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Xibalbaonyx oviceps. Stinnesbeck et al

Xibalbaonyx oviceps. Stinnesbeck et al
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           1 3 PalZ Paläontologische Zeitschrift ISSN 0031-0220 PalZDOI 10.1007/s12542-017-0349-5 Xibalbaonyx oviceps  , a new megalonychid round sloth (Folivora, Xenarthra)rom the Late Pleistocene of theYucatán Peninsula, Mexico, and itsaleobiogeographic significance Sarah R. Stinnesbeck, Eberhard Frey,Jerónimo Avíles Olguín, Wolfgang Stinnesbeck, et al.           1 3 Your article is protected by copyrightand all rights are held exclusively byPaläontologische Gesellschaft. This e-offprintis for personal use only and shall not be self-archived in electronic repositories. If you wishto self-archive your article, please use theaccepted manuscript version for posting onyour own website. You may further depositthe accepted manuscript version in anyrepository, provided it is only made publiclyavailable 12 months after official publicationor later and provided acknowledgement isgiven to the srcinal source of publicationand a link is inserted to the published articleon Springer's website. The link must beaccompanied by the following text: "The finalpublication is available at”.  RESEARCH PAPER  Xibalbaonyx oviceps , a new megalonychid ground sloth (Folivora,Xenarthra) from the Late Pleistocene of the Yucata´n Peninsula,Mexico, and its paleobiogeographic significance Sarah R. Stinnesbeck 1 • Eberhard Frey 1 • Jero´nimo Avı´les Olguı´n 2 • Wolfgang Stinnesbeck 3 • Patrick Zell 4 • Heinrich Mallison 5 • Arturo Gonza´lez Gonza´lez 6 • Eugenio Aceves Nu´n ˜ ez 2 • Adriana Vela´zquez Morlet 7 • Alejandro Terrazas Mata 8 • Martha Benavente Sanvicente 8 • Fabio Hering 3 • Carmen Rojas Sandoval 7 Received: 27 June 2016/Accepted: 25 March 2017   Pala¨ontologische Gesellschaft 2017 Abstract  Here we describe a new genus and species of giant ground sloth,  Xibalbaonyx oviceps  (Megalonychidae,Xenarthra), from the drowned cave system of the north-eastern Yucata´n Peninsula. The specimen is Late Pleis-tocene in age and was discovered in the Zapote sinkhole(cenote) near Puerto Morelos in the Mexican state of Quintana Roo.  Xibalbaonyx oviceps  differs significantlyfrom all hitherto known Megalonychidae including thosefrom the Greater Antilles and South America. The newtaxon suggests a local Caribbean radiation of ground slothsduring the Late Pleistocene, which is consistent with thedispersal of the group along a Mexican corridor. Keywords  Ground sloths    Pleistocene    Yucata´nPeninsula    Mexico Kurzfassung  Die Unterwasserho¨hlen auf der nordo¨stli-chen Halbinsel Yukatan zeigen eine artenreiche Ansamm-lung von Großsa¨ugern aus dem spa¨ten Pleistoza¨n undfru¨hen Holoza¨n. Hier beschreiben wir die neue Gattungund Art eines Riesenfaultiers,  Xibalbaonyx oviceps  (Me-galonychidae, Xenarthra), aus der Zapote Doline (Cenote)in der Na¨he von Puerto Morelos im mexikanischen Bun-desstaat Quintana Roo. Das Exemplar unterscheidet sichsignifikant von allen bisher dokumentierten Megalonychi-dae einschließlich derjenigen von den Großen Antillen undaus Su¨damerika. Das neue Taxon deutet auf eine lokalekaribische Radiation von Bodenfaultieren wa¨hren desSpa¨tpleistoza¨ns hin, die mit der Ausbreitung der Gruppeentlang des mexikanischen Korridors u¨bereinstimmt. Schlu ¨sselwo ¨rter  Bodenfaultiere    Pleistoza¨n    YukatanHalbinsel    Mexiko Handling Editors: Irina Ruf, Mike Reich. &  Sarah R. Stinnesbeck 1 Geowissenschaftliche Abteilung, Staatliches Museum fu¨rNaturkunde Karlsruhe, Erbprinzenstraße 13,76133 Karlsruhe, Germany 2 Instituto de la Prehistoria de Ame´rica, Carretera federal 307,km 282, Solidaridad, 77711 Solidaridad, Quintana Roo,Mexico 3 Institut fu¨r Geowissenschaften, Ruprecht-Karls-Universita¨tHeidelberg, Im Neuenheimer Feld 234, 69120 Heidelberg,Germany 4 Abteilung fu¨r Naturgeschichte, Hessisches LandesmuseumDarmstadt, Friedensplatz 