Thread: Ice age extinctions - Is this nonsense?

A 'smoking gun' on Ice Age megafauna extinctions -- ScienceDaily

The above reference refers to the mass extinctions of megafauna that happened at the end of the last glaciation period. It ascribes the loss to a change of vegetation, and especially the reduction in protein rich forb plants. The writers call this a 'smoking gun' for extinction.

Now frankly, I do not believe that is true. The reduction in certain plant species may be a factor, but I seriously doubt it is the main factor. My reason for saying this is simply that the world has gone through ten periods of glaciation in the current Ice Age, each of which had an inter-glacial period which must have had the same effect of changing plant species. Yet all those mega-fauna survived nicely until the last one, when they died.

My view is that the thing that killed them off must have been a new factor, that did not apply in the previous 2 million years. What is that? The obvious new factor is that humans entered the scene this last end of glaciation period. Humans, not a change of vegetatation, caused the megafauna extinctions.

Originally Posted by skeptic

The reduction in certain plant species may be a factor, but I seriously doubt it is the main factor. My reason for saying this is simply that the world has gone through ten periods of glaciation in the current Ice Age, each of which had an inter-glacial period which must have had the same effect of changing plant species.

There is no justification for assuming that the effect must have been the same in each glaciation. The severity and duration of the glaciations differed. The diversity of species and their ecological relationship would change after each glacial and interglacial. In a boxing match the single blow that fells an opponent may not be the most powerful strike - it may simply be the end result of cumulative impacts.

John

What are the odds that the megafauna experience nine end of glaciation events, and the plant biodiversity and abundances changes for nine should be such as to let them continue, but then just as humans arrive, the plant diversity changes are so severe as to kill them?

Is it not more reasonable to suggest that the arrival of humans is the key event?

I don't think the available data make it reasonable to arrive at either conclusion.

You are looking for a smoking gun for the megafauna. Perhaps we should be looking for the smoking gun for that killed the forb plants. And the smoking gun before that. If our eye is only on the mega-fauna at each glacial cycle we miss the critical details within the entire ecology. Not very scientific!

This is a data gathering stage. Hypothesis generation at this point can move such research forward, but the proposals should be viewed much as cocktail lounge chatter.

John

What you say is true, but we are not the scientists investigating this. We are simply engaged in a discussion.
As part of a debate, I consider it reasonable to suggest differing probabilities.

I think it's doubtful. As best we can tell, the Sanqamon and first two Yarmouth interglacials are pretty similar in amplitude and transition timing to the current one other than ours will ultimately last a LOT longer.

Far more likely human impacts, perhaps combined with some other environmental stress, such as climate change is responsible for the megafauna extinctions.

My suspicion is that it's probably some version of the two together. So that skeptic's hypothesis is in the category of a "straw that broke the camel's back". In this case, a rather large and clunky straw.

What I mean is that the loss of vegetation and other stresses had always depleted the health and the numbers of these animals at such times. The effect of humans need not be very big. It only needs to be big enough to have tipped marginal, over-stressed populations into irretrievably small numbers and eventual extinction. And such extinctions are always part of a cascade of effects.

Humans do not have such a good record. As Adelady knows, after the arrival of the first humans in Australia, more than 100 species of megafauna died out. In my country, it was 50 species of native birds. Records for Europe are limited, because humans have been there so long, but a number of species are known to have gone extinct there also.

In the Pacific, with the movement of polynesians across the various islands, a total of about 2,000 bird species went extinct. The same thing happened in the Caribbean when the Carib Indians first colonised.

So to me it is not exactly unrealistic to think of the humans colonising the frigid north, as the glaciers retreated, and causing major extinctions also.

Originally Posted by skeptic

John

What you say is true, but we are not the scientists investigating this. We are simply engaged in a discussion.
As part of a debate, I consider it reasonable to suggest differing probabilities.

But you have made a clear statement as to what you believe the probability to be. I can buy into saying, "I think this is a plausible explanation", but if you extend that to "I think this is the most likely", then I believe you are making a conclusion based upon insufficient data.

Thus you say:

So to me it is not exactly unrealistic to think of the humans colonising the frigid north, as the glaciers retreated, and causing major extinctions also.

