Cranial material includes the skull roof, occiput, and braincase (Fig. 1, Supplementary Fig. 2). As in dicraeosaurids7,8, the frontals are co-ossified along the midline. Supratemporal fenestrae are 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 midway between the anterior and posterior margins of the supratemporal fenestrae, as in advanced dicraeosaurids and some diplodocids9. There is a hook-like posteroventrally-directed process on the main body of the squamosal, as is also seen in a mild form in the diplodocid Kaatedocus, and prominently in dicraeosaurids7,8,9. In lateral view, the squamosal ventral process projects anteroventrally, implying the presence of an anteroventrally oriented quadrate and a long slit-like lower temporal opening, as is typical for diplodocoids2,7. The postorbital ventral process has a subtriangular transverse cross-section. This process is not strongly compressed anteroposteriorly, which is highly unusual for a eusauropod1, though this morphology also occurs in the rebbachisaurid Limaysaurus (MUCPv-205). As in dicraeosaurids7, the sagittal crest on the supraoccipital is prominent and plate-like in Lingwulong. Suuwassea10, Amargasaurus (MACN N-15), and Lingwulong (but not Dicraeosaurus and other sauropods) possess a deep slot-like fossa on the occiput, lateral to the proatlantal facets (Fig. 1). Basal tubera are prominent, unlike the derived state in rebbachisaurids such as Limaysaurus and Nigersaurus, where they are very reduced7. Above the basipterygoid process, the left otosphenoidal ridge bears the broken base of a dorsoventrally flattened ‘leaf’-like process, a derived state in dicraeosaurids2,8. In lateral view, with the skull roof horizontal, the broken bases of the basipterygoid processes project anteroventrally at approximately 45° (Fig. 1), as in flagellicaudatans and some titanosaurs2,8,11. Unlike most sauropods, but similar to dicraeosaurids2,8, there is a deep slot-like channel on the ventral midline of the basisphenoid of Lingwulong, extending between the bases of the basipterygoid processes. IVPP V23704 preserves 29 teeth in a ‘U’-shaped arc (Fig. 1, Supplementary Fig. 3), suggesting that the whole set either became detached from the jaw as a unit, or that jaw elements decayed, leaving the teeth in situ. This is probably a reliable indication that the jaw margin was not square, unlike those of most other diplodocoids2,8,12. We tentatively identify these as dentary teeth, based on distolabially facing wear facets: this would mean that there were ~15 dentary teeth in life. Wear facets resemble those of diplodocoids, being typically set at ≥45° to the apicobasal axis7. As in other diplodocoids, tooth crowns do not overlap each other in an imbricate arrangement1,2. The lingual surface of the crown is convex mesiodistally, creating an elliptical horizontal cross-section, a derived state that occurs convergently in diplodocoids and titanosaurs1,2.

The true number of cervical, dorsal, and caudal vertebrae in Lingwulong is unknown, although we estimate 11–12 dorsals. As in dicraeosaurids7, the ventral surfaces of the cervical centra are deeply excavated anteriorly to produce a pair of pneumatic fossae separated by a prominent midline keel (Supplementary Fig. 4). A deep lateral pneumatic opening is present on the anterior cervical centra, but is shallow or absent in more posterior cervical and dorsal vertebrae. Although the absence of deep lateral pneumatic openings in presacral centra is plesiomorphic for sauropods1,2, this also occurs as a derived reversal in dicraeosaurids7. In Lingwulong cervical centra, a small accessory fossa is located posteroventral to the main lateral pneumatic fossa (Supplementary Fig. 4). This feature has previously been reported only in diplodocids7,8,9, but it is also variably present in the dicraeosaurid Amargasaurus (MACN N-15). Neural spines are bifurcated from the middle cervical vertebrae to approximately dorsal vertebra 5. Cervical neural spines lack the extreme elongation seen in more advanced dicraeosaurids such as Dicraeosaurus and Amargasaurus7,13,14. In lateral view (Fig. 2), there is a deep ‘U’-shaped notch between the prezygapophyses and anterior spine margin, and the angle between the postzygodiapophyseal lamina (PODL) and spinopostzygapophyseal lamina (SPOL) is ~90°; both features being characteristic of dicraeosaurids13,14. The metapophyses of Lingwulong are directed dorsally to create a deep and transversely narrow ‘V’-shaped notch, an intermediate condition between that seen in most sauropods with bifid presacral spines and the extremely tall and narrow notch in advanced dicraeosaurids2,14. Lingwulong possesses the derived shortened cervical ribs seen in other diplodocoids7,8,9.