1, 64283 Darmstadt, Germany 5 Museum fu¨r Naturkunde – Leibniz-Institut fu¨r Evolutions-und Biodiversita¨tsforschung, Invalidenstraße 43,10115 Berlin, Germany 6 Museo del Desierto, Carlos Abedrop Da´vila 3745, NuevoCentro Metropolitano de Saltillo, 25022 Saltillo, Coahuila,Mexico 7 Instituto Nacional de Antropologı´a e Historia, Carreterafederal 307, km 128, 77710 Tulu´m, Quintana Roo, Mexico 8 A´rea de Prehistoria y Evolucio´n del Instituto deInvestigaciones Antropolo´gicas de la Universidad NacionalAuto´noma de Me´xico, UNAM, 04510 Coyaca´n, Mexico  1 3 PalZDOI 10.1007/s12542-017-0349-5  Introduction The earliest fossil of a sloth is reported from the latestEocene of Cerro Blanco, south Argentina (McKenna et al.2006; Gaudin and Croft 2015). Ground sloths are widely known from the later Paleogene and Neogene of SouthAmerica (Pujos et al. 2016), but must have reached NorthAmerica by island-hopping about nine million years ago(Hirschfeld and Webb 1968; McDonald et al. 2013a). This arrival thus dates prior to the formation of the Isthmus of Panama (Woodburne 2010), although the timing of thisland bridge is still under discussion (MacPhee and Itur-ralde-Vinent 1995, Montes et al. 2015). Evidence for island dispersal into North America comes from a Miocene site inthe Antilles, where the palate of   Imagocnus zazae  (incertaesedis; MacPhee and Iturralde-Vinent 1994) was reported byMacPhee and Iturralde-Vinent (1994), whereas  Pliometa-nastes  (Hirschfeld and Webb, 1968), reported from Floridais the earliest known genus of Megalonychidae in NorthAmerica (Hirschfeld and Webb 1968; Pujos et al. 2016). This latter specimen dates back to 9–8 million years(Hirschfeld and Webb 1968; Carranza Castan˜eda andMiller 2004; Morgan 2005). Webb and Perrigo (1985) suggested that the genus  Megalonyx  evolved from  Plio-metanastes  4.8 million years ago in North America(Hirschfeld and Webb 1968; McDonald 1977; Flynn et al. 2005; Morgan 2005).  Megalonyx  was a widespread genusand was present throughout North America as far north asthe Yukon Territory in Alaska (Hirschfeld and Webb 1968;McDonald 1977; McDonald et al. 2000). Mexican reports exist from the States of Nuevo Leo´n, Sonora and Puebla(McDonald 1977, 2002). Four species have been described from Mexico, which differ in osteology, size, and theirchronostratigraphic ranges (Hirschfeld and Webb 1968):  Megalonyx jeffersonii  (Desmarest, 1822; Harlan 1825),  M.wheatleyi  (Cope, 1871),  M. mathisi  (Hirschfeld and Webb,1968), and  M. leptostomus  (Cope, 1893; Hirschfeld andWebb 1968; McDonald 1977). Megalonychidae are a phenotypically diverse family of ground sloths, among them the arboreal, extant two-toedsloth ( Choloepus ), which is up to 0.7 m long and weighs 4–8kg (Adam 1999; Hayssen 2011), as well as massive ground sloths like the North American  M. jeffersonii  (Desmarest,1822), with an estimated mass of one metric ton and a lengthof 3 m (Steadman et al. 2005; Pant et al. 2014). Geo- graphically, the extant two-toed sloths  C. didactylus  (Lin-naeus, 1758) and  C. hoffmanni  (Peters, 1858) range fromHonduras in Central America to Bolivia and Brazil in SouthAmerica. The small extinct semiarboreal sloths  Acratocnus and  Neocnus  (White 1993, 1997) from the Pleistocene– Holocene of the Antilles are close relatives of   Choloepus (White and MacPhee 2001; Gaudin 2004). Fossil sloths from the West Antillean islands (e.g.,Cuba, Hispaniola, Puerto Rico, Curac¸ao and Grenada)show a wide morphological variation, hence all of them arereferred to Megalonychidae (White and MacPhee 2001).The record from Cuba is particularly diverse and abundant(MacPhee et al. 2000). According to White and MacPhee(2001), Antillean megalonychid sloths are divided into twosubfamilies: the large terrestrial Megalocninae (  Megaloc-nus  and  Parocnus ) and small semiarboreal sloths Choloe-podinae (  Acratocnus ,  Paulocnus ,  Neocnus ). Fossil remainsof the Megalocninae  Megalocnus  and  Parocnus  are mainlydocumented from Cuba and Hispaniola (Van der Geer et al.2010).Fossils of the subfamily Choloepodinae (i.e.,  Acratoc-nus ,  Paulocnus , and  Neocnus ) are presently restricted toCuba, Hispaniola, Puerto Rico, and Curac¸ao, except for theextant two-toed sloth (White and MacPhee 2001).Both groups range throughout the Pleistocene andHolocene (White and MacPhee 2001; Van der Geer et al.2010). MacPhee et al. (2000) hypothesized that the Antil- lean sloths became extinct after human arrival on theislands during the Mid- to Late Holocene.  