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A New Docodont Mammal from the Late Jurassic of the Junggar Basin in Northwest China

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A New Docodont Mammal from the Late Jurassic of the Junggar Basin in Northwest China A new docodont mammal from the Late Jurassic of the Junggar Basin in Northwest China HANS−ULRICH PFRETZSCHNER, THOMAS MARTIN, MICHAEL W. MAISCH, ANDREAS T. MATZKE, and GE SUN Pfretzschner, H.−U., Martin, T., Maisch, M.W., Matzke, A.T., and Sun, G. 2005. A new docodont mammal from the Late Jurassic of the Junggar Basin in Northwest China. Acta Palaeontologica Polonica 50 (4): 799–808. Fieldwork in the early Late Jurassic (Oxfordian) Qigu Formation of the Junggar Basin in Northwest China (Xinjiang Au− tonomous Region) produced teeth and mandibular fragments of a new docodont. The new taxon has a large “pseudo− talonid” on the lower molars, and by retention of crest b−g exhibits closer affinities to Simpsonodon and Krusatodon from the Middle Jurassic of Europe than to the other known Asian docodonts Tashkumyrodon, Tegotherium,andSibirotherium. It differs from the Haldanodon–Docodon−lineage by the “pseudotalonid” and large cusps b and g. A PAUP analysis based on lower molar characters produced a single most parsimonious tree with two main clades. One clade comprises Docodon, Haldanodon, and Borealestes, and the other Dsungarodon, Simpsonodon, and Krusatodon plus the Asian tegotheriids. Analysis of the molar occlusal relationships using epoxy casts mounted on a micromanipulator revealed a four−phase chewing cycle with transverse component. The molars of the new docodont exhibit a well developed grinding function be− sides cutting and shearing, probably indicating an omnivorous or even herbivorous diet. A grinding and crushing function is also present in the molars of Simpsonodon, Krusatodon, and the Asian tegotheriids, whereas Borealestes, Haldanodon, and Docodon retain the plesiomorphic molar pattern with mainly piercing and cutting function. Key words: Docodonta, Dsungarodon, occlusion, Jurassic, Qigu Formation, Junggar Basin. Hans−Ulrich Pfretzschner [hans−ulrich.pfretzschner@uni−tuebingen.de] and Michael W. Maisch [michael.maisch@ uni−tuebingen.de], Institut für Geowissenschaften, Universität Tübingen, Sigwartstraße 10, 72076 Tübingen, Germany; Thomas Martin [[email protected]], Forschungsinstitut Senckenberg, Senckenberganlage 25, 60325 Frankfurt am Main, Germany; Andreas T. Matzke [[email protected]], Department of Paleobiology, Smithonian Institution, National Museum of Natural History, PO Box 37012 MRC 121, Washington, D.C. 20013−7012, USA; Ge Sun [[email protected]], Research Center of Paleontology, Jilin University, 6, Xi−Minzhu Street, Changchun 130026, China. Introduction Martin and Averianov (2004) based on a lower molar from the Middle Jurassic Balabansai Svita near Tashkumyr in A long time docodonts were regarded as a small group of Kyrgyzstan. Here we present dental remains of a new Late Mesozoic mammals restricted to the Jurassic of Europe and Jurassic docodont which were collected in 2001 at Liu− North America (e.g., Simpson 1928, 1929; Kühne and huanggou in the valley of the Toutunhe river southwest of Krusat 1972; Kron 1979; Krusat 1980; Kermack et al. 1987; Urumqi during field work of the Sino−German cooperation Lillegraven and Krusat, 1991). The first Asian docodont re− between the Jilin University (Changchun) and the Eberhard− ported was Tegotherium gubini from the Late Jurassic of Karls−Universität (Tübingen). Shar Teg in Mongolia, that originally was described as an un− The Junggar Basin is one of the largest sedimentary bas− usual symmetrodont (Tatarinov 1994). Nessov et al. (1994) ins in Xinjiang Autonomous Region and contains a continu− announced a badly damaged possible upper docodont molar ous succession from the Permian to the Late Cretaceous that from the Middle Jurassic Balabansai Formation of Kalma− is largely covered by Cenozoic sediments. In the center of the kerchin in Kyrgyzstan which could not be determined at the basin the sedimentary infill approaches 16,000 m of which specific or generic level. Prasad and Manhas (2001) assigned about 6,000 m represent fluvio−lacustrine Mesozoic depos− an upper premolar and a fragmentary lower molar from the its. The locality at Liuhuanggou, 40 km southwest of the city supposedly Lower–Middle Jurassic Kota Formation of India of Urumqi and west of the Toutunhe river, is highly fossili− to docodonts of Laurasian affinity (“Haldanodon grade”). ferous in several levels in the Toutunhe and Lower Qigu For− Maschenko et al. (2003) described three incomplete denta− mations. The Toutunhe Formation is dated as Callovian and ries of an Early Cretaceous docodont, Sibirotherium rossicus the Qigu Formation, which is at the locality 731 m thick, as from the Shestakovo locality in Western Siberia. The first Oxfordian, based on spores and palynomorphs (Ashraf et al. unquestioned docodont from Central Asia was reported by 2004). About 470 m above the Toutunhe/Qigu boundary a Acta Palaeontol. Pol. 50 (4): 799–808, 2005 http://app.pan.pl/acta50/app50−799.pdf 800 ACTA PALAEONTOLOGICA POLONICA 50 (4), 2005 bonebed was discovered during field work in 2000. This rowska et al. (2004), which is equivalent to the Mammalia− bonebed has yielded numerous mainly isolated bones and formes of Rowe (1988) and McKenna and Bell (1997). teeth of hybodontid sharks, actinopterygians, temnospon− Institutional abbreviations.