Lingwulong shenqi

After our latest titanosaur entry and a week off, here's... another sauropod. This one's different though: it comes from early on in the history of sauropods, and shines a light on the early diversification of the group. I introduce Lingwulong shenqi, debuting as the world's oldest known dicraeosaurid at somewhere around 175 million years old, and the first substantiated dicraeosaurid from Asia. These "oldests" and "firsts" are more important than they might sound.

Genus and species: Lingwulong shenqi; "Lingwu" refers to the area of discovery, "-long" is Mandarin Chinese for "dragon", as seen in increasing frequency in Chinese dinosaur names, and "shenqi" is Mandarin Chinese for "amazing", reflecting the authors' feelings about finding such an early dicraeosaurid (Xu et al. 2018). This gives us the "amazing Lingwu dragon".
Citation: Xu X., P. Upchurch, P. D. Mannion, P. M. Barrett, O. R. Regalado-Fernandez, Mo J., Ma J., and Liu H. 2018. A new Middle Jurassic diplodocoid suggests an earlier dispersal and diversification of sauropod dinosaurs. Nature Communications 9: Article number 2700. doi:10.1038/s41467-018-05128-1.
Stratigraphy and geography: Lower–Middle Jurassic Yanan Formation, perhaps the fourth of four or five members, near the top, per the supplementary information. The age of the formation is uncertain, but it is bracketed by other formations that indicate deposition occurred between the late Toarcian and Bajocian age. This puts it in a time frame of about 175 to 170 million years ago. The locality is the Lingwu Geopark in the Ningxia Hui Autonomous Region of China (Xu et al. 2018).
Holotype: LM V001a (Lingwu Museum), a braincase and some associated skull bones, plus some dentary teeth (Xu et al. 2018). This may not sound impressive, but then you also get to throw in the partial remains of several more individuals contributing most of the rest of the skeleton.

Figure 2 from Xu et al. (2018). Their caption is as follows: "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"

A little bit of explanation:
First off, Dicraeosauridae is a group within Diplodocoidea, along with Rebbachisauridae and Diplodocidae, making dicraeosaurids cousins to such beloved dinosaurs as Apatosaurus, Brontosaurus, and Diplodocus. (And presumably also Atlantosaurus, currently comfortably into its second century of being ignored.) Dicraeosaurids tended to be small as far as sauropods go, with relatively short necks and long neural spines, both sometimes very exaggerated. Brachytrachelopan represents the shortest of the short-necked, to an extent that it actually looks kind of goofy, as if someone was building a normal sauropod but ran out of money and had to substitute a half-sized neck. Amargasaurus took the neural spines to extremes, with very long and spiky cervical neural spines. Because most dicraeosaurid cervical neural spines are deeply split (the term is "bifid"), this translates into two parallel rows of long spines, which various artists have interpreted as supporting full or partial dual "sails" or a single thick ridge, or being more or less bare spines. Not coincidentally, it's also the one dicraeosaurid that gets made into toys.

Derived sauropods can be divided into two branches: macronarians (Camarasaurus, brachiosaurids, titanosaurs, and a bunch of things that are harder to place) and diplodocoids (rebbachisaurids, dicraeosaurids, and diplodocids). These two groups together make up Neosauropoda. There are a number of candidates for ancient neosauropods, but (and stop me if this sounds familiar) they're either poorly represented, understudied, or both. This is where you find things like Abrosaurus, Bellusaurus, Cetiosauriscus, Jobaria*, and various ersatz Bothriospondylus hanging out. A true dicraeosaurid from approximately the Early–Middle Jurassic boundary would comfortably outpace all of the questionable "earliest neosauropods" and drive the radiation of neosauropods back millions of years (Xu et al. 2018). By definition, if you have an EJ–MJ dicraeosaurid, then there has to be EJ–MJ diplodocids, rebbachisaurids, and macronarians as well. (And here we are, stuck with limited Early and Middle Jurassic terrestrial records.)

