American lion reconstruction by Sergiodlarosa via Wikimedia Commons

Talk about the American lion today and most people will think you mean the cougar (Puma concolor), a beautiful, lithe predator sadly extinct from most of the Eastern United States, but still doing well in the west, and in South America. However, talk to me about the American lion and we can discuss something a little more exciting: Panthera [leo] atrox! Back in the Pleistocene, lions were “top cat” and had a greater range than puny Homo sapiens: Spain, Siberia, South Africa, Syria were all home to lions (Panthera leo) or cave lions (Panthera [leo] spelaea). So too was North America. Here, a unique subspecies/species had been present since at least the Sangamon interglacial (130-120ka BP) cut off from other lion populations by the thick wall of ice that covered most of Canada. Fossils of this cat have been found as far south as Mexico, but not in South America (reports of lions in Peru are actually supersized jaguars, Panthera onca, testament to how difficult it is to separate the Panthera cats without their distinctive coats). Like its African cousin, the American lion was probably no fan of dense rainforest, which made the isthmus of Darien an impassible barrier.

Statue of Joseph Leidy, holding the Natchez jaw in his left hand. Public domain image.

The first palaeontologist to identify a lion in the American fossil record was the great Joseph Leidy, who found a very interesting piece of mandible with molars, premolars, and canine from the site of Natchez, Mississippi, collected in 1836. The jawbone is massive and covered in a heavy coating of iron oxide. However weird the fossil, Leidy was obviously proud of his inference as he chose to be immortalised in sculpture holding the piece of bone (the statue can be seen beside the academy of natural sciences in Philadelphia). Leidy was the first to suggest that lions had roamed the prairies of North America, but since then researchers have been eager to turn atrox into anything other than a lion! We have ancient DNA evidence that firmly cements the American lion’s position with the cave lion, but luminaries as great as G. G. Simpson preferred to think of atrox as a giant jaguar! This misattribution even continues today, with a recent paper by Christiansen and Harris also calling atrox a jaguar.

If not a jaguar, what exactly is Panthera leo atrox? Above all else, it was a truly enormous cat. Considerably larger than the sympatric sabretooth Smilodon fatalis, and probably the largest felid that ever lived, the average American lion was about 25% larger than the largest African lion, with a noticeably different look. Probably maneless (like the cave lion) but with longer legs and a proportionally smaller skull, it was a group-living animal (but with smaller pride size). Evidence for this can be found in the remains of P. atrox from the incredible tarpit site of Rancho la Brea in greater Los Angeles, where it is the fourth most common fossil carnivore after dire wolf (Canis dirus), dirktooth (S. fatalis), and coyote (C. latrans). [Even so, there are approx. 30 Smilodon bones for every atrox]. At la Brea, there is an excess of young males; in African lions, this is the period when they would be leaving the natal pride to set out on their own for the first time- at this critical age curiosity can kill the cat.

Bottom to top: African lion (Panthera leo), cave lion (Panthera spelaea), American lion (Panthera atrox). Image © Nobuyuki Yamaguchi

Another site, famous for its American lion fossils is Natural Trap Cave (NTC) in Wyoming. This cave consists of an 80-foot drop from a semi-concealed roof entrance that was rapidly fatal to any animal unlucky enough to plunge down it. A semi-articulated lion skeleton (KUVP31417/KUVP33057) consisting of skull, mandible, left femur, tibia, and fibula was found there. This lion was a real survivor, prior to its tumble down the hole. The teeth are worn practically to the gum, while the leg bones show signs of osteoarthritis so severe that it probably had trouble walking. Maybe the short, sharp drop was a kinder ending for this animal than the inevitable slow decline into starvation that awaited it. The lion material is so well preserved that it was one of the few American sites to contain ancient DNA (see Barnett et al.). NTC was in the news last year (2014) as it was reopened for study for the first time in 30 years by a plucky group of speleologists, geologists, and palaeontologists looking to collect some more fabulous data from this crucial site. Much of the excavation was livetweeted by @laelaps, @paleololigo, and @johnlogsdon, so pay attention to them for further updates!

Written by Ross Barnett (@DeepFriedDNA)

Further Reading:

Barnett, R., B. Shapiro, I. Barnes, S. Y. W. Ho, J. Burger, N. Yamaguchi, T. F. G. Higham, et al. “Phylogeography of Lions (Panthera Leo Ssp.) Reveals Three Distinct Taxa and Late Pleistocene Reduction in Genetic Diversity.” Molecular Ecology 18, no. 8 (2009): 1668-77. [Full Text]

Burns, J. A., and R. R. Young. “Pleistocene Mammals of the Edmonton Area, Alberta. Part 1. The Carnivores.” Canadian Journal of Earth Sciences 31 (1994): 393-400.[Abstract]

Christiansen, P., and J. M. Harris. “Craniomandibular Morphology and Phylogenetic Affinities of Panthera Atrox: Implications for the Evolution and Paleobiology of the Lion Lineage.” [In English]. Journal of Vertebrate Paleontology 29, no. 3 (Sep 12 2009): 934-45.[Abstract]

Kurtén, B. “The Pleistocene Felidae of Florida.” Bulletin of the Florida State Museum Biological Sciences 9, no. 216-273 (1965).[Full Text]

Leidy, J. “Description of an Extinct Species of American Lion: Felis Atrox.” Transactions of the American Philosophical Society 10 (1853): 319-21.[Full Text]

Martin, L. D., and B. M. Gilbert. “An American Lion, Panthera Atrox, from Natural Trap Cave, North Central Wyoming.” Contribs. to Geology, Univ. Wyoming 16, no. 2 (1978): 95-101.[Abstract]

Merriam, J. C., and C. Stock. The Felidae of Rancho La Brea. Carnegie Institute of Washington Publications, 1932.[Book]

Montellano-Ballesteros, M., and G. Carbot-Chanona. “Panthera Leo Atrox (Mammalia: Carnivora: Felidae) in Chiapas, Mexico.” The Southwestern Naturalist 54, no. 2 (2009): 217-22.[Abstract]

Simpson, G. G. “Large Pleistocene Felines of North America.” American Museum Novitates 1136 (1941): 1-27.[Full Text]

Stock, C. “A Census of the Pleistocene Mammals of Rancho La Brea, Based on the Collections of the Los Angeles Museum.” Journal of mammalogy 10, no. 4 (1929): 281-89.[Abstract]

Wheeler, H. Todd., and G. T. Jefferson. “Panthera Atrox: Body Proportions, Size, Sexual Dimorphism, and Behaviour of the Cursorial Lion of the North American Plains.” In Papers on Geology, Vertebrate Paleontology and Biostratigraphy in Honor of Michael O. Woodburne, edited by L. B. Albright III. Flagstaff, Arizona: Museum of Northern Arizona Bulletin, 2009.[Full Text]

Yamaguchi, N., A. Cooper, L. Werdelin, and D. W. MacDonald. “Evolution of the Mane and Group-Living in the Lion (Panthera Leo): A Review.” Journal of Zoology 263 (2004): 329-42.[Abstract]