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Sinobaatar</Emphasis> Gen. Nov.: First Multituberculate from the Jehol

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Sinobaatar</Emphasis> Gen. Nov.: First Multituberculate from the Jehol gyuan, western Liaoning, China, which preserves clear Sinobaatar gen. nov.: First impressions of both dorsal and ventral sides of a subadult individual. The specimen clearly shows morphologies of multituberculate from the dentition, skull, and fore- and hindlimbs. It is the first Jehol Biota of Liaoning, representative of multituberculates in the Jehol Biota, and 1) the most complete pre-Late Cretaceous multituberculate Northeast China specimen. Most groups of Mesozoic mammals are poorly HU Yaoming1,2,3 & WANG Yuanqing1 documented; only fossil multituberculates are relatively 1. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese abundant and their dentitions display distinct evolutionary Academy of Sciences, Beijing 10044, China; trends. Therefore, the dental features of the new multitu- 2. American Museum of Natural History, New York, NY 10024, USA; berculate specimen can be used as evidence in estimating 3. Biology Program (Ecology, Evolutionary Biology, and Behavior), the geological age of the Jehol Biota through correlation Graduate School and City College, City University of New York, NY 10016, USA of mammalian fossils. Correspondence should be addressed to Hu Yaoming (e-mail: yhu@ 1 Systematic paleontology amnh.org) or Wang Yuanqing (e-mail: [email protected]) Class Mammalia Linnaeus, 1758 Abstract A multituberculate skeleton from the Lower Order Multituberculata Cope, 1884 Cretaceous Yixian Formation at Dawangzhangzi, Lingyuan Family Eobaataridae Kielan-Jaworowska, City, Liaoning Province, Northeast China, provides new Dashzeveg and Trofimov, 1987 morphological information for early multituberculates. The Sinobaatar gen. nov. specimen is the holotype of Sinobaatar lingyuanensis gen. et sp. nov. It has a narrow skull that lacks the superorbital crest Type species. Sinobaatar lingyuanensis gen. et sp. or postorbital process. The dental formula is 3·?·5·2/1·0·3·2. nov. The dental morphology, especially that of cheek teeth, of S. Diagnosis. As for the type species. lingyuanensis is similar to that of Eobaatar, which places it in Etymology. “Sino-”, Latin, China; “-baatar”, the family Eobaataridae. The postcranial skeleton of Sino- Mongolian, hero, which has been used as the suffix of baatar is similar to that of other multituberculates. As in generic names of many Asian Cretaceous multitubercu- Holotheria, Metatarsal V of Sinobaatar articulates only with lates. the cuboid and has no contact with the calcaneus, which probably represents the primitive condition of multituber- Sinobaatar lingyuanensis gen. et sp. nov. culates. Nine carpals of Sinobaatar resemble those of Zhang- heotherium, except the centrale being larger than the trape- Holotype. Skeleton of a subadult individual, pre- zoid. The dental features of Sinobaatar show again that eo- served mainly in impressions of both dorsal and ventral baatarids are obviously intermediate between Late Jurassic sides on the slate and its counterpart, respectively (Insti- multituberculates and the later forms. Because eobaatarids tute of Vertebrate Paleontology and Paleoanthropology are only known from the Early Cretaceous, the finding of catalogue number: IVPP V12517) (fig. 1; Plate ĉ). All Sinobaatar, therefore, supports that the age of the Jehol Bi- the pictures were taken from the casts. ota is most likely Early Cretaceous. Diagnosis. Narrow skull; with two infraorbital Keywords: Lingyuan, western Liaoning, Yixian Formation, Early foramina; no superorbital crest or postorbital process; Cretaceous, Jehol Biota, multituberculates, Sinobaatar. dental formula 3g?g5g2/1g0g3g2; both I1 and I2 small; I3 larger than I1-2; cusp formulae for upper cheek Multituberculates, an extinct mammalian group liv- teeth: P4, 3Ή4; P5, 3Ή5Ή4; M1, 3Ή4Ή1; M2, 1Ή3Ή41); ing from the Late Jurassic through the Paleogene, have lingual cusps of M1 obtusely conical; labial cusps of M2 morphological features intermediate between the primitive relatively low; anterior two cusps of lingual row on M2 mammaliaformes, such as the Jurassic morganucodontids, not completely separate; lower incisor conical and com- and the living therians. Their evolutionary history has pressed with complete enamel; P4 roughly rectangular in been one of the important topics about the early evolution lateral view with a slightly convex dorsal edge; P4 having [1ü3] of mammals . So far, however, most multituberculate 11 serrations and 10 ridges; a basal cuspule present on the fossils were known from the Late Cretaceous and the labial side of the crown; cusps on lower molars tending to early Cenozoic. Not much about early multituberculates close with each other; cusp formulae for lower molars: M1, has been known, and their phylogeny remains controver- 4Ή?; M2, 3Ή2; labial cusps relatively low with fine [4] sial . A multituberculate specimen was