In the footprints of Smilodon populator

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In the footprints of Smilodon populator

In 2018, Angolin and colleagues published a record of a set of footprints from Late Pleistocene Argentina (50 kya) that were most likely made by Smilodon populator. 

*This image is copyright of its original author

A and B represent the manus (front paws) and C and D the pes (hind paws). The manus print was larger than the pes print. The manus measured 17.6 cm in width and 19.2 cm in length. The pes measured measured 13.0 cm in width and 8.5 cm in length. Based on the anatomy, size, and locality of the prints, Angolin and colleagues were confident the maker of these tracks was Smilodon populator. 

From these prints, aspects of the anatomy of the species can be inferred. For one, the prints support the notion that Smilodon populator was front heavy, with more robust forelimbs than hindlimbs. This notion is supported by the depth of the manus footprints being deeper than that of the pes footprints. As such, S. populator was very distinct in its body shape and has no extant felid mimic for comparison today. Another interesting revelation noted from the well developed medial and lateral lobes of the interdigital pads of the prints is that S. populator was partially or even fully plantigrade, strikingly different from extant felids which are digitgrade. Mauricio Anton illustrates the difference in a plantigrade and digitigrade posture in the hindlimbs in this artistic rendition:

*This image is copyright of its original author

The top image shows the hindlimbs in the digitigrade posture and the bottom image shows them in the plantigrade posture. According to the footprints, even the forelimbs were at least to some degree plantigrade, and thus one can imagine how that would modify the posture in the above drawing. Namely, the metacarpals would be much lower and perhaps almost in contact with the ground. Such a plantigrade posture is reasonable as it may better support the excessive mass the frame of S. populator  carries.

Next, the very large size of the species may be displayed by these tracks as asserted by Angolin et al. (2018). The manus tracks are larger than the even the largest tracks from P. spelaea (Deidrich 2011). In this sense, it is reasonable to infer that S. populator was very much larger than other cats. However, it must be noted the pes footprints are not as impressive. They are smaller than even the average P. spelaea (Deidrich 2011). This discrepancy shows the limitation of using footprint measurements in size comparisons when species are proportioned very differently. Nonetheless, it is still probably safe to say the specimen that left these tracks was bigger than most of today's largest felines. Finally, based on the lack of claw marks, the footprints show that S. populator had retractable claws like the majority of other felids. 

All in all, these tracks help reinforce our understanding of this lost giant. In the footprints, we see a cat at its core that has adaptations we have never seen during the Holocene. Who knows what new finds the future holds as we work toward recreating the long lost past.

References:
Agnolin, F. L., Chimento, N. R., Campo, D. H., Magnussen, M., Boh, D., & De Cianni, F. (2019). Large Carnivore Footprints from the Late Pleistocene of Argentina. Ichnos, 26(2), 119-126.

Diedrich, C. G. (2011). Late Pleistocene steppe lion Panthera leo spelaea (Goldfuss, 1810) footprints and bone records from open air sites in northern Germany–evidence of hyena-lion antagonism and scavenging in Europe. Quaternary Science Reviews, 30(15-16), 1883-1906.


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