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bulletin de l'institut royal des sciences naturelles de belgique sciences de la terre, 68-supp: 3-70, 1998 bulletin van het koninklijk belgisch instituut voor natuurwetenschappen aardwetenschappen, 68-supp: 3-70, 1998 Sino-Belgian Coopération Program "Cretaceous Dinosaurs and Mammals from Inner Mongolia"1 1. New Bactrosaurus (Dinosauria: Hadrosauroidea) material from Iren Dabasu (Inner Mongolia, P. R. China) by Pascal GODEFROIT, DONG Zhi-Ming, Pierre BULTYNCK, LI Hong and FENG Lu with the collaboration in the field of SHANG Chang-Yong, GUO Dian-Yong, DONG Yu-Long, SUN Yan, ZHANG Zhe-Min, Hugo DE POTTER, Georges LENGLET, Thierry SMITH and Eric DERMIENCE mm d'Erenhot (Mongolie intérieure, R.P. Chine). Ce gisement renfermait les squelettes disloqués d'au moins quatre individus de Thadrosaure primitif Bactrosaurusjohnsoni Gilmore, 1933. L'étude de ce nouveau matériel permet une bonne reconstitution ostéologique de cette espèce; il a ainsi pu être clairement établi que c'était un animal sans crête. La *pgftg-ï!r) , £31- superfamille des Hadrosauroidea forme un groupe monophylétique M, caractérisé par 11 synapomorphies. Bactrosaurus johnsoni est l'Ha- drosauroidea le plus primitif actuellement connu: il ne possède en effet Ie ft, E % ( Bactrosaurusjohnsoni GILMORE, pas de nombreux caractères dérivés observés chez les autres membres suffisamment bien connus de ce taxon. La position basale de Bactro¬ 1933) ft ft-fr, saurus johnsoni dans la phylogénie des hadrosaures plaide en faveur d'un âge Crétacé supérieur plutôt précoce pour la Formation d'Iren Dabasu. Mots-clefs: Bactrosaurusjohnsoni, Hadrosauroidea, Formation d'Iren Dabasu, Mongolie intérieure, ostéologie, phylogénie. #-7C, Introduction In March 1995, the Inner Mongolian Museum at Hohhot and the Royal Belgian Institute of Natural Sciences at iii: ïlfAlÊ, tö Brussels signed an agreement for co-operative explora¬ *t!G ff, f*££ tion of dinosaur and early mammal sites in Inner Mon¬ golia (Sino-Belgian Dinosaur Expédition = SBDE). The joint exploration was initially intended to collect more dinosaur material documenting the replacement of Early Abstract Cretaceous iguanodontids by hadrosaurids at the? begin¬ ning of the Late Cretaceous and the phylogenetic rela- In 1995, the Sino-Belgian dinosaur expédition discovered a rich bonebed in the Iren Dabasu Formation (Late Cretaceous) of Erenhot tionships between the two groups. The primitive hadro- (Inner Mongolia, P.R. China). This bonebed comprised the scattered saurs Gilmoreosaurus mongoliensis and Bactrosaurus skeletons of at least 4 specimens belonging to the primitive hadrosaur johnsoni are known from Inner Mongolia since the work Bactrosaurus johnsoni Gilmore, 1933. The study of the new material of Gilmore (1933). Rozhdestvensky allows an accurate osteological reconstruction of this species, e.g. (1966) subse- definitely showing that it was a flat-headed hadrosaur. The superfamily quently described the "iguanodonts" Probactrosaurus Hadrosauroidea is diagnosed as a monophyletic group characterized by alashanicus and P. gobiensis, also from Inner Mongolia. 11 synapomorphies. Bactrosaurus johnsoni is the most basai taxon of Moreover, the latter author (1952) established the species the Hadrosauroidea, as it lacks numerous apomorphies observed in the other well known taxa within this superfamily. The basai position of Iguanodon orientalis (= I. bernissartensis, according to Bactrosaurusjohnsoni in hadrosaur phylogeny speaks for an early Late Norman, 1996) for dinosaur material discovered in a Cretaceous âge for the Iren Dabasu Formation. nearby area in southeastern Mongolia. As the taxonomy and Key-words: Bactrosaurusjohnsoni, Hadrosauroidea, Iren Dabasu For¬ phylogenetic relationships of late iguanodontids and mation, Inner Mongolia, osteology, phylogeny. early hadrosaurids is unresolved (e.g. Brett-Surman, Résumé ' En 1995, l'expédition dinosaurienne sino-belge a découvert un riche Program supported by the Prime Minister's Services - Office "bonebed" dans la Formation d'Iren Dabasu (Crétacé supérieur), près for Scientific, Technical and Cultural Affairs. 4 Pascal GODEFROIT et al. Fig. 1 - Generalized map of the central part of the Inner Mongolia Autonomous Région, showing itinerary of the Sino-Belgian expéditions in 1995 and 1996. Inset map shows the Inner Mongolia Autonomous Région. 1979; Weishampel & Horner, 1986; Maryanska & 1 1.2° 112 *05 1120iff Osmolska, 1981a; Norman, 1990), description of new 1 CHINA material will contribute to the understanding of the pro- mongolia! blems oulined above. 1 43045' 1 During September 1995, the SBDE worked near Erenhot » .!49 1 y—IREN, V\95E5H and a rich bonebed 2^145 comprising at least four hadrosaur 1 skeletons was excavated in the Iren Dabasu Formation. In *4l X / late August and September 1996, the SBDE explored X / mainly the Bayan Mandahu area (see Dong et al., 1988; Dong, a 1993). Several Protoceratops skulls, nearly ■»"" '—X. / ' complete ankylosaur skeleton, a complete turtle, several X / 43°40' \/ lizard and mammal skulls and many eggs were discov- Erenhot ered. The itinerary followed by the two SBDE expédi¬ tions shown in Kilometers is Figure 1. 