Ancient Jaguars

[KRA123]

(12-21-2020, 11:38 AM)tigerluver Wrote:

(12-21-2020, 11:17 AM)KRA123 Wrote:

(12-21-2020, 10:43 AM)tigerluver Wrote: Please fill in the gaps in my memory, but the largest Pleistocene P. onca specimens are extrapolated from dentition, not skulls. That can mean two things. This cat had disproportionately large dentition for its skull, so dentition overestimated its size. Or, dentition are more common to find than skulls and thus better represent a wider size range within the species/population. 

The mandible fragment is a great find! The M1 is 21.1 mm, so it's right in the range of a modern jaguar. 

The excel file in this post details the dental record of the jaguar. The average M1 lengths are:

Extant P. onca: 20.17 mm (n=15, 17.4-22.5 mm)
P. o. augusta: 23.08 mm (n=14, 20.7-25.4 mm)
Pleistocene South America P. onca: 22.82 mm (n=15, 22-23.5 mm)

Based on isometric scaling between the aforementioned averages, P. o. augusta would be 1.5x the mass (1.144^3) of extant P. onca and Pleistocene South America P. onca would be 1.45x (1.131^3) the mass. Based on my studies of tigers and ancient lions, dentitions scale with positive allometry in comparison to skull length. I'd expect the same trend in jaguars. Therefore, I'd expect the mass difference to be greater as well.

Can you do this comparison while exclusively using Pantanal jaguars (as opposed to just modern ones) as the modern reference? That's what really needs to be done in order to properly investigate a potential size difference for augusta, since augusta is clearly larger than many modern Jaguar populations. Every study I've read over the years that compares skull measurements of augusta and the largest modern jaguars indicates that there isn't much difference in size in the measurements, as with the jaw fragment that Balam posted.

How many skulls are out there? I’ll take a look at Merriam and Stock later to see if there is a difference in dental proportions.

Is there data available on the mandibles of extant Pantanal jaguars?

I'm not sure how many skulls there are, but isolated skull elements like mandibles etc. can of course be compared between populations. If you look at my first post in this topic, I think I linked to a study that compared some augusta skull measurements with those of a large modern jaguar
*OK, I checked ant that's not the one, I'll have to look for the right one. Reply