Megaherbivores of the late Pleistocene in the proto-pampas of Buenos Aires province, Argentina

Also see https://www.inaturalist.org/journal/milewski/55189-the-empty-pampas-epitome-of-a-biogeographical-mystery-part-1# and https://www.inaturalist.org/journal/milewski/83093-predator-prey-relationship-between-the-largest-sabre-tooth-felid-smilodon-populator-and-the-largest-litoptern-meridiungulate-marauchenia-patachonica-in-south-america-in-the-late-pleistocene#

In the late Pleistocene (https://en.wikipedia.org/wiki/Late_Pleistocene), the following megaherbivores (with body mass exceeding one tonne) occurred in the general vicinity of what is now the port city, Buenos Aires (https://en.wikipedia.org/wiki/Buenos_Aires).

My reference is Cione et al., 2003 (https://web.archive.org/web/20110706084815/http://www.ege.fcen.uba.ar/materias/general/Broken_ZigZagMACN_5_1_19_.pdf).

This fossil fauna is, in palaeontological terms, called the Lujanian fauna (https://en.wikipedia.org/wiki/Lujanian#:~:text=Fauna%20include%20ground%20sloths%2C%20litopterns,and%20the%20armadillo%2Dlike%20Pachyarmatherium. and https://markgelbart.wordpress.com/2020/05/19/the-lujanian-land-mammal-age-the-south-american-equivalent-of-the-rancho-la-brean-land-mammal-age/ and https://www.researchgate.net/figure/Date-of-first-and-last-appearance-of-species-of-Lujanian-fauna-in-both-regions-a_fig5_345652149 and https://pubmed.ncbi.nlm.nih.gov/24676170/).

At that time, sea level was lower than it is today, exposing a wide coastal shelf (https://www.researchgate.net/figure/Map-showing-currents-and-bathymetry-around-the-South-American-continent-Bathymetry-scale_fig2_240692517).

Therefore, the coast was far to the east.

This suggests that

  • the climate was drier than it is today, and
  • the vegetation was savanna, not treeless grassland.

It was this megafauna that Homo sapiens encountered, when our species first arrived, about ?13,000 years ago (https://en.wikipedia.org/wiki/Peopling_of_the_Americas and https://www.the-scientist.com/features/the-peopling-of-south-america-67860 and https://www.smithsonianmag.com/science-nature/how-humans-came-to-americas-180973739/ and https://www.buffalo.edu/news/releases/2017/02/032.html).

Of the taxa of megaherbivores listed and illustrated below, now extinct (https://link.springer.com/chapter/10.1007/978-1-4020-8793-6_2) are

PROBOSCIDEA: GOMPHOTHERIIDAE (https://www.sciencedirect.com/science/article/abs/pii/S0277379114005046):

PILOSA: MEGATHERIIDAE:

PILOSA: MEGALONYCHIDAE:

PILOSA: MYLODONTIDAE:

CINGULATA: CHLAMYPHORIDAE:

NOTOUNGULATA: TOXODONTIDAE:

LITOPTERNA: MACRAUCHENIIDAE:

ARTIODACTYLA: CAMELIDAE:

DISCUSSION

The richest fauna of megaherbivores in modern times is that of Africa, where five genera remain sympatric (https://www.cambridge.org/core/books/megaherbivores/BAAC70497C8D70FBEAE32F462515151B and https://www.booktopia.com.au/megaherbivores-r-norman-owen-smith/book/9780521426374.html and https://www.rhinoresourcecenter.com/pdf_files/136/1368291242.pdf?view).

These are

By comparison, the megaherbivores of the Lujanian fauna were surprisingly diverse, constituting

  • six orders instead of three (with Proboscidea and Artiodactyla occurring in both cases), and
  • 15 genera instead of five.

The single greatest difference is in the xenarthran (https://link.springer.com/chapter/10.1007/978-3-319-98449-0_6) orders Pilosa and Cingulata, containing ground sloths and glyptodonts. The ground sloths varied from mainly browsing (Megatheriidae) to mainly grazing (Mylodontidae).

These xenarthran forms, with what was presumably an extremely slow pace of life (metabolism, reproduction, and growth, https://www.cell.com/current-biology/pdf/S0960-9822(19)30775-4.pdf), have no counterparts in modern faunas of savannas and grasslands.

In the Holocene fauna of South and central America, no megaherbivores whatsoever remain.

The order Artiodactyla was the only one of the Lujanian orders of megaherbivores remaining as an extant herbivore at the time of European arrival in 1516, where Buenos Aires now stands.

And even in this case, the form involved (Ozotoceros bezoarticus celer, https://www.inaturalist.org/observations?taxon_id=601879 and https://ampargentina.org/en/areas/campos-del-tuyu-eng/) has a body mass of only 30 kg - which is a mere 3% of the one-tonne criterion for megaherbivores.

This extreme and abrupt loss of large animals, from what is now the pampas of Buenos Aires province (https://en.wikipedia.org/wiki/Buenos_Aires_Province), remains a great puzzle of Biology.

Posted on August 11, 2023 10:19 AM by milewski milewski

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