Chinese Science Bulletin 2003 Vol. 48 NO.11 1129-1134 unknown morphological information of triconodonts. Its presence in Jehol Biota also helps us to estimate the age of A new species of Gobiconodon the biota. (Triconodonta, Mammalia) I Systematic paleontology Manunalia Linnaeus, 1758 and its implication for the Triconodonta Osborn, 1888[8,9] Gobiconodontidae Chow and Rich, 1984[10] age ofJehol Biota* Gobiconodon Trofimov, 1978 1 Gobiconodon zofiae sp. nov. LI Chuankui , WANG Yuanqing 1, HU Yaoming 1,2,3 2 Diagnosis. A gobiconodont similar to G borissiaki & MENG Jin in size; skull narrow and elongated; dental formula 1. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese 2'1'4'4/1'1'4'5; upper molariforms with distinct cingula, Academy of Sciences, Beijing 100044, China; cusps A, Band C aligned anteroposteriorly; cusps E and F 2. American Museum ofNatural History, New York, NY 10024, USA; prominent but cusp D degenerated; cingulids of lower 3. Biology Program (Ecology, Evolutionary Biology, and Behavior), Graduate School and City College, City University ofNew York, NY molariforms indistinct; cusp b smaller than cusp c; cusp e 10016, USA distinct and cusp f absent; infraorbital foramen posteriorly 2 Correspondence should be addressed to Li Chuankui (e-mail: li.chuankui located above M ; branches II and III of the trigeminal @pa.ivpp.ac.cn) nerve having a common exit on anterior lamina of petrosal; Abstract A new species ofGobiconodon is found from the the dentary with four mental foramina; the ossified Yixian Formation ofwestern Liaoning, China. The new taxa, Meckel's cartilage present on the medial surface of the G zofiae sp. nov., has a confluent opening for branches II dentary. and III of the trigeminal nerve on the anterior lamina of the Holotype. A skull, with right half damaged, and petrosal. G zofiae sp. nov. is similar to Repenomanms in hav­ associated lower jaws of the same individual (Institute of ing an ossified Meckel's cartilage connecting the lower jaws 1 Vertebrate Paleontology and Paleoanthropology catalogue and ear region. The new species, with enlarged 1 /11, posteri­ number: IVPP V12585, Fig. 1). orly located infraorbital foramen and four mental foramina, Locality and age. Lujiatun, Shangyuan, Beipiao distinctly differs from the other species of Gobiconodon. The new material indicates that Gobiconodon has four, not five, City, Liaoning Province, China; First Member of the upper molariforms. The presence of Gobiconodon in Jehol Yixian Formation; Early Cretaceous[ll]. Biota makes it possible to correlate Jehol Biota with faunas Etymology. The species is named after the first in eastern Asia and North America, and suggests the age of name of Polish paleontologist Prof. Dr. Zofia Kielan­ the Yixian Formation to be Early Cretaceous. Jaworowska, a contemporary leading expert on Mesozoic Keywords: Jehol Biota, Triconodont, Gobiconodon, cranium, Early mammals. She was awarded the Romer-Simpson Medal Cretaceous. by the Society of Vertebrate Paleontology (N. A.) in 1995. DOl: lO.1360/02wd0134 Skull. The preserved skull is about 45 mm long. The left side of the skull is squished while the right side is The two thirds of mammalian evolutionary history totally damaged. Most sutures between bony elements are are within Mesozoic[l], but fossils of Mesozoic mammals indiscernible. The skull is narrow and elongated. The ba­ are sparse and mostly fragmentary. Since the publication sicranial portion is 26.5 mm long (from posterior side of of Owen's monograph on Mesozoic mammals in 1871[2], M4 to the posterior edge of condyle). The facial portion is only a few complete skeletons of Mesozoic mammals about 18.5 mm long. The length ratio between basicranial have been found in the world. In recent years, however, and facial portions (about 1.4) is the largest among complete skeletons of four kinds of Mesozoic mammals Mesozoic mammals. In other Mesozoic mammals with were found in Jehol Biota, including the symmetrodont relatively long basicranial portion, such as Vincelestes[12] Zhangheotherium[3], triconodont Jeholedens[4] and Repe­ and Repenomamus, the corresponding ratio is about 1.1. nomamus[5,6], and multituberculate Sinobaatar[7]. Except On the palate the suture between the maxilla and palatine 4 Repenomamus, specimens of the other three mammals are is anterior to M . The posterior edge of the major palatine crushed and partly exposed. Like those of Repenomamus, foramen is just posterior to the suture, but the foramen a newly found skull of a smaller triconodont is preserved itself is damaged on each side. There are four large em­ three-dimensionally. The specimen represents a new spe­ brasures on the palate surface of the maxilla, just medial cies of Gobiconodon and provides some previously to the molariforms. Each of embrasures is posteromedial

