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  2. Everything you heard about the KT boundary is wrong

Everything you heard about the KT boundary is wrong

By jlynch on March 28, 2007.

I don't have time to comment at the moment (perhaps over the weekend), but this looks interesting:

The big dinosaur extinction of 65 million years ago didn't produce a flurry of new species in the ancestry of modern mammals after all, says a huge study that challenges a long-standing theory.

Scientists who constructed a massive evolutionary family tree for mammals found no sign of such a burst of new species at that time among the ancestors of present-day animals...

Instead, they showed an initial burst between 100 million about 85 million years ago, with another between about 55 million and 35 million year ago, researchers report in Thursday's issue of the journal Nature.

The Nature paper is here.

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evolution
mammals

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Unfortunately, this is one for the "spin outdoes facts" file. The paper says that the *extant* lineages (extant = alive now) did not diversify immediately after the K-T boundary.

But the paper *does* say that mammalian species diversity *did* spike after the K-T event:

The supertree therefore contains no evidence that the diversification rate of the extant mammalian lineages increased soon after non-avian dinosaurs went extinct. Although there is strong palaeontological evidence that mammalian diversity, driven by a massively elevated rate of speciation, generally rose rapidly immediately after the K/T boundary4, there is in fact no conflict between the palaeontological and neontological interpretations of the known facts. Most diversifications immediately after the K/T boundary were in groups such as multituberculates, plesiadapiforms and 'archaic' ungulates4, as plots of the numbers of genera known in each sub-epoch indicate (Fig. 2c). These groups declined or went extinct early in the Cenozoic era and so are barely, if at all, represented in the phylogeny of living species.

So all they are really saying is that the extant mammal clades at 0 mya were not the dominant lineages that were radiating wildly 65-60 mya. 60 million years is a very long time. Why should this be shocking, exactly?

(PS: This might even be one big by-product of the general process of speciation and extinction. By any account, most species and lineages die out. Therefore, as you go further back in time, the modern extant crown clades will encompass a smaller and smaller portion of fossil diversity, even on a model where speciation and extinction are completely random.)

I haven't had time to read the paper yet, so thanks for the comment.

By John Lynch (not verified) on 28 Mar 2007 #permalink

I could be the one totally wrong, of course -- but what would be interesting would be a comparison of the speciation of extant lineages versus some null model around the KT boundary.

Whatever the exact siginificance of the paper, I think your title is a _slight_ exaggeration. What _I_ know about the KT boundary could be summarised as iridium/asteroid/dead-dinosaurs.

You're right! When I saw "KT Boundary" I assumed that it had something to do with physics or astronomy. Boy, was I wrong!