Macrauchenia patachonica
Fig 1. An artists interpretation of an adult Macrauchenia patachonica with offspring. This illustration uses a prorhisces similar to that of the elk (Alces alces)
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Taxonomy
Macrauchenia patachonica is the sole valid species of the genus Macrauchenia (16). The genus name means ‘Long llama’, despite this being suggestive of an affinity with the camelids Macrauchenia belongs to a unique family of mammals called Macraucheniidae which also includes the late Pleistocene Xenorhinotherium bahiense (12). Within the family, the species Macrauchenopsis ensenadensis of the middle Pleistocene (16) appears to be the closest relative, followed by the aforementioned Xenorhinotherium (12).
The Macraucheniids belong to an entirely extinct order of South American animals called Litoptera, which also contains the equally enigmatic Proterotheriids of which the Late Pleistocene Neolicaphrium recens is a member (16). The phylogenetic placement of Litopterns is very unclear, recent studies have put them variously as a sister group to the odd-toed ungulates (Perissodactyla) (3) or the African mammals (Afrotheria) (1), in either case they are a lineage distantly related to any extant mammal.
Distribution and Age
Fossils of Macrauchenia patachonica range from southern Patagonia to the Pampas in the East and from Southern Chile to Southern Peru in the West (5). The species Macrauchenia patachonica is known from the Ensenadan (0.8 – 1.2 mya) in the Middle Pleistocene (Blanca et al 2021), but are most common in the subsequent Lujanian age (11kya – 800kya), which stretches to the end of the Pleistocene in South America (Blanca et al 2021). The extinction of Macrauchenia occurs sometime around the Pleistocene-Holocene boundary.
Fig 2. Fossil sites of Macrauchenia patachonica and the estimated natural range based on Phylacine modelling (18). Images are samples of nature areas within the natural range.
Terms of use: The images used are attributed to (From top image to bottom): Allan Patrick, Deyvid Setti and Eloy Olindo Setti, and Hardscarf. Under a CC BY-SA 2.0, 3.0 and 4.0 license respectively. All images are edited.
Morphology and Ecology
Macrauchenia is a peculiar looking animal, it’s bodyplan is reminiscent of a camel, but distinct in many ways. It would have been a large animal, estimates vary but usually place it around a metric tonne (Farina et al 2005) The animal had a relatively long neck, which may have aided in browsing or served a different unclear purpose (10).
Macrauchenia was probably digitigrade, meaning it walked on its toes rather than its entire foot or on hooves, a feature unlike most modern megafaunal herbivore (10)s, with a notable exception being elephants which are also digitigrade but have fleshy pads as supporting structures. The limbs were long and strongly built, with the species probably capable of running at high speeds between 43 and 68 km an hour according to estimates by Blanco et al 2021. Puzzlingly the forelimbs of Macrauchenia are much more powerful and suited for running than the hindlimbs, the difference in limb proportions is higher than anything found in living ungulates (10) and it indicates a separate function of the forelimbs. If Macrauchenia was a browser this could explain the powerful forelimbs as a browsing aid, or perhaps the species utilised digging as a means of feeding on roots or digging for water in arid habitats (10). A more locomotive explanation may include using the forelimbs to rapidly brake during running (10). Blanco et al 2021 suggests that Macrauchenia ran with its head and neck positioned horizontally with the body, exerting a greater load on the front limbs. The hind limbs may be comparatively short because they were used in rapid acceleration which favours shorter tendons, perhaps to quickly escape from predators and/or swift movement between feeding areas (10). Additionally, the limbs are well suited to resist sideways forces, which has been interpreted as an indication of swerving as an anti-predatorial behaviour (11).
The nasal openings are located at top and back of the skull, similarly to the blowhole in whales, a unique feature in terrestrial mammals (10). Due to the lack of an analogue, it is difficult to ascertain the function of the strange location of the openings, perhaps like often depicted it was connected to a proboscis, similarly to in tapirs (10, 14). Evidence of a proboscis can be found in a putative pictograph of the close relative Xenorhinotherium bahiense from early South American peoples (15). A 2018 paper suggested that Macraucheniids lacked the skeletal adaptations of a true proboscis and indicated that the adaptations resembled those of the European Elk (Alces alces) and may constitue a prorhisces, which is a nasal extension that lacks the musculature to move independently (15). In elk this is an aquatic adaptation used for buoyancy and/or air capacity (15), but this seems unapplicable in the xeric landscapes inhabited by Macrauchenia. Intead it may have played a role in avoiding dust entering the nose as with Saiga antelopes (Saiga tartarica), which would make sense in the arid grasslands often inhabited by Macrauchenia (10).
