure mould the left premaxilla is onlypreserved as anexternal the medial part of is exposed, whereby mostof complex premaxillomaxillary the right of flange anterior direction. Therefore, the entire alveolar in articulation but has been sheared to the left in ible in ventrolateral view. mandible The remains around itslongaxisina way that the skull isvis theskull,whichslightly twisted tothe is left side of Both mandibular rami overlie the ventral surface / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------/2017 sse ntergtslna.Temda aeo medial face of seen onthe right is splenial. The slightly eroded but likely wasevenly rounded as the left splenial is of posterior terminus ial. The the splen- equivalent on the posterior margin of anteriorlythat openU-shapedincision matches its the lateral face showsan anterior marginThe of sal andventral margins are parallel to each other. splenial andisslightlylaterallyconvex. dor The theanteriorlyadjacent thelength of fourth of lateraldial aspect.The face measures about one right one showsits lateral,The the left one itsme 4). (Figurepreserved are angulars Both Angular: preparation. face hasbeen partially destroyed byunprofessional the bone sur sigmoidal suture. Afaint striation of and contactsthe surangular with a the jugal of theanterior base at thelevelto terminate pears of only visible on the left mandibular ramus, but ap is splenial the of flange medial The angular. the a posteriorly directed forms U-shaped suture with the pterygoid where it to the posterior margin of the the maxillary middle archesof 15 mm anterior at level each splenial terminates of lateral part of sub-parallel ning to thelateral one. ventro The - posterior direction withthe medial margin run- each splenial slightly converges in ventral face of the dentaries following their curvature. The of splenials lie in articulation withthe medial margin the each bone. lateral The marginsof of pansion sis measures theabout longitudinalone ex- fifth of 15° at the anteromedial one. The splenial symphy- about 10° at the anterolateral margin and about the mandibular symphysis of with anapertural angle of % 50 posterior the forms symphysis nial sple- The 4). (Figure skull the of torsion slight the eral and the left one inventromedial view due to entire right one is seen in ventrolat length. The - Splenial: Both splenialsare preserved over their preparation. the bones hasbeen scratched away during ture of thesurfacestruc- longitudinal striae, but muchof slightly sculptured appears withirregular shallow the dentaries lateral margin. bonesurfaceof The parallels the the dentary medial marginThe of becomes convex paralleling the squamosal. again - - - - CRANIUM (FIGURE4) Surangular bone surfaceisbadlyscratched. a squamate suture. forming millimeters the Again appear to underlieangulars the splenials for a few open V-shaped suture. Attheir anterior ends, the a posteriorly thesurangularin posterior marginof es posteriorly. Each angular contacts the vertical increas the angular gradually curvatureThe of gin, which runsnear parallel to the ventral one. surangular with itsregularly concave mar dorsal eachconcave. angular is Eachbone contactsa maxilla, while theventral missing.part is Howev - the suture with the represents the lateral part of thirdalveolus. visible maxillary overlap This likely the the maxilla reaching the level of al margin of ly the lateral premaxillary wall overlaps the later the transverse convexity being strongest. Posterior flange, alveolar the of whichand convexsmooth is all directions, in with surface internal the of mold the premaxilla there is aninternal main of flange, which isnow missing. alveolar Medial to the preserved re- the to dorsally broken is which bone, premaxilla preservedis asaslender seam of Premaxilla: determined. the bone cannot be visible. original shape of The fossa the glenoid are posterior cotylar process of the ticular process tipof and the dorsomedial theretroar of the posterior-mostOnly terminus overlainmostly is bythe angular and surangular. the left be seenon mandibular ramus, where it (Figure 4):Onlythe left articular can Articular smooth. the bone appears terior direction. surface of The curves medially, therebyslightly diverging pos in the bone and parallel-sided, the posterior third of straight are surangulars the of flange medial the splenial medially. While the anterior two thirds of eral face, covering the suture between angular and the lat medial face has three times the length of the angular, while its the lateral face of length of each bonehasabout two thirdsthe lateral face of lateral,its poses the left one itsmedial face. The

Ol h aea agno the right Onlythe lateral margin of The right surangular ex(Figure 4):The - Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------h ail n h neirpoeso thepter the maxilla andthe anterior processof teriorly they taper between the palatinal part of ly the palatines hadsub-triangular outlines. An- palatine is overlain by the right splenial. Most like- the right of pared and exposed. lateral The half ispre- transverse extent, but only the medial half preserved. left palatine The preserves the entire the palatines are Palatine: Onlyfragments of the pterygoids. position 22 and separates the anterior processes of tooth maxillary minates posteriorly at the level of reliably reconstructed. preservedAs the vomer ter bone nor itsposterior or anterior extension canbe the the right splenial. Neither the overall shape of the left maxilla and the palatinal part of gin of vomers the are preserved between the medial mar of portions insignificant two Only Vomer: respective toothpositions. are preserved but they cannot be assigned to their seven teeth fromthe left maxilla remnantsThe of theleft dentary. adjacent to thelateral margin of the alveolar flangeare visible of eral-most portion the lat the middle part of nial. A few fragments of which areoverlain mostly bythe left sple- third of the palatinal part are preserved, the posterior of conical recurved theleft maxilla, the posterior two thirds teeth. Of slightly contain 32 to 30 and 23 21, to 12 5, numbers Alveolae maxilla. right the on identified are positions tooth 32 together the squamosal asexposed. Al about one third of maxillosquamosal suture The coversed terminus. ed suture andtapering to apoint withthe jugal, symphysis,an obliquely posteriorly direct it forms the dentary the middle of nates at the level of maxilla is preserved. Anteriorly the bone termi right the of flange alveolar entire The Maxilla: teeth. lary There were at least four widely spaced premaxil the left dentary.are preserved to the left side of referredare to the left premaxilla topographically lie adjacent to the right premaxilla. Two teeth that three premaxillary teeth al third. remnants The of suture transversemaxillary was at least its laterin that premaxillo the suggests maxilla the of flange the alveolar er, the damaged anterior margin of /2017 97 97 ------

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 98 98 concavity the confluent with the medial margin of recess, which continues anteriorly inan elongate foramen pterygoideum therea shorttriangular is laterallyis concave. Immediately anterior to the suture being laterally convex. anterior one The the of foramen pterygoideum, the posterior half thepterygoid andthe of the posteromedial corner the pterygoidsigmoidal between is of the corpus the medial margin of W-shaped. contact of The pterygoidoparasphenoidalphenoid. The suture is meet the medianlineposterior to theparas in pterygoids The thecorpus. one third the length of times as wide as the caudolateral margin, and is thepterygoidsigmoidal, about four is margin of the lateral margin posterior straight. The anditis with 130° of angle an at medially inclined is and the squamosal of jacent with the medial terminus posterior third. caudolateral The margin liesad- convex initsanterior two thirds andconcave in its issigmoidal being laterally the corpus al margin of the maxillary tooth position 32. The later level of expands anteriorly corpus untilthe sition 18.The tooth po maxillary anteriorly reaches the level of and corpus the cess, than longer whichfifth one is and an anterior irregularlypro- pentagonal corpus arounded pterygoidPterygoid:of The consists adductor chamber. the concavity the anterior margin of that forms not preserved.is Mediallyandlaterally therea is the palatines, but the contact posterior margin of the topterygoids approximately in the middle of struct. Evidentlytheyclosely approached the ec- recon- to difficult is thus and preserved poorly is the palatines by matrix. posterior margin The of the cranium are obscured ture on the left sideof the palatinomaxillarysu the middle two thirdsof themaxillae. However, thepalatinal part of gin of the palatines contact the medial mar margins of suturepreserved is onthe right side. lateral The this the pterygoid. Two thirdsof lateral processof suture curves laterally and accommodates a low thepterygoid, the the anterior processof base of the pterygoids. Close to the posterior process of a laterally convex loosecontactwiththe anterior the palatines forms ygoid. medial margin The of / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - - - /2017 h aaie h eiladltrlmriso the palatine. medial and lateral The margins of the peduncular contact with times the width of latter This threecontact is and contactsthe jugal. the postorbital as preserved of tine. corpus The peduncle faces anteriorly andcontacts the pala ble between the left palatine The and the left jugal. Postorbital:boot-shaped postorbital is visi This thesebones. dent reconstruction of confi a permit not do which fragments, their of position topographical the by identified only are basioccipital and the otoccipitals Occipitals: The anteriorly. cave shallows in itsposterior third andgradually con- the parasphenoid is deeply of the corpus of vacuity. the interpterygoidal ventral The face of concaveis deeply the posterior margin forming the parasphenoid minus. anterior margin The of at its anterior ter the corpus reaches the width of phenoid expands to a bifurcated process, which ramina pterygoidea. Further anteriorly the paras- parasphenoidal rostrum andprotrude into thefo- concave. Twothe shorttriangular processesform Itsventral its corpus. face is deeply mum widthof wide asthe maxi as about half parasphenoid is al foramina the facinganteriorly. neckof The the posterior interpterygoide ed anterior third of thebottle lying between the expand- of the neck tle-shaped with aW-shaped posterior margin and Parasphenoid:bot- parasphenoidis The thebone. of riorly with a tubercle close to the posterior margin ante opening W-configuration and a in arranged prominent ridges of the pterygoid has a relief of ium andthe medial one the vomer. corpus The borders the foramen incisiv anterior terminus the maxilla, the palatinaliscontacts the pars of times its minimum diameter. lateral The margin the processdiverge to about three al margins of process. Further anteriorly the lateral and medi- the the narrowest point lyinginthe basal third of thisprocessare concave with medial margins of the pterygoid. lateral The and anterior processof the the parasphenoid marksthe base of minus of vacuity.large interpterygoideal anterior ter The the pterygoids. It bordersa anterior processesof ------PALATAL VACUITIES (FIGURE4) eosrcino theboneoutline. a reconstruction of thefragment are toodamaged to allowfor of gins the incomplete preservation. mar The because of the right squamosalinstead cannot be excluded of thatpossibility this fragment represents afragment ramus where the jaw articulation should be. The rate is preserved. It contacts the right mandibular possibly the left quad- Quadrate: Afragment of and narrow. likely thatis thesupratemporal fenestra short was the adductor chamber. It of the roof of or half at least the posteri posterior margin andformed that eachsiosaurs bone likelyhada wideconvex complete, to other ple it is assumed inanalogy the margins is badly preserved. Although none of Squamosal: and even. anterior process. suturemedially convex The is pterygoid at to the the transition from the corpus goid are concave. ectopterygoid The contactsthe - the ectoptery anterior and posterior margins of obscuredis bythe rightmandibular ramus. The theectopterygoid one. lateral-most The part of being about one third aslong as the lateral visible is trapezoidal in outline with the medial margin ectopterygoidthe left one in medial aspect. The ly preserved. right one is visible The in lateral, Ectopterygoid: Both ectopterygoids are poor remains uncertain. the bone preservation the outline of the state of concave,the postorbital appear deeply but from Anterior interpterygoidal vacuity: Anterior interpterygoidal vomeral foramen was mostlikelyanelongate oval. the the vomer. outline of the lateral The margin of the left maxilla and medially by medial margin of theanterior pterygoidal process, laterally bythe of It is posteriorly bordered by the anterior terminus about 5 mm and is three times as long as it is wide. men ispreserved. It has a longitudinal diameter of to (O’Keefe,the left 2001)]:Only vomeral fora to Buchy etal. Vomeral foramen [foramenaccording incisivium ly bordered bythe vomer, laterally bythe anteri Both squamosals are Bothsquamosals present but , (2006), “internal naris” according , (2006), “internal Anterior Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------DENTITION (FIGURE4) h egho theparasphenoid. the lengthof fourth one about are They margin. raised by off vacuities are twiceaslongtheyare wideandset pterygoid and medially by the parasphenoid. The pterygoid foramina are laterally bordered by the Posterior vacuities: interpterygoidal they comefrom thefrontoparietal area. that cannot be further identified. Presumably roof the skull ygoideal vacuity there are fragments of small replacement teeth or tooth fragments occur the bulktainty (tooth1, 8,11). The positions of cer with there identified were teeth fragmentary spective alveolar diameter. Onlythree small likely interalveolar space thata little is larger than the re- the preorbital rostrum are separated byan of half upper jaw indicates that the teeth in the anterior the of margin preserved badly The C). 5 (Figure the largest being about one quarter the size of dentition isodont, despite is the smallest teeth The thealveoli. the diameterof served crowns, the diameter at the tooth cervix or extrapolation basedonthe few teeth with pre theteeth areassessable only froman and size of arrangement preparation, insufficient and vation the bad preser el sculpture remain. Because of the enam preparation scratch marksno details of striatedcoarsely enamel. However, dueto the erately recurved pointedtips.few crowns A show their respective diameter. from They have conical andmod independent 4:1 about of crown the All preserved teeth show aheight/width ratio of choana (Buchy by that someauthors this vacuity represents the the palate at thesamelevel.hypothesized Itis of width level with tooth position 31 covers one third through23 maximumpositions tooth Its 32. illary likelythatpears this vacuity extended from max the pterygoids. It ap the anterior processes of theposterior the vomerand likelycoveredmissing is portion of because to reconstruct difficult is theIts length specimen. largest palatal aperture of parasphenoid, thislongoval vacuity isby far the or pterygoideal processes andposteriorly by the et al. , 2006). Inside the interpter , 2006).Inside /2017 The The 99 99 ------

