A New Middle Jurassic Diplodocoid Suggests an Earlier Dispersal and Diversification of Sauropod Dinosaurs
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ARTICLE DOI: 10.1038/s41467-018-05128-1 OPEN A new Middle Jurassic diplodocoid suggests an earlier dispersal and diversification of sauropod dinosaurs Xing Xu1, Paul Upchurch2, Philip D. Mannion 3, Paul M. Barrett 4, Omar R. Regalado-Fernandez 2, Jinyou Mo5, Jinfu Ma6 & Hongan Liu7 1234567890():,; The fragmentation of the supercontinent Pangaea has been suggested to have had a profound impact on Mesozoic terrestrial vertebrate distributions. One current paradigm is that geo- graphic isolation produced an endemic biota in East Asia during the Jurassic, while simul- taneously preventing diplodocoid sauropod dinosaurs and several other tetrapod groups from reaching this region. Here we report the discovery of the earliest diplodocoid, and the first from East Asia, to our knowledge, based on fossil material comprising multiple individuals and most parts of the skeleton of an early Middle Jurassic dicraeosaurid. The new discovery challenges conventional biogeographical ideas, and suggests that dispersal into East Asia occurred much earlier than expected. Moreover, the age of this new taxon indicates that many advanced sauropod lineages originated at least 15 million years earlier than previously realised, achieving a global distribution while Pangaea was still a coherent landmass. 1 Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology & Paleoanthropology, Chinese Academy of Sciences, 100044 Beijing, China. 2 Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK. 3 Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK. 4 Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK. 5 Natural History Museum of Guangxi, 530012 Nanning, Guangxi, China. 6 Lingwu National Geopark Administration, 750400 Lingwu, Ningxia, China. 7 Lingwu Historic Relic Administration, 750400 Lingwu, Ningxia, China. These authors contributed equally: Xing Xu, Paul Upchurch, Philip D. Mannion Correspondence and requests for materials should be addressed to X.X. (email: [email protected]) NATURE COMMUNICATIONS | (2018) 9:2700 | DOI: 10.1038/s41467-018-05128-1 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-05128-1 auropods were gigantic long-necked herbivorous dinosaurs Horizon and locality: Yanan Formation, late Early to early that dominated many Jurassic and Cretaceous terrestrial Middle Jurassic (late Toarcian–Bajocian), Lingwu Geopark, near S 1,2 2 faunas . Although sauropods were globally distributed , Ciyaopu, Ningxia Hui Autonomous Region, China. several subgroups displayed restricted geographic ranges that Diagnosis: Autapomorphies: prefrontal anterior process directed potentially reflect endemism caused by the fragmentation of laterally; orbital dorsal margin strongly ornamented by deep, Pangaea3. The absence of Diplodocoidea from the otherwise rich longitudinal grooves and tubercles; long-axes of the free tips of sauropod faunas of East Asia has thus been interpreted as a the basal tubera directed anteromedially; capitate process genuine biogeographic pattern4–6. mediolaterally long (length:height ratio c. 5.0); occipital condyle From 2005 onward, we organised four excavations at a new articular surface wide transversely (width:height ratio c. 1.54); dinosaur site in the lower Middle Jurassic Yanan Formation at lateral surface of cervical prezygapophyseal process bears a ridge Ciyaopu, Lingwu, Ningxia Hui Autonomous Region, northwest formed by a linear array of tubercles; subcircular facet-like region China (Supplementary Notes 1 and 2, Supplementary Fig. 1), at the summit of metapophyses in middle cervical-anterior dorsal which resulted in the discovery of fossil material comprising vertebrae; small process projects anterodorsally from the anterior 7–10 partial skeletons (including portions of two skulls), ran- margin of the transverse process, near its distal end, in anterior ging from juveniles to adults. Here, we name a new sauropod dorsal vertebrae; anterior dorsal metapophyses twisted along their based on this material, and demonstrate that it is, to our length; anterior caudal neural spines bear subtriangular facet-like knowledge, the earliest diplodocoid (and therefore also the areas, extending from summit to spine mid-height. earliest neosauropod) sauropod, and the first from East Asia (Supplementary Notes 3–7). This discovery has major impli- cations for calibrating the timing of neosauropod diversifica- Description tion, provides the first insight into a previously hidden aspect of Cranial material includes the skull roof, occiput, and braincase their evolutionary history, and questions East Asia’shypothe- (Fig. 1, Supplementary Fig. 2). As in