* The Chinese version ofthis paper was published on Chinese Science Bulletin (in Chinese), 2003, 48: 177-182, which should be referred for citation ofthe naming ofthe new species, Gobiconodon zofiae sp. nov.

Chinese Science Bulletin Vol. 48 No. 11 June 2003 1129 REPORTS

Fig. 1. Gobiconodon zofiae sp. nov. IVPP V12585, Holotype. 1, Left view ofthe skull; 2, ventral view ofthe skull; 3, lateral view ofthe left dentary; 4, medial view ofthe left dentary. e.f, Ethmoidial foramen; fps.r.o., foramen pseudorotundum ovale; fl.p., posterior lacerate foramen; fen.o., fenestra ovale; infra.f, infraorbital foramen; Ltr., lateral trough; OMC, ossified Meckel's cartilage; opt.f, optical foramen; pal.emb., palatine embrasure; prom., promontorium; sph.fis., sphenoidal fissure; spl.f, sphenopalatine foramen.

1130 Chinese Science Bulletin Vol. 48 No. 11 June 2003 to each tooth; the one posteromedial to M2 is the largest. pression, at the tip ofthe pterygoid fossa is the mandibular 4 There is also a small embrasure medial to the p . The foramen, with a diameter about 1.4 mm. Anterior to the posterior edge ofthe palatine is tongue-like and extends to foramen is the main part of the meckelian groove, which the level of the sphenoidal fissure. The pterygoids are extends anteriorly on the internal surface of the dentary. largely damaged on both sides, but the bases ofbifurcated The groove gradually attenuates anteriorly, and reaches pterygoid plates are visible. Both basisphenoid and the posterior edge of the symphysis. No evidence indi­ basioccipital are elongated. The infraorbital foramen is cates the presence ofthe coronoid. 2 located just above M . The posterior opening of the in­ Dentition. The II is only partially preserved. It 2 2 fraorbital canal is low in the orbit. The facial process of seems larger than the 1 . 1 is single-cusped, with the tip the lacrimal is large. There is a large lacrimal foramen on curved posteriorly. The single-rooted upper canine is lar­ 2 2 the anterior edge ofthe orbit. The orbit is moderate in size, ger than 1 and p . The pI is broken. It is a small sin­ with a weak postorbital process. There is a large round gle-rooted tooth, judged from its alveolus. The sin­ optical foramen below the postorbital process. Posterior to gle-rooted p2 is slightly smaller than 12 in size, with an the optical foramen, there is a vertical artificial fissure incipient cingulum. The large p3 is double-rooted, and as extending to the bottom of the orbit. The foramen at the high as the MI. It has a small cusp posterior to the main top ofthat fissure is probably the ethmoidial foramen, and cusp. The p 4 is double-rooted and sub-molariform. Its size the opening at the bottom of the fissure is part of the is less than one third ofthat ofthe MI. Its crown is as high breakage. The sphenopalatine foramen is anterior on the as cusp E of MI. The main cusp occupies most portion of bottom of the orbit. The sphenoidal fissure is large. A the crown. There are one anterior cusp and one posterior large foramen, 2 mm in diameter, is present on the ante­ cusp, with the anterior one being larger. Molariforms are rior lamina of the petrosal, 5 mm posterior to the sphe­ aligned anteroposteriorly. MI is oval in crown view and noidal fissure. There is a groove-like impression extend­ narrower than the M2 and M3. Its cusps A, B and Care ing anteriorly from the foramen. The foramen is probably aligned anteroposteriorly. Cusp A is damaged; its pre­ the confluence of foramen pseudorotundum and foramen served base indicates it as the largest cusp of the tooth. 