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 100 100 AXIAL SKELETON (FIGURES3,5,6;TABLE 2) interdigitated. gests that the teeth from the upper and lower jaw theteeth are spread outlaterally sug manyof the teeth impossible.is That the distribution of ing premaxillomaxillarysuture anycomment on the miss ed onminimumBecause of assumption. the upper jaw includingthe ones we reconstruct- in positions tooth 42 least at are there Altogether alveoli. the respective are three times the diameter of pear widely spaced with interalveolar spaces that and the three posterior-mostap- toothpositions abrasion of stages different in visible are alveoli struction would betoo speculative. However the the maxilla veryis badly preserved andrecon- of the posterior third rostrum. dental margin The of the the preorbital part of of in the posterior half ually increases byapproximately onethird from the grad diameter of ina. The a blunt median ridge flanked by a foram- paired of Cervical vertebrae XVIII through XXIalsohave the respective centrum. one-thirdis the widthof depression The ridges. sharp of pair a by flanked keel abruptly changes intoamediandepression, cal XII to cervical vertebra XVIII, this between the foramina (Figure 6). From cervi- 1997). There is a bluntgia (Rieppel, median keel whichare consideredfor diagnostic Sauroptery- in ventral aspect, exposing the paired foramina, the cervical vertebrae I through XIIare visible of centra column hasbeen twisted to the right. The thecervicalvertebral because there that part of brae XIII to XXI are visible in ventrolateral aspect Verte2:3. of ratio length/width a have and lous the axis. All cervical vertebrae are slightly procoe tion withthe occiput andisposteriorly followed by with confidence (Figure 5).The atlas is in articula identified is it bone, broken of mass a in lies tem sys atlas/axis the Although 5). 3, (Figures visible 21cervicalvertebrae vertebrae: are Cervical thegirdles. the bonesof tion, but the trunk region is partially obscured by vertebralThe column ispreserved in full articula / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------/2017 agno the respective neural spine for about margin of pophysesextend posteriorly beyond the posterior the neural spines. postzyga The lateral face of the blunt elevation beginning on the middle of postzygapophysesare missing. Theyarise from a vertebra XVII, where the with the exception of the cervical vertebral column neural spines of postzygapophysesThe are visible on all preserved andlow laterally facing ridge.sharp neural spines isvery slightly convex a and bears of azy- all the margin (Figure dorsal of gantrum 6). The base the as identified tentatively is and the respective neural spines anterior marginsof the of ulation. bulge The coversthe ventral half azygosphene /zygantrum artic the presence of the preceding cervical vertebra, suggesting ses of protrudes anteriorly between the postzygapophy theanterior margin that a bulgeis at thebaseof the cervical vertebrae XIII through XVIII,there one concave, but bothremain almost parallel. In the anterior margin isconvex and the posterior atspines neural 15° vertebrainclined all In XVII. about to increases and XII vertebra at 3° about inclined posteriorly. inclination This begins with vertebrae XII through XVIIare gins, thoseof with almostparallel anterior and posterior mar the anterior-most cervicalvertebrae are vertical of cervical vertebra XVII. While the neural spines reached 1:1is in vertebral body untilaratio of the ually increases withrespect to the width of the neural grad spines Posteriorly the height of the respective vertebral body.third the width of one- is spine neural visible first the of height The respective peduncles are visible from the right side. VI through XVIIthe including their neural spines the animal. From cervical vertebra venile stage of are not fusedto the cervical centra due to the ju arches neural these that indicates This 6). 5, ures cervical neural archesThe are tilted laterally (Fig therespective cervicalcentrum. length of the and it extends over the posterior two thirds of 2:1 articular facet a length/width has ratioThe of the centra. oval facet on the ventrolateral face of are headed and articulateribs vical single at along the anterior-most to the posterior-most. cer The ------Figure 5 column, B)interpretative linedrawing. pn vrtefl egho itsarticular facet and spine over the full length of therespective neural yondthe anterior margin of latter vertebrae theprezygapophysesprotrude be- three the In 6). 5, (Figures XVI to XIV and XI, Prezygapohysesare only visible in the cervicals X, and incervicalXVIIslightly caudoventrally, too. gapophysesare inclined slightlylateroventrally, the postzy- neural spines. articular facets of The the the lateral face of of anteriorly over one half neural spine, whereas the articular faces continue the respective one third the longitudinal extent of

Mauriciosaurus fernandezi INAH CPCRFG2544P.F.1.Cervical vertebralcolumn; A)photograph of thecervicalvertebral Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín would nothave disarticulated from their respective are seen.Otherwise the neural archesand spines which onlypatches the neural arches of duncles of the cervical ribs. same holdstrue for The the pe- prezygapophysesare at least partially covered by in anotch.the Inall others and donotterminate the preceding vertebra the posterior two thirds of X and XI,theprezygapophysesvicals overlie only cer In vertebrae(Figured). cervical IX 5 and VII the possible zygosphene, which isonlyvisible in of anteriorly ina notchterminate onthe lateral face /2017 101 101 -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 102 102 Figure 6 rib. through XII; A)photograph B)interpretative of linedrawing. thesection, Abbreviations:ns=neural spine,na=neural arch,cr=cervical Thoracic vertebral Thoracic (Tablecolumn 17 tho - 2):Only vertebrae. wide. cervical is transitional to the thoracic This is it than longer times five about is XX vertebra of rib cervical The 5). (Figure XX vertebra vical fromcer anterior to 1:2 in the most ones 1:1 in the cervical ribs changes aspect ratiofacet. The of the articular the length of to about two thirds of the cervical ribs declines longitudinal extension of posterior-most cervicalrib. Atthe constriction, the the expressed longitudinally with the exception of constricted, whereasrib is moreis theconstriction the of part middle The 5). (Figure point sharp a posteriorly orientated process in that terminates creases inlength byabout one third due to a the cervical ribs in XXI the lateral margin of theribs. Fromvertebra XIII until of distal ends XII have the same longitudinal diameter as the the cervical ribsII through articular heads of The pophyseal articulations. centra in one line held together solely by the zyga / Mauriciosaurus fernandezi Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín INAH CPCRFG2544P.F.1.Detailofcervicalvertebralcolumn,from section cervicalvertebraVII - - - /2017 bu h ideo the vertebral centrum. Here, about the middle of with ashallowconstriction that the narrowest is in rounded by circumference, a sharp which merges rior andposterior articular arefaces ventrally sur the foramina inlongitudinal direction. ante The lowmedial to ridgesruns but sharp face. Apairof foramina onthe ventral lous andshow a pair of 2, Figure 7).The are platycoe vertebrae have a 2:3 length (Table/ width ratio of the thoracic ure 8). Like the cervicals the centra of coracoids isvisible through the latter bones (Fig those vertebral bodies covered by the outline of The 8). 3, (Figures gastralia the by XVI and XV VII through XI are covered vertebrae by the coracoids, and Thoracic vertebrae. thoracic 23 least clear which sacral it is. the animal had at Thus its position relative to the . However, it is not from sacral a represent must these of One 8). 3, are covered by the ventral pelvic plates (Figures ered by(Figure the coracoids 8).Three vertebrae racic vertebrae are visible, because three are cov- - - - - et al. (Schumacher height its equals approximately centrum a of width the given hereinpolycotylids is underthat premiseratio the width Because theheightofvertebraecannotbe measuredcomparison thelength/23. for least vertebrae isat the numberof thoracic numbering oftheposteriorsisArabic,becauseposteriorvertebra I cannot Notealsothat beidentified withcertainty(seealsotext). Table 2. , 2016). hrcctotal:20 thoracic I XIV XXI XV XII XI X IX VIII VII VI IV III II XIII XX XIX XVII XVII XVI XV XIV XIII XVIII XVII XVI XIX V XII XI X IX VIII VII VI V IV ubrcnrmlnt etu it egh it ai egto erlsielengthcervicalrib III heightofneural spine length/widthratio axis centrumwidth centrumlength atlas number total:21 cervical Counts andmeasurementsofthevertebraeinmm XXIII XXII XXI XX Mauriciosaurus fernandezi ubrcnrmlnt etu it eghwdhrtonme etu eghcentrumwidth centrum length number length/widthratio centrumwidth centrumlength number 29 24 25 25 30 24 27 25 20 24 27 20 22 20 20 17 20 20 18 29 27 22 20 20 20 20 18 20 17 17 17 14 27 14 25 13 ? ? ? ? ? ? ? ? INAH and CPCRFG2544P.F.1.Counts measurements of thevertebral column inmillimetres;the 50 46 50 53 53 38 38 37 37 43 43 54 36 34 30 27 25 26 26 26 21 21 22 16 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0.58 0.47 0.51 0.52 0.52 0.74 0.74 0.67 0.63 0.55 0.58 0.66 0.74 0.72 0.76 0.65 0.65 0.81 0.66 0.63 0.62 0.4 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín arl adltotal:25 sacral/ caudal 14 12 13 30 30 30 25 17 16 15 18 19 11 10 30 30 30 24 21 24 23 22 21 20 1 9 8 7 6 5 4 3 2 ? ? ? ? ? ? ? ? ? ? ?? ? none 20 20 36 28 26 21 15 18 21 12 20 20 20 20 25 26 27 42 35 30 23 22 14 20 15 18 27 22 15 15 15 14 ? ? ? ? ? ? ? ? ? ? ? 29 34 37 39 38 38 39 41 41 32 29 20 21 26 18 39 39 39 ?? ?? ?? ?? ?? ?? length/width /2017 ratio 0.69 0.59 0.54 0.51 0.52 0.66 0.66 0.66 0.66 0.62 1.05 0.71 0.69 1.16 0.66 ? ? ? 103 103

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 104 104 a typicalpolycotylid pattern(Schumacher Figure 7 cides with other cides polycotylids. Allcaudalvertebrae ten, which coin- be estimated to a maximum of caudals, missing canthusonly numberThe of oblique break andthuslacktheir left lateral faces. sacrals. posterior six caudalslie along an The three are there case which in vertebrae, 15 least at bers. caudalvertebral The of column consists the caudals have been designated Arabic num - caudal vertebrae remains unclear. Consequently, therefore, the exact border between the sacral and tainty because they are covered by the ischia, and cer with identified be cannot sacrals of number Sacral and caudal vertebral column (Table 2): The exposed (Figure 8). which isonlyvisible on thosevertebrae that are long ovalmostly vertebral foramen nutritivum, medial to each ventrolateral keel there is asmall, thecentrum.Immediately two third thewidthof whichslightly concave is inall directions andis ticular circumferences andbordersaventral face, ventrolateral both ar connects longitudinal keels blunt articular faces (Table 2, Figure 7). A pair of the centrum is about one fifth narrower than at the / Mauriciosaurus fernandezi Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín INAH CPCRFG2544 P.F.1.Thescatterplotof thelength/width ratioindices of the vertebraeshows et al. , 2016). - - /2017 visible on caudals2,3and5through 8. therespective posterior vertebra. facetsare The of hemal arches are limited to the anterior margin become more rounded. articular facets for The the circumferences at the intervertebral articulations the and deepen slightly constrictions the 13, to 7 the anterior articular face. From caudal vertebrae at diameter the of fifths three to decreases bodies the vertebral their centra, where the diameter of ference and a constriction around the middle of caudal vertebrae have a sharp, ridge-like circum- theyare wide. Likethetrunkvertebrae the basalsix rior-most preserved vertebrae are twice as long decreases posteriorly.width gradually poste The While their length remains about constant, their caudals have planar intervertebral articulations. a slightopisthocoely.dle suggesting Allfollowing the caudalfirst is concave in the mid tion facet of the posterior vertebral articula ventral margin of one quarter shorter thanthepreceding one. The is vertebra this 1:3 of ratio length/width a With posterior to theischiumregardedis caudal 1. as vertebra first The aspect. ventral in exposed are - - - Figure 8 line drawing; abbreviations: cv = cervical vertebra, thv = thoracic vertebra, cav = caudalvertebra, cav vertebra. = thoracic line drawing;= cervicalvertebra,thv abbreviations: cv The ribs gradually increase in length from ribs gradually The thorac rib V are straight. rib IV andthe middle section of thoracic curved of posterodistally. distalhalf The the body all ribs are regularly the right side of of the ribs IVandV tralia. With theexception of all overlain by the ventral girdle plates- and the gas the ribs iscompletely visible, because they are of the cervical and the following thoracic ribs, none rib, transitional between which morphologically is thoracic left first the of exception the With umn. the thoracic vertebral col- visible on either side of are reconstructed byextrapolation from thoseribs thoracic ribs ribs(Figure of Thoracic 8): 20 pairs