1 1 1 1 1 0 12 3 4 New Bactrosaurus material from the bonebed discover- Fig. 2 - Location of fossil locality SBDE 95E5 and American ed in the Iren Dabasu Formation in the Erenhot Museum of Natural History localities 141 (type lo¬ area is described in the present paper and discussed cality of Bactrosaurus johnsoni), 149 (type locality from a taxonomical and phylogenetical point of view. of Gilmoreosaurus mongoliensis), 136 (type locality Our opinion on the age of this material is also pre- of Alectrosaurus olseni) and 140 (type locality of sented. Archaeornithomimus asiaticus). Bactrosaurus, Dinosauria, Inner Mongolia 5 Location and général characteristics of the fossil lo- sequence in which 13 sediment samples were taken (Fig¬ cality ure 3). The succession is composed of poorly sorted, fine to very coarse, slightly lithified, brownish grey and buff The new Bactrosaurus material was collected from a quartz sand. Samples 3 and 7 are more clay-rich. Quartz bonebed (Locality SBDE 95E5) about 16km NE of Eren- grains are mostly medium to fine sized, subrectangular to hot and 7 km E of the small sait pan Iren Nor. The co- subrounded (larger grains are generally subrounded), ordinates measured in the field (N 43° 44.442; E 112° translucent to milky and occasionally reddish due to 10.723) indicate that the locality is very close to the staining by iron oxides. Argillaceous and slightly calcar- AMNH locality ("Quarry") 140 (Gilmore, 1933, fig. 1) eous coatings are common. Traces of mica and dark- and within a 1 km distance from AMNH 141, the type coloured grains occur. Granulometric curves of samples locality of Bactrosaurus johnsoni (Figure 2). The 1, 2, 6 and 13 (the bonebed) show 2 or 3 peaks (7 pm, 200 bonebed belonging to the Late Cretaceous Iren Dabasu pm and 800 pm, respectively). Formation covered a surface of 7.20 x 4.60 m, was 10 cm thick and was lying at the top of a 40 to 55 cm thick sandy According to Berkey & Morris (1927), the Iren Dabasu Fig. 3 - Sketch showing bonebed and lithologie succession at Locality SBDE 95E5 near Erenhot. Inset map of the Inner Mongolia Autonomous Région shows location of Erenhot. 6 Pascal GODEFROIT et al. Formation was deposited in lacustrine and fluvial envir¬ the bonebed; almost ail belong to Bactrosaurus johnsoni onments. Currie & Eberth (1993) interpret the forma¬ and they may represent at least four individuals. A few tion as a low-sinuosity braided fluvial system with a main articulated series, with five to ten vertebrae, of dorsal and NW direction and with ancillary NE and SW orientated caudal vertebrae were collected (Plate 1, Fig. 2). The flow Systems. central southern half of the bonebed is characterized by the accumulation of well preserved pelvic bones and Several hundred skeletal elements were recovered from humeri (Plate 1, Fig. 1), with one nearly complete sa- Duration Ma PERIOD AGE STRATIGRAPHJC RANGES OF TAXA ♦ Boréal scak m.y. -65- Maastrichtian 6.3 70- C O s: a Campanian 12.2 80 I? <§ M u Santonian 2.3 C0 sa T3 • Coniacian 3.2 4-» Ö 3 90 O Turonian 4.5 to t3 -ö to g - O 3 <u (U ctf cS Cenomanian 5.4 <3 to C 3 00 0 S) C £ 3 100- X- (S ca O co </] t* O O w V- (L> T3 U 55 XI Albian 13.3 ÎS. ctj Ü 55 c3 X S Q 3 110- g u I 1 O V) <D a O cd OQ 8.8 • t—< Aptian tl vh E P CÖ cd 120- x/i U O W Barremian 6.0 3 '8 V cd 3 x <3 130- Hauterivian 5.0 S O <3 Valanginian* 4.5 -Cl 140- Ryazanian* 5.4 Berriasian U Port- M landian' CO Tithonian 8.8 oo Volgian* 150- Fig. 4 - Stratigraphical distribution of selected iguanodontians. Hadrosaurinae: dashed line indicates range of Aralosaurus tuberiferus from Kazakhstan, according to Rozhdestvensky (1977); Lambeosaurinae: dashed line indicates range of Jaxartosaurus aralensis from Kazakhstan, according to Rozhdestvensky (1977); Bactrosaurus-. full line indicates âge of Iren Dabasu Formation favoured in the present paper, dashed line indicates âge proposed by Jerzykiewicz & russell (1991), dotted line indicates âge proposed by Currie & eberth (1993); Camptosauridae: dashed line indicates range extension of the family according toICamptosaurus depressus\ *: stratigraphie level in Kazakhstan corresponding to the transition Kizylkumemys shuwalovi - Lindholmemys martinsoni. Time scale according to Gradstein & ogg (1996). Bactrosaurus, Dinosauria, Inner Mongolia 7 crum. Although the orientation of the elements is very nosaur faunas is that the primitive hadrosaurs Bactro¬ variable, a majority of slender and elongated bones (e.g. saurus johnsoni and Gilmoreosaurus mongoliensis, char- ribs) show a NE-SW orientated long axis. This observa¬ acteristic and common in the Iren Dabasu Formation, tion corresponds well with the NE and SW ancillary flow have not been reported in the Bayn Shire Formation of Systems recognized by Currie & Eberth (1993). Pes and Mongolia; there is only mention of one undescribed manus bones are rare.