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Ectothermic Tetrapod Track and Field

June 16, 2011

1980s scifi is wonderful in many ways. The horrible hair cuts. The time period technology (cordless phones the size of an mailbox). Some semblance of special effects, dated as they may be. And in this case Lizards.

(Spoiler alert!!)

If you didn’t see the original thirty years ago, or the sequel, the remake or whatever else there is out there. V is about lizard people from space (with big hair, colorful jumpsuits and giant sunglasses). I hadn’t seen any of the versions until a few weeks ago. My partner found it on Netflix and insisted we watch. Less than an hour in is the bit reveal:

“They’re lizard people? Oh well that will be easy. Just get them to chase you. Lizards can run and breathe at the same time”

She gave me her skeptical look. The one reserved for when I say things such as:

“Isn’t there some monkey that is also a marsupial?”
“Don’t aardvarks have vestigial gills?”

An understandable reaction if you are familiar with the type of science “facts” I come up with after a few beers. It seems far fetched though somewhat plausible. I immediatly took to Google-Scholar to prove myself not crazy (this time). Within a few minutes I pulled up a PDF of this:

Carrier, R (1987) The Evolution of Locomotor Stamina in Tetrapods: Circumventing a Mechanical Constraint. Paleobiology, Vol. 13, No. 3

The maximum sustainable speeds of lizards are roughly ten times lower than those of mammals of equal body size (Garland 1982). As a group, ectothermic tetrapods are unique among vertebrates in having no members with high stamina

I was mostly right. Some lizards do have trouble breathing and running at the same time. The problem seems to be centered on the mechanics of how they move their legs.

Schematic representation of relevant skeletal and muscular elements in a lizard running bipedally. During locomotion the muscles (dashed lines) of the thorax are expected to contract unilaterally, first on one side and then on the other during each locomotor cycle. Such unilateral con- traction elicits lateral bending of the trunk and stabilizes the pelvis against forces applied by the appendicular muscles. In this example, propulsive force applied to the ground (arrow) by the right hind limb exerts a counter-clockwise rotational torque on the pelvis. Axial musculature of the left side contracts to anchor the pelvis. Unilateral activation of the thoracic musculature is suggested to be incompatible with effective aspiration breathing. Modified from Snyder (1962).

There you go. Apparently running makes use of muscle movement that makes breathing a tad difficult. Though I caution readers, this seems to apply to some subset of lizards. I don’t know the animal taxonomic terms very well, so it could very only apply to the small harmless ones, while the ones you’d really need to run way from have 4.2 speed.

We haven’t finished V yet (it’s a miniseries) so I don’t know how things end.
The hope, is that this applies to lizards from space.

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One Comment leave one →
  1. May 1, 2014 5:31 pm

    Can you tell us more about this? I’d love to find out more details.

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