Mauriciosaurus fernandezi INAH CPCRFG2544P.F.1.Detailof thetrunk including thegirdles;A)photograph, B)interpretive Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - preceding ribs. pelvic plates are about one third thinner than the thatThose are partially visible between the left visible ribs thediameter remains nearly constant. thelongestthoracic ribs.all following In that of whichone thirdis higherthan pair, theheadof the thoracic ribsislargest in the third diameter of the longest thoracic ribs. The one third the size of gion, where theymeasure probably onefourth to decrease in length towardsgradually the sacral re equal size until thoracic segment XIII andthen approximately maximumlength. Theyremain of ic segment I through IX,where theyreach their /2017 105 105 -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 106 106 GASTRALIA (FIGURES8,9) pciepr ftheribshaft. spective partof the re the diameter of compacta, has about half cavity, This separated from which the issharply ribs are cavity abraded, the medullary isvisible. theshaft.Where the the middlepart of in corpus the costal contact,whichtwice the has diameter of oval andconcave articular facet for the vertebro transversely facing, ventrolaterally off-set an to es the ribs diverg- of In medial direction the corpus exposed. not seen in any other rib with anarticular head concavity This maybe duetocompression and is edge and aconcave external sharp anterior face. face,its articular head witharounded internal a the left triangular cross-sectionatside shows a sharply on III rib Thoracic exposed. where flat racic segmentXIIthecostalarticular facets are II these facets are convex andposterior to tho ribsIIIthroughI and the thoracicribs XII.In of slightly concaveular facet is the thoracicpairs in must be fusedto synapophyses. costalartic The fore, thoughinvisible, the par- and diapophyses articular facets. single There and together form In all ribs, the capitula and tubercula are confluent lsoeigatrol tarcntutdageo cles opening anteriorly at a reconstructed of angle anterior-mostThe has two gastrale medial ossi ossicles isdifferentgastralia. inall these lateral gastral ossicles.of arrangement The lateral gastral is a transversely orientated series of ossicles,ally adjacent to the medial gastral there at ters the medial fractures andmirrored. Later they were reconstructed according to the diame- are ossicles these gastral missing; medial parts of ing three. in the slab (Figure Due to a gap 8) the about one third wider than the posteriorly follow a medialplate. to form anterior-most The two are pairedcontact each ossicles medial gastral other in medial direction. widelyV-shaped The un- are sixtransversely converging oriented gastralia underlying bonesduringearly diagenesis. There basket collapsed andwaslater crushed over the occurred when ures the gastral 8,9). Deformation preservedbasket is gastralia The mostlyinsitu(Fig- / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------/2017 Gastral V and VIshare ribs onemedialgastral tip. inasharp terally andterminates suture. Lateral ossicle IIIcurves gastral caudola oblique an in first the of face lateral the contacts the third lateral ossicle gastral of medial terminus tacts the second along its entire anterior face. The dially adjacent one. LateralIII con ossicle gastral the other two but about twice as long as the me asthick rib isonlyhalf the gastral ossicle of the medial one. third The andlateral-most gastral the two isonethird shorter than lateralThe of tral ossicles. medial two The are spindle-shaped. lateral gas as the others. There are three of pairs tral likely havingossicle thick been abouttwiceas Gastral rib IVhasthe most massive- medial gas lateral ossicleII. gastral of IV articulates ossicle gastral withthelateral face lateral posteriorly facingtip. medial face of The which curves caudolaterally, ending in a sharp anteriorly overlapped by lateral ossicle IV, gastral I andII aswideossicles half III is ossicle rib II.However,in gastral ment as lateral gastral paired- lateralin asimilararrange ossicles gastral four ally facingtip.of Gastral rib IIIalsoconsists caudolater inasharp dolaterally and terminates lateral-most ossicle iscurved20°. The gastral cau- about clined caudolaterally at of an acute angle between lateralin IIIandIVis ossicles gastral other in atransverselydirected suture. suture The dle-shaped lateral ossicles that gastral contact each spin four of pairs to 140°. Gastrale III consists of 120 open posteriorly at a reconstructed of angle sicle, which, likethe next following two orthree II andIIIshareGastral os ribs onemedialgastral ly facingtip. rounded caudolateral inasharply and terminates one but is the same thickness. It curves posteriorly the spindle-shaped threehas times the length of ally, thereone more is lateral ossicle, gastral which the respective ossicle. medial gastral Later of arm aslongone lateral thatossicles gastral are half spindle-shaped thetwo followsa pairof terior of ribs IIandIII.Laterallygastral adjacent to the an- contact or overlaps ossicle of the median gastral close in lies two the of posterior The 150°. about ------(FIGURES8,10;TABLE 3) GIRDLES (FIGURES8,10;TABLE 3) rected tip. in aslimandpointed posteriorly di terminating first and curves sharply posteriorly in its distal fifth the than longer fifth one is ossicle gastral second ossicle V. medial gastral face of lateral-most The dal in outline and articulates with the caudolateral ossicles. medialanelongatingone is trapezoi The - twoonly rib has lateralgastral sixth The gastral tip.minates inasharp as longthe curvessecond, posteriorly andter the third. lateral-most ossicle, The gastral which is spindle-shaped and hasabout the same length as VI. Lateral ossicle IV is also gastrale gastral cle of ossi gastral lateral first the and V ossicle gastral Lateral ossicle IIImedially contacts medial gastral latter. the of fifth four measures it and II ossicle ossicle lies posteriorly adjacent to lateral gastral lateral ossicle IV. gastral third The lateral gastral II is twice as andlong laterallyas the first contacts caudolaterallyThe following lateral ossicle gastral ossicle VI. medial gastral of the lateral termini which, number one, might represent anterior of basal lateral spindle-shaped ossicles, gastral the three a paired bundle of Gastral of rib V consists the medianpartismissing. VI. However, ossicle medial gastral of lateral arms the represented five rib gastral of edge anterior the cles would the base if have forming formed ossicle.gastral In thiscase the lateral ossi- gastral adjacent, which might have underlain the medial ossicle. Likely, thereone posteriorlya second was coid istrapezoidal in outline. Its maximum length be tentatively restored (Figures cora 8,10).The the bones canthusonly outline of animal. The ofthe the immaturity to due ossified barely are lection and preparation. preserved The remains are also preserved, but were damaged during col theclavicles thescapula.Remnants of the size of coracoids. coracoid isthree The times a pair of scapulae and interclavicle,fragmentary a pair of a shoulder girdleThe as preservedof consists Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - - - swd stecru fthe initsmiddle of as wide asthe corpus during life. scapular process dorsal The isalmost which most likelywasorientated dorsolaterally thismargin scapularprocess, arisesthe dorsal of the scapula isslightly concave. Inthe middle third a cartilaginous extension. lateral The margin of demarcated probably that ridge a low by off set the scapula is anterior marginabout 90°. The of the medial margin against at sharply and angled strongly thescapulais convex anterior margin of anteriorly expands into a low ventral process. The and has anevenly convex medial margin, which aslongthe coracoid scapula is about half The collection. crude methodof the the interclavicle are nowbecause missing of the and the specimen. Parts of status of ontogenetic early the reflect may features These about 120°. the posterior and the medial marginscomprises between angle The otherwise smooth. coracoid is the surface of contralateral external coracoid. The at the suturerior margin with the andterminates theposte- on thelateralcommences extremity of that rim low a by off set convexand is which gin, about 90° andmerges withthe posterior mar of medially at an angle the coracoid turns margin of with the clavicles inadults. Posteriorly, the lateral are no further anterior extensions that interlock there theindividual thejuvenile status of cause of the fossa Be glenoidea. the posterior extension of by a small laterally facing protuberance that marks lateral marginconcave. is Anteriorlydelimited itis thecoracoid.The the anterolateral margin of of barely visible, occupiesthe posterior-most fourth the fossa which glenoidea, is coracoidal part of The margin. medial the with 50° approximately the anterolateral of an acute angle margin forms tion this margin becomesalmoststraight, whereas the anterolateral margin. Inposterior direc of with theconvexity strongestthe medialthird in the coracoid isconvex anterolateral margin of the bones. The at of the anterior-most terminus medial margin inaserrated suture, which diverges lateral contact eachcoracoids other along their about is twicethe minimum contra width.The /2017 107 107 - - - -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 108 108 unlikely to be a taphonomic artefact a diagenetic artefact. a diagenetic unlikely tobeataphonomicartefact Because of thenearinsitu Table 3.Mauriciosaurusfernandezi Figure 9 oaodmax.length coracoid nodata nodata interclavicle corpuslength scapula shoulder girdle Measurements ofthegirdlesinmm the coracoid and the lateral one forms the scapu the coracoid andthe lateral one forms al concavityarticulates withtheproximal edge of and laterally bares ashallow concavity.medi This strongly convex initsmiddle third, but medially by from the corpus a low ridge, and is is set of the scapula mineralized. posterior margin The of the process. Evidentlythisprocesswas notyet fully processabout onethirdis wider than thebaseof scapular the dorsal ly convex margin dorsal of the scapula of at an about angle 45°. of The slight part and isinclinedposteriorly the corpus against /

Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Mauriciosaurus fernandezi it tgeodfsa5 ? 65 depth ofnotch 55 53 caudal margin width atglenoidfossa max. dorsalwidth max. width positionof thelateralterminiof thegastraliaand thelining-up oftheossiclesmedian convergenceis INAH CPCRFG2544P.F.1.Measurementsofthegirdlesinmm. INAH CPC RFG 2544 P.F.1. Gastral basket reconstructed according to the best preservedreconstructed according INAH elements. tothebest CPCRFG2544P.F.1.Gastralbasket 2 3 lu hf egh13103 103 shaftlength ilium 130 120 2 ? 224 125 224 etrgtpelvicgirdle right left 9? 39 5?icimlnt hog hf 3 130 135 lengththroughshaft ischium ? 95 - - - /2017 ui eghtruhsat10142 140 lengththroughshaft fthescapulaissmooth. of face Otherwise the external genetic deformation. dia- plastic some suffered likely,scapula more the verywas ridge either the shallow,bending angle or, Because there the corpus. is nobreak along the of themedialpart process against dorsal angled was thescapulawith ridge thelateralthis part of the bone toitscaudolateral corner. Along gin of the anterior mar reaches from the lateral third of thescapulashowsa blunt straight ridge that of face external the fossaThe glenoidea. lar part of chord width ofcaudal ctblrwdh3 34 35 spinal width acetabular width ctblrwdh5 52 50 acetabular width a.wdho lt 7 170 55 175 max. widthofplate 52 width atacetabulum 3 115 135 etright left 010 10 - PELVIC GIRDLE(FIGURES8,10,TABLE 3) rxmtl 5.Temda riua ae fthe proximately 45°. The medial articular facet of about 10°. Posteriorly the divergent ap- is angle of third the contralateral ischia diverge at anangle ly directed in itsposterior third. Inthe anterior with aconvex medial margin becominglateral the ischiumorientatedis medially plateThe of the acetabulum. pubic partof the face with the ischium, the lateral part forms sur contact the represents part medial The 130°. the lateral against two-thirdsis angled at about thispeduncle the posterior margin of dial third of the bone. me- The surfaceof onthe external step face thatboarded is byconcave, a deeply rounded medial margin there sur is a recess inthe external the pubic plate. Anterior to the postero- width of posteriorly facingpeduncle that has one-fourth the the arepubis concave deeply andconverge to a posteromedialThe and caudolateral margins of becomes thickest close to its posteromedial corner. contralateral pubic bonesaspreserved. pubis The the bone in life, which explains the separation of this marginacartilaginous extension suggests of line and slightly expanded. A rim that parallels the pubic plate is semi-circular in out margin of six times larger craniomedial thanthe ilium. The being one third larger than the ischium and about the pelvic elements pubis isthe largest8). The of crushed caudolaterally during diagenesis (Figure served intheir correct position, the ilia being thepelvicgirdle are almostpre- elements of The theinterclavicle. might bepartof but it has nocontact with the scapula, and thus identified,is clavicle, right the of likely fragment, insignificant an Only determined. be cannot icle the clav- below the matrix. original shape of The irregularly broken while the lateral margin dips the fragment is clavicle. anterior margin The of the ment likely represents the original margin of frag- this medial margin thescapula.The of of the craniomedial articulation face medial third of the left clavicle. It articulates with the tral part of sub-rectangular bone likelyrepresenting the cen Anteriorlyadjacent totheleft scapula therea is Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - - - PECTORAL LIMBS(FIGURE11;TABLE 4) 4) APPENDICULAR SKELETON (FIGURES11–13;TABLE humeral head therea low is and blunt deltoid tu the Immediately distal to the anterior margin of a cartilaginous coatingsurface suggesting in life. is low and regularly rounded with a finely wrinkled almost circular in cross-section. humeral head The 1.6. Towards the caput humeri the shaft becomes approximately tion withalength/ height ratio of longitudinallyis oval the humerus incross-sec of slightlysigmoidallycurved The shaft Humerus: served thantheright. ly basedontheleft forelimb, whichbetter is pre the pectoral limbs ismain- reconstructionThe of ro oadaeei olpeo thepelvicgirdle. prior toadiageneticcollapseof the acetabulum of the roof thickest andformed concave. anteriorly The oriented the basal part is slightly convex andthe apical third beingslightly margin isbipartite with the basal two thirds being gently convex. theiliumis medial The margin of convex.whichthe ilium, sharply is lateral The served of and merge with the posterior terminus and medialmarginsconverge posteriorlypreas base, which isanteriorly convex. Both the lateral length is four times the width at its acetabular outline with the apex facingposteromedially. Its elongate iliumis with aroundedThe triangular theacetabulum. thirds from theischiadic partof the face articulates withthe pubis, the lateral two- the ischum. craniomedial third The of margin of the medial peduncle has one-fourth the length of the anterolaterallyThe facingarticular facet of animal. the of axis long the anteriorlyagainst 46° about a peduncle that is orientated at of an angle terior margins,lateral in direction, converge into therea slightconvexity. is Bothanterior and pos the ischium the posteromedial margin of third of tworior oneandonly thirdslong.as the middle In that poste anterior margin than of being deeper the the ischium are concave, the concavity of of rior third. anterior and caudolateral The margins ischia reaches itsmaximumin the ante thickness /2017 109 109 ------