4 pseudovale, the common exit of the second (V2) and third Cusp B buttresses the posterior cusp of the p . The cin­ (V3) branches of the trigeminal nerve. There is a deep gulum surrounds the crown, with cusps E, F and D being lateral trough between the anterior lamina and the prom­ at the anteromedial, anterolateral and posterior comer, ontorium of the petrosal. The promontorium is elongated respectively. Among them, cusp E is the largest, while cone-shaped. The long diameter of the fenestra ovale is cusp D the smallest. The crown structure of the M2 and about 0.7 mm. The bones lateral to the fenestra are dam­ M3 is similar to that of MI. Cusp B of M2 is smaller than aged. The perilymphatic foramen is located in a deep cusp C. The wear facet medial to cusp B faces anterome­ fossa. The posterior lacerate foramen is Z-shaped due to dially, while the facet medial to cusp C faces posterome­ the shifting ofthe petrosal. dially. Cusps E and F are large, and cusp D is quite small. Lower jaw. The horizontal ramus of the dentary is The cingulum ofthe M2 is more developed than that ofMI. slender. The preserved portion is 38 mm long, and 4.8 mm There are several cuspates on the lateral and posterome­ 3 high at MI. The low edge ofthe dentary is largely straight. dial portions of the cingulum. M is the widest among The anterior tip of the bone extends anterodorsally. There upper molariforms. Its crown structure is almost identical 2 are four mental foramina on the lateral surface of the den­ to that of the M , except that its lateral cingulum is wider, tary, with each being under canine, P3,P4, and M2, respec­ and there are six distinct accessory cusps on the lateral tively. The masseteric fossa on the lateral surface of the cingulum. The M4 is the smallest among upper molari­ dentary is deep and extends anteriorly to a point just pos­ forms. Its posterior part is degenerated. The anterior part terior to the M4. The low edge of the fossa broadens. The of the crown is damaged. Cusp C is small. Cusp D is ab­ symphysis of the dentary extends posteriorly to the level sent. There is a cingulum surrounding the posterior part of between P2 and P3. The pterygoid fossa on the medial sur­ the crown. Among upper molariforms the degree of worn face of the dentary is shallow. A partially preserved ossi­ increases posteriorly. fied Meckel's cartilage is preserved anteroventral to the The lower incisor (II) is large. Its crown is damaged pterygoid fossa. The preserved ossified cartilage is 1.3 and the cross-section is oval, with the long diameter being mm thick and about 8 mm long. Both anterior and poste­ 1.9 mm. The lower canine is cone-shaped. Its crown is rior ends of the cartilage are damaged. An impression, curved posteriorly, with two vertical crests along the me­ where the anterior part of the cartilage contacts the den­ dial side. The PI-P3 are single-rooted. The PI is similar tary in life, is visible just anterior to the place the pre­ to the lower canine in size and shape. The P2 is conical. Its served portion of the cartilage attaches the dentary. This crown is medially curved, with weak anterior and poste­ impression can be regarded as a part of meckelian groove rior cingulids. The P3is as high as the P2, and slightly lar­ system. Similar impression is visible on the dentary of ger than the latter. It has a distinct posterior cuspid and a I3 Gobiconodon hoburensis (PPS 1O-37ci ]. Above the im- weak internal cingulid. The double-rooted P4 is molarized.

