I wonder if one or more phylogenetic threads of dinosaurs survived the mass extinction.

In other words, are all living birds equally related to any given ancient dinosaur, or do some birds relate more to some ancient dinosaurs while other birds are more related to other ancient dinosaurs?

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    Birds are theropod dinosaurs – Chinmay Kanchi Nov 6 '17 at 14:50
  • @Chinmay Kanchi: No, they're not. They're DESCENDED from theropod dinosaurs. Saying they are is like saying mammals are synapsid reptiles, or that all of them are really just fish :-) And we can see this by noting that there were many different orders of birds in existence long before the K-T extinction event. – jamesqf Nov 6 '17 at 19:49
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    Fish is paraphyletic, but the rest is true. Mammals ARE synapsids when strict taxonomy is respected. Scientifically speaking, Donald Trump is a reptiliomorph, and Vladimir Putin is an eupelicosaur. If you deny that you'll also have to deny that you're a mammal. – lolmaus - Andrey Mikhaylov Nov 6 '17 at 21:12
up vote 6 down vote accepted

I suppose that by the mass extinction, you are referring to the Cretaceous–Paleogene extinction event that happened 66 mya. The Most Recent Common Ancestor (MRCA) of all birds lived about 113.3 mya (early Cretaceous, according to this in oneZoom.org).

So yes, the MRCA of all birds is definitely older than the Cretaceous–Paleogene extinction event. As you said, this also mean that some ancient dinosaurs are/were more related to some extant birds than some extant birds are related.

You (the OP) might not need it but some other readers might need clarification about phylogeny with the post If dinosaurs could have feathers, would they still be reptiles?

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    That's awesome! According to OneZoom, the following groups independently survived the Cretaceous-Paleogene mass extinction INDEPENDENTLY: ostriches; [cassowary, tinamou, moa, etc]; [waterfowls, magpie geese]; screamers; gamebirds; [sunbittern, kagu]; oilbirds; potoos; nightjars; frogmouths; [hummingbirds, swifts]; tropicbirds; [flamingos, grebes]; [sandgrouses, hoatzins]; [pigeons, doves]; [cranes, rails]; [bustards, floricans]; [some cuckoos, roadrunners]; [other cuckoos], turacos, [herons, shearwaters, pelicans, penguins, albatrosses, etc]. – lolmaus - Andrey Mikhaylov Nov 6 '17 at 19:44
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    That's absolutely amazing! Earlier I thought that a single Jurassic Park-like feathered dinosaur survived the extinction and evolved into birds, but it turns out that before the dinosaur extinction birds were already very diverse! – lolmaus - Andrey Mikhaylov Nov 6 '17 at 19:45
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    Of course, I enumerated the groups using names of modern representatives of the groups, and 66M years ago their ancestors might have looked differently and maybe more primitively, but they were already birds (almost?) as we know them today! All those monophiletic groups of dinosaurs-birds were already established, whereas ALL human ancestors were tiny lemur-like creatures. O_O – lolmaus - Andrey Mikhaylov Nov 6 '17 at 19:53
  • What was the largest bird that survived the KPG boundary and did any flightless birds do do? cool topic Remi and Andrey. From the other topic Remi, i didn't find evidence that less compact genomes can evolve more efficiently. It was an logic from lessons prior to sequencing. – com.prehensible Nov 6 '17 at 20:34
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    @bli of course, as you say is right. Bird is still a monophyletic clade. The only point is that some of the birds lineage already existed before the K-P extinction. You can call them ancient dinosaurs if you want. As all birds are Dinosauria, all modern birds as well as those ancient birds are all Dinosauria. That's all. See eventually If dinosaurs could have feathers, would they still be reptiles? – Remi.b Nov 14 '17 at 15:58

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