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico REFERENCES 110 110 insertion tubercle for the the humeralshaftmayrepresent the margin of the humerus. Alow elevation on the posterior of berosity that extends about one-seventh the length lar facets run nearly parallel to each other. The the radiohumeral one. Botharticu the length of facet between andradial has three fourth articular facet with the radial one. articular The about 100° withthe slightly concave of an angle with the proximal articulation facet and includes a rightangle theradiusforms anterior marginof facet cannot be reconstructed. slightlyconvex The the covered bymatrix thatso the actual shape of still the humerus is er, the radial articular face of Howevdoes not match itshumeral counterpart. - theradius theproximal articular face of ture of curvaface with the humerus isthe longest. The outline.in regularly The convex proximal articular the and roughly pentagonal twice the size of 0.7,isabout radius hasa length/width ratioThe of aswell asthehumerus.ulna andpisiform bones. However, there betweena gap is radius, and ulna lie in articulation with their neighboring andulna: Radius complex isslightlyconvex.pisiform the ulna/ facet straight, with the radius isthat of about 170°. While the articulation of an angle thatas for theradius. Botharticular faces include size equal of are they together and confluent are merus. articular facets for The ulnaandpisiform the hu- the distal-most extremityrim that of forms and ulnaare separated bya very low interarticular articular facets forthe humeral shaft. The radius with the anterior andthe posterior extremity of rated from the shaft bya blunt ridge that merges andsepa- flat is face articular distal The flange. with the distal articular face inaregularly rounded imately 120° withthe humeral shaft andmerges approx- of anangle or supracotylar ridge forms shows convexity a deep at its base. posteri The slightly curvesonly anteriorly, the posterior one diameter. While the anterior supracotylar ridge humerus diverge toabout twice the longitudinal the direction the anterior and posterior marginsof distal in shaft the of middle Fromthe 1975). son, / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Alatclrfct fradius Allarticular facetsof m. coracobrachialis (Robin- - - - /2017 Figure 10 clavicles andduring theinterclaviclewere lost collection. with theearlyontogeneticstatusof of thespecimen.Parts the and therounded pubic bones.Thesefeaturesmaybealigned wide, are they as long as are that ischia the Note reconstructed. contralateral obturatorforamina; dottedlinesand lightgrey= the separated have may that cartilage of areas large likely with with likelyconfluent coracoscapularforamina, B)pelvicgirdle Reconstruction ofthegirdlesin A)shoulderventral aspect; girdle h un hs lnt/it rto f 08, is 0.83, of ratio length/width a has ulna The cave and over its entire length it contacts the ulna. radioulnar articulationlength. The is slightlycon- equal radioulnar articular facets, which are of 120°withboth the radioradial and the straight of the radius,slightly concave is an angle andforms the longitudinal expansionof over one fourth of extends contact between radius andintermedium

Mauriciosaurus fernandezi INAH CPCRFG2544P.F.1. Figure 11 drawing. formed byformed the tiny straight articular face with the theulnais posterior marginmedial facet. The of facet, whicha little is shorter thantheulnointer convex 120°withtheslightly ulnoulnar of angle 110° to the ulnoradial facet and at an of angle the ulnohumeral facet and liesat an length of two-thirdsstraight. It has is the the intermedium articular facet with about110°.The of an angle the ulnohumeral facet. Both include the length of the respective facet on the radius. It has one-third a notch that accommodatesulnoradial facet forms humerus, but is separated from it by a gap. The the articulation facet of the respective concavityof face is covered by wrinkles. convexity The matches the bone. convex The articular longest margin of convex ulnohumeralarticulation facebeingthe roughly hexagonal inoutline with the regularly

Mauriciosaurus fernandezi CPC RFG 2544 P.F.1. Left pectoral limb in ventral aspect; A) photograph, B) interpretative line interpretative photograph,B) A) aspect; in ventral Leftpectorallimb P.F.1. 2544 RFG CPC Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - imal margin of the pisiform isabout one third the pisiform imal margin of asymmetricallyconvex about 20°. The prox- of the bone converge distally at anangle marginsof facet with the ulna. Both posterior and anterior straight, and isthe same length as the articular isalso the pisiform posterior marginulna. The of the articular facet with the posterior margin of trapezoidal is withanalmoststraight pisiform The cartilageduringlife. ered by athinlayer of other, that suggesting the articular facets were cov lie in closecontacttoeach Allcarpalia Carpalia: thebone. theposteriormargin 110°against of of facet and isorientated at an angle ulnointermedial the straight, is equals the length of the pisiform articular facet with about110°.The of an angle facet and the two describe as theulnointermedial as long fourth proximal facet is half This carpal. /2017 111 111 -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 112 112 Table 4.Mauriciosaurusfernandezi au eghpoioitl? ? proximodistal proximodistal manus length total length cI+I ogtdnl? longitudinal dc IV dc II+III dc I ulnare longitudinal intermedium front flipper Measurements oftheextremitiesinmm radiale element extrazeugo-podial radius ulna ueu hf egh170 shaftlength humerus The supernumerary carpal element is alsotrap- carpal supernumerary The lies in itsanteriorthird. pisiform the the proximal margin of strongest convexity of longer than itsevenly convex distal margin. The / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín rxmdsa ? proximodistal ogtdnl? longitudinal rxmdsa ? ? proximodistal proximodistal ogtdnl? longitudinal rxmdsa ? ? proximodistal longitudinal proximodistal proximodistal longitudinal rxmdsa 25 proximodistal rxmdsa 17 proximodistal 30 longitudinal rxmdsa 25 proximodistal ogtdnl35 longitudinal a.dsa it 105 max. distalwidth uea ed48 humeral head max. width ogtdnl15 longitudinal ; measurements of= distal tarsal. theextremitiesinmm;abbreviations:dc=distalcarpal, dt right 25 35 ? ? 20 15 ? ? 300 510 8 180 left 18 20 15 15 25 20 24 20 20 25 35 5tibia 25 45 55 ? ? /2017 dt IV tI+I ogtdnl2 17 20 longitudinal dt II+III dt I iuaelniuia 725 27 longitudinal fibulare nemdu ogtdnl2 25 24 longitudinal intermedium tibiale hind flipper lmn ogtdnl915 9 22 longitudinal 20 element 3 8 longitudinal extrazeugo-podial element 2 longitudinal extrazeugo-podial element 1 extrazeugo-podial ity merges withthe proximal articular facet with eachother notch. by anterior convexThe a sharp two low convexities that are separated from of ezoidal. articular face with the ulna consists The rxmdsa 118 21 proximodistal proximodistal proximodistal ogtdnl1 16 18 longitudinal rxmdsa 816 15 18 18 proximodistal proximodistal ogtdnl2 21 22 longitudinal rxmdsa 020 20 proximodistal rxmdsa 219 17 22 19 proximodistal proximodistal ogtdnl3 30 34 longitudinal rxmdsa 10 proximodistal proximodistal rxmdsa 310 13 20 proximodistal 23 proximodistal proximodistal longitudinal a.dsa ih1085 100 max. distalwith eoa ed5 55 55 femoral head max. width hf egh15180 185 shaft length longitudinal 280 505 etright left 510 28 30 30 43 42 14 12 - teroproximally articula facing intermedioulnar ishexagonal. straight an- The intermedium The I. distal carpal mal faceof andproxi the intermedium - the anterior face of the posterior margin between bridgesthe gap of caudolaterally The orientated part intermedium. the radiale and articulates with the anterior face of the of margin anterior the against 55° in angled these two is anterolaterallyThe orientated facet of that include about an 55° angle of with each other. equal length two straight articular facets of of sists radiale is regularly convex. posterior face con The the anterior face of I. The distalcarpal margin of that matches a respective notch onthe anterior in ablunt process the radiale terminates margin of about 7°. Distallythe posterior ity at of an angle straight and curves proximally the concav against - the radiale is theposterior margin of mal fourth of proxi I. The along itscontactwithdistalcarpal shorter than the anterior one and slightly concave most parallels the posterior margin, whicha little is the bone andal- all marginsof the longest is of the radiale slightlyconvexThe anterior margin of us, which isabout three times asbig as the radiale. anterior margin thebonearticulates withtheradi its With 0.4. about of ratio length/width a with radiale is longitudinally elongated pentagonal The each other. gap. Both the proximal and distal margins parallel convexity therea posteriorly is diverging articular are slightly convex. the former Along the gin of the distal mar whereas the posterior two thirdsof element contacts theulnare, itsmarginconcave, is as itsposterior margin. Where the supernumerary ement articulates with the ulnare is about as long distal marginel alongwhichthe supernumerary The 30°. about divergeand of atdistally angle an equal lengths Posterior and anterior margins are of thebone. of the concavitythe proximallies in half the sinusoidal posterior margin, inwhich length of the element measures two thirdspernumerary of the su- sinusoidal proximalThe articular facet of minates in a caudoproximally orientated tubercle. slightly concave is facet with the pisiform andter the articular of posterior half The the pisiform. Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------eso f cI/I saltl agrta hto a little dcII/IIIis larger than that of tension of proximodistal The 0.75. ex - length/width ratioof which is rounded quadrangular in outline with a its posterior marginI articulates dc II/III, with dc its distal margin it contacts mcIandII/III.With element and the radiale; with carpal the accessory one. With itsproximal margin dcIcontactsboth and about one sixth shorter than the proximal are evenly convex, while thestraight distal oneis the bone mal, anterior and posterior margins of proxi 0.6.The line withalength/width ratio of pectoral limb. dcIisrounded rectangular in out (dc) are visibleAll three in the left distal carpals area wasdestroyed while theslabwasbroken. (mc)V,likely articulated with metacarpal but this facingmargin. distal concavity The carniodistally the ulnare and its the posterior articular facet of is included between same angle about 100°. The the posterior one. of Both facets include anangle tal articular facet is about one third longer than thebonehaving dis beenlost.The of sal corner the ulnare are slightlyconcave, thecaudodor of posterior and distalmarginsarticular facet. The ulnarea shallow in concave craniodistallyfacing Caudoproximally contactsthe the pisiforme theulna. margin of ulnare matches the slightly concave posterodistal the a tiny sectionwhile the proximal margin of in the bone contactsthe intermedium margin of proximal andposterior margins. anterior The itsanterior, along facets articular defined clearly 1.2.There are no with a length/width ratio of ulnareThe is longitudinally rounded in outline dioradial articulation. tion faces posteriorly and is as large as the interme proximoposteriorly. articula intermedioulnar The facing is andthus about70°withtheformer of articulation and describes an angle termedioradial the in- ticulation is about two-thirds the length of ar articulation isexposed. intermedioulnar The the slightly compacted intermedioanterior face of articulation facetvisible.is the articular sur Thus theintermedioradial which marginthe dorsal of the ulna, leaving a small interarticular gap, inside tion parallels the posterodistally facingmargin of /2017 113 113 ------

