| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | March 14, 2018 |
| Latest Amendment Date: | August 16, 2018 |
| Award Number: | 1758110 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Yurena Yanes
yyanes@nsf.gov (703)292-0000 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | April 1, 2018 |
| End Date: | March 31, 2022 (Estimated) |
| Total Intended Award Amount: | $129,780.00 |
| Total Awarded Amount to Date: | $129,780.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
160 ALDRICH HALL IRVINE CA US 92697-0001 (949)824-7295 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Croul Hall Irvine CA US 92697-3100 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Sedimentary Geo & Paleobiology |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The Rancho La Brea tar pits of Los Angeles, California contain thousands of bones from large mammals --dire wolves, sabertooth cats, coyotes, extinct bison, horses, and others-- trapped in sticky surface oil deposits during the last Ice Age. This unparalleled fossil assemblage allows rigorous studies of extinct mammal biology, especially of carnivores which are rare at most fossil sites. The La Brea fossils span a critical time in Earth's history (approximately 50,000 years ago to the present) that includes major events such as the end of the last Ice Age, the arrival of humans in North America, and an extinction that killed two thirds of the large mammals on the continent. This unique deposit will be used to investigate relationships between major environmental changes and evolutionary variation (size, diet, etc.) in large mammals, information that is critical for promoting the survival of wildlife today. The project involves significant community outreach in the greater Los Angeles area through the Tar Pits Museum and will create educational content that will be available online for high school teachers across the country.
The major impediment to system-level study at Rancho La Brea is a paucity of radiocarbon dates and the resulting inability to correlate biotic change with time. This project will intensively radiocarbon date samples from multiple pits spanning the last 50,000 years to establish the first detailed chronology for the entrapment of four extinct species of large mammals, and one extant species. It will involve the collection and compilation of census data for these species to track changes in total abundance and diversity, as well as data on morphological and dietary changes. A well-resolved chronology will allow these data on evolutionary changes in mammals and the Pleistocene megafaunal extinctions to be linked to existing records of major paleo-environmental changes. This work will have broad implications for our understanding of extinctions, survival, environmental variables, and humans on mammalian ecology, which is directly relevant to modern conservation.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The aim of this project was to use bone samples from extinct large mammals (megafauna) excavated from the asphalt deposits at Rancho La Brea in Los Angeles and archived at the Tar Pits Museum, to study how ecological changes in the LA Basin affected those species and to investigate when and why they went extinct.
We used radiocarbon dating to put the specimens for seven extinct species: ground sloths, camels, bison, horses, lions, dire wolves and sabretooth cats; plus the coyotes which survived, into their correct time frame. Since the probability of finding and dating the very last survivor is essentially zero, we then relied on computer modeling to estimate the true extinction ages based on those measured dates. For the species that survived longest at La Brea (bison, horse, dire wolves and sabretooth cats) the calculated extinction dates span a small age range centered on 13,000 years Before Present (BP). Importantly, this is significantly earlier than the start of the so-called Younger Dryas cold event that affected much of North America (but not coastal southern California) for 1200 years, starting ~12850 BP. This involved a rapid transition to near-glacial conditions, and this abrupt climate shift and resulting ecological disturbances have been put forward as a cause of megafaunal extinctions elsewhere.
However, as pointed out above, this scenario clearly does not apply at La Brea, and we need to consider regional climate records for southern California which illustrate a very different trajectory. A study of climate proxies in sediment cores taken from Lake Elsinore ~100 km southeast of Los Angeles has pollen abundances and other proxies for temperature, lake levels, and surface runoff indicating a progressive warming and drying trend starting ~14,500 BP, leading to a decline in juniper and establishment of oak woodlands. This was followed at ~13,200 BP by an almost complete disappearance of juniper coupled with a decline in oak and a large increase in chaparral scrub flora, and was accompanied a massive spike in the charcoal content of the Elsinore sediments. The overall picture at the time of the megafaunal extinctions is therefore one of prolonged warming and drying leading to an abrupt and very large increase in fire frequency and/or area burned, and a dramatic expansion of chaparral scrub at the expense of woodland habitant.
Whether or not humans played a part in the extinctions is unclear: there were probably people in California by that time as there were in other areas of the West, but the archaeological record of their presence is extremely sparse. However, regardless of any human contribution, the evidence suggests that climate had primed the ecosystem for dramatic (and for the megafauna, catastrophic) change. The Spanish-American philosopher George Santayana famously said "Those who cannot remember the past are condemned to repeat it", or words to that effect. Given a past climate trajectory that seems eerily similar to the one we appear to be on today, the most important broader impact of studies like this one may be to publicize the message of just how disruptive and far-reaching the consequences can be.
Last Modified: 05/25/2023
Modified by: John R Southon
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