There are some disagreements on the diet of Macrauchenia patachonica (7, 9). Examinations of phytoliths (Small pieces of silica which build up in plants) in one individual suggests that the species integrated wooded vegetation, shrubs and grasses into its diet (7), overall this individual was a mixed feeder with a slight preference for grasses (7). The animal incorporated grasses which thrive in different amounts of rainfall and temperature, indicating a somewhat wide grazing niche (7).
The abundance of microscopic scars and pits left on the enamel of Macrauchenia are indicative of a primary grazer, with very few individuals showing a low degree of scratches (5). This is because grass has a tough structure to breakdown and often include particles of dirt when ingested (5). The structure of the teeth suggests it was not suited for extensive breakdown of grass, but this may simply indicate that breakdown occurred in the stomach, much like in some Artiodactyls (5) but can also be suggestive of a primarily browsing role (4).
The carbon-13 concentrations in the fossils of Macrauchenia suggests a mixed consumption of C3 and C4 plants, which usually indicate a mixed feeding diet (2, 5, 9), with C4 components indicating grazing and C3 elements primarily browsing. However, the abundance of C3 grasses demonstrated in the diet of an individual call this conclusion into question. (7). Instead this could indicate that the species inhabited a relatively arid grassland, a mixed grass-woodland biome, or some combination of the two (5).
These discrepancies in diet can perhaps be accounted for by the extensive range with climatic variability of Macrauchenia patachonica, which occupied large swathes of Southern South America and would have inhabited habitats as different as the cold drylands of Patagonia to the subtropical Pampas grasslands (5), the areas in Patagonia inhabited may have had temperatures ranging from -10 degrees celsius to +20 as well dry regions with almost no rainfall (5), as such available vegetation would have differed considerably.
Macrauchenia may have been a group living animals, since three individuals have been found together (10), little can be inferred about their group behaviour and it is unclear how large such units were. In combination with capable running and huge size, it has been suggested that Macrauchenia covered large distances in search of food and may even have been migratory (10).
Macrauchenia would have overlapped range with a host of other large herbivores including giant ground sloths such as Megatherium, Lestodon and Mylodon, the glyptodonts Glyptodon and Doedicurus, the equines Equus ferus and Hippidion francisci, Toxodon platensis, various species of cervid and the enigmatic Neocaliphrium recens. In terms of carnivores, Smilodon populator appears to have been the primary predator of Macrauchenia based on Carbon-13 and Nitrogen-15 concentrations in the two species, in fact in the pampas it appears to have been the dominant prey item in the diet of the sabertooth cat (2). The extinct canid Protocyon troglodytes also appears to have been a significant predator of Macrauchenia (2) and the jaguar (Panthera onca) on occasion (2), though due to the large size of Macrauchenia this may have been primarily juvenile or sub-adult individuals. It’s unclear what the role of Arctotherium tarijense and Theriodictes tarijensis were as predators of Macrauchenia.
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Fig 3, The illustrated cranium of Macrauchenia patachonica,. Note the large nasal openings at the top of the skull, a feature unique to the Macrauchenids
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Citations
1. Avilla, L.S. & Mothé, D.. (2021). Out of Africa: A New Afrotheria Lineage Rises From Extinct South American Mammals. Frontiers in ecology and evolution 9.
2. Bocherens, H., Cotte, M., Bonini, R., Scian, D., Straccia, P., Soibelzon, L. & Prevosti, F.J.. (2016). Paleobiology of sabretooth cat Smilodon populator in the Pampean Region (Buenos Aires Province, Argentina) around the Last Glacial Maximum: Insights from carbon and nitrogen stable isotopes in bone collagen. Palaeogeography, palaeoclimatology, palaeoecology 449, 463-474.
3. Chimento, N.R. & Agnolin, F.L.. (2020). Phylogenetic tree of Litopterna and Perissodactyla indicates a complex early history of hoofed mammals. Scientific reports 10 (1),13280.