*Jobaria, dinosaur flavor-of-the-month for November 1999; I'd just barely started Thescelosaurus! at that point. It and Afrovenator (named in 1994 from the same formation) may be the greatest dinosaurian one-hit-wonders of the 1990s. Lots of press at the time, but hardly any attention now.

Furthermore, known dicraeosaurids had been limited to the Late Jurassic and Early Cretaceous of Argentina, Tanzania, and a couple of spots in the western United States, outside of a brief period when Nemegtosaurus and Quaesitosaurus, future guests in "Your Friends The Titanosaurs", were thought to be dicraeosaurids. Lingwulong, being some millions of years older than the Late Jurassic and from central China, represents significant temporal and geographic extension of the dicraeosaurid record. It also provides a check on geographic hypotheses that make East Asia an isolated area with a unique localized (endemic) dinosaur assemblage in the Jurassic. Xu et al. (2018) interpreted Lingwulong as evidence that East Asia was not an isolate, and that the apparent endemic fauna may be related to geographic and temporal sampling issues.

Of course, these points all hinge on Lingwulong actually being a dicraeosaurid. After all, you don't have to go back all that far in time to find Nemegtosaurus and Mamenchisaurus comfortably ensconced as diplodocids, when all it took were some pencil-like teeth and skid-shaped chevrons to get you into the club. Xu et al. (2018) found a number of characteristics placing Lingwulong among the dicraeosaurids, and among the diplodocoids in general. Conveniently, Lingwulong is not only among the most completely known early sauropods (up there with Barapasaurus, Gonxianosaurus, and Kotasaurus), but is far better represented than the great majority of sauropods, with everything accounted for except parts of the skull, hands, and feet, and some vertebrae. The presence of multiple individuals can give some idea of variation as well, although we just have the preliminary description at this point.

A few anatomical observations: Lingwulong has the short dicraeosaurid neck, and it features the dicraeosaurid combination of short cervicals and cervical ribs that are only as long as their host vertebra, instead of extending back along one or more additional vertebrae. Many sauropods have one or the other feature, but few have both. A potential implication is that what the dicraeosaurid neck lost in length it made up for in maneuverability, but then you have to factor in the tall cervical neural spines of some dicraeosaurids. However, Lingwulong was not blessed with tall cervical neural spines, making it more like Brachytrachelopan than Amargasaurus or Dicraeosaurus. The neural spines from the shoulders to the base of the tail are tall, though. Interestingly, the skeletal restoration has a scapula broad enough to satisfy even the most long-winded of scapulimancers (which is actually more of a rebbachisaurid thing, but rebbachisaurid scaps are more racket-shaped), but the scapula chosen to illustrate separately is more slender. The lower jaw is unusual in that the "chin" had a pointed U-shape in dorsal or ventral view instead of being more squared-off, as seen in rebbachisaurids (most famously the unmistakable face of Nigersaurus) and diplodocids; a more gentle "U" is seen in other dicraeosaurids (Whitlock 2011).

Also of note: Judging from the figures, Lingwulong would have been of substantial size for an early sauropod and for a dicraeosaurid. The femur appears to a little less than 170 cm (67 inches) long (Amargasaurus and the two Dicraeosaurus species are around 100 cm), and from quick and dirty measurements the body is restored as around 18 m (60 ft) long. (Yeah, I know about the hazards of figures and scale. At least the individual femur and the femur in the restoration work out the same.) Interesting; it's one data point, but it could imply that dicraeosaurids became smaller over time. (Or that Lingwulong was just an unusually large dicraeosaurid.)

References

Whitlock, J. A. 2011. Inferences of diplodocoid (Sauropoda: Dinosauria) feeding behavior from snout shape and microwear snalyses. PLoS ONE 6 (4):e18304. doi:10.1371/journal.pone.0018304.

Xu X., P. Upchurch, P. D. Mannion, P. M. Barrett, O. R. Regalado-Fernandez, Mo J., Ma J., and Liu H. 2018. A new Middle Jurassic diplodocoid suggests an earlier dispersal and diversification of sauropod dinosaurs. Nature Communications 9: Article number 2700. doi:10.1038/s41467-018-05128-1.