dicraeosaurids7,8, the frontals sized status as an isolated island continent during the Jurassic are co-ossified along the midline. Supratemporal fenestrae are (Supplementary Notes 4–7). large and open dorsolaterally: this is the plesiomorphic state and contrasts with the reduced openings in many other dicraeosaurids and rebbachisaurids7,8. The frontoparietal suture is located mid- Results way between the anterior and posterior margins of the supra- Systematic paleontology. temporal fenestrae, as in advanced dicraeosaurids and some diplodocids9. There is a hook-like posteroventrally-directed pro- Sauropoda Marsh, 1878 cess on the main body of the squamosal, as is also seen in a mild form in the diplodocid Kaatedocus, and prominently in Neosauropoda Bonaparte, 1986 – Diplodocoidea (Marsh, 1884) dicraeosaurids7 9. In lateral view, the squamosal ventral process Dicraeosauridae Janensch, 1929 projects anteroventrally, implying the presence of an ante- Lingwulong shenqi gen. et sp. nov. roventrally oriented quadrate and a long slit-like lower temporal opening, as is typical for diplodocoids2,7. The postorbital ventral Etymology: Lingwu, after the region where the specimens were process has a subtriangular transverse cross-section. This process found; long, the Mandarin Chinese for ‘dragon’; and shenqi, the is not strongly compressed anteroposteriorly, which is highly Mandarin Chinese for ‘amazing’,reflecting the unexpected unusual for a eusauropod1, though this morphology also occurs discovery of a dicraeosaurid in the Middle Jurassic of China. in the rebbachisaurid Limaysaurus (MUCPv-205). As in Holotype: Lingwu Museum (LM) V001a, a partial skull dicraeosaurids7, the sagittal crest on the supraoccipital is pro- comprising the braincase, skull roof, and occiput, and an minent and plate-like in Lingwulong. Suuwassea10, Amargasaurus associated set of dentary teeth (Fig. 1), found in quarry II. (MACN N-15), and Lingwulong (but not Dicraeosaurus and other Paratype: Lingwu Geopark (LGP) V001b. A semi-articulated sauropods) possess a deep slot-like fossa on the occiput, lateral to partial skeleton including a series of posterior dorsal vertebrae, the proatlantal facets (Fig. 1). Basal tubera are prominent, unlike complete sacrum, the first caudal vertebra, partial pelvis, and the derived state in rebbachisaurids such as Limaysaurus and incomplete right hind limb. The holotypic braincase was found Nigersaurus, where they are very reduced7. Above the basipter- close to the anterior end of the dorsal series and the right ygoid process, the left otosphenoidal ridge bears the broken base scapulocoracoid, suggesting that they potentially belong to the of a dorsoventrally flattened ‘leaf’-like process, a derived state in same individual. However, we conservatively treat them as dicraeosaurids2,8. In lateral view, with the skull roof horizontal, separate individuals because the skull was not found in close the broken bases of the basipterygoid processes project ante- association with cervical elements, and because there are other roventrally at approximately 45° (Fig. 1), as in flagellicaudatans individuals nearby within the quarry. and some titanosaurs2,8,11. Unlike most sauropods, but similar to Referred specimens: Institute of Vertebrate Paleontology and dicraeosaurids2,8, there is a deep slot-like channel on the ventral Paleoanthropology (IVPP) V23704, 29 dentary teeth preserved in midline of the basisphenoid of Lingwulong, extending between a ‘U’-shaped arc; LGP V002, a partial skeleton including several the bases of the basipterygoid processes. IVPP V23704 preserves dorsal and caudal vertebrae, both scapulocoracoids, partial 29 teeth in a ‘U’-shaped arc (Fig. 1, Supplementary Fig. 3), sug- forelimbs, and partial pelvis; LGP V003, a partial skeleton gesting that the whole set either became detached from the jaw as including a nearly complete dorsal series and sacrum, two a unit, or that jaw elements decayed, leaving the teeth in situ. This anterior caudal vertebrae, and both ilia; LGP V004, a small is probably a reliable indication that the jaw margin was not individual represented by an anterior cervical vertebra, an square, unlike those of most other diplodocoids2,8,12. We tenta- anterior dorsal vertebra, and right tibia; LGP V005, a partial tively identify these as dentary teeth, based on distolabially facing skeleton preserving the sacrum, pelvis, and a semi-articulated wear facets: this would mean that there were ~15 dentary series of 25 anterior and middle caudal vertebrae; LGP V006, a teeth in life. Wear facets resemble those of diplodocoids, partial skeleton preserving several cervical vertebrae, incomplete being typically set at ≥45° to the apicobasal axis7. As in other scapulae and complete coracoids,