For those interested at all in mammoths, you probably know about them going extinct. Some of you will also know that a very few mammoths managed to survive the immediate, main extinction, managing to make it until about 4,000 years ago before the last one bit the bullet.
In my curiosity, I frequent several blogs. On more than one, every time the subject comes up about the mammoth population going extinct at the onset of the Younger Dryas cold period 12,800 years ago, some bloke brings up the facts of these small island populations of mammoths, the last group of which survived until more or less 4,000 years ago. They are correct about those mammoths surviving. But are they right about that not being an extinction event at 12,800 years ago?
There is a post-extinction-event condition called “Dead Clade Walking“. Wiki does a decent job of introducing the subject, so I will quote from them:
Dead clade walking also known as “survival without recovery” refers to a clade (group) of organisms which survived a mass extinction but never recovered in numbers, becoming extinct a few million years after the mass extinction or failed to recover in numbers and diversity.
Now, I first heard of Dead Clade Walking on the TV show Elementary, a Sherlock Holmes in modern day New York City series. I had not heard of the term when Holmes used it. He actually DID explain what it meant to Dr. Watson, and when he did, that piqued my interest.
It piqued my interest because the principle of it seemed to be exactly what happened to those small mammoth groups that survived for up to another 8,000 years – only to finally die out, anyway.
So, I looked it up. Here is a Univ of Chicago article about it, Survivors of Mass Extinctions May Not Evolve As Winners.
“Everybody knows that some groups are so affected by mass extinctions that even though they may survive, they are but a shadow of their former selves and succumb soon after the main event,” said Karl Flessa, a professor of geosciences at the University of Arizona. A major problem with this bit of common scientific knowledge, he said, is that it had never been successfully demonstrated.
“Jablonski’s contribution is to add long-needed rigor to documenting and understanding the phenomenon,” Flessa said. . .
. . .Jablonski found post-extinction losses among survivors of 10 to 20 percent, a number lower than during the mass extinction times themselves, but significantly greater than seen during “normal” times. . .
. . .“So there’s an extra ripple of extinction in the aftermath of each of the big events, sorting out the survivors into winners and losers,” Jablonski said.
. . .“Some clades manage to stagger on for tens of millions of years,” Jablonski said.
So I seem to have assessed this correctly. It is exactly what seems to have happened to the mammoths.
Now, as those wankers keep pointing out, there was not only the one they talked about, on Wrangle Island, north of Siberia and at 71.5°N 180°W. There also was another one other group Santa Rosa Island, one of California’s Channel Islands. Both populations are thought to have swum across from the mainland, and for some reason were not able to get back. If either one had, we might not be talking about them being extinct.
But, for whatever reason, none of them did swim back – or at least not enough to procreate.
ISLANDS ARE NOT GOOD PLACES TO BE AFTER THE EVENT
By staying on the islands, each was doomed. Perhaps they would have been doomed anyway. But extinctions and islands kind of go together, in our normally Gradualistic times. The Younger Dryas onset waS not one of those times. Depending on who you listen to, there was either a marauding band of Killer Clovises, a proboscidean pandemic, a climate tipping point – or, as I think, a Killer Comet with their name on it. Whatever it was, it came on suddenly (even some of the the Gradualist geologists who study it think that it happened in the geological eye blink of less than 20 years).
Archaeologists Meltzer and Grayson wrote that
That island faunas are vulnerable . . . is not surprising. As Steadman (1997) has observed, island birds are at risk in these settings because they have relatively small population sizes, are confined to tightly bounded areas of land that may undergo rapid environmental change, and may have lost—and in some cases have clearly lost—the mechanisms needed to cope with introduced pathogens, predators, and competitors. Much the same can be said for all island vertebrates, and to all of this must be added the fact that the isolated nature of islands means that there are no nearby sources of conspecific individuals to replace dwindling local populations. No wonder, as Steadman et al. (1991, p. 126) point out, “animals on oceanic islands tend to be more vulnerable to extinction or extirpation than their continental counterparts” and that, as Paulay (1994, p. 134) notes, island faunas are “among the most vulnerable in the world.”
DEAD CLADE WALKING – WTF IS IT?
In a 2001 scientific paper entitled “Lessons from the past: Evolutionary impacts of mass extinctions”, by Universtiy of Chicago Professor of Geophysical Sciences David Jablonski. He wrote about Dad Clade Walking:
Clade survival is no guarantee that preextinction trends will persist or be reasserted in the postextinction setting. Each extinction has examples of clades that survived the extinction event only to fall into a marginal role or eventually disappear (dead clade walking). These include bellerophontid snails and prolecanitid ammonoids at the Permo-Triassic boundary, the brachiopod order Spiriferoida after the end-Triassic extinction, and the planktic foraminiferal Zeauvigerina lineage after the K-T event. . .
. . . My preliminary, unpublished analysis suggests that the intervals after mass extinctions tend to be significantly enriched in taxa that failed to cross the next stage boundary, relative to other intervals before the extinction event; in other words more clades that survived a mass extinction tend to dwindle or disappear shortly after the event than would be expected by chance.
In other words, life is really TOUGH after an extinction event. Put a surviving species on an island and then add whatever caused the Younger Dryas biological and climatological changes to that, and the mammoths were going to be tested to the limit. To the last ones.
THE OVERKILL THEORY IS DEAD
Probably almost all of you who know about mammoths know that the prevailing theory about their extinction blames humans, who were new to the New World and went berserk running around North America, slaughtering them all until there were none left. This theory is called The OverKill Theory. The idea was originated by one Paul C. Martin [first name corrected], back in the 1960s. The bad guys in that scenario were a people known today simply as Clovis. They are named after the amazingly crafted spear points first found in Dent, CO, but named after a more studied site outside the town of Clovis, NM.
One of the odd things about the Clovis people is that they went extinct then, too.
And one of the odd things about the Overkill Theory is that it has been challenged by Grayson and Meltzer (in 2002) and others and found very much wanting. They vetted the claimed Clovis-mammoth kill sites, and out of 76, only 12 made the grade. Two mastodon sites also passed.
But of the other 31 species that ALSO went extinct at that time, NOT ONE Clovis kill site has ever been found. NONE. NADA. NUNCA. NEVER.
Meltzer and Grayson rip a new anal orifice in the Overkill Theory:
As the assessment we have provided here shows, however, there is no evidence that Clovis people preyed on a wide variety of now-extinct large mammals. . .
. . .Indeed, it is significant that for 33 extinct genera, and for 26 of the 28
extinct herbivores, there is no archaeological evidence at all for hunting,
and only a limited number of kill/butchering sites for the other two. . .
. . .Of the 76 localities with asserted associations between people and now extinct Pleistocene mammals, we found only 14 (12 for mammoth, 2 for
mastodon) with secure evidence linking the two in a way suggestive of predation. . .
. . .This is not to say that such hunting never occurred: we have clear evidence that proboscideans were taken by Clovis groups. It just did not occur very often. . .
. . .No statistical analysis is needed to observe that the late Pleistocene peoples of North America cannot be shown to have been preying on a full-array of now-extinct herbivores. Archaeologists have pointed this out all along (e.g., Hester, 1967; Jelinek, 1967). . .
. . .However, the issue is not whether Clovis groups were “capable” of hunting the Pleistocene fauna to extinction, but whether they actually did so, and that is an archaeological question. The archaeological answer is clear enough: they did not. This is why overkill finds so little support among those who are familiar with the empirical record of late Pleistocene archaeology and paleontology.
[Updated – correction: Paul C. Martin’s name I wrote down as “Charles C. Martin”. My bad. Correction made. H/T Mark Gelbart]