Freak Felids - A Discussion of History's Largest Felines

[tigerluver]

Now I'll share my thoughts of Smilodon, Smilodon populator specifically.

The largest specimen estimate for S. populator is 358 kg by Christiansen and Harris 2005 based on a humerus. I have some concerns over the estimates of this study.

Christiansen and Harris themselves cite and state that allometry is more often positive, thus bigger bone should be a proportionately heavier animal. Though, their data says otherwise. Working with the numbers I've made two observations:
1. On the species scale, the smaller big cats are much stouter than the larger ones, and thus negative allometry as species (note, not individual) size increases. 
2. On the individual scale, individuals of a species relate to each other with positive allometry. Bigger animals are stouter within a species. 

Now it gets messy and confusing. To try to compensate for this, I decided to limit the database to only lion and tigers on the basis that these two species are closest in size to the prehistoric giants. Using tigers and lions as the database works under the assumption that the fossil in question is in the middle ground in terms of built (tigers are significantly heavier in proportion in lengths and even width measurements in some case as tigers have thinner bones yet heavier masses). The smaller cats are simply too proportionately different in Christiansen and Harris's database (althoughg Anyonge finds positive allometry across the board, on a species and individual scale, though he did not publish his database, so further analysis is impossible). From there, I generate the log equations to estimate mass.

There is one major problem, the tiger and lion database derivation works well only in the case of bone lengths, but when applied to bone widths, everything so haywire. The reason? Tigers have thinner bones, yet are heavier, and vice versa for lions. As the database is composed of more small tigers, the allometry becomes extremely negative, to the point which I consider unreasonable. 

This hindrance also extends to the Christiansen and Harris equations. The main culprit for this problem is the tiger's oddness. Its specimens lie far right, at the largest weights, yet its diameters are lower than they should be. This creates a stronger false negative allometry for the other species, thus giving lower estimates. Therefore, I feel that Christiansen and Harris's estiamte for the largest S. populator may be an underestimate.

Like we compared Baikal to the giant Ngandong specimen to validate an estimate, let's compare this Smilodon bone to some extant specimens. The parameters (in mm) of this humerus bone that I'll discuss are:
Length: 387.5
Least circumference: 155

Forget comparing this bone to a cat for now, it's way too stocky. The stockiness is probably not due to cursoriality either, as Smilodon wasn't much of a runner with its bobtail and for the fact that the relatively stout boned cursorial lions of today are not even close to this fossil humerus. Let's compare these measurements to a Grizzly humerus (in mm):
Length: 400.5
Least circumference: 146.25
Mass: 435.5 kg

The Smilodon humerus is, interestingly enough, even wider than the Grizzly bone even though it is shorter. From this, Smilodon was not built like a bear, it was built like a Smilodon. 

Now the point we all love, mass. The Smilodon humerus is about 3% shorter and 6% wider than the bear humerus, leading me to believe we have a specimen which probably weighed around the bear's mass. Of course, Smilodon being built differently from a cat and a bear in terms of dimensions (e.g. the sloping back) would likely have an effect on mass. But from what we have available, the bear bone is a good reference point. So, what do you guys think?

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