Fig. 2 Skeletal reconstruction and exemplar skeletal remains of Lingwulong shenqi. Silhouette showing preserved elements (a); middle cervical vertebra in left lateral (b) and anterior (c) views; anterior dorsal vertebra in left lateral (d) and anterior (e) views; posterior dorsal vertebra in lateral view (f); sacrum and ilium in left lateral view (g); anterior caudal vertebra in left lateral (h) and anterior (i) views; right scapulocoracoid in lateral view (j); right humerus in anterior view (k); left pubis in lateral view (l); right ischium in lateral (m) views; right femur in posterior view (n); and right tibia in lateral view (o). Abbreviations: ap, ambiens process; ar, acromial ridge; ip, iliac peduncle; naf, notch anterior to glenoid; np, neural spine; podl, postzygodiapophyseal lamina; ppr, prezygapophyseal process ridge; prp, prezygapophysis; pvf, posteroventral fossa; slf, shallow lateral fossa; spol, spinopostzygapophyseal lamina; sprl, spinoprezygapophyseal lamina; wls, wing-like structure. Scale bars = 100 cm for a and 5 cm for b–o Full size image

Anterior dorsal centra are strongly opisthocoelous, but from approximately dorsal vertebra 4 onwards they become amphicoelous, as in other diplodocoids8. Posterior dorsal neural spines are tall (spine:centrum height ~2.0), with spine height increasing towards the sacrum (Fig. 2). Such tall dorsal neural spines are a synapomorphy of Diplodocoidea, although in advanced dicraeosaurids (e.g., Dicraeosaurus) the spine:centrum height ratio increases to ~4.01,2,7,8,9. In middle dorsal vertebrae, the spines have a ‘paddle’-shaped morphology, in which their lateral margins gradually flare outwards as they approach the transversely rounded summit (Fig. 2, Supplementary Fig. 5), a derived condition seen in the middle and posterior dorsal spines of rebbachisaurids and dicraeosaurids7,8,13. In Lingwulong, the posterior-most dorsal spines more closely resemble those of non-diplodocoids (e.g., turiasaurs and non-titanosaurian macronarians) in possessing well-developed subtriangular aliform processes that project laterally from the summit.

The sacrum (Fig. 2, Supplementary Fig. 6) comprises five fused vertebrae. Sacral centra lack lateral pneumatic fossae and are mildly amphicoelous. Sacral centra 3 and 4 are the most constricted transversely. Neural spines 2–4 are coalesced, as in most flagellicaudatans2. Sacral ribs 2–5 fuse distally to form a ‘sacricostal yoke’1, but only sacral ribs 2–4 actually contribute to the dorsal margin of the acetabulum.

Caudal centra are shallowly amphicoelous and subcircular in transverse cross-section. They lack lateral pneumatic fossae below the base of the rib, unlike some rebbachisaurids, diplodocines, and many titanosauriforms7,8,9,15. In anterior caudal vertebrae (Fig. 2, Supplementary Fig. 7), the low rounded spinoprezygapophyseal laminae (SPRLs) extend onto the lateral surface of each spine, a derived state observed in flagellicaudatans1. The first 11 caudal neural spines are unusual in having subtriangular facet-like areas on their lateral surfaces that extend from the summit to approximately spine mid-height. The ventral tips of these facets are expanded laterally to form small processes (Supplementary Fig. 7), resembling the triangular projections seen in some rebbachisaurids8. The anterior-most caudal ribs of Lingwulong have the wing-like structure present in most diplodocoids2: the anterior surface is deeply excavated and the dorsolateral corner forms a distinct projection (Fig. 2, Supplementary Fig. 7). In most diplodocoids, however, the latter projection is a low ‘shoulder’-like region, whereas in Lingwulong it is a prominent dorsally-directed prong. Mid-tail chevrons are ‘forked’, as occurs in non-neosauropod eusauropods and flagellicaudatans1,16.

