Herbivore dinosaurs...

[DinoFan83]

I'd like to make a post on the size of an unnamed giant mamenchisaurid fossil reported here: http://www.china.org.cn/english/culture/72851.htm
The diameter of this animal's femur is exactly twice that of Mamenchisaurus youngi (15 cm according to the supplementary material of Benson 2014), and assuming relative geometric similarity it would be twice as big linearly and 8 times more massive. (Greg Paul's estimation for M. youngi in the 2016 Princeton Field Guide to Dinosaurs was 16 meters and 7 tonnes, but his model is somewhat shrinkwrapped and a healthy model is probably closer to 8).
So based on the healthy model for Mamenchisaurus youngi at least, this animal would be around 32 meters long and 64 tonnes.

Sizes like this are also supported by the length of the hindlimb - while it is incomplete it is 3 meters as preserved, and would be even larger complete.
On his website, Greg Paul estimates a Mamenchisaurus hochuanensis with a 135 cm femur to weigh 14 tonnes, and given that femur length, his skeletal yields a hindlimb length of 2 meters (link). Scaling that up to the incomplete hindlimb length alone yields over 47 tonnes, and would be even larger using the full hindlimb to scale (which would be 358 cm based on Mamenchisaurus youngi given a 112.5 cm femur and 66.5 cm tibia for M. youngi as well as the greater diameter). Given that hindlimb length, as well as his length estimation of 20 meters in the 2016 Princeton Field Guide to Dinosaurs, the hindlimb would be about 35.8 meters and 80.3 tonnes scaling from M. hochuanensis.

As for what it is, it could be a new species, but given its size and where it was discovered I wouldn't be surprised if it turns out to be a new specimen of Mamenchisaurus sinocanadorum. Reply