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 114 114 h xeto fthe distal-most ones, the phalan- the exception of incomplete digits IIandIV being the longest. With 9-12-11 (preserved)is -12 (preserved) -11 with the themanus Phalanges: of phalangeal formula The said abouttheirshape. be can more Nothing 5). (Table metacarpalia all about 2 is reconstructed for length/width ratio of From their corpora. what ispreserved a is much of are nowas missing the metacarpalia imal endsof mcIthe prox WithMetacarpalia: the exception of mc IV, but therelevant area isdestroyed. ly, there wasa contact with the anterior margin of Distally, dcIVarticulates with mcIIIandIV. Like- dcII/III. articulates with the posterior margin of dcIV its posterior third. anterior margin The of in the intermedium contacts the distal margin of the proximal margin, which times the length of distal margin about 120°. The hasthree of angle about100°,withtheposterior one an of an angle anterior margin the proximal articular facet forms as the anterior andposterior margins. With the aslong proximalThe articular facet is about half slightly abraded. is and thus acrack the edgeon of 0.75,issituated which hasalength/width ratio of dc IV,gins are slightly convex. distal margin The of outline. proximal, The anterior and posterior mar preservedAs the bone isirregularly pentagonal in the preserved distal carpals. IV isthe smallest of dc I, dc about one third the size of With a size of this contact is obscured by afracture in the slab. dcII/IIIarticulated with mcIIandIII,but gin of dcIinonepoint.Likelythe distal mar margin of dcII/IIIcontactsthe posterior terior margin of convex dc III.The an convex anterior margin of whileintermedium, the posterior concavity fits the the bone precisely matchesthe distalconvexity of the proximalII/III. The dc concavityof facet of posterior the of length the one-fifth is that facet dcII/IIIismarked by ashort,straight of corner showsthe strongest convexity. caudoproximal The distal margins being convex. distal margin The margins being concave and withthe anterior and ly inrightangle, withthe proximal andposterior Like indcII/IIIall margins meet approximate aslong. dc I,but cranioposteriorly it is about half / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - - - /2017 PELVIC LIMBS(FIGURES12,13) hnatrol.Tepseirfc fthe than anteriorly.femur in posterior face of The the shaft teriorly with respect tothe long axisof rounded distal articular facet extends further pos- vex thanthe anterior face. Therefore, the evenly the femur is more con- posterior face of shaft. The the mid- about twice the longitudinal diameter of distally. At the distal articular face the bone has the femur diverge gradually posterior margins of the shaft the anterior and From the middle of by acartilaginouscap. wrinkles, which duringlife were probably covered is low and regularly rounded. Its surface bears fine caputfemoris the shaft. The for aboutonethird of distally totheanatomicaland extends neck distally the femur. It commences on the posterior face of thirdit. The trochantera shallow elevation forms oris isa shallow circumference distally adjacent to fem- caput the of neck anatomical The fifth. one the articular facet, the bone expands by about of almost circularcomes incross-section.At the frill straight shaft. Atthe caput femoris, the shaft be a little a it is and ithas smaller in all dimensions approximately 1.8, but a length/width ratio of line with itslongitudinally oval cross-section and Femur: femur The resembles the humerus inout itlffho themanus from astraightline. distal fifthof line up with each other and inthe lines gradually articulation distal direction, the interphalangeal the posteriorly following phalanges. In striction of articulations lie in the con- interphalangeal The in obliquearranged rowsdirected posterodistally. the manus are of phalanges in the proximal half onthe penultimate phalanx. The its counterpart imal articular facet that does not precisely match a rounded tapering tip and a slightly convex prox the proximal ultimate facet. The phalanges show distal articular facet is about one fifth smaller than theproximal articular facet. The the extensionof at the medial constriction isabout two thirds of In each phalanx,the minimum transverse section 1.77. alldigitsIIIis the phalangesof width ratio of articulations. length straight interphalangeal The hourglass-shaped withalmost ges are uniformly - - - - length/width ratioofthephalanges (ph)is1.77. Table 5.Mauriciosaurusfernandezi Figure 12 drawing. ray III ai ...... ? ? 1.8 9 2.3 1.4 14 2 13 14 1.6 10 1.7 16 10 1.7 17 12 1.8 20 12 2.1 22 10 2.1 21 hind left 10 ratio 21 width length ray III egh2 2 01 716 17 17 20 `23 ? ? ? ? 27 length it 6????1 11 08 10 10 11 13 ? ? ? ? 16 width ai . . . . . 2 1.7 1.7 1.8 2.1 ? ? ? ? 1.6 ratio Average length/widthratiototal front left Measurements ofmetapodialsandphalangesinmm

Mauriciosaurus fernandezi h1p h3p h5p h7p h9ph10 ph9 ph8 ph7 ph6 ph5 ph4 ph3 ph2 ph 1 h1p h3p h5p h7p h9p 0ph11 ph10 ph9 ph8 ph7 ph6 ph5 ph4 ph3 ph2 ph 1 INAH CPCRFG2544P.F.1;measurements of metapodialsand phalangesinmm.Theaverage INAH CPC RFG 2544 P.F.1. Left pelvic limb inventralaspect; A)photograph, INAH CPCRFG2544 P.F.1.Leftpelvic B)interpretative line 7965? Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín vrg frontright average 1.86 1.85 hind right h1p ph3 ph2 ph 1 . . 2 2.6 2.3 32 22 23 23 0911 9 10 h1ph2 ph 1 . 1.8 1.7 1415 527 25 /2017 average 1.77 2.3 1.8 115 115

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 116 116 its distalextremity touches yet- another supernu element contacts the posterior one,merary while its - caudoproximal the anterior supernu corner the fibula. touches the With posterior extremity of element supernumerary anterior The fibula. the proximal margin, which lies inline with that of terior marginsare fourth abouton longer than the with the apex facingdistally. anterior and pos The the two isrounded triangular in outline tioned of posi- anteriorly most The fibula. the to posterior elements are preservedsesamoidal supernumerary epipodial elements:Two Supernumerary thefibulare. margin of tal convexity match aconcavity onthe proximal the dis- one point,while the posterior two thirds of in intermedium the contacts fibula the convexity the femur by agap. With itscraniodistal face of like the latter is separated from the distal articular The fibula lies posteriorly adjacent to the and confluent. and convex are faces articular all tibia than the tibia (length/width ratio: 0.7). Like in the thelongitudinalextension a little more thanhalf only has but well as oval irregularly is fibula The inonepoint. with tibialeandintermedium articulates loosely tibia Distally, the fibula. the of the anterior convexity of the anteroproximal half tibia. With itsposterior extremity the tibia contacts the theproximodistalof dimension thathalf gap is ular face, butseparated itis from the latter bya the distal femoral artic of with the anterior half regularly convex and confluent.The tibia lies level about 0.7.Allfacetsare theboneis width ratio of third longer than the posterior ones. length/ The outline with the anterior margin being about one fibula:irregularly tibiais The and oval Tibia in goethitic substance. the hind limbby a considerable containing a gap femurThe isseparated from the distal elements of intercondylar ridge. an of trace no with confluent are fibula and tibia for facets articular The shaft. thefemoral rior andtheposterior extremity of fromridge merges the shaft.This withtheante A blunt ridge separates the flat distal articular face flange.rounded regularly a in face articular distal about 120° andmerges withthe of cludes anangle / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - /2017 about 120°. The posterior and the caudoproximalabout 120°. The meets with the posterior margin at of anangle the fibulare is straight and caudoproximal facet of about 90°. The posterior margin at of anangle and posteriorly merges withthe shallowly convex one anterior the than longer third one is fibulare the posterior margin 90°.The of at of an angle vex processthat merges withthe distal convexity anteroproximalcon a sharply in facet terminates the anterior margin. At its anterior extremity the about 120° with of straight and includes an angle almost is fibulare the of The marginfibula. anteroproximalthe of margin distal the of half rior marginconcave is andarticulates withtheposte- but isroughly pentagonal in outline. Itsanterior intermedium, the as size same the is fibulare The dtII/IIIandIV.proximal convexities of the touches margin distal Its fibulare. the of one articulates with the anterior the intermedium of fibula,the respectively.of posterior The extremity the tibia and the craniodistal corner of tal corner touches the posterodis- the intermedium margin of more convex thanthe distal one. proximal The the bone an oval outline, the proximal margin are giving convexareconfluent margins articular and iale butthe same proximodistal has extension. All one thirdis shorterthanthetib intermedium The dtI. the anteriorconcave margin of distalconvexity The intermedium. articulates with tibia andwithitsposterior extremity itcontactsthe the the distal margin of extends over two thirds of notch initsposterior third. Anteriorly, the tibiale ets are convex, but the proximal atiny one bears longitudinally than transversely. Allarticular fac- is anirregularly oval bone, which istwice as long fibulare and a supernumerary element.The tibiale intermedium, tibiale (= astragalus), the tarsals: of Tarsalia: Four the proximal elements form row element withitsdistalextremity. bone articulateswith theanterior supernumerary the cranioposterior. The ter is twice the length of element. Its proximodistalsupernumerary diame the anterior ment isoval andone-third the size of ele supernumerary posterior The fibulare. the to element, whichmerary liesposteriorly adjacent - - - - posterior and distal margins. other margins The marked dtIVis byslightly convex outline of The than dt II/III,but alittle larger proximodistally. In longitudinal direction, dt IV isonethird shorter point. a single dtII/IIIcontactsIVin extremity of posterior mtIIandIII.The mal articular faces of distal margin, which protrudes between the proxi- the separated by a slightly more convex part of almost equal length. Both are convex and only of divided intotwo the bone is facets distal margin of The tibiale and intermedium. distal convexities of dt II/III is convex and punctually contacts the of one fourth proximal smaller thandtI.The margin dt II/III, which isirregularly oval in outline and dtIarticulates withthe anterior margin of ity of posterior extrem mt II. The posterodistal- corner With itsdistal margin dt I contactsmtI,withits the proximal margin. the length of vex andishalf dt I isstrongly con posterior margin80°. The of margin andthe proximal articular facet about is between angle theanterior about100°.The of as the distal one with which it includes anangle dt I isaslong imal one. anterior margin The of margin isabout one third smaller than the prox The distal corners. the at confluent and convex anterior,The distalandposterior marginsare all it is concave articulates and withfirmly the tibiale. allmargins; the longestof dtIis terior margin of about one fourth smaller than the tibiale. an The approximately DtIis tarsalia. trapezoidal and in a row distally adjacent to the proximal row of There are three distal tarsals, which are arranged thedistalmargin. the size of element is about half supernumerary the tarsal of ele ment posterior to the fibula.The proximalsupernumerary margin anterior the and fibula the fibulare, the between gap the bridges fibulare and the ezoidaloutline, in one third ithas thesize of element that epipodial is trap a supernumerary the bone articulates with the posterior margin of point, respectively. caudoproximal The margin of one in V mt and IV dt contacts fibulare the gin, long asthe anterior margin. With itsdistalmar equal length and together they are as facets are of Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------lar facet and the distal articular facet is about one the proximal articu the extension of two thirds of imum transverse section at constrictionisabout min- The (Table5). 1.77 is III digits all of langes thepha- the manus. length/widthratio The of articulations,most straight interphalangeal asin ones, the phalanges are hourglass-shaped withal the distal-most the longest. With the exception of being IV (preserved)digit 6 the with -12-14-14-11 the is Phalanges: of phalangeal formula The mtIV. theposteriormargin of third of itsanterior margin mt V contactsthe proximal of thirdWith one 5°. byabout body the of axis long aline which the isinclinedagainst digits I-IV form the between mtI-IVandthebasalphalanges of IV are slightly concave. articulation The surfaces mt I, IIandV. mt II and ticular facets of of Those metatarsalia are slightlyconvexare as thedistalar all proximalarticular facet. The articular faces of the proximal ference has one-fourth the width of theyare anteroposteriorly. mid-shaftcircum The are approximately twiceaslongproximodistally as distalarticular slightly convex.face is The MtII-V the shaft ismostlyobscured by matrix. ference of interdigitates circum with dt I anddt II/III. The - I andshowsa proximally orientated processthat about one quarter longer proximodistally thanmt latterlies in close contact with mt II. The bone is mt I digit I distally. posterior margin The of of with dtIproximally andwiththe basal phalanx surfaces are slightlyconvex andarticulate loosely ly visible. Both the proximal and distalarticular the bone andisbare- the shaft lies inthe middle of proximodistal direction. narrowest The pointof rection, mt I isabout one fourth shorter than in the third shorter than mtIII-V. Incranioposterior di in articulation. MtIisthe shortest being about one preserved are metatarsals five All Metatarsals: mtV.the anteriorfaceof the posterior one with the proximal two thirds of the distal one inlength, articulates with mtIVand respectively. posterior concavity, The which equals point, a in fibulare and intermedium the touches dtIV ly circular outline. proximal The margin of near a convex, forming evenly and confluent are /2017 117 117 ------

