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tyranno scavenging issues



The Ruxton & Houstan paper on scavenging tyrannos is interesting, but is 
afflicted by some flaws that continue to question whether paleobiology is yet 
being done as a science. 

The researchers use a speed of about 1.5 km/h as the foraging speed for a 
reptilian tyrannosaur. This is actually reasonable for reptilian energetics, 
and is superior to past studies that try to attribute unsustainably fast 
walking speeds to reptiles. However, the way they estimate a reptilian 
walking speed as a fraction of top speed is spurious. Sustainable walking 
speed is not related to top speed. Tortoises can walk at speeds not much 
lower than those of lizards than can run far faster. It is dependent upon 
aerobic exercise capacity, which is very  low in all reptiles of all sizes, 
so a reptilian tyrannosaur would not have been able to forage at speeds 
exceeding 2 km/h. Ground birds and mammals can sustain walking speeds of 3-10 
km/h. 

Another problem is that we actually know the foraging speeds of large 
theropods, from a large sample of trackways that consistently record the long 
strides only made at speeds of 3-10 km/h. This is not feasible with reptilian 
energetics, so R&H should have restored scavenging tyrannosaurs only with 
high energy budgets and exercise capacity (also indicated by their very rapid 
growth), it should not have been a secondary possibility as in their paper. 

G Paul