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It is as long as P3, but only half as high as the latter. The has a high cusp b; the dentary has three mental foramina anteriorly located cusp a occupies more than half of the and is thickened anteriorly; the infraorbital foramen is crown. Cusp b is small and low. Cusp c is relatively large located anteriorly. The size of G ostromi is about twice and separated from cusp a by a groove. The internal cin­ that ofthe new specimen, and its II is smaller than 12[14]. gulid is weak. The lower molariforms have similar crown G zofiae has ossified Meckel's cartilage preserved structure. The cingulids are not developed on lower mo­ medial to the dentary, and there is no indication on the lariforms. Cusp a of MIis very large. Cusp c is larger than dentary for the attachment of postdentary elements, which cusp b, both being separated from cusp a by a deep groove. makes it clear that ear ossicles are separated from lower Cusp d is small. The tiny cusp e is medial to cusp b. There jaw. This condition is similar to that of Repenomamus, is no cusp f. There is no visible wear facet on MI. The M2 another triconodont mammal from the same locality[6]. is larger than MI. Its cusp e is distinct; and there is a weak The presence of ossified Meckel's cartilage indicates that wear facet anterolateral to cusp a. The M3 is larger than in the early history of mammalian evolution not only the M2, with cusp e developed. There are distinct wear facets posterior end of the Meckel's cartilage is ossified as on the lateral sides of cusps a and b. The M4is the largest malleus, its middle portion is also ossified as a slender and most worn among lower molariforms. It has well bony bar that connects the lower jaw and ear region. For developed cusps d and e. A large wear facet is developed extant mammals, the Meckel's cartilage also bridges lateral to the deeply worn cusp b and facets slope anter­ lower jaw and ear region in the early stage of develop­ olaterally. The M s is the smallest among lower molari­ ment, but only its posteriorly end is ossified as malleus forms. The wear facet on the tip ofcusp a is not developed, latterly. The presence of ossified Meckel's cartilage in but the wear facet lateral to cusp b is large, extending to early mammals indicates that in these mammals the the root. Although cusp f is indiscernible on lower mo­ meckelian groove of the dentary is not for postdentary lariforms, these teeth are still tightly locked, as those of elements, which are precursors of mammalian ear ossicles. other Gobiconodon species. The degree of worn from The presence of ossified Meckel's cartilage in early slight to deep is MI-M2-M3-Ms-M4. The occlusal rela­ mammals is the direct evidence for the origin of definitive tionship between upper and lower dentitions of G zofiae is mammalian middle ear. similar to that of G hoburensis[13], in that cusp A of an G zofiae has very small but molarized and dou­ upper tooth occludes laterally between cusps a and b of a ble-rooted p4 and P4. On the lower jaw of G hoburensis posterior lower tooth, while cusp B occludes with cusp c (PSSlO-37a) the P4 has been shed, but its alveolus indi­ of the corresponding lower tooth. Therefore, there are five cates double-rooted condition, different from sin­ lower molariforms but only four upper ones in G zofiae, gle-rooted conditions of preceding teeth. The P4 of G bo­ which differs from the reconstruction by Kielan­ rissiaki (PSSlO-15a) is also molarized, but has only a sin­ Jaworowska and Dashzeveg Fig. 8 of ref. [13]) for Gobi­ gle root. G ostromi has two specimens showing different conodon based on fragmentary material. In their recon­ conditions. MCZ 19806 has a single-rooted P4on the right struction, there are five upper molariforms. side, but double-rooted P4on the left side. MCZ19965 has 2 Comparison and discussion no P4 but a diastema at its place. The differences in the development of P4 among different specimens of Gobi­ The new species (Gobiconodon zofiae sp. nov) conodon may indicate different ontogenetic stages. shows diagnostic dental characteristics of Gobiconodon, The finding of G zofiae also helps us to reconstruct but also has distinct differences from other species of the genus[13,14]. It is similar to G borissiaski in size, but has the dental formula of the genus. All upper jaw material of double-rooted P4; its lower molariforms have no cusp f; its previously known species of the genus is fragmentary. upper molariforms have cusps A, Band C aligned antero­ The dental formulae for these species are only partially posteriorly; the dentary has four mental foramina; the in­ known. The dental formula is 7·7·7'5/1'1'4·7 for G boris­ fraorbital foramen is posteriorly located. G hoburensis is siaki; 7·7'4'5/1'1'4'5 for G hoburensi; and 2·1-7·7/1'1-3­ much smaller than the new species; and the cusps of its 4·5 for G ostromi. Based on these three species, the lower lower molariforms are incompletely differentiated; its MI dental formula of the genus is 2'1'3-4'5, which is

