Findings in title quoted from the linked content^1,2 about research funded by numerous organizations, including the United States National Science Foundation, The Royal Society of London, and the National Natural Science Foundation of China.

From the linked summary:^1

>Mamenchisaurus sinocanadorum was discovered in approximately 162-million-year-old rocks from the Xinjiang Uyghur Autonomous Region of northwest China in 1987 by the China–Canada Dinosaur Project team, for which it was named in 1993.

>Although Mamenchisaurus sinocanadorum is known only from a handful of bones from the neck and skull, the research team was able to reconstruct its evolutionary relationships and thus make comparisons to the unusually complete skeletons of its closest relatives.

>This allowed them to conclude that Mamenchisaurus sinocanadorum had a neck approximately 15.1 meters long, the longest of any known sauropod.

>Lead author Dr Andrew J. Moore, Stony Brook University palaeontologist, said, ‘All sauropods were big, but jaw-droppingly long necks didn’t evolve just once.

>‘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-metre-long neck, it looks like Mamenchisaurus sinocanadorum might be a record-holder – at least until something longer is discovered.’

ETA:

>The question of how sauropods managed to evolve such long necks and large bodies without collapsing under their own weight has puzzled scientists since their discovery.

>When studying Mamenchisaurus the team were able to use computed-tomography (CT) scanning to reveal that the vertebrae were lightweight and hollow with air spaces comprising about 69–77% of their volume, similar to the lightly built skeletons of birds.

>However, such featherweight skeletons would also be more prone to injury. To combat this Mamenchisaurus had 4-metre-long rod-like neck 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.

^1 New fossil analysis reveals dinosaur with the longest neck of any animal ever, 15 Mar. 2023, https://www.nhm.ac.uk/press-office/press-releases/new-fossil-analysis-reveals-dinosaur-with-the-longest-neck-of-an.html

^2 Andrew J. Moore, Paul M. Barrett, Paul Upchurch, Chun-Chi Liao, Yong Ye, Baoqiao Hao & Xing Xu (2023) Re-assessment of the Late Jurassic eusauropod Mamenchisaurus sinocanadorum Russell and Zheng, 1993, and the evolution of exceptionally long necks in mamenchisaurids, Journal of Systematic Palaeontology, 21:1, https://doi.org/10.1080/14772019.2023.2171818