This is more guarded than your earlier comment:

My view is that the thing that killed them off must have been a new factor, that did not apply in the previous 2 million years. What is that? The obvious new factor is that humans entered the scene this last end of glaciation period. Humans, not a change of vegetatation, caused the megafauna extinctions.

In this statement you are making a definitive statement. In the later one - the second quote above - you are simply noting the possibility that humans were responsible. The definitive statement is - in my view - unscientific, the latter statement is scientific.

John

Don't take the wording too seriously. As I said, this is just a debate. You are welcome to say that you consider my conclusions wrong, or improbable. But in a debate, it is not unscientific to present an opinion.

I had always assumed the megafauna died out due to humans over hunting them. Why would glaciation kill them off? Their size is a benefit in the cold, because it creates a better surface-area-to-volume ratio. ....unless they couldn't find food.

Kojax

We know the cold did not kill them off, because the extinction happened after it warmed up, for the interglacial period. The paper I quoted stated that it was the loss of high protein forb plants that killed them. My view is that, if forbs are vulnerable to warmings, then why did they not largely die off during the previous 10 interglacials, and thus destroy the megafauna more than a million years ago?

The new factor was humans.

Do they have any way of estimating what the human population was and what the mammoth population was? Is the time it takes from birth to reproduction about the same as an elephant?

On the one hand it doesn't seem like there'd be enough humans spread out across the arctic to wipe them all out. On the other hand, a mammoth looks slow, like a freezer full of meat lumbering past you. If the plants they needed were confined to a very narrow range, though, they would be easier to hunt.

Unfortunately I can't actually access Dr. Eske Willerslev et. al.'s paper without shelling out money and the version on his site at
A "smoking gun" on the Ice Age megafauna extinctions – University of Copenhagen
does not add much.
He is not claiming his idea explains all the extinctions of the megafauna but that it can explain some of them.

Dianne made a good point about them being forced into restricted areas, but before saying it was humans that caused an extinction it might be good to show they were in the area at the time.

Diane

The way I see it, if there are a bunch of humans and a bunch of mammoths together, and the humans want to eat mammoth, they will hunt mammoth babies, not adults. Just like African lions sometimes hunt baby elephants, not adults. If the humans kill enough mammoth babies, then the mammoths go extinct.

It seems that at least the Clovis hunters killed families of them at a time.
MAMMOTH HUNTING | The Handbook of Texas Online| Texas State Historical Association (TSHA)

Clovis peoples seem to have been skilled hunters well-versed in mammoth-herd behavior; they used that knowledge and their technology to confront, contain, and kill small family units of three to five animals at sites such as Lubbock Lake and Miami. Exactly how this was accomplished is still a subject of debate. If indeed mammoths behaved as modern African elephants do, then the key would be in the killing first of the matriarch and the subsequent dispatching of the rest of the small herd as they milled around her.

If we accept the hypothesis that the Clovis stone culture derived from the Solutrean, and accept the point found off virginia as part of that continuation:
Then, maybe what wiped out the north american megafauna is what also removed(most of?) the Solutrean-Clovis people? ("most of" considers folsum as a continuation of clovis)

Then we need a new "smoking gun".

Gamma ray burst? Bolide? Other?

(gee, it'd be nice to see the dna evidence from one single identifiable Clovis person)

Sculptor

The people were never wiped out. Just one culture evolving into another. Some recent DNA studies have shown that both modern American natives, and old corpses are descended from a tribe in Siberia. Not a wave of different peoples. One people, who diverged.

Skeptic:
To the best of my knowledge, no skeletons that were from people of the clovis culture have been found, identified as clovis people, nor tested for dna.
The clovis stone culture is significantly different from anything found in siberia.
It would be highly unlikely/improbable that any migrants from siberia would so differ/change from their parent stone cultures.

I do not doubt that "Some recent DNA studies have shown that both modern American natives, and old corpses are descended from a tribe in Siberia."
The thing is, that we do not have dna data from all early peoples of north america, and specifically none from clovis people. So, any claims to a single starting point of migration are based on inconclusive/incomplete evidence.