Table 1 Measurements ofthe dentition ofGobiconodon zofiae sp. nov. IVPP V12585 (in mm) 12 C p 2 p 3 p4 M' M2 M3 M4 I'-M4 LWLWLWLWLWLWLWLWLWL 1.25 0.70 1.75 0.95 1.15 0.70 2.05 0.85 1.10 0.65 2.50 1.60 2.55 1.65 2.60 1.85 2.00 1.60 18.60

I, C P, P2 P3 P4 M, M2 M3 M4 Ms I,-M ------s DDDD LWLWLWLWLWLWLWL 1.90 1.05 0.85 1.15 1.25 1.00 1.25 0.55 2.30 0.90 2.30 0.95 2.50 1.05 2.55 1.00 1.95 0.75 20.30 L, Length; W, width; D, diameter.

1132 Chinese Science Bulletin Vol. 48 No. 11 June 2003 confirmed by the complete dentition of G zofiae. But be­ The Khoboor fauna has two species of Gobiconodon, G fore the discovery of G zofiae, the information about the borissiaki and G hoburensis[13,18]. The age of the fauna is upper dentition of the genus is insufficient. The idea that considered late Aptian or early Albian. One specimen of G Gobiconodon has five upper molariforms is based on borissiaki is from Ilek Layer of Siberia, which is Neoco­ reconstruction of fragmentary specimens[13,14]. The com­ mian or Aptian to Albian in age[19]. G ostromi is from plete dental material of V 12585 indicates that the upper Cloverly Formation of Montana in North America; its age dental formula of Gobiconodon is 2·1·3-4·4. is also Aptian to Albian[20,21]. Some unidentified speci­ In V 12585, there is only one foramen on the anterior mens of Gobiconodon are also found from Mazhongshan lamina of the petrosal, and there is a groove-like impres­ area, Gansu, China[22]. The fauna is believed Barremian to sion extending anteriorly from the foramen, which sug­ Albian in age. G hopsoni is based on a fragmentary gests that the foramen provides exit for V2. But there is no specimen from Ashile, Mongolia, which probably belongs other foramen for the exit of V3 in this area. Therefore, it to Valanginian[23]. A lowerjaw with a fragmentary M2was is quite probably that V2 and V3 share the same foramen, described by Godefroit and Guo [24] as a new genus and so called foramen pseudorotundum-ovale, as their com­ species, Hangjinia chowi, from Early Cretaceous of mon exit. The condition in Gobiconodon is different from Hangjin Qi, Inner Mongolia, China. As pointed out by that of all other Mesozoic mammals, in which V2 and V3 Rougier et al., Hangjinia is a derived gobiconodontid, exit the braincase separately[17]. In many Late Cretaceous rather than an aberrant one as originally proposed[23]. So mammals, V2 exits through the anterior lacerate foramen, all of the fossil record indicates that the stratigraphic dis­ V3 exits through the foramen ovale in pterygoid region. tribution of Gobiconodon is limited in middle to late Early Hopson and Rougier speculated that triconodonts, similar Cretaceous (Table 2). G zofiae is from First Member of to monotremes and multituberculates, have V2 existing the Yixian Formation[25,26]. The overlying basaltic andesite through the anterior lacerate foramen while V3 through from the Second Member of the formation has yielded an 39 the foramen pseudovale[17]. The condition in Gobiconodon, average 4°Ar; Arage 0 f 128.2 ± 0.8 Ma, which. suggests which is a member of triconodonts, does not support this that the age of the First Member is possibly around 130 speculation. Similar condition is also found in advanced Ma[27]. In western Liaoning area, Tuchengzhi Formation cynodonts[17], which possibly suggests that Gobiconodon uncomformably underlies the Yixian Formation. Single retains a primitive character state. The skull of V 12585 is crystal total fusion 40ArP9Ar analyses of the Tuchengzhi long and narrow. The length ratio between its basicranial sanidine gave a mean age of 139.4 ± 0.19 Ma[28]. Based on and facial portions is similar to those of some extant in­ these data, it seems reasonable to assign the First Member sectivores, such as Talpa, and larger than that of all other of the Yixian Formation to Hauterivian (132 ± 1.9 -127 known Mesozoic mammals. Its functional implication ± 1.6 Ma, in late Neocomian) [29]. The mammal fossil evi­ needs further study. dence is congruent with the isotopic dating, which further The presence of Gobiconodon in Jehol Biota helps supports that the Yixian Formation and its fossil assem­ us to estimate the age of the biota. Among known verte­ blage is Early Cretaceous in age, rather than Late Jurassic, brates of Jehol Biota, Gobiconodon is the only named as argued by some studies[30]. Recent study on some in­ genus present in both parts of Asia and North America. vertebrate fossils reaches a similar conclusion[31].

