Freak Felids - A Discussion of History's Largest Felines

[tigerluver]

(12-04-2017, 08:57 AM)peter Wrote:

(12-03-2017, 11:56 PM)tigerluver Wrote: Panthera atrox in South America?

A new paper was just published stating that a fossil pantherine of South America, known as P. onca mesembrina, has been misidentified at least a few times. The true identity of this cat they assert is Panthera atrox. Their assertion is based on morphological similarities of the specimen to P. atrox rather than the jaguar. The skull they reference is the best example of their point. The paper.

*This image is copyright of its original author

*This image is copyright of its original author

Take a look at the above photos. Which species does the skull in the top photo looks most similar too? Based on visibility of the incisive foramina and the nasal shape, the authors conclude that the skull is actually of P. atrox.

At first take, the logic looks good. However, Dr. Ross Barnett disagrees, mentioning on twitter that cats of these areas have been DNA tested and shown to be jaguar. He cited this paper. 

The authors in a way already had a response built into the paper to such a rebuttal, stating that the ancient jaguar and American lion would have shared the domain. So what does everyone think? Is this skull of a jaguar or an American lion?

JAGUAR OR LION

Based on the shape and relative length of the nasals (a), the shape and relative width of the rostrum (b) and the transisiton from the maxillary bone to the arches ©, I would get to Panthera leo.


JAGUAR SKULLS

Based on the skulls I saw, I'd say that jaguars are closer to lions and leopards than to tigers. Of these three (Panthera leo, Panthera onca and Panthera pardus), however, jaguar skulls show more features typical for tiger skulls.


EVOLUTION

I remember a discussion on another forum quite some years ago. The discussion was about the Americas, lions, jaguars and evolution and it started with a very old skull attributed to Panthera atrox. I participated, but to a degree only.

My feeling was not everything was known about the two big cats in the Americas (referring to Panthera leo and Panthera onca). 

I know there was a split in Panthera a long time ago. Based on the skulls I saw, my guess is tigers split first. They're different from the other three species (not counting P. uncia for now), whereas the other three (P. leo, P. onca and P. pardus) seem to be related. 

Of these three species, lions could be crucial. Their way of life offered many opportunities. When they spread out, they met no opposition. Not in the open landscapes they preferred. 

Leopards adapted to woodland and elevated regions, but jaguars seem to be typical forest cats. I always wondered about the robustness of jaguars, as they mostly hunt smallish animals. In South-America, there are no large herbivores in the forests. Not any more, I mean. Jaguars didn't quite adapt. In a way, they seem to be overpowered. Why is that?

My guess was (referring to the discussion mentioned above), that they're relatively new. Did they migrate from Europe? Lions could and did cross Berengia and settled in the northern part of the Americas, but solitary big cats struggled to cross Berengia. This means that lions should have been the only representative of Panthera in the Americas. But they're not. So where did jaguars come from?

The only logical explanation I could find back then was they have to be related to Panthera atrox. When the climate changed in the Americas and big herbivores started to disappear, lions had to adapt. Maybe prides were replaced by small groups first and maybe some individuals started living on their own later. Maybe the conditions in the northern part of the Americas were too difficult to survive and maybe the conditions in the south offered more opportunities. Over time, individuals in the south adapted to forest life and water.


SIZE AND ROBUSTNESS

The scenario discussed above can explain why jaguars of large size only occur in regions where the forest is less dense (Venezuela, the Pantanal and a few other regions): open woodland offers more opportunities for large herbivores and those who hunt them would be able to maintain a large size. 

This scenario however still doesn't explain the robustness typical for jaguars. So what is the reason?

My feeling is that jaguars are big cats that had to scale down over time in order to survive. The question is where the scaling down started. Did Panthera onca develop in Europe and split a long time ago, or did they develop from a population of Panthera atrox in the southern part of North-America? 

Skulls can help to a degree. Jaguar skulls are closer to Panthera tigris and Panthera leo than to Panthera pardus. My take is they're closer to Panthera leo. Maybe the features in jaguar skulls also seen in tiger skulls are a result of adaptation to forest life.

Quoting the discussion of the South American P. atrox to start another discussion here. Namely, the relationship between S. populator and P. atrox with the new information that P. atrox existed further south than previously thought.

If it is of help for the discussion, the South American P. atrox skull measures around 340 mm complete.

A few niche partitioning scenarios come to mind. As mentioned by @GrizzlyClaws One scenario would be essentially the opposite of the situation in North America, whereby Smilodon would be the larger predator of the two and prey mass ranges would be assigned accordingly. This scenario would be the best fit if we assume Smilodon arrived in South America before P. atrox and used this time to become a superpredator in terms of mass due to the open niche. The smaller P. atrox specimens were pushed to the south later, allowing them to coexist with the larger S. populator if this scenario were to be true. This could be explain why the South American skull is rather small. 

Nonetheless, a single skull cannot speak for the true size of the South American population. This leaves many more questions for discussion. Did two similar size predators coexist or was one indeed pushed to become smaller? If so, was the 10%-20% size difference enough for niche partitioning? Knowing P. atrox was an animal built for a more open landscape, perhaps size did not solely allow niche partitioning but habitat preference did as well. On top of all these questions, could the closeness of niche between P. atrox and S. populator be part of the formula that doomed both species to extinction in the south? Remember, P. onca was able to get past the Pleistocene extinction while both these giants disappeared rather suddenly. Please share your thoughts! Reply