recently recov- ridges; the centrale larger than the trapezoid; metacarpal V ered from the Early Cretaceous Yixian Formation in Lin- 1) The Chinese version of this was published on Chinese Science Bulletin (2002, 46(5): 372ü386), which should be referred for citation of the naming of the genus and species. Chinese Science Bulletin Vol. 47 No. 11 June 2002 933 NOTES not contacting the triquetrum; proximal end of metatarsal lar in crown view. Its main cusp row extends from the V articulating only with the cuboid, and not in contact anterolingual corner to the posterolabial corner. The mid- with the calcaneus. dle cusp is the largest among five cusps on the main cusp Locality and age. Dawangzhangzi, Lingyuan City, row. There are three cusps labial to the posterolabial part Liaoning Province, China; Yixian Formation; Early Cre- of the main cusp row. Lingual cusps are lower than the taceous[5]. main cusps and are present at the posterolingual margin of Etymology. The species is named after Lingyuan, the tooth crown. M1 is roughly rectangular in crown view the name of the city where the type specimen was col- with a slightly convex posterior margin and a low cusp at lected. the posterolingual corner. There are four cusps on the me- Skull and lower jaw. The skull of the holotype dial row, and three on the labial row. The crown of the was crushed (Plate ĉ(a)ü(c)). The nasal is large and erupting left M2 is trapezoid in crown view, with the ante- extends to anterior margin of orbit. A large lacrimal is rior part wider than the posterior one. The labial cusp is situated at the anteromesial corner of the orbit. No postor- low and ornamented with ridges. A deep groove separates bital process is present. The lambdoid crest is profound, the lingual and medial cusp rows. while the sagittal crest and superorbital crest are not de- The lower incisor is conical and compressed trans veloped. In the ventral view, the anterior end of palatine versely. Its crown is completely covered by enamel. The 5 1 reaches the level between P and M . The suture between P2 is reduced and single-rooted. The crown of P3 is spear- the palatines and the maxillae is U-shaped. Internal nares head-like and supported by two roots. The crown of P4 is are located between the M2s. The base of zygomatic proc- 4.0mm long and 2.1mm high with a slightly convex dorsal ess of maxilla is wide, with its anterior margin external to edge. There are 11 serrations along the dorsal edge. Each P2 and posterior margin external to the middle of P5. There of them has a corresponding ridge that extends anteroven- are two infraorbital foramina external to P3 and P4. trally, except the first serration. An isolated basal cusp is The horizontal ramus of the dentary is robust with present on the labial side above the posterior root. The ventral margin of the exodaenodont lobe of P is distinct the maximum depth beneath P4 and M1. The ascending 4 ramus is slender and extends posterodorsally at about 45° and V-shaped. The left M1 is partially visible and the right to the horizontal ramus. The base of its anterior margin is one is missing. The anterior and labial margins of M1 are roughly straight. There are four cusps on the labial row. lateral to M2. The condyle is short and sturdy. Only one mental foramen is present on the lateral surface of the The anterior two cusps are pyramidal in shape. The poste- dentary. The masseteric fossa is shallow. The pterygoid rior two cusps are relatively low. The most anterior cusp shelf is relatively wide and is positioned at the ventrome- of the lingual row is at the position corresponding to the dial margin of the posterior part of the lower jaw. The groove between the anterior two cusps of the labial row. The posterior part of the lingual cusp row is invisible on mandibular foramen is below the M2 and above the ante- rior tip of the pterygoid shelf. the specimen, but it is deduced that there is one or two Dentition. The dental formula is 3g?g5g2/ more cusps. Partially exposed M2 from each side makes it possible to reconstruct its crown structure. Both the lin- 1g0g3g2 (Plate ĉ(b)ü(e)). Ornamentation on cheek gual and labial margins of its crown are straight, with the teeth is weak. labial margin being slightly longer. Its anterior margin is The crown of I1 was broken, and its root is slightly transversely straight, while the posterior margin intersects smaller than that of I2. The crown of I2 is conical, while 3 with the direction of the tooth row. The cusps on the lin- that of I expands transversely with a small posterior tu- gual row are higher than those on the labial one. There are bercle. Connecting area between premaxilla and maxilla is two cusps on the lingual row; the anterior one is higher damaged on the left side and not exposed on the right side, than the posterior. Three cusps are on the low labial row. and it is thus unknown if there is upper canine or not. All The labial cusps of M2 are low, and the cusps on lower upper premolars are double-rooted.
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