Ancient Jaguars

[Balam]

(04-26-2021, 05:49 AM)tigerluver Wrote: Really enjoyed your posts, thanks @Balam !

Good catch on P. balamoides, seems like at least two studies think it's Arctotherium.

Agreed, the next step for the P. atrox in South America idea would be testing one of the remains that are attributed to P. atrox.

We can try to get a rough estimate of the divergence then using the branch lengths. Using the 0.02 scale, the branch length of the P. leo and P. pardus split is about 0.036. The P. onca an P. onca mesembrina split branch length is 0.021. So the genetic gap between P.leo/P. pardus is 1.71 times the gap between P. onca/P. onca mesembrina. In other words P. onca and P. onca mesembrina are 1.71 times more closely related than P. leo/P. pardus. We then have to find a way to calibrate this change to time to find a rate of change. I found a study that estimates the divergence of P. leo/P. pardus at 4.35 MYA. So the rate of change over time would be 4.35 MYA divided by 0.036, equaling 121.1 MYA/1 unit of change. Using stoichiometry, P. onca and P. onca mesembrina would have diverged 2.54 MYA. This is around the divergence of P. leo and the cave lions. By this, P. onca mesembrina would be its own species but most closely related to the jaguar. Molecular dating is fickle however and the confidence intervals are wide.

Evidence into the possibility that P. onca mesembrina is its own taxon is that despite the fossils being around only 10 kya old, they are distinct from extant P. onca. This would mean there was no interbreeding which can define speciation depending on the timespan. 

This could explain why there is a large gap in size noted by Chimento and Agnolin (2017) between P. onca mesembrina and fossil P. onca. They were indeed distinct populations and perhaps size served as a sympatric barrier. 

I wonder if the cave paintings simplify rosettes into spots or if they were accurate. They probably are simplified but if not could show a difference in the coat pattern of P. onca? mesembrina. 

It is still possible P. atrox existed in the region prior to the time of these cave paintings. However, I am leaning toward digging more into P. onca? mesembrina more.

Really good points! Certainly, the idea of P. onca mesembrina being in fact P. mesembrina is an interesting proposition that will require more data and genetic studies to further corroborate but it seems well within the realm of possibilities to me. I still find the likelihood of P. atrox making it so far south into the continent unlikely and believe that the remains studied on the 2017 paper belong to a P. onca ecotype or close relative. What is interesting about this are the "mini-clades" that formed within the genus Panthera, primarily three different clades that comprise closely related species: the lion, jaguar, and tiger clades, in parallel to the Neofelis sp. analogy I've done in the past.

Tiger clade: 

- Panthera zdanskyi
- Panthera tigris

Lion clade:

- Panthera leo? fossilis
- Panthera youngi
- Panthera atrox
- Panthera spelaea
- Panthera leo

Jaguar clade:

- Panthera toscana
- Panthera gombaszoegensis
- Panthera onca (including Panthera onca augusta)
- Panthera onca? mesembrina

Clouded leopards:

- Neofelis nebulosa
- Neofelis diardi

Speciation is a complex subject that is constantly changing and we should always be open to new information that can allow us to have a better understanding of the phylogenetic relationships between species. Jaguars have been relatively understudied in comparison to their other pantherine cousins so further future studies on them and their prehistoric relatives will be very interesting to go over they get published in the future. What is clear to me is that jaguar morphology has always been volatile in relation to the environments they inhabited which is depicted on their diverse biomass, with some pretty drastic size difference among extant jaguars, and even greater discrepancies on absolute values among extinct forms. Reply