Predator-prey relationship between the largest sabre-tooth felid (Smilodon populator) and the largest litoptern meridiungulate (Macrauchenia patachonica), in South America in the late Pleistocene

@tonyrebelo @jeremygilmore @paradoxornithidae @diegoeseolivera @andrespautasso @marshall20 @matthewinabinett

Also see https://www.inaturalist.org/posts/82986-megaherbivores-of-the-late-pleistocene-in-the-proto-pampas-of-buenos-aires-province-argentina#

Felids (https://en.wikipedia.org/wiki/Felidae) evolved in the Old World.

Meridiungulates (https://en.wikipedia.org/wiki/South_American_native_ungulates) evolved in South America when this continent was still isolated, unconnected to North America (https://www.youtube.com/watch?v=X0AqBCT8n4g).

When a land-bridge arose from North America to South America, about 2.7 million years ago (https://en.wikipedia.org/wiki/Great_American_Interchange), felids met meridiungulates - and began to prey on them.

By the late Pleistocene, both the sabre-tooth felid Smilodon (https://en.wikipedia.org/wiki/Smilodon) and the litoptern genus Macrauchenia (https://en.wikipedia.org/wiki/Macrauchenia) had undergone gigantism in South America. This resulted in

• the largest felid on Earth (Smilodon populator, 300 kg, https://prehistoric-fauna.com/Smilodon-populator), and
• the largest of all litopterns (https://prehistoric-fauna.com/Macrauchenia-patagonica).

Two decades ago, this is how the BBC (https://en.wikipedia.org/wiki/Walking_with_Beasts) reconstructed the scene:
https://www.google.com.au/search?q=BBC+reconstruction+of+macrauchenia&sca_esv=556915837&sxsrf=AB5stBgHlq20nzot7-1jomxc76IzFUmw7A%3A1692052814558&source=hp&ei=Tq3aZKKuIJOd4-EP4p6T4AI&iflsig=AD69kcEAAAAAZNq7XmCDDyrcWcQoxkvcH2ZnRl2pG1bl&ved=0ahUKEwiijc73m92AAxWTzjgGHWLPBCwQ4dUDCAs&uact=5&oq=BBC+reconstruction+of+macrauchenia&gs_lp=Egdnd3Mtd2l6IiJCQkMgcmVjb25zdHJ1Y3Rpb24gb2YgbWFjcmF1Y2hlbmlhMgUQIRigATIFECEYoAFIpp4BUJgIWLqTAXAEeACQAQKYAa4CoAGKP6oBCDAuNy4yOS4xuAEDyAEA-AEBqAIKwgIHECMY6gIYJ8ICBxAjGIoFGCfCAgQQIxgnwgIHEAAYigUYQ8ICExAuGIMBGMcBGLEDGNEDGIoFGEPCAggQABiKBRiRAsICExAuGIoFGLEDGIMBGMcBGNEDGEPCAg0QABiKBRixAxiDARhDwgINEC4YigUYsQMYgwEYQ8ICFhAuGIoFGLEDGIMBGMkDGMcBGNEDGEPCAggQABiKBRiSA8ICChAAGIoFGLEDGEPCAhMQLhiKBRixAxjHARjRAxjUAhhDwgILEAAYgAQYsQMYgwHCAgUQABiABMICBRAuGIAEwgIHEAAYgAQYCsICBhAAGBYYHsICCBAAGBYYHhgKwgILEAAYFhgeGPEEGArCAggQABiKBRiGA8ICBxAAGA0YgATCAggQABgIGB4YDcICCBAhGBYYHhgdwgIHECEYoAEYCg&sclient=gws-wiz#fpstate=ive&vld=cid:30826782,vid:sap-lHLrMC0 and https://www.google.com.au/search?q=BBC+reconstruction+of+macrauchenia&sca_esv=556915837&sxsrf=AB5stBgHlq20nzot7-1jomxc76IzFUmw7A%3A1692052814558&source=hp&ei=Tq3aZKKuIJOd4-EP4p6T4AI&iflsig=AD69kcEAAAAAZNq7XmCDDyrcWcQoxkvcH2ZnRl2pG1bl&ved=0ahUKEwiijc73m92AAxWTzjgGHWLPBCwQ4dUDCAs&uact=5&oq=BBC+reconstruction+of+macrauchenia&gs_lp=Egdnd3Mtd2l6IiJCQkMgcmVjb25zdHJ1Y3Rpb24gb2YgbWFjcmF1Y2hlbmlhMgUQIRigATIFECEYoAFIpp4BUJgIWLqTAXAEeACQAQKYAa4CoAGKP6oBCDAuNy4yOS4xuAEDyAEA-AEBqAIKwgIHECMY6gIYJ8ICBxAjGIoFGCfCAgQQIxgnwgIHEAAYigUYQ8ICExAuGIMBGMcBGLEDGNEDGIoFGEPCAggQABiKBRiRAsICExAuGIoFGLEDGIMBGMcBGNEDGEPCAg0QABiKBRixAxiDARhDwgINEC4YigUYsQMYgwEYQ8ICFhAuGIoFGLEDGIMBGMkDGMcBGNEDGEPCAggQABiKBRiSA8ICChAAGIoFGLEDGEPCAhMQLhiKBRixAxjHARjRAxjUAhhDwgILEAAYgAQYsQMYgwHCAgUQABiABMICBRAuGIAEwgIHEAAYgAQYCsICBhAAGBYYHsICCBAAGBYYHhgKwgILEAAYFhgeGPEEGArCAggQABiKBRiGA8ICBxAAGA0YgATCAggQABgIGB4YDcICCBAhGBYYHhgdwgIHECEYoAEYCg&sclient=gws-wiz#fpstate=ive&vld=cid:d4718a6d,vid:jLyMwPinGFE

Adults of Macrauchenia patachonica (https://upload.wikimedia.org/wikipedia/commons/f/f1/Phenacodus_primaevus_and_Macrauchenia_patachonica.jpg) weighed about 1100 kg - similar to the extant rhinoceros Diceros bicornis (https://en.wikipedia.org/wiki/Black_rhinoceros).

