Box #16 in our count down is Mamenchisaurus…
Mamenchisaurus: the “Mamenchi Lizard”
Mamenchisaurus lived in the lush forests of late Jurassic China. Many other long-necked sauropods are known from the area, their bones washed down into a deep lake, but Mamenchisaurus holds the record for the longest neck. From a total length of almost 50 feet (15m), nearly half of that was neck!
The Mamenchisaurus above has heard something suspicious and raised its head high for a better look, but how did it hold its neck in the humdrum of daily life? Paleontologists can take the dry bones and see how they fit, like puzzle pieces. Doing this, they have found that there was some upward bend at the base of the neck, which had more flexibility moving up than down. The middle of the neck had more flexibility bending down than up, and the head was naturally angled downward and did not raise up very well. This led some to believe that Mamenchisaurus was primarily a low browser.
This sounds great in theory, but the truth is far more complicated. In life, Mamenchisaurus would have cartilage between the bones, plus layers of muscle, connective tissue, skin, and possible fat. Even studying cadavers (dead bodies) of ostriches, which include all these soft tissues, the amount of flexibility is very different than a living animal. Living bodies have fluid to allow the parts to slide and move past each other without friction. True, the skeleton and sleeves of tissue can limit movement in certain directions, it seems fairly obvious that Mamenchisaurus could not bend its neck like a snake’s spine, but animals can move in ways that can surprise us, or hold their bodies in ways that seem counter intuitive when we first see it.
Take a rabbit, for example. On a living animal, it appears to have hardly a neck at all, and the head appears to be held down from the shoulders. Look at the skeleton, and one can see that a rabbit has a surprisingly long neck, and it angles sharply at the base of the neck and the base of the head in a tight S shape. When we compare thousands of different mammals, birds, reptiles, and amphibians, we find that there are few exceptions to this rule.
Does this mean that Mamenchisaurus would hold its head high at every moment? No. A relaxed animal will lower its head. Think of a calm, sleepy horse vs. a nervous horse. A high head is a sign of anxiety, of alertness. Whereas a relaxed animal will lower its head to an angle, and this is true of many animals, not just mammals.
So a relaxed Mamenchosaurus may well have held its head at a slope, while a nervous one held its head high like the one above. So what does the downward flexibility mean?
Being able to bend your head down to the ground is useful for drinking, but there’s another possibility as well. Some have analyzed the tail of Mamenchisaurus and propose that it would have been good at rearing up on its hind legs. For balance, the head would need to be about in line with the body, and being able to bend the neck downward suddenly transforms a supposedly low browser into an animal that can reach as high as possible. Its hips may even allow it to walk very slowly on its hind legs when doing this. Goats and elephants are among several animals that do this today. An ability to shuffle around and keep your balance while you eat is definitely an advantage the heavier an animal gets!