[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: sauropod necks-buckaroobwana is back! ha ha ha ha ha !!

Hi Jonathan.

You said:
        Alternately, I suppose the animals could have kneeled. Or could
they? Matt, any ideas?

Good question. The joint surfaces of most sauropod bones are pitted and rugose in nature. When cartilage caps the ends of long bones or wrist bones, the surface of the bone in contact with the cartilage will grown little "fingers" up into the cartilage which help to keep the cartilage and bone surface stuck together. The very prominent pits and "fingers" (rugosities) at the ends of sauropod long bones and their wrist bones suggests that there was quite a bit of cartilage in their articular capsules.

The end of the thigh (femur) in sauropods is quite well rounded, while the top of the shin (tibia) is relatively flat or just slightly concave. This arrangement appears to have allowed the knee to flex to a decent degree (at least 45 degrees from vertical -- in the CM Camarasaur, the knee is flexed almost 90 degrees, but it is hard to tell if this is natural), and perhaps the extra cartilage we cannot see allowed it to flex more. The elbow joint is more problematic. Part of my talk at SVP revolves around this aspect of sauropod locomotion, and so as not to give away the "big surprises" (don't get too excited) all I will say for now is that the forearm (humerus) can swing about 20-30 degrees from vertical in both fore and aft directions in a parasagittal plane, the manus appears to be able to flex about 30 degrees or so, and the elbow may have been able to flex as much as 30-40 degrees (until I actually publish this stuff, these degrees of flexion should be treated with extreme caution -- i.e., this is still incomplete data!). The forelimbs of sauropods are very, very weird.

Therefore, while it seems that sauropods should be able to kneel and flex their elbows, another possibility is that sauropods didn't flex so much and spent their entire lives on their feet -- sleeping, eating, etc. Wild speculation here, but perhaps they only laid down in water or to mate in water. Seems rather quirky, I know. Futhermore, all sauropods, except for titanosaurs, have almost no olecranon process (i.e., the thing you point to as your elbow). In most vertebrates, the olecranon process acts as a sort of lever arm for a big group of forearm extensor muscles commonly called the Triceps brachii. Therefore, it's difficult to imagine that sauropods frequently flexed their elbows -- they don't have a decent lever arm to yank their forearm back in place. Titanosaurs, well, that's for another time.

Maybe sauropods could kneel down, but from what I've seen, I doubt they did it very often. I imagine sauropods would rely on their necks (and maybe in part on the water content of their vegetative meals) to get to water.

Matt Bonnan

Get Your Private, Free Email at http://www.hotmail.com