Macrauchenia patachonica also resembled rhinos in retaining three toes on each foot.

However, M. patachonica was unlike any ungulate (https://www.sciencedirect.com/science/article/abs/pii/S0016699521000425).

It combined the following:

• lengthening of the cervical vertebrae (https://en.wikipedia.org/wiki/Cervical_vertebrae), without development of neural spines on the vertebrae of the withers (compare https://en.wikipedia.org/wiki/Neural_spine_sail#/media/File:A_wisent_skeleton.JPG),
• extreme reinforcement of the upper bone of the forelimb (humerus) against sideways stresses,
• disparity between fore- and hindlimbs, in that the femur (https://en.wikipedia.org/wiki/Femur) is anomalously long relative to the tibia (https://en.wikipedia.org/wiki/Tibia), and
• retraction of the nasal bones (https://en.wikipedia.org/wiki/Nasal_bone), so that the nares (https://en.wikipedia.org/wiki/Anterior_nares) are posterior to the orbits (https://upload.wikimedia.org/wikipedia/commons/6/62/Anales_del_Museo_P%C3%BAblico_de_Buenos_Aires_%281864%29_%2817980766940%29.jpg and https://www.prehistoricstore.com/item.php?item=1832).

Together, these oddities suggest that M. patachonica

• ran with the neck horizontal (unlike the upright neck of running giraffes),
• specialised on jerking sideways - to a degree unknown in any ungulate - as an evasive tactic during attack, and
• was difficult to asphyxiate by the clamping action of the felid mouth (compare https://www.facebook.com/watch/?v=750842359339379 and https://www.youtube.com/watch?v=XZZKeplSUeM).

Farina et al. (2005, http://www.scielo.org.ar/img/revistas/ameg/v42n4/html/v42n4a07.htm and http://www.scielo.org.ar/scielo.php?pid=S0002-70142005000400007&script=sci_arttext&tlng=en) have suggested that the sideways evasive action was one of 'swerving', when chased by S. populator.

This seems reasonable enough, in as far as it goes.

However, what Farina et al. (2005) may possibly have missed is the following addition to the rationale.

It seems to be uncontroversial that

• Panthera leo, after leaping on to large-bodied prey, obtains purchase with both the teeth and the claws (https://www.youtube.com/watch?v=kIj3jmpKaTs and https://www.123rf.com/photo_14228714_male-lion-attack-huge-buffalo-bull-while-riding-on-his-back.html and https://www.alamy.com/stock-photo-lion-pride-attacking-a-buffalo-a-lioness-leaps-onto-the-back-of-a-13074844.html and https://www.alamy.com/stock-photo-male-lion-on-the-back-of-a-buffalo-being-hunted-by-a-pride-of-lions-102211687.html?imageid=2D0E73A6-7646-4D90-BE44-0260A14D95CF&p=161494&pn=1&searchId=31a81c5cb0c72629e4d4e552bbdaaf30&searchtype=0),
• this hectic use of the upper canines was unlikely in sabre-toothed felids, particularly Smilodon, because these teeth were specialised for surgical precision - and thus fragile,
• S. populator depended on immobilising its prey by means of a combination of its body mass, the strength of its forelimbs, and the traction of its claws, unaccompanied by the teeth, and
• only once the prey animal was felled could the teeth be applied, presumably to the throat.

Based on this 'concensus view', plus an assumption that S. populator hunted alone, my original thought is as follows.

Crucial to evasion of this particular specialised predator would have been an ability not only to swerve, but more particularly to 'buck sideways', in order to shake the body of the felid off the body of M. patachonica.

Such dislodging of the predator would allow the prey animal to resume acceleration in an attempt to outdistance the pouncer.

Sideways bucking in M. patachonica would help to explain the odd configuration of the bones - particularly the upper limbs but also the feet (retention of three toes) and the neck (carried horizontally).

Extant ungulates buck mainly vertically, as best-illustrated in rodeos (https://en.wikipedia.org/wiki/Rodeo and https://en.wikipedia.org/wiki/Bucking_horse and https://www.youtube.com/watch?v=v35XURqbJ7M).

However, this has limited effectiveness against e.g. Panthera leo, because the felid can latch on with the teeth as well as the claws, and up-and-down movement is difficult when the body mass of the predator exceeds a quarter of that of the prey.

Bucking sideways would tend to use the body mass of the felid against it, with only the traction of the claws to overcome.

Certain ungulates possess dermal shields (https://academic.oup.com/biolinnean/article-abstract/36/1-2/169/2646965?login=false and https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1095-8312.1989.tb00489.x). Equus quagga is an extant example, with reinforced hide on the haunches (please see comment below).

If M. patachonica possessed a dorsal dermal shield in addition to the adaptations mentioned above, then this would limit the traction of the claws in the first place.

However, this is probably unknowable, given that all litopterns (https://en.wikipedia.org/wiki/Litopterna) have been extinct for thousands of years, leaving us with only bones, not skin.

Posted on August 14, 2023 11:00 AM by milewski