Ice Age North American big mammals’ extinction

This August 2019 video says about itself:

Until the end of the last ice age, many giants called North America home. It has long puzzled scientists why these animals and other megafauna — creatures heavier than 100 lbs. (45 kilograms) — went extinct about 10,000 years ago.
Rapid warming periods called interstadials and, to a lesser degree, ice-age people who hunted animals are responsible for the disappearance of the continent’s megafauna, according to studies.

Both research and the debate surrounding the reasons for the extinction of these animals will undeniably continue. In the meantime, researchers continue to find fossils of these massive creatures.

Here’s a look at 14 such extinct giant animals from the last North American ice age, and what scientists know about their lives.

1. North American Horses
2. Glyptodon
3. American lion
4. Smilodon fatalis
6. Mastodons
7. Mammoths
8. Giant Short-faced bear
9. Dire wolf
10. American cheetah
11. Ground sloths
12. Giant beaver
13. North American Camels

From the University of Nebraska-Lincoln in the USA:

Division by subtraction: Extinction of large mammal species likely drove survivors apart

Disappearance of mammoths, other giants likely reduced interactions of smaller mammals

September 19, 2019

Summary: A new study suggests that the extinctions of mammoths, dire wolves and other large mammal species in North America drove surviving species to distance themselves from their neighbors, reducing interactions as predators and prey, territorial competitors or scavengers. The discovery could preview the ecological effects of future extinctions, the researchers say.

When a series of large mammal species began going extinct roughly 12,000 years ago, many surviving species began going their separate ways, says new research led by Macquarie University and the University of Nebraska-Lincoln.

Published Sept. 20 in the journal Science, the study analyzed distributions of mammal fossils across North America following the last ice age, after the retreat of massive glaciers that had encroached south to the modern-day United States. The aftermath saw the disappearance of many famously large mammal species: mammoths, mastodons, saber-toothed cats, dire wolves and ground sloths, among others.

Surviving mammal species often responded by distancing themselves from their neighbors, the study found, potentially reducing how often they interacted as predators and prey, territorial competitors or scavengers.

The ecological repercussions of the extinctions are likely still echoing today and could preview the effects of future extinctions, said study co-author Kate Lyons.

“For 300 million years, the (cohabitation) pattern of plants and animals looked one way — and then it changed in the last 10,000 years,” said Lyons, assistant professor of biological sciences at Nebraska. “This paper addresses how that happened in mammal communities.

“If connectedness among species makes ecosystems more stable, what this suggests is that we’ve already lost a lot of those links. What this potentially tells us is that modern ecosystems are probably more vulnerable than we think they are.”

Led by Macquarie’s Anikó Tóth, the team analyzed records of 93 mammal species at hundreds of fossil sites during three timespans: 21,000 to 11,700 years ago, when the extinctions began; 11,700 to 2,000 years ago; and 2,000 years ago to the present. The researchers then assessed whether, and to what extent, a given species lived among each of the other 92 at those sites.

That data allowed the team to calculate how often a random pair of species would be expected to cohabit a site, providing a baseline for whether each pair overlapped more or less often than predicted by chance — aggregating vs. segregating, respectively. The proportion of aggregating pairs generally declined following the extinctions, and the strength of associations often dropped even among species that continued to aggregate, the researchers found.

“The loss of the giant carnivores and herbivores changed how small mammals such as deer, coyotes and raccoons interacted,” Tóth said. “Our work suggests that these changes were triggered by the ecological upheaval of the extinctions.”

Tóth, Lyons and their 17 co-authors effectively ruled out climate change and geography as drivers of the growing division. Surprisingly, the team also concluded that surviving species began cohabiting less frequently even as they expanded into larger swaths of their respective geographic ranges.

Lyons said the specific reasons for the seeming paradox and the overall trends are unclear, though the ecological consequences of losing species such as the mammoth could explain them. Mammoths toppled trees, compacted soil and, by eating and excreting masses of vegetation, transported nutrients around ecosystems, Lyons said. Those behaviors helped sustain the so-called mammoth steppe, an ecosystem type that once covered vast areas of the Northern Hemisphere. The loss of the mammoth effectively doomed the mammoth steppe, possibly compartmentalizing the expanses of land that hosted many species.

“If you’re an open-habitat species that used to occupy the mammoth steppe, and now the mammoth steppe has gone away, you might inhabit, say, open grassland areas that are surrounded by forests,” Lyons said. “But that meadow is much smaller. Instead of supporting 10 species, it now might support five. And if those patches of open habitat are spread farther apart, you might expand your geographic range and potentially your climate range, but you would co-occur with fewer species.”

Also uncertain: why common species became more common, and some rare species became even rarer, following the extinctions. Continuing to study the dynamics underlying such trends could help sharpen perspectives on current ecosystems and their possible fates, the researchers said.

“We had a complement of large mammals in North America that was probably more diverse than what we see in Africa today,” Lyons said. “Additional extinctions could have a cascading effect and huge implications for the mammal communities that we have left.”

Tóth, Lyons and their co-authors represent 18 institutions from Australia, the United States, Chile, Portugal, Finland, Canada and Denmark. All are members of the Evolution of Terrestrial Ecosystems Program at the Smithsonian Institution, which funded the team’s research.

This video is called The Short-Faced Bear: America’s Top Predator.

From the University of Arkansas in the USA:

Anthropologist contributes to major study of large animal extinction

September 20, 2019

As part of an international research group based at the Smithsonian Museum of Natural History, anthropology assistant professor Amelia Villaseñor contributed to a large, multi-institutional study explaining how the human-influenced mass extinction of giant carnivores and herbivores of North America fundamentally changed the biodiversity and landscape of the continent.

In their study published today in Science, researchers from Australia, the United States, Canada and Finland showed that humans shaped the processes underlying how species co-existed for the last several thousand years. Smaller, surviving animals such as deer changed their ecological interactions, the researchers found, causing ecological upheaval across the continent.

The researchers’ work has implications for conservation of today’s remaining large animals, now threatened by another human-led mass extinction.

The study’s primary author is Anikó Tóth at Macquarie University in Sydney, Australia. Tóth collaborated with Villaseñor and several other researchers at the Smithsonian’s Evolution of Terrestrial Ecosystems Program, as well as researchers at other institutions.

Tóth and the co-authors focused on how large mammals were distributed across the continent in the Pleistocene and Holocene geological epochs. (The Pleistocene Epoch occurred from about 2.5 million to 11,700 years ago. Starting at the end of the Pleistocene, the Holocene is the current geological epoch.) To do this, the researchers analyzed how often pairs of species were found living in the same community or in different communities.

To rule out community changes that were the result of reduced diversity or lost associations involving extinct species, the researchers analyzed only those pairs in which both species survived. Prior to the extinction, co-occurrence was more common. After extinction, segregations were more common.

Villaseñor’s research focuses on human fossil remains as a way to understand how human ancestors interacted with mammal communities for the last 3.5 million years. Her more recent research explores how modern humans have shaped today’s ecosystems.

“Rather than thinking of humans as separate from ‘natural’ environments, our research has illuminated the major impacts that humans have had on the ecosystem for many thousands of years,” Villaseñor said. “The results of this paper and others from our group illuminate the outsized impacts that human-mediated extinction has had in North America.”

By the end of the Late Pleistocene in North America, roughly 11,000 years ago, humans contributed to the extinction of large mammals, including mammoths and sabre-toothed cats. Recent work, driven by today’s crisis in biodiversity, has looked at understanding the ecological and evolutionary legacies of this event. There was ecological transformation across the continent — the mammoth steppe disappeared, vegetation and fire regimes changed and large carnivores were lost.