Which doesn't mean that any such claim is inaccurate. But it does mean that any such claim remains speculative. And, conclusive proof for any such claim remains elusive.

Sculptor

Your proviso of my statement is OK. Obviously we cannot do DNA on corpses we have not found.

And, I didn't mention the Anzick child, as I do not find the information from that burial conclusive.
Mostly, it created more questions and opened doors into further studies of the blending of cultures and peoples.
......................

3. Anzick, Montana: The Anzick site in Montana is reported to be a Clovis burial and cache. At
Anzick, 12 radiocarbon dates were obtained from the cranial elements of a purported Clovis
infant skeleton and 2 dates on associated bone foreshafts. Collagen extracted from the foreshafts
yielded an average age of 11,040 + 35 14C yr B.P. (S7). The human skeletal remains were dated
during three separate research programs. The first batch of seven dates on bone comprise five
chemical fractions that were considered reliable and averaged to 10,680 + 50 14C yr B.P. (S2).
Later, a single purified collagen sample yielded a date of 11,550 + 60 14C yr B.P. (CAMS-
35912). This measurement is rejected because subsequent dating of the same XAD fraction and
preceding fractions from newly sampled bone did not replicate the 11,550 14C yr B.P. result.
The source of the contaminating 14C-depleted carbon is unknown. A more recent series of dates
from a single cranial fragment provided four new radiocarbon ages. These fractions confirm
previous date estimates for the skeleton of 10,705 + 35 14C yr B.P. The 14C dates on the skeleton
versus the dates on the bone foreshafts suggest that the skeletal remains and Clovis artifacts may
not be related and that the foreshaft ages more accurately date the site. The 10,700 year old
human remains could post-date the Clovis cache, but additional research is needed to resolve this
issue. A more recent, late Paleoindian or early Archaic human skeleton was also found at the
site (S7). The association of any of the human remains with the Clovis cache is problematic
because the site had been excavated accidentally with heavy machinery before the human bones
and artifacts were recognized and later recovered at some distance from the actual site. Thus, the
directly dated Clovis artifacts—the foreshafts—appear to accurately date the site.

from:
https://www.sciencemag.org/content/s...Waters_SOM.pdf

I don't know if DNA would prove much anyhow because the Colvis culture is based on tool use much like the European labelling of Celtic people was based on their use of a certain style of axe.
It is possible that a lot of different peoples adopted the Clovis style of spearpoint and later adopted the Folsom style, possibly because the animals they hunted changed during the Younger Dryas.

Confirmed Clovis dna could prove the Solutrean hypothesis.

There seems to be confirmed pre-Clovis people/stone-culture here in the Americas. So when the clovis stone culture spread over the land, there was most likely sharing and adaptation by and with other people's stone cultures. There is scant archaeological evidence to support the notion that the large clovis points were for hunting the megafauna(if memory serves, clovis points in situ with megafaunal remains is less than 1% of all clovis sites). The question then arises, why invest time and energy in making such large stone points? There is also scant evidence that the clovis "points" were only used as spear points.

Often earlier speculations tend to shape developing concepts within the dicipline, and sometimes, they are proven to have been wrong.
Much as some people within the community declared that the anzick boy-child was of the clovis culture, and then of asian descent and therefore clovis was of asian decent: Mistakes are made and then requoted as fact.
I would hazard a guess that most of the mistakes were "honest mistakes" while some were intentionally misleading to push an agenda, and some were fudged to more closely resemble the paradigm du jour. Sorting these out from real archaeological evidence is every bit as important as properly excavating a site, and that, is where many who requote other's mistakes as fact have come up short.

I find the (above quoted) bone foreshafts intriguing.

I cannot imagine why anyone would claim that massive climate change like a glaciation would not cause extinctions. It's extremely difficult to believe.

Originally Posted by Schneibster

I cannot imagine why anyone would claim that massive climate change like a glaciation would not cause extinctions. It's extremely difficult to believe.

