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Re: What is an "active ectotherm"?



Fish can be very active and fast swimmers despite having low body temp and/or
low aerobic capacity because swimming is 5 to 12 times more energy efficient
than walking the same distance (in animals of the same body mass; the
disparity depends on how streamlined the fish is; cost of locomotion on land
is largely independent of leg design and posture*; also increasing size does
not make it energetically easier to walk faster**). It is simply impossible
for land animals with reptilian energetics to SUSTAIN high levels of
activity. They can run briefly for very brief periods, but quickly become
exhausted. Some lizards can walk constantly for hours, but only at 1 mph or
less. Nor can they migrate or move about in social groups like fish. That
almost all dino trackways were made at speeds above 3-5 mph, and many were
social and/or migrated, shows that they had higher aerobic capacity than
living reptiles. 

* Experiments prove that animals with sprawling or heavy legs walk with the
same energy efficiency as those with erect or gracile legs. If you do not
like that fact too bad. 

** The mass specific cost of locomotion declines with size, so elephants walk
cheaply. However, aerobic capacity declines at about the same rate so there
is not a major advantage. 

GSPaul