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

RE: "running" elephants




Richard Forrest wrote: There is a problem in considering elephants as models for dinosaur locomotion: A large elephant weighs 5 tons. A large sauropod dinosaur weighed 80 tons - 16 times the weight.

To model the locomotion of a sauropod dinosaur on that of an elephant on
comparable top modelling the locomotion of an elephant from something
weighing about 300 kilos - a small horse, or a cow - which can do all sorts
of things elephants can't.
=======================================================

I didn't see anything in my sentence about sauropods, or any other specific dinosaur, so I assume Richard is speaking in general to other persons. I've worked on dinosaurs for quite a few years so I'm aware of the mass differences between larger sauropods and elephants, too. (And also that some sauropods weighed much less than 80 tons, and some elephants can weigh more than 5 tons) So of course I agree with the basic point.

[I should emphasize that our paper did not conclusively establish that elephants run; it is a preliminary report (hence the short paper) but I think it's very likely to be correct once we do the final work]

Additionally, I'm not a big fan of using particular extant animals as "models", analogs, or what have you for dinosaurs. I prefer understanding the principles and mechanisms that make living animals work, and using multiple lines of evidence to see how those principles might apply to extinct animals. I don't find analogs/models as very testable (even indirectly) or insightful. They mostly head toward dead ends, not in new or fertile research directions. [This is where I differ from what National Geographic's March article discussing my work said; it seemed to say that I see elephants as analogs for tyrannosaurs, which I actually do not but they thought it was vague enough]

IF elephants use a bouncing (biomechanically running) gait, such as Groucho running (a bouncing gait with more flexed limbs), the principle applicable to dinosaurs would be that even large dinosaurs might have been able to extend their range of locomotor performance by using a similar mechanism. This is testable indirectly with computer models, etc. Such a mechanism avoids an aerial phase and its impact on touchdown, has lower peak ground reaction forces, and is less jarring to the body (dampened propagation of forces throughout the body), but the downside is that it does not allow the same long strides and high speeds as running with an aerial phase, and it costs more energy per step because of the more flexed limbs. We were a little surprised to find hints that elephants bounce, as we did not think that was a mechanism open to huge animals, especially elephants with their stereotyped columnar stance. "Bounce" isn't a word often connected with elephants, but they do it (to a point).

Other points of potential dino-interest from the research includes the accurate measurement of near-max speeds in Asian elephants (15 mph), useful for those who think speed scaling methods for dinosaurs are useful, and the kinematic data (a huge set, 42 individuals and 188 trials, multiple strides per trial, wide size and speed range) are likewise useful for revising Alexander's trackway speed estimate equations, which badly need an overhaul. And so on. It's a preliminary report but we decided to publish it because there was a good fun story with a solid answer on speed and footfall pattern, it should stimulate more interest in elephants, and it promotes doing hands-on research with large animals rather than speculations, analogies, and anecdotes.

Cheers,
John



===========================================
John R Hutchinson
NSF Postdoctoral Research Fellow
Biomechanical Engineering Division
Stanford University
Durand 209, BME
Stanford, CA 94305-4038
http://tam.cornell.edu/students/garcia/.trex_www/naturepaper.html
http://www.stanford.edu/~jrhutch/fast_elephants/wanalee/index.html
(650) 736-0804 lab
(415) 871-6437 cell
(650) 725-1587 fax
===========================================