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dinosaurs and endothermy



I couldn't resist... I forwarded one of Greg Paul's messages to John
Ruben to see if he would like to comment.  He took me up on my offer:

  Date: Tue, 12 Sep 1995 12:33:12 -0700 (PDT)
  From: John Ruben <rubenj@BCC.ORST.EDU>
  To: rowe@lepomis.psych.upenn.edu
  Subject: dinos again

  Mickey - thanks for the note.  Paul's assertions are both misleading and 
  inaccurate.  Specifically:

     1.  We have NO (=none, zero, nada) way of knowing just what dinosaur 
         aerobic scopes (or active rates of oxygen consumption) were like. 
         Many were surely active animals (as are many extant varanid
         lizards, some of which maintain almost mammal-like levels of 
         routine activity [e.g., komodo dragons and the Racehorse Goana 
         of Australia. See papers by Bennett]), but this says nothing
         about resting metabolic rates or possible endothermy. 

         Some people (including Paul) have suggested that the pneumatized
         (hollow) bones of some dinosaurs suggest they had a bird-like lung, 
         thus (so the story goes) they must have had a bird-like aerobic
         metabolic capacity. However, a bird-like lung does not 
         necessarily imply a high aerobic capacity, and more to the point,
         dinosaurs were highly unlikely to have had an avian lung: Bird rib
         structure is related to respiration by being hinged in a 
         specialized way, such that on inhalation the breastbone is lowered
         but lung volume is diminished (rather than expanded as in typical 
         mammals and reptiles).  On exhalation, the process is 
         reversed. There is no evidence that ANY dinosaur possessed 
         hinged ribs even vaguely reminiscent of the avian condition.  
         The most parsimonious interpretation is that they possessed 
         alligator- or croc-like lungs. The hollow bones of some 
         dinosaurs seems more likely to be related to the need for 
         a less massive skeleton.

         Occasionally, some workers (including Paul) have suggested 
         that dinosaurs must have mammal- or bird-like    
         hearts to maintain cardiovascular pressure sufficient for their
         needs. Consequently (so the story goes), since they had 
         bird-like hearts, they must have had bird-like metabolism.  This 
         is inaccurate-- it is generally not appreciated by 
         non-specialists that many living crocodiles maintain
         systemic and pulmonary blood pressures not too discrepant from 
         mammalian values and some tree snakes achieve blood pressure 
         that EXCEEDS typical avian and mammalian numbers (see papers by 
         Grigg and others by Lillywhite).

         Finally, Paul seems unaware that in some lizards, oxygen 
         consumption during exercise EXCEEDS that of many mammals during
         at least routine levels of activity. Little wonder that some 
         varanid lizards have been clocked as running 30 kilometers/hr for
         distances up to one kilometer. This compares closely with the  
         human record for the half-mile!!  
    
         To summarize:
         1.  Paul's assertions notwithstanding, there is not the slightest 
         bit of reliable evidence regarding the magnitude of dinosaur aerobic
         scope.  

         2. Dinosaurs need not have been warm-blooded to have achieved 
         elevated aerobic scopes.
  
       Significantly, in their forthcoming review entitled "Dinosaur 
  Biology," (Annual Review of Ecology & Systematics, 1995, 26:445-471,
  Farlow, Dodson and Chinsamy conclude that "No evidence shows that
  dinosaurs were endotherms, and some suggests that they were not."
  (p.445).
       
       I hope this is helpful.  Feel free to copy/publish whatever
  parts of this e-mail are of interest to you or your readers.

                          John R.