ESS Presentation Flashcards
- The nature of Siberian megafaunal demise during the Late Quaternary Extinction
o I guess we’re opening with a palaeontology presentation… I know how much of a crowd pleaser that is.
o But what I’m going to talk about, as my slightly revised title to what you might have on your sheets suggests, is what happened to the megafauna of Siberia during the LQE.
o And hopefully, all will become clear.
- Introduction
o So we live in a ‘zoologically impoverished’ world.
o It’s missing many of the biggest and most impressive large mammals that became extinct, geologically speaking, very recently.
o Apparently human society just isn’t able to adopt an environmentally sustainable lifestyle, and it’s figuratively bringing the zoological world to its knees.
o You know, to a point where the largest species in the world today only reside in Africa and some in south-eastern Asia.
o It’s possible that this behaviour traces back to the Late Quaternary, when the migration and spread of Neolithic humans occurred coincidentally, in many parts of the world, with the loss of most megafauna.
o So that’s a positive start.
- Introduction #2
o Up until very recently, maybe the 90’s-early 2000’s, all of the Late Quaternary extinctions were thought to have taken place between 50 and 10 ka, but that was it, that was them over.
o However, the newest evidence indicates that some megafaunal species, like the Woolly mammoth and giant deer, lived to become extinct in the Holocene within Siberian refugia.
o I should probably mention as well, that of the 150 genera of megafauna that were living on the continents at the beginning of the Late Pleistocene, 50 ka, at least 97 of those genera were lost by 10 ka at the end of the Pleistocene.
- Siberian refugia
o So just to explain what refugia are, for anyone who doesn’t quite know, and to kind of put things in a geographical context:
o Refugia is plural dor refugium, which is an area inhabited by one or more relict species – species that are struggling.
o And the refugia here are shown by these localities with the youngest mammoth remains, including Wrangel Island, which is quite an important place.
o But I’ll come on to that.
o And this here is Siberia – it basically extends eastwards from the Ural Mountains to the ocean, where the Pacific meets the Arctic; and stretches south from the Arctic to Kazakhstan and the borders of Mongolia and China. It’s essentially northern Asia. It is northern Asia.
- What are megafauna?
o In most papers you read about the LQE, they’ll say, for example, x amount of megafauna weighing 45 kg and over went extinct over the course of whatever time interval.
o But as Brook and Bowman pointed out in 2004, this body mass threshold has just been arbitrarily defined and if used, might exclude information on medium and small sized animals that also went extinct.
o So then to account for that, you’ll see some papers going as low as 7 kg.
o I’ll mention here too, the reason megafauna, almost, preferentially became extinct was mainly because they have low reproductive rates and so it’s harder for them to recover after any collapse in population size.
- Dating the extinctions
o Many of the Late Quaternary extinctions fall within the range of radiocarbon dating
o And therefore the spatio-temporal histories of extinct megafauna are determined by directly radiocarbon-dating their remains.
o This allows for a really great potential in resolving detailed chronologies of the extinctions (in contrast to the problems related to stratigraphic resolution for older extinction episodes)
o So any of the extinctions post-dating 30-35 kyrs BP are within the reliable chronological range of radiocarbon dating.
o And in some cases this range can extend back to ca. 40-50,000 years BP.
o BP just mean before 1950, btw.
o But the fact that we’ve got this reliable chronology is really important for testing hypotheses of the nature of the extinctions, in any part of the world, not just Siberia.
- A time perspective
o So the Quaternary Period as a whole encompasses the last 2.6 million years, up to the recent.
o And is divided into two epochs: the Pleistocene and the Holocene
o The Holocene is the most recent epoch and started 11.7 thousand calendar years ago to today.
o And the “Late Quaternary” is kind of an informal term that refers to the past 0.5–1.0 million years.
o If you see a date given like this (point to cal.), it just means that the radiometric date, or whatever they used to date it, has been calibrated to calendar years.
o So dates are usually either given as uncalibrated radiocarbon dates (ka), or as calendar dates, which include calibrated radiocarbon dates.
o But back to the main point, in northern Eurasia the Late Quaternary extinctions were staggered over a long period of time, over 30 millennia.
o So this allows us to potentially discriminate between possible causes really well, whereas for example in Austrailia and North America at that time, everything was going on at the same time and there’s no real good way to discriminate.