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 118 118 SOFT TISSUES(FIGURES2,14–18) which isaboutonefourth larger thanthepes. a straight line,form the caseinmanus,is as they pes the of fifth distal the in and other each line upwith langeal articulation surfacesgradually lowing phalanges.- Indistal direction, the interpha the posteriorly fol- lies withinthe constriction of the manus, articulation where the interphalangeal approaches lationsgradually the situation seenin articu the interphalangeal the line of nation of posterior proximal face. Further distally the incli- their the phalanges indigit IV by onethird of of digit V,is whichoverlaps the posterior margins direction, and withminimal overlap. Anexception are inoblique arranged rows withaposterodistal the digits I-IV two proximal-most phalanges of the penultimate phalanx. The articular face of ular facet that does notprecisely match the distal tapering tip and aslightlyconvex proximal artic phalanges, where preserved, they show a rounded ultimate The one. proximal the than smaller fifth ing. material The especially wellis preserved on the ribs show such a coat- facesof the external the respective nor centra. Neither the gastralia of ribs, the space between them andthe ventral face the of half the dorsal face of coats the internal It 14). 2, (Figures cavity body the of wall dorsal finely sometimes striatedblack materialglossy is restricted to the granular, to amorphous The the caudalvertebral column(Figure 18). restricted to the tail base left and right hand sideof substance a light todarkgreyamorphous glossy (5) and 17), 15, (Figures limb hind left the of base and longitudinal furrows along the trunk and the withshallow,rial ornamented transverse but sharp limb (Figures 13, 15 - 18), (4) a reddish-grey mate the left hind and alongthe posterior margin of the flippers tail, as well as in the proximal areas of reddish and along theneck substance amorphous an (3) 15), (Figure base neck the of side right the dark grey material organized a in transverse on bars (2) 14), (Figure cavity body the to restricted is preservation tissue soft black in the specimen: (1) materiala glossy that of types five are There / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - /2017 otergthn ieo tebs fthe cervical the base of To the right hand side of not permitted. too small andfurther was the samplewas sampling in poultry (Wangin poultry peritoneum pigmented with melaninalso occurs (Greer,systems 1989;Porter, 1967).However, a UV radiation fromdamaging thereproductive and isthought to screen solar radiation and block mates that inhabitdesert or highaltitude habitats squa- diurnal nal cavityknownis from a variety of the abdomi especially coating part of the dorsal melanocytes. Apigmented visceral peritoneum toneum thatheavilywas likely pigmented with that the black lining represents the visceral peri organic matter. Therefore,more it appears likely of inconsistentwithaliquidmass wrinkled relief or fibrous a shows it places in centra; the of faces the ribs and the ventral ing the medial sections of equally thin insidethe entire body cavity includ vertebral However,column. the black substanceis the ribcage along the thoracic arcadesdorsal of the liquidized organic matter concentrates in the (1) it should be expected that toneum. In caseof apigmented visceral peri resents the remainsof material the thorax. (2) The rep- wall of the dorsal body cavity under anoxic conditionsthat now coat the inside liquidized that intestines putrefied the rial: (1) itrepresents the remnantsbituminous of taphonomic optionsthat would explain thismate the bodycavity. the right sideof There are two (Schweitzer 25°C around temperatures and conditions oxic a mineralthat preferably precipitates underdys- typical absorption bands for bands Goethite Fetypical absorption substance. Atest with EDAX probing yielded the allowed toremove averysmall piecefrom the In order to do a geochemical analysis, we were early ontogeneticstages. from amelanistic visceral peritoneum especially in havecould radiationmassiveand to sun benefited bly cruisedcloseto the water surface were exposed unknown. Plesiosaurs, at least those that prefera a black peritoneum in chickensand teleosts is of (e.g. leosts, where it even represents a diagnostic feature Page and Burr, 2011).However, the function et al. , 2013). Forinvestigations2013). further , et al. 02,adanme fte , 2012), and a number of 3 O(OH), ------Figure 13 drawing. theyare either preserved inadark-greysubstance flanks, bodywhere the along occur also structures alight-grey mass. transverse The rectangular of patches confluent are there clavicle the of lateral the scapula and Along the anterior margin of In places they are preserved molds. as internal where they occur within a pale reddish substance. ly well preserved at the cervicothoracic transition, organized in longitudinal rows. They are especial preserved the structures are densely packedand Where 15). (Figure bands transverse in ganized substance. Rarely, theyare square. Someare or tres long by two mmwidepreserved in adark-grey millime ten to five structures rectangular mately approxi- left cervical ribstherea sequenceof is the vertebral of column along the ventral termini

Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Right pelvic limb in ventral aspect; A) photograph, B) interpretativeline B) photograph, A) aspect; ventral in limb pelvic Right P.F.1. 2544 RFG CPC INAH Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - or oval. between Inthe angle femur andiliumthe the softtissue the structures becomecircular of to terminolaterally. Towards margin the external parallel-sided rowsextending from craniomedially longitudinally.ters Many are in oblique, arranged transversely millimeters andonetotwo millime- five about measure and rectangular dominantly 17). Along the body wall, the structures are pre red and grey(Figure substances with amorphous preservation styles, by also interrupted large areas similar rectangular structures occurinthe same In the space between the right femur and ilium grey andred substance. amorphous ed by areas of parallel-sided longitudinal rows that are- interrupt the rectangular structures are organizedalmost in molds (Figure 16). In someplaces or as internal /2017 119 119 -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY 120 120 Figure 14 not the external faces of thegastralia. notthe externalfaces outlines theblack,glossycoating of oftherightthoracic theribsarethe internalfaces cavity.Note covered that bythesubstance but lel-sided longitudinal rowsthat may have covered 12 x2millimeters. They were in paral arranged about squamae, orientated transversely a size of vaulted regular squamationof likelyconsisted and body. neck ventral and the lateral The of skin squamaemostlyfrom the preted as remnants of can alsobe excluded. structures The canbe inter preparation orautolysis.as shrinking Artefacts of taphonomic effects such to represent the results of structuresThe described above appear too regular amorphous. in thetail. Allsofttissuetypesdetected here are between them. No such structures are visible sub-circular structures are foundoccasionally of decreases to about one millimeter or less. Lines distance their and finer exceedingly become lines ters. Indistal directions the longitudinal parallel millime 14 x 12 to up sizes reaching trapezoidal and the structures preserved between the lines are In the transitional zone theydiverge anteriorly flipper.hind of edge trailing the to perpendicular lines bordering the structures become increasingly / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín

Mauriciosaurus fernandezi INAHtissue preservation CPCRFG2544P.F.1.Soft inside thebodycavity;yellowbrokenline - - - /2017 the body. Possibly contributed both factors to the marine Mammaliawhere itstreamlinesmodern been richmanythe casein is adipose tissueas in tissuemayhave cially squamates. subdermal The thicker thaninmostextantsue was reptiles, espe- the body cavity tis- (Figure 19 B), or the subdermal composed, when basket collapsed into the gastral de- particularly not and flexible still was body the the ventral side of thatsuggests either of the skin the substance tissue.of thickness The subdermal and the skin rial very likely isadecay product of mate This 16). 3, (Figures surrounding the from off set clearly margins lateral sharp with wide mm 150 – 100 approximately are trunk the tail and aswell in somepatches along the sides of reddish and substancealong neck amorphous The flexibility. millimetric, sub-circular squamae giving the skin small, most likelycovered bylongitudinal rowsof was flippers the of flap trailing The zone. folding becomes tern radially a arranged, forming flexible the entire belly. the flippers thisAt pat the base of - - Figure 15 cervical vertebra, cr=cervicalrib. photograph, B)interpretativelinedrawing;= abbreviations:cv Soft tissuepreservation attheleft sideoftheneckbase;A) al. Lingham-Soliar, 2000; Robinson, 1975; Sanders 1989; Halstead, Godfrey,1984; 1982; Riess, and a flexible trailing edge and used as hydrofoils (Frey vides strong evidence for plesiosaur flippers having pro the tail. This - curves into the lateral wall of the femur the posterior margin of the middle of the flipperthe andbony from core the of depth of one-third has seam This 13). A, 11 3, (Figures per flip- hind right the of margin posterior the along the left humerus andasaseam terior margin of between the bones but also asa patch at the pos- reddish substance isnot only visible amorphous the flippers the of area distal the In preserved. as reddish substance the amorphous preservation of , 2004; Taylor, 1981). Furthermore, the propo- the Taylor,Furthermore, 2004; 1981). ,

Mauriciosaurus fernandezi INAH CPCRFG2544P.F.1. Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín et Figure 16 rectangular squamaearearranged inlongitudinal rows. the transversely line drawing.Noteinterpretative photograph,B) Soft tissue preservation along theleft sideof thetrunk; A) epidermal, but thereevidenceno is forepidermal, scute-like surface,the external on theyare to be assumed face. Because these structures are preserved only lar or trapezoidal inoutlinesur with asmooth areas between the furrows are roughly rectangu straight mostly or slightlycurved (Figure 18).The are that furrows running crisscross fine of pattern the tail base. areas These are characterized by a and flipper hind right the of base the trunk, the substance,dish especiallyinthe posterior third of red substance thatthicker thanthe is amorphous a dark reddish or dark-grey There are patches of the lateral body wall. contour by aposteriorfoldskin that merged with body the in integrated were flippers the of dials