Imagocnus zazae  (incertae sedis), from the Domo deZaza Site in Cuba, is of Early Miocene age and thus revealsthe long evolutionary history of West Antillean sloths.The ground sloth record from South America hasmarkedly expanded during the past decade (Cartelle et al.2008; De Iuliis et al. 2009; McDonald et al. 2013b; Pujos et al. 2016). Megalonychidae are known from the Oli-gocene of Patagonia (  Deseadognathus  Carlini and Scil-lato-Yane´, 2004) and Bolivia and the Early Miocene of Patagonia ( Eucholoeops  Ameghino, 1887; De Iuliis et al.2014;  Megalonychotherium  Scott, 1904). Several genera,e.g.  Ortotherium  (Ameghino, 1885),  Pliomorphus (Ameghino, 1885),  Torcellia  (Kraglievich, 1923a),  Para-nabradys  (Scillato-Yane´, 1980),  Megalonychops  (Kra-glievich, 1930) were recorded from the Late Miocene of the Entre Rı´os Province in Argentina (Ameghino 1885;Kraglievich 1923a; Brandoni 2011). Further records come from the Pleistocene of Venezuela (  Megistonyx , McDon-ald et al. 2013b), Brazil (  Ahytherium ,  Australonyx , DeIuliis et al. 2009; Cartelle et al. 2008), Peru, and Chile (  Diabolotherium , Pujos et al. 2007).The migration routes and evolutionary relationshipsamong ground sloth species in North and South Americaare still poorly understood, due to possible geographicalor habitat barriers and the scarcity of well documentedfossil remains from Central America. Mexico may haveformed a corridor between the two continents and thusplayed a crucial geographic role for migration, specifi-cation and the distribution of Neogene sloths in theAmericas. S. R. Stinnesbeck et al.  1 3  Nevertheless, the published database on ground sloths inMexico is sparse and none of the species reported from thecountry has been documented osteologically (McDonald1985, 2002; Gonza ´lez Gonza´lez et al. 2008; Ferrusquı´a-Villafranca et al. 2010; Pujos et al. 2016). For instance, Megalonychidae, e.g.,  Pliometanastes  Hirschfeld andWebb, 1968,  M. jeffersonii  Desmarest, 1822 and  M.wheatleyi  Cope, 1871, are known to have occurred in NorthMexico (McDonald 2002; Ferrusquı´a-Villafranca et al.2010), but  Nothrotheriops shastensis  Sinclair, 1905,  Ere-motherium laurillardi  Lund, 1842,  Glossotherium  sp. and Paramylodon harlani  Harlan, 1825 may also have inhab-ited large parts of Mexico during the Pleistocene, eventhough their record is extremely sparse when compared toNorth America (McDonald 2002).  Nothrotheriops shas-tensis  had the widest distribution across Mexico, rangingfrom the Federal States of Sonora, Nuevo Leo´n, BajaCalifornia, San Luis Potosı´, Jalisco, Michoaca´n, to theValley of Mexico and the Yucata´n Peninsula (McDonald2002; Gonza´lez Gonza´lez et al. 2008; Lucas 2008; Chatters et al. 2014; De Iuliis et al. 2015). Information on envi- ronmental and faunal changes in Mexico is also highlyscattered and varies enormously depending on the regionand author in terms of quantity, quality, chronologicposition, geographic distribution, and statistical signifi-cance (Leyden et al. 1994; Bradbury 1997; Cervantes- Borja et al. 1997; Metcalfe et al. 2000; Brenner et al. 2002; Ferrusquı´a-Villafranca et al. 2009). Recent findings fromthe Yucata´n Peninsula (Fig. 1) including those documentedhere demonstrate that ground sloths not only were commonelements of the south Mexican megafaunal assemblage, butalso showed a remarkable diversity (McDonald 