Ancient Giants in Warmer Times

Fig.1. Woolly Mammoth at the Royal BC Museum, Victoria, British Columbia (Credit: Tracy O via Flickr)

Between 40,000 to 10,000 years ago, the world experienced a mass extinction of megafauna, a diverse group of animals that included such members as the mastodon and the woolly rhino. Although humans are often blamed for the disappearance of these creatures - either through overkill or habitat modification - the underlying causes are more complicated than previously thought

The end of the last glacial period around 11,650 years ago saw the rise of modern human civilization as we know it, with societies transitioning from hunting and gathering to more agrarian lifestyles. Humans spread quickly around the world in growing numbers and modified megafaunal environments as they went. However, a recent study published in the journal Science suggests that climate change played a much larger role in the disappearance of megafauna than previously thought


Fig.2. Artist’s rendition of the Earth during the last glacial period (Credit: Ittiz based on image by Thomas Crowley)

Recording Extinction

Although the Late Pleistocene was part of a glacial period, it experienced sporadic warming events, sometimes changing regional temperatures up to 16°C. These climate shifts had not been well studied until an international team of scientists, led by University of Adelaide researcher Alan Cooper, found a link between ancient warming events and megafaunal extinction.

They combed through past genetic and palaeontological studies of ancient animals and uncovered 31 specific events of megafaunal extinction or regional replacement by a similar species. Ice core records accounting for more than 56,000 years of climatic data were then compared to species extinctions. Environmental and palaeontological records often show some discrepancy in accurate dates, so Cooper and his colleagues used a Venezuelan sediment core that had both fossilized shells and temperature information to create a common timescale.

Cooper et al. found that species extinctions coincided with sporadic warming events throughout the Late Pleistocene. Although many animals disappeared in areas with little to no human presence, the researchers did not see the same connection between warming and extinction until humans spread around the world. This understanding of climate conditions and animal extinction survival led Cooper and his team to hypothesize that abrupt shifts in climate drastically changed stable populations. Instead of acting as the sole cause, humans could have interrupted the ability of animals to adapt to climate change, thereby exacerbating ecological effects on the survival of a species.

Cores, Collections, and Ancient DNA

In addition to creating a common timescale that connects species histories to climate variability, Cooper et al. showed that the analysis of ancient DNA adds important details to the fossil record. Morphological studies of fossils are the backbone of palaeontology, but they might not catch small genetic differences within or between species, such as those found in the megafauna genomic studies. New techniques have made the study of ancient DNA more accessible than ever and allow researchers to return to bones for more thorough analysis. Additionally, the combination of environmental records, like sediment or ice cores, with genetic analyses paints a new picture of human prehistory. Past extinction events are often difficult to analyze, but a new understanding of climatic effects carries important lessons. If ancient humans could interrupt a species’ ability to adapt, modern humans are most certainly doing the same.




References:
Cooper, A., Turney, C., Hughen, K. A., Brook, B. W., McDonald, H. G., & Bradshaw, C. J. A. (2015, August 07). Abrupt warming events drove Late Pleistocene Holarctic megafaunal turnover. Science, vol. 349 (6248): 602-606. doi: 10.1126/science.aac4315

American Association for the Advancement of Science: EurekAlert! (2015, July 23). What killed off the megafauna? [Press release]. retrieved from http://www.eurekalert.org/pub_releases/2015-07/aaft-wko072015.php

Switek, B. (2015, April 29). You Just Missed the Last Ground Sloths. National Geographic. Retrieved from: http://phenomena.nationalgeographic.com/2015/04/29/you-just-missed-the-last-ground-sloths/

Glossary

megafauna
Large animals with adults growing to over 45kg. Ancient and extinct megafauna include mastodons , woolly mammoths, and giant ground sloths. Modern day megafauna include great white sharks, ostriches, elephants, and blue whales.
Late Pleistocene
The end of the Pleistocene Epoch (~2,600,000 to 11,650 years ago) which was dominated by the spread of glaciers over North America and northern Eurasia. Archaic human species and other megafauna died out and modern humans spread to every continent except for Antarctica.
glacial period
An interval within an ice age marked by colder temperatures and the spread of glaciers, which comes in between interglacial periods (warmer temperatures).