Ancient Jaguars

[Balam]

A couple of things to keep in mind when mentioning size overlap between skulls of Pleistocene and extant jaguar forms, in order to reach a solid conclusion one has to evaluate a multitude of skulls to see the size variation within one specific group. This way we can deduct which skulls may belong to females, subadult, and which belong to males. With Pantanal jaguars, we have an extensive dataset of skulls that show a maximum length of around 320 mm, by comparison, the ones from Pa. onca mesembrina approach 340 mm.

A great paper to read for those interested in looking into this further is Craniometric variation in Jaguar subspecies (Panthera onca) from Colombia, by Esteban Payan. Payan is Panthera's regional director for Latin America and the main authority in jaguar ecology in Colombia. He has taken over people like Rafael Hoogesteijn in conducting fieldwork around many Colombian and Brazilian sites to study current jaguar trends. His paper goes into depth by examining the craniometric variations of multiple jaguar populations in Colombia, treating several populations as possible subspecies to see if there was enough differentiation in size and shape of the skulls to substantiate a taxonomic revision. The conclusion from the paper is that there isn't, but nonetheless he reiterates that the skulls from the Pleistocene jaguar were significantly larger than any of the skulls he examined for the multiple supposed jaguar subspecies:

*This image is copyright of its original author

With all the fossil evidence there seems to be a widely accepted scientific consensus that Pa. onca augusta was simply larger than anything seen with extant jaguars today. But if that notion is to be challenged, we are going to need to bring forward multiple skulls to analyze and compare, and unfortunately, most of the skulls that are retained from this species are kept in museums that release very little public information about their sizes. 

The mandible from Mexico is, in my opinion, more than enough solid evidence to showcase that jaguars from the past were larger versions of what is found today, which makes perfect sense as they used to prey on megafauna whose biomass and quantity far surpassed what jaguars are able to feed on naturally these days. It's likely that the large sizes for populations like the Pantanal or Llanos simply represent individuals that didn't dwarf to the same degree as those from forested areas because they retained access to large amounts of mid-sized prey. Still, their sizes do not reach the maximum proportions of their Pleistocene counterparts.

One last point I'd like to make is that the basal species that gave rise to New World jaguars, P. gombaszoegensis was estimated to have been able to attain a mass very similar to the high estimates given for P. o mesembrina and augusta (I'm happy to go over the data for this species at a later time). The reduction in jaguar sizes is a recent phenomenon driven by the ecological constraints of the Holocene, historically they were significantly larger. Reply