Table 2 Geologic and geographic distribution of Gobiconodonts in the world Taxon Material Horizon and locality Age Author(s) Reference Gobiconodon 10 upper and Khoboor, Mongolia Aptian-Albian (K,) Trofimov (1978) [18] borissiaki lower jaws Guchinodon 21 upper and Khoboor, Mongolia Aptian-Albian (K,) Trofimov (1978) [18] hoburensis lower jaws Gobiconodon 2 incomplete Cloverly Fm., Montana, Aptian-Albian (K,) Jenkins & Schaff(1988) [14] ostromi skeletons USA ?Gobiconodon 1 fragmentary Siberia, Russia Neocomian - Albian Maschenko & Lopatin (1998) [19] borissiaki lower jaw Gobiconodon 3 upper and Kielan-Jaworowska & Khoboor, Mongolia Aptian - Albian (K,) [13] borissiaki lower jaws Dashzeveg (1998) fragmentary lower Ejinhoro Fm., Hangjin Hangjinia chowi Early Cretaceous Goefroit & Guo (1999) [24] jaw with M 2 Qi, Inner Mongolia, China Gobiconodontidae damaged skull Xinmingbao Group, Late Barremian-Aptian Tang et al. (2001) [22] indet. and teeth Mazongshan, Gansu, China (K,) Gobioconodon 2 upper and ?Vanginian-Neocomian Oshih (Ashile), Mongolia Rougier et al. (2001) [23] hopsoni lower jaws (K,) 2 fragmentary ?Vanginian-Neocomian Gobiconodon sp. Oshih (Ashile), Mongolia Rougier et al. (2001) [23] lower jaws (K,) Gobiconodon partial skull and First Member ofthe Yixian Hauterivian (K,) Li et al. (2002) this paper zofiae lower jaws Fm., Liaoning, China

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culates, Monotremes, Early Therians and Marsupials (eds. Szalay, Acknowledgements Drs. Xu Xing, Wang Xiaolin, Zhou Zhonghe, Zhang Fucheng, and others who involving in the Jehol Biota Project of F. S., Novacek, M. 1., McKenna, M. C.), New York: Springer­ the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Verlag Press, 1993,95-107. Academy of Sciences, helped collecting the specimen. Mr. Xie Shuhua 16. Kermack, K. A., Mussett, F. L. S., Rigney, H. w., The skull of prepared the specimen. Zhang Fucheng helped taking the photos. The Morganucodon, Zool. 1. Linn. Soc., 1981,71: 1-158. authors are also grateful to Profs. Chang Meemann and Li Jinling for their critical reading ofthe original manuscript. This work was supported 17. Hopson, 1. A., Rougier, G w., Braincase structure in the oldest by the Major Basic Research Project of the Ministry of Science and known skull of a therian mammal: implications for mammalian Technology of China (Grant No. G2000077700), the National Natural systematics and cranial evolution, Amer. 1. Sci., 1993, 293-A-A: Science Foundation of China (Grant No. 49832020), and the Chinese 268-299. Academy of Sciences (Grant No. KZCX3-J-03). 18. Trofimov, B. A., The first triconodonts (Mammalia, Triconodonta) References from Mongolia, Dokl. Akad. Nauk. SSSR, 1978,243: 213-216.

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1134 Chinese Science Bulletin Vol. 48 No. 11 June 2003