A group of scientists think they’ve found the answer to what caused the disappearance of most of the megafauna species that lived near the La Brea Tar Pits. They took sediment cores from several sites near the tar pits and measured the quantities and composition of pollen and the amount of charcoal present–an indicator of fire frequency. They radio-carbon dated the layers of the core. They also used radio-carbon dates from 172 specimens of megafauna species in the region including saber-tooth, giant lion, dire wolf, coyote, bison, camel, horse, and ground sloth. They fed this data into a statistical model and concluded as the climate became warmer and drier, the environment became more susceptible to fires set by increasing populations of humans. The anthropogenic fires transformed the landscape from juniper-oak woodlands into a semi-arid chapparal, and the only surviving megafauna species (that they studied) was coyote. (A chapparal is a dry landscape covered in pine, shrub, flowering herbs, grass, and cactus, and the climate consists of mild winters and hot summers.) These extirpations in Southern California occurred about 1,000 years before the extinctions in the rest of the North American continent, but they occurred at the same time these species were in decline elsewhere. Camels and ground sloths disappeared a few hundred years before the other species in this study, but I should note (which this study does not) that the most recently dated specimen was likely not the last surviving member of the species–there still could have been a considerable population that perchance left no fossil evidence. A serious flaw in the conclusion reached by this study occurred to me.
This illustration is a ridiculous exaggeration, and I think it is based on a seriously flawed assumption. From the below referenced study.
List of species used in the below referenced study and their final extirpation date estimates.
The authors of this study assume the transformation of juniper/oak woodlands to a dry chapparal environment resulted in the local extirpations of megafauna here. The problem with this hypothesis is that at least 3 of the species used in this study thrive in semi-arid chapparal like environments. Lions live in semi-arid environments all across Africa. Wild horses are most common in the American southwest where they roam deserts. And camels, of course, are known to live in arid environments, and today introduced wild camels survive in Australian deserts. I realize the North America Pleistocene versions of these species are not exactly the same as modern species, but they were highly adaptable and lived all across North America, and they endured all kinds of sudden dramatic shifts in climate, including peak Ice Ages which caused widespread arid conditions. I seriously doubt a shift to more open drier conditions negatively affected horses, camels, and lions. I think populations of these species would increase in this type of environment.
Horses thrive in the semi-arid type of environment that the below referenced study erroneously assumed caused their extirpation in southern California.
Camels also can endure semi-arid conditions. I think the authors of this study blundered in their conclusion.
19 scientists put their name on this paper. I find it hard to believe this obvious flaw in their conclusion occurred to none of them. It occurred to me before I finished reading the paper. I contacted the lead author of the paper and pointed out this flaw, but so far, he has not responded. It seems as if scientists want to bridge the gap between climate models of extinction with those who hold humans are solely responsible. Put me in the latter camp. The increase in fire frequency is proxy evidence for the presence of humans. Direct hunting by humans increased megafauna mortality above the ability of these large slow-reproducing animals to maintain their populations. It was overhunting by humans, not a change in fire regime that caused the extinction of these species. It is the simplest explanation, and the only one that makes sense to me.
Reference:
O’Keefe, R. et. al.
“Pre-Younger Dryas Megafaunal Extirpations at Rancho La Brea Linked to Fire-Driven Shift”
Science August 17, 2023
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