Mauriciosaurus fernandezi INAH CPCRFG2544P.F.1. /2017 121 121 - - -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico OSTEOLOGY / COMPARATIVE ANATOMY 122 122 Figure 17 edge. structures perpendicular tothe more distalpartofthetrailing the trailing flapcontinuesonthetailbase.Alsonote thefibrous limb; A)photograph, B)interpretative line drawing. Notethat Soft tissuepreservation, attheposteriorbaseofright pelvic many lizards, e.g. the tail and itsmassive base. In the conical shape of ular fibrous texture and is evidently responsible for stance.showssubstance Occasionally this an irreg reddish or dark-greydescribed amorphous sub (Figurebordered 18). Itis laterally bythe above the tail, especially on the right side column of thevertebral preservedstance is of both sides on sub A light to darkand glossy greyamorphous structures. / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Mauriciosaurusfernandezi the fat tailed geckos, the posterior INAH CPCRFG2544P.F.1. - - - /2017 7.1. COEVAL POLYCOTYLIDS 7. Comparativeanatomy many cervicalvertebrae as Furthermore, dentition anisodont. in both Africanspeciesis The the mandibleevenly is convex. ventral margin of cross-section,the jaw marginsare straight and the straight is and rounded in Mauriciosaurus trum of the . In contrast,the ros anterior margin of the mandible level below the ventral margin of vertically festooned jaw margins andaconvex while that of co. rostrum The of been foundMoroc onlyinthe Early Turonian of et al. these, (Buchy Manemergus . Two fernandezi saurus of Turonian, andthusare about coeval with Mauricio taxa occur during the Late Cenomanian and Early seven genera in eight species and two un-named According to Druckenmiller andRussell (2009), Benson, 2011,2010). Druckenmiller and Russell, 2009;Ketchum and (e.g. and accepted Polycotylidae are described About seven genera of in and the ral hemal arches,spines which are small thetransverse processes, the neu- of dimensions the tail are delimited by the the muscle of masses because tissue,subdermal, likelywas thedeposit adipose ed these greyrepresent masses remains of preserved in the tail base of reptiles coincide withthe grey masses groups of (Frey, 1988).Topographicallyin both these tissues ilioischiocaudalisthe m. caudofemoralis and m. in the tail base betweenipose tissueisdeposited 1976). Incrocodiles,Derickson, the posterior ad- (Delome adipose tissueissubdermal uln fthetrunkcontinued ontothetail. outline of shaped mainlyby contour fat in away that the wasstabilized and Mauriciosaurus the tail base of the tail. Therefore plausible it appears that tion of Mauriciosaurus , 2005) and 2005) , Thililua hsls hnhl as haslessthan half Mauriciosaurus , suggesting a weak, suggesting musculariza Thililua Albright III et al. is dorsally concave, isdorsally Manemergus islaterally compressed, with ., 2003) have 2003) (Bardet etal., Thililua . ProvidMauriciosaurus - , 2007b, 2007c; . et al. , 2012; - - - - Figure 18 drawing. Note themassive tailbaseand thelight-greyglossysubstance onbothsidesof thevertebral column. 2000). (Sato and Storrs, the Late Cenomanian of acher andBell, 1999;VonLoh and Bell, 1998) and South Dakota (Schum- early Late Cenomanian of is reported with onespecies, P. quadratus Palmulasaurus (Albright III ly described as ly Mauriciosaurusfernandezi Pahaspasaurus haasi (Albright III from the early late Ceno- INAH CPCRFG2544P.F.1.Softtissue preservation inthetail;A)photograph, B)interpretative line et al. , 2007c),previous- et al. , from the , 2007a) Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín eto thesplenialsquantitatively,tent of theyappear to riorly. However, when comparing the anterior ex alveoli the splenials extended ante- which pair of ible and it is therefore to impossible to determine , themandibular alveolaeMauriciosaurus are invis with South Dakota is probably congeneric manian of Palmulasaurus (Schumacher et al /2017 ., 2016).In 123 123 - -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico COMPARATIVE ANATOMY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico COMPARATIVE ANATOMY 124 124 n -ofgrto oeigtepseirhl half posterior the covering W-configuration a in prominent ridgesarranged of merging with arelief They the corpus. open posteriorly,ventral face of the of isrestricted to the anterior half riciosaurus Mau - dish-like depression in the pterygoidsThe of boundary, are. alsodistinctfrom Mauriciosaurus reported to reachthe Campanian- Conacian genus The posteriortothecaput. Mauriciosaurus humerus there isa tuberosity, whichin ismissing the ischium, while on the the length of about half Eopolycotylus al one. curved The ilium of processthe glenoid isalmost as wide as the later medial margin, foramina also ina scapula where foramina along its terior processand anumber of the cervical ones, acoracoidwithprominent an- vertebrae that are about one fourth shorter than in % 50 of instead 2007b) symphysis, which is about 30 % (Albright III the mandibular splenials intheventral face of the the more massive teeth, the participation of from differs species This 2007b). mation) is Utah (top-most Dakota ForEarly Turonian of fourthA whichspecies to date restricted is to the ontogenetic stages. different to due are and Palmulasaurus ciosaurus of bones the pelvic of differences logical III Table(Albright 3 mulasaurus,[Figures11-13; 1.9 whereratiois this Pal of that than smaller (Tableis 1.77 5) of ratio foramina are present. average The length/width are diagnostic andepipodial onal epiepipodials epiepipodials. For foramenis noepipodial between the rounded In vertebrae. caudal 13 least et al. the centrum (Albright III the dorsolateral face of vertebrae, each witha large nutritive foramen on sions. Palmulasaurus showslateral interalveolar depres - lateral mandibular face, whereas the mandible of . Additionally,lasaurus a straight has Mauriciosaurus in than wider and shorter significantly be / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín , 2007a). Turonian genus Palmulasaurus has19thoracicand11caudal Eopolycotylus rankini (Albright III has21thoracicandat Mauriciosaurus Dolichorhynchops , isomorph polygPalmulasaurus, isomorph Trinacromerum andtheEarly et al. - morpho , 2007a)]. The , thoracic Mauriciosaurus there Mauriciosaurus , which bothare in Mauriciosaurus hasonly Mauri Palmu- et al. et al. - - - - - /2017 , , 2004; Williston, 1908),but notin the coracoid are present in Trinacromerum (O’Keefe, of perforations medial and Posterior 2005). hart, similar to 1.77 andthus is Mauriciosaurus the phalanges of of ratio length/width average The 2005). Everhart, mensional asin are distinctly wider than long andnotasequidi of epipodials primary 1908). The (Albright III etal. or epipodial they show adistinctarticular facet for the anteri isevenlyMauriciosaurus rounded. In Trinacromerum the propodials of ter, distalmargin 1997).The of Trinacromerum (Albright III etal. and ventrally constricted and not cylindrical asin are laterally Mauriciosaurus vertebralThe centra of T. and osborni about 38 in in 30 about of count tooth premaxillomaxillary a premaxillomaxillary teeth than Trinacromerum with positions, tooth 42 about bifurcation (O’Keefe, 2004; Williston, 1908). With Trinacromerum inananterior terminates , that of rus Mauriciosau pterygoids. Like the parasphenoid of the of the caudal half concave medial margin of thisbonein of depression the parasphenoid,whichthe ventral alsolacks of the concave lateral margins are widebecauseof vacuities (Figure 4). In noid, almost closingthe posterior interpterygoidal meet atopygoids the parasphe inMauriciosaurus pter The 1908). Williston, 2004; (O’Keefe, bone the the basalthird of to about twice the width of es. Similarly, in the process the basal third of times the width of expand intheir anterior halvesciosaurus to three margins. anterior pterygoid The rods inMauri the pterygoids adjacent to their posterior face of prominent tubercles onthe ventral a pair of bears 1908). Williston, 2004; (O’Keefe, that in anelongate process posteriorly terminates ridge the pterygoids risetoasharp eral marginsof the ventrolat Trinacromerum the posterior fourth of In 1908). Williston, 2004; (O’Keefe, ovoid gate In (Figure4). the pterygoideal similar to corpus, of Trinacromerum (Schumacher and Ever Trinacromerum thisdepressionis elon- Trinacromerum, these rods expand Trinacromerum (Schumacher and Trinacromerum these vacuities T. willistoni hasmore Mauriciosaurus , andthe Mauriciosaurus , 2007b;Williston, , 2007a;Carpen . Mauriciosaurus (Riggs, 1944). Mauriciosaurus Mauriciosaurus Polycotylus ------

polycotylids, and when theyare, they mostly are inal area. Gastral baskets are rarely preserved in bones in the abdom there isnodisplacement of unlikely, because is effect taphonomic center.A a converging basket with the gastralia gastralia to One outstanding feature of the coracoid. posterior and medial perforations of contrast to primitive condition (Albright III etal. 1.77, whichit is riciosaurus a more couldsuggest more teeth in the upper jaw than 04 20; Sato 2008; 2004, bifurcated is Mauriciosaurus (O’Keefe, 2001, that of chops (O’Keefe, parasphenoid of 2008). The Dolichorhynchops the parasphenoid of the ventral face of riciosaurus nal vacuity likein concave andborder awideposterior interpalati the parasphenoids of gins of lateralpterygoid. The mar rods inMauriciosaurus Sato 2001; 2004, adjacent to their caudal margins(O’Keefe, 2008, the pterygoids on the ventral face of Mauriciosaurus Dolichorhynchops pterygoids (O’Keefe, 2008,2001;Sato the of the corpus cupies the entire ventral face of ing abean-shapedwhich dish-likedepression, oc Dolichorhynchops rhynchops Dolicho average phalangeal length/width ratio of areepipodials faintlyvisible (O’Keefe, 2008).The in being almost evenly rounded. facets for The the the propodials resemble thoseof of In 2005). hart, 2007a; Carpenter, 1997;Schumacher and Ever they articulated withtwo caudals(Albright III etal. ticular faces for the heamal arches that suggesting caudal centra bear anterior and posterior ar The (O’Keefe,2005). Sato,juveniles 2008; in 27 or 26 and adults in 30 and 26 between ranges complex the premaxillomaxillary where the tooth count of 2004, 2008; Sato slightly curve medially at their tips(O’Keefe, 2001, the anterior pterygoid rods taper anteriorly and anteriorly terminates in ablunt anteriorly process, terminates while is 1.45 (Schumacher , Mauriciosaurus isconcave, but to a lesser extent the prominent lacks tubercles of from differs Dolichorhynchops et al. et al. et al. Trinacromerum. Similar to , 2011),unliketheexpanded , 2011). In Dolichorhynchops , 2011). Dolichorhynchops in hav in Mauriciosaurus et al. isthe Mauriciosaurus the distal margins Dolichorhynchops has Mauriciosaurus , 2016). In Mau , 2016).In Dolichorhynchops Mauriciosaurus , 2007a). In et al. Dolichorhyn possesses , 2011). Mau- are Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------, ,

POLYCOTYLIDS 7.2. COMPARISON WITHNON-COEVAL fLate Cretaceous polycotylids referred to the of decayed er Alabama (Cope, 1869; O’Keefe, 2004; Schumach- and the Moreville Kansas Chalk Formation of of North America,namelyfrom the Niobrara Chalk innis the genus Polycotylus species of One single there . stated to be closely related with Georgiasaurus the middle Volga Region (SGU 104a/37, -38) and by Arkhangelsky etal. symphysisare also seen in a polycotylid described the mandibular symphysis. Such a dentition and justonetenth of the splenials informing tion of participa in itsmassive of teeth and the degree from differs Moscow, of southeast km 700 about specified), not was formation (the al. penzensis Georgiasaurus not smoothlyconvex. asinMauriciosaurus the propodials show three distinct facets and are haveepipodials foramina. distal margins The of Furthermore, the alveolar margin iselevated. All lating duetothe laterally bulging toothsockets. the jawsis undu- of the anterior half margin of in alongitudinal ventralbears keel which isabsent median suture anterior to the parasphenoid that ygoidal vacuity, the pterygoids have a common (Schumacher, 2007): it lacks ananterior interpter inthe following diagnosticfeaturesMauriciosaurus from differs Dakota South western in Formation ed from the early Late Cenomanian Graneros Pahasapasaurus unique to which couldthusberegarded asdiagnosticfeature gastralia, of only plesiosaurwiththisarrangement plesiosaurs. For the moment, in other arrangements analogues to the gastralia this structure. Most reconstructions are of phology al. 00 rmteSnoino the Penza region , 2000) from the of , 2016). Therefore, little is known about the mor Mauriciosaurus et al. skonfo h al apna f, isknown from the Early Campanian of , 2016). The cervical and trunk vertebrae cervical andtrunk , 2016).The e.g. . Mauriciosaurus (Carpenter (Carpenter haasi . The teeth are. The massive; the lateral (Schumacher, 2007)report- (Ochev, et 1977,1976;Storrs (2007) from the Campanian et al. , 2010;Schumacher isthe Mauriciosaurus /2017 Mauriciosaurus , P. latip 125 125 et - - - -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico COMPARATIVE ANATOMY A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico COMPARATIVE ANATOMY / DISCUSSION 126 126 egl o Mexico. of leogulf this enigmatic polycotylid that inhabited the Pa- consider it appropriate to erect a new genus for on the ontogenetic stage.depending We therefore andiscertainly not fernandezi Mauriciosaurus phy of basket maythe gastral represent an autapomor of chops ratio more appears primitive than inDolichorhyn with Dolichorhynchops allpolycotylids, Of vertebrae (Figure 8)(Albright III trunk twenty than more Tableand 11; 3), (Figure whichepipodials are distinctly wider than long primary 13), 12, (Figures tarsals distal three 11), (Figure foramen antebrachial missing a 3), Table 1.65 (Figure 11; meri with a length/width ratio of line polycotylidits slightlysigmoidalhu basedon Mauriciosaurus a flat barely sculptured plate. the pterygoids andtogether with them it forms of the wings between the posteromedial margins of the parasphenoid protrudes the body of part of the pterygoids. anterior The posterior margin of occipital condyle, and there is a wide notch onthe the of trudes posteriorlyto theposterior terminus on itsventral side, the basioccipital tubercle pro mandibular grooves,a keel theparasphenoidhas : there are andwideanterior and deep riciosaurus diagnostic features that are not found inMau- followingpreservesunique the it 2013, Gasparini, the emended givendiagnosis and by O’Gorman and mandible, skull a fragmentary according to spite thefactthatof only consists thespecimen Colonía Formation,Argentina. De- Cerro Bosta,Southern La Maastrichtian Early – Campanian erraini the named polycotylids isSulcusuchus latestThe of 21cervicalvertebrae (Storrs, 1999). instead of Polycotylus differs from (Bobolubow, 1912) are doubtful and thusnot valid. taceous Russiandistricts Orenburg and Saratov genus / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín h ngai osrcino Palmulasaurus enigmatic. The construction of andTrinacromerum andmore resembles that Trinacromerum phalangeal length/width . The , GaspariniandSpalletti 1990from the Late Polycotylus (Trinacromerum) from the Late Cre- is identified as a polycoty- a as identified is fernandezi , but also shares many characters most resembles most Mauriciosaurus inhavingMauriciosaurus 26 et al. , 2007a). - - - - /2017

