The simbakubwa, a giant Miocene lion.

[tigerluver]

Had some time to read up on this new find. While likely large, the size here may be heavily over-exaggerated. 

Starting with the estimation itself, note there are three estimates: one by Morlo (1308 kg), another by Van Valkenburgh (VV) for felids (1554 kg), and finally Van Valkenburgh for carnivoras >100 kg (280 kg). 

Morlo's (1999) equation has extremely overestimated other more complete specimens of creodonts. The equation is extremely positively allometric (scale factor 3.5104), thus running the innate risk of hefty, hefty overestimation. 

The VV equation for felids simply is not valid here. Felids have proportionately much, much smaller skulls compared to their bodies than creodonts. Using a felid based equation to estimate the big toothed, extremely long headed creodont will give a very inaccurate and over-exaggerated value.

Note H. sulzeri (MNHN.F.Or 311-51) estimates in this paper (Morlo: 1276 kg; VV1: 1185 kg). Now let's take a look at the post-cranial remains of the same specimen (I've also added the table so we can see how H. sulzeri compares in bone measurements to Simbakubwa:

*This image is copyright of its original author

Based on the scale bars, the ulna measures just about 320 mm and humerus' distal articular width a bit less than 60 mm. These values are no larger than the size of a small-medium lioness (150 kg). Knowing that postcranial remains are always more accurate than cranial remains, the only conclusion that is to be made is that the Morlo and VV equation have overstimated H. sulzeri by 8 times. Seeing how H. sulzeri is a bit smaller than Simbakubwa, a mass of 1500 kg just does not seem accurate for Simbakubwa.

I will skip over the second VV equation as universal equations are not accurate as a single line cannot simply account for all the variations we see in species.

Next we have the associated long bones themselves. The authors state they believe the long bones from the same locality as the jaw do not belong to Simbakubwa despite the original assignment to the same individual as the mandible by the finders of the fossils. These fossils were collected close to one another. Sorkin also believed these were from the same individual. I will leave that decision to the reader. Nonetheless, here are the specimens:

*This image is copyright of its original author

The humerus and ulna are both about 330 mm. In both cases somewhat smaller than the average male lion. If we accept these specimens as Simbakubwa, we see these specimens are a bit larger than H. sulzeri, as predicted by the dental comparisons.

The authors do acknowledge the uncertainty of estimate in the work. Here we can see how skewed estimate can be when comparing one taxa to another. Simbakubwa clearly had a bigger head than a lion, but it probably was not any bigger. Reply