Professor Adrian Lister is a palaeobiologist at the Natural History Museum (NHM) in London. Notably his research focusses on Quaternary (2.6 mill – 0 kyr BP) mammals, and he specialises in deer, elephants and mammoths. Adrian recently came to the University of Oxford’s Research Laboratory for Archaeology and the History of Art (RLAHA) to give a departmental seminar where he discussed his latest piece of research. This work has been a vast collaborative effort, but co-led with Professor Anthony Stuart from Durham University. Lister and Stuart have been working on attempting to tie together new data on the extinction of our beloved woolly mammoth. Ultimately this has led to attempting to answer big questions: who killed our woolly mammoths? Climate change? Or did we?
During the last glaciation, occurring 110-15 kyr BP, there were a range of mammoth species. These mammoths roamed steppe tundra which consisted of grass, moss, ferns, flowers and some trees and shrubs. We know that the mammoths consumed largely grasses and herbs, as evidenced by studies of preserved carcases which have intact stomachs, still containing food matter! We also know that these mammoths were adapted for cold environments and perhaps designed to avoid frostbite, as evidenced by Lyuba’s small tail and ears. We are learning more about mammoths in recent times as global warming causes thawing, revealing our lost mammoths; in the last 15 years, we have found more mammoth remains than the last 200 years and this provides us with a nuanced understanding, for example, we know from Yuka, found in 2010, that woolly mammoths had a specialised finger/thumb adaptation for picking plants and grasses.
Lyuba – Courtesy of: AMNH
The woolly mammoths are said to have gone extinct during the ice age extinctions, a time period of 40 kyr – 4 kyr BP. This was a time when our global climate was variable. Lister suggested that scientists need to know more about all of the species that became extinct during this time period to better understand why the mammoths died out. For example, in Australia, 80-90% of megafauna (large animals) disappeared during this time, including for example, the loss of Macropus titan (a giant kangaroo) and Diprotodon (giant relatives of the wombats). We know of other large extinction events, such as the K-T (a mass extinction event occurring sixty-five million years ago whereby around ¾ of all flora and fauna became extinct), but the Late Quaternary extinction, or ice age extinction is it is often referred to, is much smaller and only seems to have only affected megafuna and not flora. So, why was it unique? Many scientists have hypothesised that it is related to the timing of human expansion. In order to fully assess this, such studies have utilised models of global extinction or modelling of single species.
Is this picture accurate? Courtesy of NHM
Who killed our woolly mammoths? Climate Vs Humans
So, climate and humans remain the two leading contenders for the demise of the woolly mammoth. Though asteroid impact and disease has also been proposed, Lister believes that there is not strong enough evidence to support these hypotheses.
The warming of the Holocene coincided with the demise of the mammoth steppe. During this time, there were vast changes in vegetation, including tundra moving in from the North and forest moving in from the South, replacing dry grasslands that the mammoth used to thrive on.
However, the ‘overkill’ hunting theory has long been proposed as the answer to why the mammoths went extinct. We know that humans and woolly mammoths co-existed from archaeological research. For example, ivory carvings were found at Vogelherd cave, Southern Germany (~30 kyr BP) and the use of mammoth products are known to be used in hut production. However, these findings are not definitive and are still contentious. Bone huts have been found, for example, in Poland and Czech Republic. One hut in Mezhirich, dates to ~18 kyr BP and was composed of mandibles from 96 different mammoths. Notably, this hut was produced long before the extinction of mammoths. The radiocarbon dates on these bones additionally indicates that the bones were collected over a long period of time, so perhaps these humans were additionally scavenging the bones, rather than killing the mammoths for the hut production.
What remains less contentious is the fact that Clovis Culture (a prehistoric culture, appearing ~13.5 kyr BP in North America) expanded across the continent at a similar time to which the mammoths went extinct (~13-12 kyr BP). While kill sites involving direct evidence of Clovis Culture (e.g. evidence of tools) are rare, they do exist, for example, Naco in Arazona and Lugovskoe in Southern Siberia – these mammal finds indicate direct evidence of humans hunting woolly mammoths; though it does not provide evidence of overkill. One important fact to take home here is that there was 10 million woolly mammoths in their prime and significantly less humans – could humans really kill all of these mammoths?…
What’s Lister et al. doing?
Lister has been trying to use radiocarbon dating to better pinpoint the exact times mammoths were living in particular regions. Essentially, from this refined chronological information, he can understand the contractional range and map this against the spread of humans and changes in climate and vegetation across time. Lister has produced new radiocarbon dates for mammals through collagen extraction and ultrafiltration techniques and has additionally utilised data samples from the literature and matched this to a devised criteria. In doing this, he has removed some dates, for example, those dated pre-1980, or those that had radiocarbon dates extracted from burnt bone. A total of 1870 radiocarbon dates were used in Lister’s study and finally plotted on time slice maps to assess the contractional range of the woolly mammoth.
The study has proved interesting and has shown a number of things. Firstly, there appears to be a delayed response in mammoth response to climate change. For example, during the warming climate of the Bølling, mammoth range is still large across the Northern hemisphere. During the Allerød, as cooling takes hold, the range contracts out of Europe toward cooler climates (e.g. Siberia). This indicates a slow response from the Bolling due to delayed vegetation changes; the mammoths vacate Europe first as trees replace the mammoth steppe in Europe before other regions of the Northern hemisphere, ~12 kyr BP. After this date, we find that mammoths contract into islands, for example, between 11 and 10.5 kyr BP, mammals are living in the New Siberian Islands.
The biggest find of this study is that the contraction of mammoths, which is seemingly a result of vegetation changes, causes populations to thrive in two islands ~10.5-6.5 kyr BP. St. Paul Island, Alaska is occupied ~6.5 kyr BP and is known to have had no human influences until the historic past. Similarly, dwarf mammoths populated Wrangel Island during the mid-Holocene. The last mammoth remains have been dated to 4,333 kyr BP and 4,022 kyr BP, providing a sequence of dates on Wrangel Island. So, why did the mammoths stay so long in Wrangel? Wrangel Island’s environment is regarded as being the closest thing today as mammoth steppe and this may explain why these mammals lived so long there – the vegetation was primed throughout the Holocene to support the mammoth population.
Wrangel Island tundra – a mammoth haven. Courtesy of New World Encylopedia
But, if the environment is, even still today, suitable to host a population of mammoths on Wrangel Island, why did they go extinct? On Wrangel, humans were hunting sea mammals; we know this because we have found walrus ivory harpoon heads, dated to ~3.6-3.5 kyr BP. Therefore, timing of human arrival, occupation and hunting is scarily close to the timing of the last mammoth fossil find…is it possible for humans to have played a role in their demise? Was there a potential overlap in occupation at Wrangel?
Lister proposes a combined extinction model based on radiocarbon mapping. Mammoths were driven to a reduced population on the basis of habitat loss. Hereafter, the small and vulnerable populations were demised by hunters, though their intentions (i.e. food or culture) are still unclear.