Mamenchisaurus sinocanadorum lived 162 million year ago (Late Jurassic epoch) in what is now China.
A rendering of Mamenchisaurus sinocanadorum. Image credit: Júlia d’Oliveira.
Mamenchisaurus sinocanadorum is a very large dinosaur in the sauropod family Mamenchisauridae.
It was first described in 1993 from fossils found in the upper part of the Shishugou Formation in the Junggar Basin, Xinjiang, China.
At approximately 15.1 m (49.5 feet), its neck was more than six times longer than the necks of giraffes, the longest-necked animals alive today.
“The question of which sauropod had the longest neck is not straightforward,” said Stony Brook University paleontologist Andrew Moore and his colleagues.
“Because of their size, the largest sauropods tend to be some of the most poorly known: it’s very hard to bury such a large animal in sediment and thus safeguard it for fossilization.”
“Some fragmentary fossils suggest that other sauropod lineages independently evolved necks over 10 m (32.8 feet) in length.”
“However, poor preservation of these specimens and their closest relatives makes estimates of their neck length speculative.”
Although Mamenchisaurus sinocanadorum is known only from a handful of bones from the neck and skull, the authors were able to reconstruct its evolutionary relationships and thus make comparisons to the unusually complete skeletons of its closest relatives.
“All sauropods were big, but jaw-droppingly long necks didn’t evolve just once,” Dr. Moore said.
“Mamenchisaurids are important because they pushed the limits on how long a neck can be, and were the first lineage of sauropods to do so.”
“With a 15-m-long neck, it looks like Mamenchisaurus sinocanadorum might be a record-holder — at least until something longer is discovered.”
How sauropods managed to evolve such long necks and hulking bodies without collapsing under their own weight remains something of a biomechanical puzzle.
Remarkable specimens like Mamenchisaurus sinocanadorum provide some clues.
Using computed-tomography scanning, Dr. Moore and co-authors found that the vertebrae of Mamenchisaurus sinocanadorum were mostly air (about 69-77% of their volume) — comparable to the lightly built skeletons of storks and other birds.
However, such featherweight skeletons would also be more prone to injury.
To combat this, Mamenchisaurus sinocanadorum had 4-m- (13.1-foot) long rod-like cervical ribs, bony extensions of the vertebrae that created overlapping bundles of rods on either side of the neck.
These bundles would have stiffened the neck of Mamenchisaurus sinocanadorum, increasing its stability and making it possible to build such a lightweight neck.
“Biomechanical studies of the mamenchisaurid neck suggest that it was elevated at only a relatively shallow angle above the horizontal (20-30 degrees),” said University College London’s Professor Paul Upchurch.
“However, even at this relatively shallow angle, the extreme length of the neck would still mean that the animal’s head could reach heights of around 7.5 to 10 m (24.6-32.8 feet) above ground level, facilitating feeding on tree foliage.”
“Mamenchisaurus sinocanadorum underscores how much we can learn about sauropod evolution even from very incomplete specimens,” said Dr. Ye Yong, director of the Research Center of Jurassic Stratigraphy and Paleontology at the Zigong Dinosaur Museum.
The findings will be published in the Journal of Systematic Palaeontology.
_____
Moore et al. 2023. Mamenchisaurus sinocanadorum. Journal of Systematic Palaeontology, in press