The scapula (Fig. 2) has a strongly expanded proximal plate and a long blade with a widened distal end (but it is not racket-shaped, in contrast to those of rebbachisaurids8). The prominent acromial ridge is at ~90° to the long-axis of the blade. In cross-section, the blade is ‘D’-shaped, as is typical for all sauropods apart from early forms (e.g., Shunosaurus) and some advanced titanosaurs1. In the coracoid (Fig. 2), the notch anterior to the glenoid is weakly developed and the glenoid region does not expand markedly laterally, unlike those of some Camarasaurus-like macronarians17. The proximal end of the humerus (Supplementary Fig. 8) is strongly convex transversely (Fig. 2). As in diplodocids9, the humerus is twisted so that, with the long-axis through the proximal end extending transversely, the long-axis through the distal end is directed posterolaterally. Ulnae possess a triradiate proximal end with a deep radial fossa (Supplementary Fig. 8), as in other sauropods1,2. The radius has a ‘D’-shaped proximal end with a flattened rugose articular surface. The distal end of the radius is convex and, in anterior view, moderately beveled so that it faces laterodistally (Supplementary Fig. 8).

The ilium (Fig. 2) has a reduced ischial articulation, rounded dorsal profile, and lacks the brevis fossa, as is typical in all sauropods2. As in several other flagellicaudatans (e.g., Dicraeosaurus, Diplodocus8), the pubis bears a prominent ambiens process immediately anterior to the iliac articulation (Fig. 2): however, this process tapers in dorsoventral width towards its tip in Lingwulong, rather than being ‘hooked’. The ischium is relatively slender. In lateral view (Fig. 2), the iliac peduncle of the ischium lacks the derived constriction (‘neck’) seen in most rebbachisaurids7,8. The distal end surface of the ischium retains the plesiomorphic subtriangular profile seen in most non-macronarian sauropods2, yet the conjoined distal ends are coplanar (an apomorphy observed in macronarians and rebbachisaurids1,2 that has not previously been seen in a flagellicaudatan).

The femur (Fig. 2, Supplementary Fig. 9) resembles those of other sauropods, although the proximal head is directed medially, rather than dorsomedially2. Its fourth trochanter is a low rounded ridge on the posteromedial margin of the femoral shaft, at approximately mid-length. The tibia (Fig. 2, Supplementary Fig. 9) has a transversely widened proximal end, as occurs in most neosauropods1, with the cnemial crest directed laterally. Its distal end has a reduced medial malleolus, exposing the astragalus posteriorly, as in most sauropods1. The astragalus has a transversely and anteroposteriorly convex ventral surface and tapered medial projection. Its ascending process extends to the posterior margin of the astragalus, a derived state characteristic of neosauropods1. The fibular facet faces laterally, rather than posterolaterally as occurs in many diplodocoids7.

Our phylogenetic analysis places Lingwulong within Dicraeosauridae as the sister taxon to Amargasaurus + (Brachytrachelopan + Dicraeosaurus) (Supplementary Note 4, Fig. 3, Supplementary Figs. 10–12, 15, Supplementary Data 15). Symmetric resampling indicates that this placement of Lingwulong is the sixth best-supported node out of the 70 nodes in the tree (Supplementary Fig. 11).

Fig. 3 Time-calibrated evolutionary tree for Eusauropoda. Agreement subtree produced in TNT, with additional diplodocid taxa incorporated (see Supplementary Note 4). All macronarian taxa have been combined into a single lineage, and non-sauropod sauropodomorphs have been removed, in order to enhance clarity (see Supplementary Fig. 13 for the full version of this tree). Silhouettes of dinosaurs drawn by Scott Hartman, Mike Taylor, and Mathew Wedel, and available at Phylopic (http://phylopic.org/) under a Creative Commons Attribution 3.0 Unported license (https://creativecommons.org/licenses/by/3.0/). Global paleogeographic reconstructions from the Paleobiology Database (https://www.paleobiodb.org) Full size image

In our biogeographic analyses (Supplementary Note 6), the log likelihood ratio tests demonstrate that the +J versions of the biogeographic models are very strongly significantly better fits to the data than are the non + J versions (p-values range from 5.3e−8 to 4.4e−26: see Supplementary Data 16). Moreover, the AIC values for BAYAREALIKE + J are 18.7 (relaxed) and 23 (harsh) units lower than the next best supported model (i.e., DEC+J), which suggests that the former model can be regarded as strongly outperforming the other five models18. The results of our additional analyses of a reduced dataset were very similar to those produced by the analyses of the full dataset, with BAYAREALIKE+J being strongly preferred over other models (Supplementary Data 17).