The big issue with it is most of the mega fauna that went extinct had survives a half dozen prior glacial and interglacials, at least two of them with very similar pattern of temperature change. Yet when the human super predator shows up we see large extinctions nearly everywhere--Africa during modern human evolution (a longer period), over Europe and Asia and particularly well defined in Australia, the Americas and over hundreds of smaller islands. Whether it was by direct hunting, or more subtle environmental changes (e.g. slash burning...killing their food source etc), humans seem to play a large role--even if in conjunction with climate change.

Originally Posted by skeptic

John

Don't take the wording too seriously. As I said, this is just a debate. You are welcome to say that you consider my conclusions wrong, or improbable. But in a debate, it is not unscientific to present an opinion.

This is a latte response to your reply to my earlier post. I failed to see it when you posted a month ago.

The thing is, I do take the wording seriously. I believe, rather passionately, that precision in dialogue is important and that this is especially true in discussing scientific matters. Wooly writing can be evidence of wooly thinking and will almost certainly lead to wooly and possibly faulty conclusions.

You are absolutely correct that presenting opinions is a viable action in a debate. My point, which I feel I have adequately demonstrated in earlier posts, is that you presented an opinion as the most probable interpretation of the data and very close to being a fact. It was not presented as an opinion and as such was unscientific.

Originally Posted by skeptic

John

What are the odds that the megafauna experience nine end of glaciation events, and the plant biodiversity and abundances changes for nine should be such as to let them continue, but then just as humans arrive, the plant diversity changes are so severe as to kill them?

Is it not more reasonable to suggest that the arrival of humans is the key event?

backtracking here:

It seems as/re some south american and european archaeologists, humans were in south america at least 22-35kybp(Uruguay, Chili, Brazil---so far)
Add in archaeological evidence of people which pre-date clovis by well over 1000 years in North America.
Old paradigms in the dicipline of anthropological archaeology are falling like a series of dominoes. It is time to sort out what is speculative from the actual archaeological evidence, and come up with new hypotheses that derive from the extant evidence(many of which will also be disproven).
(a little prayer)
May the lord bless and keep the archaeologists safe, and may they keep on digging.(and publishing)

Did earlier migrations just pass through the great herds of megafauna and keep heading south looking for an easier meal?
Did humans first settle in south america- then migrate north?
Are we missing most of "the good stuff" just off shore?
Are we missing 15-20,000 years of north american evidence?
Is the old concept of migration in search of land with an abundant carrying capacity the only possible story(this would mean that some people would move a short distance to a new area, settle down, have children, and grow their population until some splintered off, continuing the migration)?
Why are many(most?) of the clovis caches of new-unused points many of which are very large---up to about 1 foot. Why were some of these cached points painted in ocre, and some not? Will we ever know?

If the story of the northern walking migration route is accurate, and the south american dates accurate, then humans should have come in contact with the megafauna of north america well over 30kybp. Which may relegate the "humans caused the extinction of the megafauna" story to the idle musings of the uninformed(or misinformed).

Originally Posted by Lynx_Fox

Originally Posted by Schneibster

I cannot imagine why anyone would claim that massive climate change like a glaciation would not cause extinctions. It's extremely difficult to believe.

The big issue with it is most of the mega fauna that went extinct had survives a half dozen prior glacial and interglacials, at least two of them with very similar pattern of temperature change. Yet when the human super predator shows up we see large extinctions nearly everywhere--Africa during modern human evolution (a longer period), over Europe and Asia and particularly well defined in Australia, the Americas and over hundreds of smaller islands. Whether it was by direct hunting, or more subtle environmental changes (e.g. slash burning...killing their food source etc), humans seem to play a large role--even if in conjunction with climate change.

I would say that the evidence says it was a combination, then. I've never been comfortable with an entirely climatic explanation, but also not with a completely human explanation either; far from being untended open country as the white settlers claimed, First People land in North America had been carefully tended and the large predators all eliminated, and the game animals tended, for thousands of years. So certainly humans could have, but this attitude of tending the land and the history it implies militate against simple unreasoning predation.

Wasn't there some controversy over whether a meteorite strike in, around 12,500 BCE, IIRC, could have contributed? I heard somewhere that had been denied, but I don't know how reliable that was, I didn't check into it. There was something about it contributing to extra severe climate change or something. Do you folks know how that came out?