2002;Ferrusquı´a-Villafranca et al. 2010). The Yucata´n Peninsula TheYucata´nPeninsulaistodaycoveredbytropicalrainforestgrowing on limestone karst bedrock, with high levels of chemical erosion and weathering. Therefore, surface recordsoffossilsfromthePleistocenearepresentlyunknownfromtheregion. Nevertheless, the drowned cave system has become afocus of investigation because of its abundant and diversePleistocene/Holocene fossil assemblage (e.g., Gonza´lezGonza´lez et al. 2008, 2013; Chatters et al. 2014). In the Mexican State of Quintana Roo, for instance, the karst cavesystem is mostly submerged and has a presumed total exten-sionof7000 km,ofwhichonly700 kmarecurrentlyexplored(Bauer-Gottwein et al. 2011). It is characterized by horizon-tally layered, thick bedded, shallow water carbonate bedrock of Mio-, Plio-, and Pleistocene age with karstification duringcold periods of the Pleistocene (Ward et al. 1985; Weidie1985; Lefticariu et al. 2006). Sea level and hydrology changes during the Pleis-tocene–Holocene transition contributed to the developmentof the extant cave ecosystem. During the Last GlacialMaximum (LGM) large parts of the system were exposeddue to a sea level up to 120 m below present levels(Blanchon and Shaw 1995; Moseley et al. 2013). The cave system was flooded during the Pleistocene–Holocenetransition, reaching modern sea levels between 6000 and4500  BP  (Smart et al. 2006; Smith et al. 2011; Grant et al. 2012; Moseley et al. 2015), thereby preserving climatic, archaeological and paleontological evidence inside (Gon-za´lez Gonza´lez et al. 2013). Ongoing investigation inwater-filled sinkholes, locally known by the Maya term cenote , revealed numerous and diverse Pleistocenemegafaunal elements, among them equids ( Equus conver-sidens  Owen, 1862,  E. occidentalis  Owen, 1863), camelids(  Hemiauchenia macrocephala  Cope, 1893), glyptodonts( Glyptotherium  cf.  floridanum  Simpson, 1929), tapirids( Tapirus bairdii  Gill, 1865), and gomphotheriids ( Cu-vieronius  sp., Osborn 1923). Ground sloth remains areparticularly abundant and well preserved. Fossil slothmaterial from the Tulu´m area was given a preliminaryassignment to  N. shastensis , but there is also evidence for anew unnamed species of Megalonychidae (Gonza´lezGonza´lez et al. 2008; Chatters et al. 2014). The megalonychid ground sloth described here wasdiscovered in the El Zapote cenote (Figs. 1A, 2) near Puerto Morelos, 36 km south of Cancu´n and 90 km northof Tulu´m, in the Federal State of Quintana Roo, Mexico.The ground sloth was discovered by underwater caveexplorer Vicente Fito in 2009 and reported to the InstitutoNacional de Antropologı´a e Historı´a (INAH) QuintanaRoo. The entrance to the El Zapote cenote is today a ver-tical chimney of 8.5–10 m diameter and a depth of 30 m,which opens to a wide bottle-shaped chamber (Fig. 3). Thechamber reaches approximately 40 m in diameter and adepth of more than 60 m. In vertical line with the sinkholeentrance a debris mount of limestone blocks and organicmatter is piled up on the cave floor (Figs. 2, 3). The skeleton was discovered at a water depth between 50 and55 m on the debris mount.The skull of the ground sloth and some postcranial bones(Fig. 2), among them fragmentary ribs and vertebrae, arespread over six bathymetric debris levels (Fig. 3). Eachbathymetric level has a height of approximately 0.5–0.7 m.Theboneshaveshiftedlaterally,butarestilllimitedtoa3 mdeep slope area. The cranium and mandible were articulatedand deposited at a depth of 50 m. The skull was wedged in aniche between two rocks (Fig. 3). The depth of 62 m of thecenote suggests that the site was flooded at an early stage of sea level rise, likely during the latest Pleistocene or EarlyHolocene (Blanchon and Shaw 1995; Smart et al. 2006; Smith et al. 2011; Moseley et al. 2015).  Xibalbaonyx oviceps , a new megalonychid ground sloth (Folivora, Xenarthra)  1 3


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