o So at the beginning of these climate events – the LGM, LGI, the Allerod, Younger Dryas and at the beginning of the Holocene, all species show dramatic range shifts in response to climatic/vegetational changes
o And these changes caused progressive range reductions and fragmentation prior to the final extinction
- Possible causes of extinction
o So before we look at the extinction patterns I’m gonna quickly run you through the different hypotheses for what could have caused the extinctions.
o These have developed over the years and through looking at different zoogeographical regions across the world.
o So we have the ‘overkill’ hypothesis, climatic/environmental change, some combination of those two, and there’s this ‘hyperdisease’ hypothesis
o Which involves the spread of disease to megafaunal species by immigrating humans
o But appears unlikely to have caused the actual observed timings of extinctions and seems unlikely to have affected the range of body sizes involved.
- Overkill
o The overkill hypothesis attributes the Late Pleistocene extinctions to the predation of megafaunal species by Stone age Homo sapiens
o And if humans had any role in driving Siberian megafauna to extinction, then these species should be found in a greater abundance in human-occupied sites (where hunters would gather the remains) than at palaeontological sites, right?
o But the species that were interested in, like woolly mammoth and woolly rhino are very rarely found in human-occupied archaeological sites in Siberia.
o So maybe the overkill hypothesis doesn’t seem as plausible for Siberia?
- Climatic change
o The hypothesis involving environmental change requires that a unique climatic event, or series of events, occurred during the Late Pleistocene due to the fact that no similar extinctions had taken place in the 0.8 Myrs before, despite a series of major climatic fluctuations.
o And that may actually be the case, with some arguing that the last glacial-interglacial cycle was significantly different
o And there were unprecedented changes in Artic Ocean circulation in the early Holocene, resulting in the replacement of open arctic steppe-tundra by modern boggy tundra and coniferous forests.
- Combination
o Yeah, there are a lot of authors who say the extinctions were caused by a combination of those two.
o And in this scenario, extinctions would basically result from human predation upon megafaunal populations that have been subject to habitat fragmentation and stresses caused by climatic and vegetation changes.
- What happened to the principal species involved?
o I haven’t got a lot of time, so I’ve chosen these three species to talk about: the woolly mammoth, the woolly rhino, and the giant deer.
o And I’ll just talk about their range distributions and how they changed, and what is thought to have caused the changes.
o And then after that, I’ll conclude and we’re done here.
- What happened to Mammuthus primigenius?
o The woolly mammoth has by far the best coverage in terms of radiocarbon dates – so that’s good.
o During the middle of the Last Cold Stage from 44-24 thousand calendar years ago, Woolly mammoths were present almost continuously from Western Europe (including the British Isles, Spain and Italy) across Eastern Europe and Siberia to China and Japan, and to the northern half of North America
o But then shortly before 13.8 cal. Ka they abruptly and completely disappeared from Europe and most of northern Asia, as you can see in this figure (point to figure).
o Importantly, this sudden disappearance correlates with the major loss of open biomes (or steppe-tundra) at the onset of the Allerød (the later, rather cooler part of the LGI) when pine woodland and boreal birch became widely established.
- What happened to Mammuthus primigenius? #2 (figure)
o So, here is a chart of radiocarbon dates made directly on woolly mammoth and giant deer material – the black disks are the mammoth dates.
o Mammoth dates for most of Europe and Siberia terminate 14 cal. Ka (12 ka) at the start of the Allerød
o But survived into the early Holocene in mainland North Siberia (Taimyr etc), and much later on Wrangel Island.
o The outlying mammoth dates 11.7 cal. Ka (10 ka) in Northeast Europe, probably represent a brief Younger Dryas repopulation from Northern Siberia
o Also notice the different patterns related to differences in ecology between the two species.
- What happened to Mammuthus primigenius? #3
o Populations of woolly mammoth did persist for a further two millennia, in the far north of mainland Siberia on the Taimyr Peninsula, associated with persistent open steppe-tundra vegetation
o At about 12 cal ka there was a slight re-expansion of mammoth ranges from Taimyr into the Yamal/Gydan Peninsulas (northwest Siberia) and then into northeast Europe
o And this was probably linked to the redeveloped cold and open vegetational conditions of the Younger Dryas.
o Younger Dryas saw a rapid decrease in temperature over most of the northern hemisphere, and is the period at the end of the Pleistocene epoch, immediately before the warmer Holocene that we’re in now.
