Freak Felids - A Discussion of History's Largest Felines

[tigerluver]

Robusticity through the ages of Panthera tigris

I've finally an estimate of the relative robusticity of each tiger subspecies. The subspecies analyzed are all those accepted by Mazak (1981). Pictures can be deceiving, but numbers are not.

Method:
Using a similar growth chart to the one posted here (I removed one value, changing the equation. I'm keeping that to myself for now due to publishing issues), I was able to statistically determine which subspecies are proportionately heavier. The bones themselves gave no indication of what's happening, so I analyzed the predicted mass of each subspecies using Panthera tigris tigris as the basis for comparison. If the subspecies fall above the prediction, it's more robust, if below, less robust. 

Results:
To keep everything short and sweet. Here are the results:

Subspecies	% Difference
P.t. corbetti	-3.5
P.t. amoyensis	12.1
P.t. virgata	4.4
P.t. altaica	-14
P.t. sumatrae	4.8
P.t. sondaica	14.8
P.t. balica	9.3
P.t tigris	0

Negatives means item fell below the line, positives vice versa.

The most striking proportianately difference is shown in the island tigers. Unanimously, they are proportionately heavier than the Bengal tiger. The Amur tiger (Russian Far East tiger) was historically the lightest built subspecies, even at its greatest length (where positive allometry makes the specimens more robust). P.t. virgata is shown here to be more robust than the Amur. P.t. corbetti is a bit less robust than P.t. tigris and much less robust than the similar sized P.t. amoyensis. 

Conclusions:
P.t. sumatrae, considered the hybrid product of mainland and island tiger, is in the middle ground between the island subspecies and the geographically closest mainland relative, P.t. corbetti. This could be evidence to support the hybridized subspecie theory.

P.t. altaica being so much less robust than the rest of the subspecies indicates a possible long-term environmental stressor. Lack of food and high cursoriality are possible problems, calling for a lighter built. The difference between P.t. altaica and P.t. virgata also gives some support to the old tiger taxonimic idea of these two being different subspecies, but a stress population of the same subspecies is also a legitamate argument. 

P.t. tigris itself is also not too robust. It falls in line with the recently evolved mainland subspecies, essentially. 

Thus, it seems, bar the primitive South chinese variety, all the modern mainland subspecies are less robust compared to the island subspecies. The more recently evovled ones, namely P.t. tigris and P.t. altaica, are especially less robust, indicating a reduction of robusticity with time. 
 
The two most primitive, long and thin skulled subspecies, P.t. sondaica and P.t. amoyensis, are proportionately the most robust of the tigers, with P.t. sondaica being the greatest. The data shows that skull width is not correlated with the rest of the body's proportional mass. This observation also leads me to tentatively say that the Pleistocene giant tigers, P.t. acutidens and P.t. soloensis, were more robust than the Bengal tigers used to predict their masses. Application of the percent differnece of P.t. sondaica to the P.t. soloensis estimate (full dimensional) results in a mass of 500 kg. Though, I dislike applying percent differences directly due to the differences not staying consistent with allometric trends. Scaling the femur to more Javan dimensions results in a mass of 470 kg. 

More to come...
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