8.1. TAPHONOMY 8. Discussion tour fat (Figures 3, 16 3, (Figures fat tour adipose tissue, alsoknown subdermal ascon- of of soft tissueinthe thick trunk andtail regionThe lecillo limestone (Ifrim ronmental conditions reconstructed for the Val palaeoenvi- the matches thus and °C 37 and °C between 21 anoxicat conditions temperatures of under Adipoceresubstance thata waxy is forms waxoradipocereinto mortuary (Figure 19 B). saponified become could tissue adipose the which a chemical reaction chambersediment formed in the fresh carcassby softwater-soaked closure of the soft tissue (Figure immediate 19 A). The en- of tained by by sediment as issuggested the thickness the polycotylid must have been con- of half dorsal the least At 8). 4, (Figure compaction subsequent the body and ticulations during the collapse of not laterally, but posteriorly intheir vertebral ar the ribs, which have rotated from the position of concluded is This A). 19 (Figure first back its with into the softwater-soaked limemud sediment, mustAfter death, have Mauriciosaurus rapidly sunk setting.the depositional tent with the preserved remains, the sediment and the followingproposed scenariois thatconsis is Mauriciosaurus explain the excellent preservation of Inorder to the thin epidermis. and disruptionof pose tissue would rapidly lead to a delamination adi- the subdermal putrefactionThe processof are plesiosaurs so rarely preserved. structures of tinous scales, isprobably the reason why dermal with thinkera- combined withathinepidermis of the body decayed prior to the final embedding final the to decayedprior body the of theventral face A). Therefore theexposedof skin 19 (Figure water bottom oxygen-deficient hostile al. et itsbody(Kahana of and the contours siosaurs the ple- the of entire skin dorsal of thin epidermis adipocere2011). The likely helped to conserve the , 1999). The belly,, 1999). The however, wasexposed to the sget h rsneo a layer the presence suggests of Mauriciosaurus – et al. 18). This adipose tissue, 18). This , 2008;Topper etal. - - - , Figure 19 posteriorly around theirvertebralarticulationsduetothesemi-consolidatedsurrounding sediment, asisseeninFigure 3. subdermaladipocere preservingtransformedthird phasetheribsepidermalinto adiposetissuehasrotated structures. In a thedelicate with thegastralia.B)Thepartof thetrunk exposed totheopenwaterdecayed and collapsed and thegastraliabasketspread.The embeddednotis belly the that notesubstrate; water-soaked soft, a embeddingsinkingposition afterin theinto throughcarcass the the four flippers. shaped, stream-lined unit that was propelled with at its base. a drop- Both tail and trunk formed ently the tail was alsomostlyimmobile especially muscle the epaxial are mass not visible. Appar of whichspines would yieldahintonthe dimensions the hypaxial muscle masses. neural The eter of processes that, in extant reptiles, mark the diam- by the low hemalarches andthe short transverse verytip. weak muscularization This evidenced is weakly muscularised tail, probably excluding the the mostof precluded a mobilityof adipose armor thatespecially massive was at the tail base. This been stream-lined adiposetissue by subdermal fossilization bodyto have potential. appears The withanextremely low saurs, had a thin epidermis that at least polycotylids, but probably all plesio suggests lecillo polycotylid fernandezi Mauriciosaurus theVal extensiveThe - softtissuepreservation of served softtissueseam(Figures 8,19B). nowgastralia protrude laterally beyond the pre flat in such a way that the the lateral extremities of the previouslyvaulted pressed basket was gastralia compaction diagenetic early to Due flippers. the preservedB). The parts are all marginal or around and thus left no trace on the skeleton (Figure 19 Mauriciosaurusfernandezi INAH CPCRFG2544P.F.1.;modelfor thetaphonomy: A)Schematicmid-trunk cross-section Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - 8.2. INDIVIDUAL AGE stage: nandezi must have died at an early ontogenetic following features that suggest (Buchy juveniles and subadults there are some records of polycotylidsare hitherto unknown,but stages of Chiappe, 2011). Neonates and early ontogenetic known iscompletely disarticulated (O’Keefe and especially polycotylids. only fetal skeleton The plesiosaurs, Little knownis about theontogeny of 6. 5. 4. 3. 2. 1.

11-13). extensive suggests epipodials cartilage (Figures betweenA widegap the propodials and acher theylong as are wide(Figures 8,10;Schum ischiaThe are short andonlythree times as and Byrd, 2012). process scapulae lack adorsal The (O’Keefe ventralThe girdle bonesare extremely thin. (Figures 8,10). terolateral and noposteromedial expansion sions. They are simple inshapewithlittle pos- coracoidslackanterior clavicularThe exten ible inthecervicals(AlbrightIII neurocentralThe sutures are unfused, asisvis et al. et al. , 2005; Schumacher 2005; , , 2016). Mauriciosaurus fer Mauriciosaurus et al. /2017 et al. , 2016). The , 2016).The , 2007a). 127 127 - - - -

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico DISCUSSION A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico DISCUSSION 128 128 8.3 LOCOMOTION ANDPOSSIBLE DIET is the first juvenile polycotylid reported from a offshore habitat. shelf deep reported polycotylid juvenile first the is al. ments but shallow water coastal habitats (Buchy et polycotylid are alsoreported from marineenviron fromkm 500 nearestthe shoreline. juvenileOther cotylids. poly anisometricgrowth of Chiappe (2011) of and O´Keefe of suggestion the confirms ciosaurus in body the to respect with flippers the of requirepower. less relationship dimensional The and low underwater amplitude flightof that would maycrepancy be explained byfrequencya high where thelocomotormusclesattached. dis- This the ventral girdle plates, elbow jointandthat of the as possible,soon priortothe mineralization of main thrust-generating structure was stabilized as meso-, meta- and acropodials that suggests the (Kear, theepi-, early 2007).The mineralization of during ontogeny, similarto pliosaurid plesiosaurs bite force asearly aspossible enhancement of the skull isbest explained by the mineralization of 7. could onlyhave been provided by the limbs and to theimmobile trunkandtail, all maneuvers models are therefore viable for all four limbs. Due the left pelviclimb. Hydrofoil locomotion edge of cluded from thesofttissue adjacent to the posterior McHenry (Dames,1895; edge trailing flexible a and propodials muscularised ly hadstrong fernandezi Mauriciosaurus limbs of The central suture (Albright III the neuro the vertebral (closing of column that of the limbs preceded skull anddistal elements of the thatsuggests ontogenetic mineralization of pattern asubadult. This showsthus features of isalmost fully mineralized and palatinalThe roof 11-13). (Figures joints interphalangeal the tween space foralmost no also dial. There is cartilage be- epipo afourth supernumerary by the presence of and metapodials, tarsals packed carpals, aswell as comotor apparatus andare contrasted by densely immatureThese the lo- features mostlyconcern /

, 2005; Schumacher 2005; , Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín h ml ieo thespecimen. smallsize of The died in the openseaabout diedin Mauriciosaurus et al. et al. , 2016).Mauriciosaurus , 2007a). The rapid , 2007a). The et al. , 2005) as con- as 2005) , Mauri ------/2017 Figure 20 strikingly resembles the trunk-tailcomplex of the resembles strikingly coriacea). Notethatthedrop-shaped outlineofthecarapace body. B)Outlinesketchof aLeatherback ( the thickestdiameterlying ofthe anteriortothemid-section andoutline with with adrop-shaped tailformafunctional unit trunkbasedthat tissue evidenceinventralaspect.Note onsoft reconstruction ofMauriciosaurusfernandezi fernandezi (1.9 m/s),which isthetravelspeed of aLeatherback Turtle. aswimmingsystem suggests speedthrust greaterthan7km/h The moreslender body ofthe plesiosaur and thefour-winged leatherback ( sea turtles. Amongthese, modern the to that of terior speedscomparablethird, swimming suggest the trunk andtail unit liesinitsan- thickest part of anatomicalThese features, andthefactthat the the slender rostrum andthe small, pointed teeth. smallitemsbecauseof of likelyconsisted riciosaurus movement to seize prey, Mau- which inthe case of prevented extreme bendingbut allowed enough overlapping cervicalribsthat saurs, bya chain of latterneck. The was reinforced, as inall plesio thrust generation, may have allowed for higher ve long andslimlimbsthat likely all participated in marine reptiles (Massare, 1988).Nonetheless, the speeds reconstructed swimming for Mesozoic of speed falls swimming within the range 20). This (Figure Mauriciosaurus sembles the bodyoutline of whichre - strikingly carapace,namic theoutline of about 7 kph (Eckert, 2002) and shows a hydrody ,ming travels at anaverage velocity of Comparison of thebodyoutline of and Dermochelys coriacea. A) Schematic outline Schematic A) coriacea.andDermochelys Dermochelys coriacea Dermochelys ), the fastest swim CPC RFG 2544 P.F.1. 2544 CPC RFG Mauriciosaurus Mauriciosaurus Dermochelys - - - - . 10. Conclusions 03 Supriadi 2013; (e.g. least atspeeds relevant swimming for polycotylids structures could have helped to reduce at gitudinal rows inthe neck, body andtail. These rectangular in transverse arranged scutes andlon- coveredsurface was withtransversely orientated (Carpenter polycotylids were the fastest plesiosaurs swimming plitude stroke.thatsupports theassumption This am- low – frequency high a suggesting 3.9, about of flippers the of ratio aspect the of construction seaturtles. soft tissuealsoallows The for are of the body thusresembles that base. shapeof The astreamlinedsuggests body contourwithafat tail apparatus. extensive The softtissuepreservation the feeding and locomotor early enhancement of skeleton and the vertebral column, resulting in an the axial distal tothe propodials preceded that of the cranial bonesandthe bones Maturization of the individual. to the early ontogenetic stage of the enigmatic features are likelydue lids. Manyof rhynchops Trinacromerum withaclosersimilarityto diagnostic features from both characters comprising species showsof a mosaic Mexico. The of line plesiosaur from the Paleogulf Mauriciosaurus unit withthetrunk. afunctional sically immobilefat tail that formed may have shared a drop-shaped body witha ba- body, it isreasonable to assume that Plesiosauria the tail withrespect to the of and the dimensions Plesiosauria conservative bodyconstruction of locities (Carpenter ering that this young juvenile roamed the open sea plesiosaurs, especially consid- and locomotion of substantially to our knowledge on the anatomy plesiosaur’ worldwide andtherefore contributes the isbestpreserved fernandezi ‘softtissue ciosaurus probably lined withablack peritoneum.Mauri Dean and Bhushan, 2010; Saravi DeanandBhushan, andCheng, u lofaue fmore basal polycoty , but also features of et al isanenigmatic polycotyfernandezi - ., 2010;Massare, body 1988).The et al. et al. 21) h bd cvt was cavity body the 2015) , , 2010). According to the Dolichorhynchops Dolicho and Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - - 11. Acknowledgements 12. References fantastic editingwork. Amézquita (MexicoSandra Ramos City) for their Camprubí, Francisco Vega, Oscar Monzon and the papers. We alsocordially thankDr.of Antoni the final version extremely constructive their reviews of for (Albstadt/Tailfingen) Maisch Michael dially thank David M.Martill (Portsmouth) and paper especiallywith respect totaxonomy. We cor the of content scientific the improve to helped ly thismanuscript that substantial earlier versionof Virginia), who provided excellent reviewsin an West (Huntington, O´Keefe Robin and (Otago) Rothschild (Rootstown,FordyceOhio) R.Ewan Bruce A. Schuhmacher Bruce (HaysM. Kansas), base and the measurement. We are very to grateful ter (Karlsruhe) assistedwith the literature data Forschungsgemeinschaft Schus(DFG). Dominik the Deutsche been possible without the support of (Nuevopublication León). This would nothave Papaloteing ittotheMuseo VerdeMonterrey in community, allowing usto describe it, and donat scientific the for specimen the securing for Garza Our special thanks go to Ing. MauricioFernández Albright III, L.B., Gillette, D.D., Titus, A.L.,2007b, Albright III, L.B., Gillette, D.D., Titus, A.L.,2007a, more than500kmaway from thenearest shore. 41–58. VertebrateJournal Paleontology, of 27, genus replacement names for the preoccupied Shale Utah, part 2: Polycotylidae; Southern of Tropic (Cenomanian–Turonian) from Plesiosaurs the UpperCretaceous Vertebrate Paleontology,of 27,41–58. Utah,part 2: Polycotylidae:southern Journal (Cenomanian-Turonian) TropicShale of from Plesiosaurs the UpperCretaceous Palmula andthe subfamily Palmulainae: /2017 129 129 - - - - -

DISCUSSION / CONCLUSIONS / A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico ACKNOWLEDGEMENTS / REFERENCES A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico REFERENCES 130 130 Bobolubow, N.N., occurrenceof 1912,The Teleosteifrom New 2003, L., Cavin, A., Blanco, Blanco, A.,Alvarado-Ortega, J., 2006. Blanco-Piñón, A., Shimada, K., González-Barba, Blanco-Piñón, A., Alvarado-Ortega, J., 2007, Bhattacharya, J.P., J.A., MacEachern, 2009, Bardet, N., Pereda Suberbiola, X., Jalil, N-E., Arkhangelsky, M.S., Averianov, A.O., Pervushov, Albright III, L.B., Gillette, D.D., Titus, A.L., / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Russie, 14, 1–7. Annuaire Géologique et Minéralogique de la andPolycotylusElasmosaurus Palevol 2,299–306. Vallecillo (NE Mexico): ComptesRendus the Agua Nueva Formation (Turonian), 552–558. 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