Missing Pieces of the Ecosystem

The extinctions of Pleistocene megafauna had a profound impact on ecosystems. Large herds of megafauna with the exception of bison were no longer foraging, trampling, and defecating on the landscape in North America. Plant communities were altered, and many predators and scavengers disappeared when all that meat was no longer available. A new study of fossil bones from sites located in the Edward’s Plateau, Texas examined some of the changes in the surviving fauna following the extinction of late Pleistocene megafauna. The authors of this study looked at bone chemistry to determine diet of species before and after extinctions, and they also estimated average size based on fossil remains (in some cases just the teeth). (I should note studies based on stable isotope analysis should be viewed with caution. See: https://markgelbart.wordpress.com/2016/06/24/trust-the-coprolites-not-the-stable-isotope-analysis/ )

Edward’s Plateau, Texas. Study area of the below reference.

The Edward’s Plateau is located in the middle of the North American continent and hosted species from the West, East, and those that had a continental distribution. During the Pleistocene there were grazers, browsers, and mixed feeders. Grazers included mammoths, bison, and horses. Browsers included mastodon, deer, pronghorn, tapir, llama, rabbits, and hare (jackrabbit). Gompotheres, camels, and peccaries were mixed feeders. The authors of this study could not obtain data from ground sloths, glyptodonts, and helmeted musk-ox to determine what they ate. Scientists found saber-toothed cats (Smilodon fatalis) and scimitar-toothed cats (Homotherium latidens) both had a specialized diet of juvenile grazers that were still nursing. These predators fed mostly upon young mammoths and bison that were still dependent upon their mother’s milk. Elephants lactate for up to 3 years after giving birth. Still nursing mammoths faced danger when they wandered away from the safety of the herd. Giant lions (Panthera atrox) and dire wolves (Canis dirus) had more generalist diets, eating grazers and mixed feeders. Black bears mostly ate plants. The lone specimen of giant short-faced bear (Arctodus simus) in this study had a diet similar to the striped skunk. Strange as it might seem, this giant bear was eating insects, mice, and fruit. Jaguars replaced other large Pleistocene predators as the main predator of juvenile bison and horses, following the extinctions of proboscideans, saber-tooths, giant lions, and dire wolves, but only for a short period of time. Horses are absent in the fossil record during the early Holocene, but this study and others suggest they lingered for a while after other Pleistocene megafauna went extinct. Eventually, jaguars become absent in the fossil record of this region, though historical accounts indicated they occurred as far east as Louisiana into historical times. They probably occurred in low numbers in this region. Cougars, formerly absent in the fossil record from this region, became more common.

In the Edwards Plateau, Texas jaguars temporarily replaced saber-toothed cats as a predator of juvenile bison and horses during the early Holocene about 10,000 years ago. Jaguars eventually became rare in this region too. Chart from the below referenced paper.

After the extinction of Pleistocene megafauna surviving herbivores responded differently. Deer and hare became larger, while cottontail rabbits and bison grew smaller. Hares and rabbits shifted to a diet of plants preferred by grazers.

Reference:

Smith, F., E. Elliot Smith, A. Villegenor

“Late Pleistocene Megafauna Extinction Leads to Missing Pieces of Ecological Space in North American Mammal Community”

PNAS 119 (39) September 2022

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