Creodonts

[tigerluver]

These wonderful new threads piqued my interest. I did a little digging and a little number crunching and look what I've found.

This is where most of Megistotherium fossils are found:
Savage (1973)

So the two massive specimens are these,

 664 mm x 471 mm skull:

*This image is copyright of its original author

Distal humerus fragment of width 123 mm and articular width 107 mm.

*This image is copyright of its original author

Savage (1973) used a bear humerus and guessed a weight attached to it come up with an estimate and also did a brain mass to body weight formula which is outdated at this point. 

Skull size is not a good measure as proportion differed in Megistotherium. Nonetheless some form of giant must've held that head up.

In terms of the humerus, the diameter is an okay measure to compare between species because widths are better related to weight than lengths are.

I packed up all of the cats of Christiansen and Harris (2005) and came with the following felid averages:

Mass: 80.3 kg 
Humeral Articular width (HAW): 42 mm

Applying isometry:

Mass Megistotherium = (HAW Megistotherium / HAW felids)^3 x mass felids
Mass Megistotherium = (107 mm / 42 mm) ^3 x 80.3
Mass Megistotherium = 1,328 kg

Now isometry probably does not work in this case. Generally really big animals have bones wider than what you expect for their weight due to weight-bearing and gait issues. So instead of using isometry, I changed the scale factor to 2.7 (some negative allometry and a scale factor I've found that works well interspecifically) to account for this physiological trend.

So the math as before except for the scale factor change:

Mass Megistotherium = (HAW Megistotherium / HAW felids)^2.7 x mass felids
Mass Megistotherium = (107 mm / 42 mm) ^2.7 x 80.3
Mass Megistotherium = 1,003 kg

So I'd say around 1 metric ton would be a good range for at least specimen. Whether it is average or large, no one can tell. Reply