I know about that, and it’s very interesting, but doesn’t change anything already said.
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I know, I wasn’t disagreeing - just wanted to share a cool thing.
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It was not explicitly stated, but just to clear away (another) common misconception:
Archaeopteryx is not the ancestor of modern birds.
One concept defines Birds (Aves) as all descendants of the last common ancestor of Archaeopteryx and modern birds. Other studies put archaeopteryx more closely to ‘non-birdy’ raptors (Deinonychosauria, Dromaeosauridae) than to true birds (all of which are labelled as ‘Paraves’)
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Seeing a cassowary actually just makes me want to run away… or hide behind a tree…
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As @elsemikkelsen points out, we do have that one protein sequence. (A form of collagen, I believe.) I think the whole “Chickens are the closest relative to T. rex” thing was from the paper that reported that sequence – if I remember right, they ran a small phylogenetic analysis, and used chickens to represent all of the modern birds. So, in their analysis, chickens were the closest relative since they were the only bird.
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I’m joking 
A bit off topic, does anybody know if emus have killed anyone?
As I recall, that’s correct, and the media did the usual thing when it comes to science reporting and ran with that without ever actually explaining what happened.
Chickens were used because it’s easy to get chickens, but if they’d used any other bird the results would have been the same. We could have been hearing, "Penguins are the closest relative to T-rex.
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Between 2001 and 2007 there were 5 deaths caused by emus and ostriches in Australia. It’s unclear how many of them were due to car accidents, as in the case of most kangaroo related deaths, but emus are more than capable of killing a person with their powerful legs and claws.
As an aside, Australia once lost a war to emus.
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Absolutely! Although I imagine if they used a few different birds they’d have gotten results that differed slightly between them – there’s still a strong element of chance. That’s what we need the stats for!
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Archeopteryx didn’t evolve in modern birds, it’s a side branch and it died out as many others. All the birds species today didn’t evolve in one moment, so they didn’t appear from 1 ancestor all together, it took time and lots of diversification.
I would say it’s not exactly like that, with different bird lineages, some groups are younger, some are older, some species evolved on our eyes (as those Galapogos hybrids) and some are older than others, so theoretically we could estimate which bird group is genetically closer to one non-avian dinosaur species, but it definitely wouldn’t be chicken.
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It does seem surprising that all modern birds could come from such a small number of ancestors. But remember, every single animal species came from the same ancestor, if you go back far enough. Heck, every single life-form. It’s just a matter of time and enough niches to fill.
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Bird evolution also illustrates the evolutionary relationship of other animals nicely as well:
Birds and crocodiles are both archosaurs, an ancient group that first arose in the Triassic. In fact, some of the early crocodylomorphs evolved convergently to look a bit like dinosaurs, as well as many other body plans, in the Triassic period before the Triassic-Jurassic mass extinction event took place and true dinosaurs took over.
Snakes and lizards are descended from lepidosaurs, another reptilian group that also arose in the Triassic and went on their own way; turtles are their own group as well.
This is how we can say that birds and crocodilians are most closely related to each other, despite modern crocodilians sharing a superficially similar appearance to lizards in body plan, scaly skin, etc.
All of these groups are part of the diapsid group, which just means that they all share the same feature: two major holes known as temporal fenestrae in their skull, while synapsids (mammals and their ancient relatives) have only one opening behind each eye.
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One has to be careful with terms such as ‘older’ or ‘more ancient’ when talking about taxonomy.
It is true that songbirds as a group have more recently arisen than galloanserae or palaeognathae - but that doesn’t mean that an Ostrich is ‘older’ or closer to T-rex than a Galapagos Finch. Both are recent, so they have the same age.
There are, however, differences in the genetic code, and in one group there may be more differences to a T-rex than in another group. But one needs to look at the genetic sequence (and would need material to compare with) to claim that one taxon is ‘more similar’ (molecular genetically) to a distant relative - and this cannot be answered by looking at the phylogenetic tree.
One can make hypotheses of course, taking into account the life span and generation time of a particular taxon, but these are not robust data
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That’s pretty much what I said, species still evolved at different “moments”, so one still will be older than others, and theoretically we would compare its genome with one of ancient dino to see if this actually means it was more stable or not, who knows, or using mutation clock we still could estimate which of the bird is “closer” to something back then, not T-rex though in this case. Anyway if we had genome for comparison we would know the answer, it’s not “all are the same as granddaughters to grandma”.
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All I will add is that is nearly impossible to ‘Know’ why certain groups thrive, and some do not. Trilobites were a very successful arthropod group that for some reason in the past, became extinct. None of us will never be certain why - we can speculate, but we will never really know. Birds bear a skeletal (and physiological) resemblance to some dinosaurs, and some dinosaur fossils show evidence of feathers. How and when birds developed is really unknown. The evolution of bird groups and species is governed by the factors that govern all evolution - natural selection, genetic drift, isolation etc.
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That is not quite how genome evolution works: different species arose through speciation at different times, but the genome continues to mutate and evolve whether speciation occurs or not. The Galapagos Finches diverged from each other very recently, while the Pacific Wren diverged from its sister 4 million years ago, but neither species is more “ancient”: both have been accumulating mutations in their genome at approximately the same rate over the last 4 million years. Sometimes evolution produces big differences in a short time, and sometimes a species seems like it doesn’t change at all for a long time, but the genome is still changing constantly, those mutations just aren’t affecting appearance very much.
We have many bird genomes sequenced now, and it is possible to estimate their relative mutation rates (that is actually part of what I’m doing for my PhD). Overall it is probably generally similar between most bird lineages, but with some notable variation, especially caused by differences in how long a generation is for each species.
It depends how you think about “closely related”. Phylogenetically, or in terms of absolute time, all birds must be equally closely related to their common ancestor. In terms of absolute DNA sequence divergence, there is going to be little difference among birds, but there will be random variation, and the lineage with the longest average generations and/or lowest mutation rates will have fewer mutations separating it from this ancestor, but that is not normally how we think about relatedness in phylogenetics.
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Yeah, it seems as two different approaches of that idea and also myself answering to the question that wasn’t there; yes, oldest appearing doesn’t mean genetically oldest, but we still could use it and see how it relates to actual genetic “stance” of it.
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It is an interesting idea for sure. I think it is similar to the “punctuated equilibrium” hypothesis, that hypothesizes that lineages mostly accumulate changes in rapid bursts during speciation events. It’s usually applied to changes in morphology/appearance, but could also apply at some level to the genome sequence (eg if speciation happens during stressful environmental conditions when mutation rate is higher, or if the new species goes through a bottleneck of small population size, which can to some extent affect the rate of accumulating DNA changes). So far punctuated equilibrium is generally not well-supported overall (with exception), and I haven’t seen anything to support it for bird genome evolution, but it would be an interesting study to see if there is an effect on the genome. I bet there is one, but I would predict that it is small and applies mostly to protein-coding changes.
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There are groups that we can recognize as older or younger, and clearly there are species that have evolved more recently than others. But even the older groups or species wouldn’t be expected to be genetically closer to those ancestors – that sort of thing can vary a bit based on generation times, but it’s not like Ostriches (paleognaths are one side of the first split we can trace forwards to modern species) stopped evolving just because the paleognaths branched off from the others.
Edit: I should have read the further discussion – others have already said this much better than I did.
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That’s why I menioned both groups and species, because groups alone sounds as if I think that they stopped evolving, no.
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