4. Dantas, M.A.T., Lobo, L.S. & Bernardes, C.. (2020). Comments on "fantastic beasts and what they ate: Revealing feeding habits and ecological niche of late Quaternary Macraucheniidae from South America” by K. de oliveira, T. Araújo, A. Rotti, D. Mothé, F. Rivals, L.S. Avilla quaternary science reviews 231 (2020) 106178. Quaternary science reviews 250.
5. de Oliveira, K., Araújo, T., Rotti, A., Mothé, D., Rivals, F. & Avilla, L.S.. (2020a). Fantastic beasts and what they ate: Revealing feeding habits and ecological niche of late Quaternary Macraucheniidae from South America, Quaternary science reviews 231, 106178.
6. de Oliveira, K., Araújo, T., Rotti, A., Mothé, D., Rivals, F. & Avilla, L.S.. (2020b). In defense of fantastic beasts and what they ate: A case reinforcing the importance of taxonomy for paleoecology. Quaternary science reviews 250.
7. de Oliveira, K., Asevedo, L., Calegari, M.R., Gelfo, J.N., Mothé, D. & Avilla, L.. (2021). From oral pathology to feeding ecology: The first dental calculus paleodiet study of a South American native megamammal. Journal of South American earth sciences 109, 103281.
8. Domingo, L., Prado, J.L. & Alberdi, M.T.. (2012). The effect of paleoecology and paleobiogeography on stable isotopes of Quaternary mammals from South America. Quaternary science reviews 55,103-113.
9. Domingo, L., Tomassini, R.L., Montalvo, C.I., Sanz-Pérez, D. & Alberdi, M.T.. (2020). The Great American Biotic Interchange revisited: a new perspective from the stable isotope record of Argentine Pampas fossil mammals. Scientific reports 10 (1), 1608.
10. Blanco, E., R., Jones, W.W., Yorio, L. & Rinderknecht, A.. (2021). Macrauchenia patachonica Owen, 1838: limb bones morphology, locomotory biomechanics, and paleobiological inferences. Geobios (Unpublished). .
11. Fariña, R.A., Blanco, R.E. & Christiansen, P.. (2005). Swerving as the escape strategy of Macrauchenia patachonica Owen (Mammalia; Litopterna). Ameghiniana 42 (4), 751-760.
12. Forasiepi, A.M. & MacPhee, R.D.E. (2016). Exceptional skull of Huayqueriana (Mammalia, Litopterna, Macraucheniidae) from the late Miocene of Argentina, American Museum of Natural History, New York, NY.
13. Gallo, V., Avilla, L.S., Pereira, R.C.L. & Absolon, B.A.. (2013). Distributional patterns of herbivore megamammals during the Late Pleistocene of South America, Anais da Academia Brasileira de Ciências 85 (2), 533-546.
14. MacFadden, B.J. & Shockey, B.J.. (1997). Ancient feeding ecology and niche differentiation of Pleistocene mammalian herbivores from Tarija, Bolivia: morphological and isotopic evidence. Paleobiology 23 (1), 77-100.
15. Morcote-Ríos, G., Aceituno, F.J., Iriarte, J., Robinson, M. & Chaparro-Cárdenas, J.L.. (2021). Colonisation and early peopling of the Colombian Amazon during the Late Pleistocene and the Early Holocene: New evidence from La Serranía La Lindosa. Quaternary international 578, 5-19.
16. Scherer, C., Pitana, V. & Ribeiro, A.M.. (2009). Proterotheriidae and Macraucheniidae (Litopterna, Mammalia) from the Pleistocene of Rio Grande do Sul State, Brazil. Revista brasileira de paleontologia 12 (3), 231-246.
17. Westbury, M., Baleka, S., Barlow, A., Hartmann, S., Paijmans, J.L.A., Kramarz, A., Forasiepi, A.M., Bond, M., Gelfo, J.N., Reguero, M.A., López-Mendoza, P., Taglioretti, M., Scaglia, F., Rinderknecht, A., Jones, W., Mena, F., Billet, G., de Muizon, C., Aguilar, J.L., MacPhee, R.D.E. & Hofreiter, M.. (2017). A mitogenomic timetree for Darwin’s enigmatic South American mammal Macrauchenia patachonica. Nature communications 8 (1), 15951.ø
18. Faurby, S., Pedersen, R. Ø., Davis, M., Schowanek, S. D., Jarvie, S., Antonelli, A., & Svenning, J.C. (2020). PHYLACINE 1.2.1: An update to the Phylogenetic Atlas of Mammal Macroecology. doi:10.5281/zenodo.3690867