Mamenchisaurus hochuanensis mah-MEN-chee-SOR-us

"Mamenchi lizard"

Mamenchisaurus silhouette — silhouette · Will Toosey (CC-BY) via PhyloPic

Length: 25 m (82 ft) — About 25 m long, ~15 tonnes — half of which is neck.
Period: Late Jurassic (160–145 Mya)
Place: Asia · China
Food: Herbivore — Plants from a wide range of heights — that astonishing neck swept across a huge volume of vegetation.
Clade: Sauropoda Dinosauria Saurischia Sauropodomorpha True long-necks. Walked on four pillar legs.

A long-necked Chinese sauropod whose neck made up nearly half its body length.

Mamenchisaurus had a neck longer than most dinosaurs had bodies — almost half of its total length was neck alone. Some species are known with necks over 12 m long, the longest of any animal ever. The neck was supported by stiff overlapping vertebrae and was probably held out roughly horizontal, sweeping side to side like a vacuum cleaner.

More about Mamenchisaurus

Discovery

Named by C. C. Young · 1954 · the Upper Shaximiao Formation at a construction site on the Yitang Highway in Sichuan Province, China

The first fossil was discovered in 1952 during highway construction work in Sichuan Province. The partial skeleton was later studied and named Mamenchisaurus constructus in 1954 by Chinese paleontologist C. C. Young.

Mamenchisaurus means 'Mamenchi lizard'. It combines the Chinese Pinyin mǎ (horse) and mén (gate), with chi an alternative transliteration of xī (stream or brook), plus the suffix -saurus from the Greek sauros (lizard). It was meant to honor the place where the first fossil was found.

Portrait of C. C. Young — C. C. Young A renowned Chinese paleontologist who studied and named the type species Mamenchisaurus constructus in 1954, and who described additional species and shifted the genus between several families over the following decades.

For the curious → Is Mamenchisaurus even a single valid group?

The genus is poorly defined and its taxonomy is increasingly confused, making the phylogenetic relationships hard to understand. Several analyses have failed to recover Mamenchisaurus as monophyletic, which suggests the genus may need to be revised. Additional research on the type species, M. constructus, is required to better understand it.

For the curious → Why has its family kept changing over the decades?

Young first noted that the chevron bones suggested an affinity with Diplodocidae, then in 1958 assigned the genus to Titanosauridae. After M. hochuanensis was described, Young and Zhao created the family Mamenchisauridae in 1972, but a 1995 analysis by Upchurch instead placed it in Euhelopodidae. Later analyses returned it to Mamenchisauridae, just outside Neosauropoda.

What we know

Neck made up nearly half the body length — the longest known of any animal.
Up to 19 neck vertebrae — most sauropods have 12 to 15.
Lived in Late Jurassic China, in what was then a forested, humid environment.
Some species had small head crests, others didn't.

What we guess

Whether the neck was held high (like a giraffe) or low and sweeping (like a vacuum cleaner) — most evidence favors the latter.
How it pumped blood up the neck — heart size or smaller hearts in series.
How it kept the long neck stable while moving and feeding.