—The holotype and referred spec− dyles, turtles, crocodiles, dinosaurs and mammals (hara− imens are deposited in the Sino−German Project collection myids and docodonts) that appeared in lenses in a series of (SGP/2001/21–26), currently housed at the Institute for Geos− greenish siltstones and fine sandstones (Maisch et al. 2001, ciences (IFG), University of Tübingen, Germany. The collec− 2003, 2004; Martin and Pfretzschner 2003). The docodont tion remains property of the People’s Republic of China and remains are described in this study. will be transferred to a public Chinese collection after the sci− entific studies are finished. The final repository will be an− Material and methods nounced in an internationally accessible journal. Other abbreviations.—L, length; W, width; asterisk * indi− About 20 to 30 kg of sediment from the bonebed were cates preserved length or width in incomplete specimens. screenwashed at a mesh size of 0.5 mm and the remaining concentrate was picked under a stereomicroscope. For bio− mechanical experiments epoxy casts of the docodont teeth Systematic palaeontology were made using CAF 3 (Rhône−Poulenc) for moulding and Araldit M and hardener HY 956 for casting. Subsequently Mammalia Linnaeus, 1758 the teeth were mounted on SEM−stubs with acetone−soluble Docodonta Kretzoi, 1946 conductive mount and sputtered with gold for SEM study. The cast of the upper molar was mounted on a metal axis that Docodontidae Simpson, 1929 could be rotated freely, whereas the cast of the lower molar Genus Dsungarodon nov. Pfretzschner and Martin was mounted on a Narishige micromanipulator which al− Derivation of the name: Named after the Junggar Basin (formerly lowed precise positioning of the tooth in all three dimensions Dsungar) and @*@v, stem of @*@bH (Greek) tooth. Dsungarodon (mas− of space. This arrangement was used to study all stages of the culine), tooth from the Junggar Basin. occlusal relationships during the chewing cycle under a Type species: Dsungarodon zuoi sp. nov. stereomicroscope. From each stage a digital photograph was Diagnosis.—Upper molar characters: (1) cusp X hook shaped taken and 25 to 47 images of one chewing cycle were com− and recurved buccally; (2) basin developed between cusps bined to a movie sequence at the computer (available on the A−C−Y−X; (3) cusps A and C high and slender and consider− APP website at http://app.pan.pl/acta50/app50−799SM.htm). ably higher than cusps X and Y; (4) buccal crests forming a Although the cusp homology of docodont molar teeth with cutting edge; (5) lingual portion mesial to the A−X−crest is re− that of other mammals has not yet been established, we follow duced; (6) distal margin C−Y of the lingual portion of the tooth the terminology proposed by Butler (1988, 1997) for practical not deeply indented; (7) strong ectoflexus; (8) outline of the reason and because we think that this homology is likely to be tooth crown triangular. correct (Fig. 1). The purely descriptive cusp terminology of Lower molar primitive (–) and derived (+) characters: (1) Kermack et al. (1987) and Sigogneau−Russell (2001, 2003) is cusp e and f reduced (+); (2) crest b−e well developed (–); (3) more unbiased but has proven rather cumbersome for the mor− crest b−e protruding to the mesial end of the tooth (+); (4) phological descriptions. The docodont wear facet terminology crest e−g missing (–); (5) crest b−g well developed (–); (6) en− is after Jenkins (1969). We follow the stem−based definition of larged anterior basin (pseudotalonid) (+); (7) cusp g en− Mammalia, proposed by Luo et al. (2002) and Kielan−Jawo− larged, similar in height to cusp c (+); (8) region distal to cusps a and c reduced (+). distal Differential diagnosis.—The upper molar of the new taxon mesial lingual differs from those of Haldanodon exspectatus by the follow− ing characters: (1) cusp X hook−shaped and recurved buccally; lingual (2) basin developed between cusps A−C−Y−X; (3) cusps A and C high and slender; (4) buccal crests forming a cutting edge; (5) lingual portion mesial to the A−X−crest reduced; (6) distal margin C−Y of the lingual portion of the tooth not deeply indented; (7) strong ectoflexus. Dsungarodon differs from Simpsonodon oxfordensis by the following upper molar char− acters: (1) buccal cusps A and C much more slender and con− siderably higher than cusps X and Y; (2) lingual part of the tooth more narrow and more constricted; (3) outline of the Fig. 1. Restoration of right lower (A) and upper (B) molar of the new tooth crown more triangular. docodont with designation of cusps (occlusal view). Reconstructed broken At the lower molars, the new taxon differs from Tego− areas are shaded. Cusp designation follows Butler (1988). therium, Sibirotherium,andTashkumyrodon by exclusion of PFRETZSCHNER ET AL.—NEW JURASSIC DOCODONT FROM CHINA 801 1mm Fig.
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