English: A scale diagram showing four different Mamenchisaurus species, M. constructus, M. youngi, M. hochuanensis and M. sinocanadorum. Several other species have been assigned to Mamenchisaurus over the years. However, many of these are either dubious or have more limited information published and have not been included in the diagram above.

• M. construtus was described in 1954 and is the type species of Mamenchisaurus.^[1] The species was founded on a fragmentary specimen (IVPP V. 790); Therefore, the proportions shown here are not absolute but based on various reconstructions of the type specimen and other mamenchisaurs. Published estimates suggest an animal around 13 to 15 meters (43 to 49 ft) in length.^[1][2]

• Mamenchisaurus is sometimes considered a 'wastebasket taxon', with numerous questionable species assigned to the genus.^[3] With future revisions of the genus, it is possible that some or all of the referred species could get removed from Mamenchisaurus.

•M. youngi, described in 1996, is known from a very complete type specimen with articulated remains (ZDM 0083).^[4] The M. youngi type specimen has an overall length of around 16 meters (52 ft).

•M. hochuanensis, described in 1972, is known from a fairly complete type specimen with articulated remains (CCG V 20401).^[4][5] Another memenchisaur specimen, ZDM0126, was referred to M. hochuanensis in 2001. This specimen is often used to fill in some of the missing areas of the M. hochuanensis type specimen, such as the forelimbs and skull. However, later studies have cast doubt on the referral of this specimen.^[3][6] The silhouette above is based on reconstructions that combine CCG V 20401 and ZDM0126. The overall length of M. hochuanensis is around 21 to 22 meters (69 to 72 ft), with a neck around 9.3 meters (31 ft) long.

•M. sinocanadorum, described in 1993, is based on a very fragmentary holotype specimen (IVPP V10603). Material includes parts of the skull, the lower jaw, four cervical vertebrae and a single cervical rib). Based on this limited material and extrapolating out from other mamenchisaurs, suggest that M. sinocanadorum was fairly large. Earlier size estimates, based on comparison to M. hochuanensis, have suggested a length of around 26 meters (85 ft) with a neck around 12 meters (39 ft) long.^[7][8] In 2023, Moore et al. re-assessed M. sinocanadorum and found it closely related to Xinjiangtitan. They estimated the minimum neck length of M. sinocanadorum, based on linear extrapolation from Xinjiangtitan, at 14.4 meters (47 ft) and 15.1 meters (50 ft), including the possibility of allometry.^[6] Moore et al. did not provide a total length estimate, the silhouette shown here is based on a Xinjiangtitan reconstruction but scaled up by 1.08. In addition, two large neck vertebrae were discovered that probably belong to a giant mamenchisaur, but they have yet to be formally described. These vertebrae are from the same formation that M. sinocanadorum was discovered, and Paul suggested they might be the same species. They possibly suggest a mamenchisaur slightly larger.^[2][9][10] Moore et al. could not support the referral due to no overlapping material.^[6]

• M. youngi silhouette based on a skeletal reconstruction by Scott Hartman.[2] M. constructus silhouette based proportionally on from [3] and [4], M. hochuanensis based proportionally on [5]. M. sinocanadorum is based proportionally on a Xinjiangtitan skeletal reconstruction by Gunnar Bivens.[6]

• Humans scaled to 170 cm (5 ft 7 in) and 160 cm (5 ft 3 in).

References

1. ↑ ^{a b} Young, C.C. (1954), On a new sauropod from Yiping, Szechuan, China. sinica, III(4), 481-514.
2. ↑ ^{a b} Paul, G.S. (2016). The Princeton Field Guide to Dinosaurs Second Edition, Princeton University Press.
3. ↑ ^{a b} (2020). "Osteology of Klamelisaurus gobiensis (Dinosauria, Eusauropoda) and the evolutionary history of Middle–Late Jurassic Chinese sauropods". Journal of Systematic Palaeontology 18 (16): 1299–1393. DOI:10.1080/14772019.2020.1759706.
4. ↑ ^{a b} PI, L., OU, Y. and YE, Y. 1996. A new species of sauropod from Zigong, Sichuan, Mamenchisaurus youngi. 87–91. In DEPARTMENT OF SPATIAL PLANNING AND REGIONAL ECONOMY (ed.), Publication in Geoscience Contributed to the 30th International Geological Congress. China Economic Publishing House, Beijing.
5. ↑ Young, C.C., and Zhao, X.-J. (1972). "Mamenchisaurus hochuanensis sp. nov." Institute of Vertebrate Paleontology and Paleoanthropology Monographs, A, 8:1-30.
6. ↑ ^{a b c} Moore, Andrew J. (2023-01-01). "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). DOI:10.1080/14772019.2023.2171818. ISSN 1477-2019.
7. ↑ Russell, D.A., Zheng, Z. (1993). "A large mamenchisaurid from the Junggar Basin, xinjiang, People Republic of China." Canadian Journal of Earth Sciences, (30): 2082-2095.
8. ↑ Taylor M.P. (2012). Why sauropods had long necks; and why giraffes have short necks, [1]
9. ↑ Paul, G.S. (2016) http://dml.cmnh.org/2017Jan/msg00090.html.
10. ↑ Paul, G.S. (2019). "Determining the largest known land animal: A critical comparison of differing methods for restoring the volume and mass of extinct animals". Annals of the Carnegie Museum 85 (4): 335–358. DOI:10.2992/007.085.0403.