When its fossils might be those of another big cat.
This is the case with Panthera atrox, on the right in the above image.
Paleontologists used to call this enormous ice-age predator an American lion, and recent genetic studies do link Atrox to modern lions. (Barnett and others; Switek)
However, some experts disagree, saying that Atrox was either a jaguar or unique – a separate species. (Christiansen and Harris; Sues)
Why does it matter today?
Because, if you take out Atrox, the historical range of modern lions shrinks considerably. And that makes a huge difference to conservationists who are trying to protect this endangered species.
During the ice ages, Panthera atrox used to roam what are now the US and Mexico. (Barnett and others)
At almost 800 pounds, it was one of the few carnivores at La Brea’s asphalt pits that could scare Smilodon fatalis (on the left) away from a kill (Antón), even if Atrox didn’t have saberteeth.
That lack of a notable feature like saberteeth has made things very difficult for paleontologists trying to identify this animal correctly.
Cats all look pretty much alike under the skin. In addition, there are always fewer carnivores than plant eaters, and cats tend to die in places that don’t preserve fossils very well. (Turner and Antón)
So there is very little field evidence to study.
Ever since 1853, when fragmented fossils of an ice-age big cat were first called “Atrox” (meaning “cruel”), this animal has been classified variously as a lion or a jaguar. (Sues; Switek)
Good arguments were made on both sides. It’s just really, really hard to classify cat fossils.
With Atrox, it doesn’t help that lions and jaguars (and leopards) belong to the same natural evolutionary group, called a clade (Hemmer), and once shared a common ancestor. (O’Brien and Johnson)
Then scientists discovered that the La Brea asphalt pits near Los Angeles are carnivore traps. Yay!
Since then, eighty almost complete Atrox individuals have been excavated and studied. Some experts, including the curator of the Page Museum at La Brea, have looked at these fossils very closely. They believe that Atrox can’t be connected to any modern species. (Christiansen and Harris; Switek).
Others have managed to extract some Atrox DNA. They report that it’s close to modern lion DNA. (Barnett and others; Switek)
So which do you believe: what you can see or what the lab tells you?
It’s hard to answer that question when there aren’t any living Atrox cats around.
For laypeople, DNA techniques are akin to magic and therefore can’t be judged. It’s also very impressive to us that many paleontologists accept the Atrox DNA results.
But getting good results from ancient DNA is very challenging, even when there is no complicating modern human DNA to worry about. (Rizzi and others)
In the long run, it’s going to take more research to settle this question beyond doubt.
Edited June 7, 2020.
Featured image: Atrox (right) and Smilodon (left) at the La Brea asphalt pits museum, by Joe Mabel. CC BY-SA 3.0.
Antón, M. 2013. Sabertooth. Bloomington: Indiana University Press.
Barnett, R.; Shapiro, B.; Barnes, I.; Ho, S.; and others. 2009. Phylogeography of lions (Panthera leo ssp) reveals three distinct taxa and a late Pleistocene reduction in geneic diversity. Molecular Ecology. 18(8):1668-1677.
Christiansen, P., and Harris, J. 2009. Craniomandibular morphology and phylogenetic affinities of Panthera atrox: Implications for the evolution and paleobiology of the lion lineage. Journal of Vertebrate Paleontology. 29(3): 934-945.
Hemmer, H.; Kahlke, R-D.; and Vekua, A. K. 2001. The jaguar – Panthera onca gombaszoegensis (Kretzoi, 1938) (Carnivora: Felidae) in the late Lower Pleistocene of Akhalkalaki (South Georgia; Transcaucasia) and its evolutionary and ecological significance. Geobios. 34(4):475-486.
O’Brien, S. J., and Johnson, W. E. 2007. The evolution of cats. Scientific American. 297 (1):68-75.
Rizzi, E.; Lari, M.; Gigli, E.; De Bellis, G.; and Caramelli, D. 2012. Ancient DNA studies: new perspectives on old samples. Genetics Selection Evolution. 44:21. https://gsejournal.biomedcentral.com/articles/10.1186/1297-9686-44-21 Last accessed September 5, 2017.
Sues, H-D. 2010. “The ‘American lion’ is not a lion.” National Geographic Society. https://voices.nationalgeographic.org/2010/05/08/the_american_lion_is_not_a_lio/ Last accessed September 5, 2017.
Switek, B. 2011. American lion, or giant jaguar? In search of Panthera atrox. https://www.wired.com/2011/10/american-lion-or-giant-jaguar-in-search-of-panthera-atrox/ Accessed August 21, 2017.
Turner, A., and M. Antón. 1997. The Big Cats and Their Fossil Relatives: An Illustrated Guide to Their Evolution and Natural History. New York: Columbia University Press.