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Natural Science Forum / Biology / Paleontology / April 2005Ratre origins
What is the sort of consensus on the origin of a Ratire birds and how they spread. > What is the sort of consensus on the origin of a Ratire birds and how > they spread. You mean ratite birds? There is at present no real consensus. Paleognaths are clearly monophyletic. It's suggested that they are gondwanan in origin. Whether ratites were flightless before separation of the current groups is unclear. >> What is the sort of consensus on the origin of a Ratire birds and how >> they spread. [quoted text clipped - 3 lines] > origin. Whether ratites were flightless before separation of the current > groups is unclear. Just out of curiosity, what is your opinion on some of the very theropod-like birds that are coming out of China? Could they possibly represent the "split" that led off to the ratites, or are they more like the path between dinos and the more common birds? Now that I mention it, are ratites really all that much closer (except in some obvious cases, in size) to dino ancestors, than say a duck? Just curious! No claims, hypotheses, or speculations! Regards bk >>>What is the sort of consensus on the origin of a Ratire birds and how >>>they spread. [quoted text clipped - 10 lines] > ratites really all that much closer (except in some obvious cases, in size) > to dino ancestors, than say a duck? All living birds are equally close to other dinosaurs. None of the Chinese feathered theropods, or the birds in those deposits either, is closer to ratites than to ducks or any other living bird. > Just curious! No claims, hypotheses, or speculations! > > Regards > bk > >> What is the sort of consensus on the origin of a Ratire birds and how > >> they spread. [quoted text clipped - 8 lines] > represent the "split" that led off to the ratites, or are they more like the > path between dinos and the more common birds? Molecular data suggests that the ratites as a group evolved less than 80 Ma - although they possess some primitive characters, they aren't among the oldest bird lineages. If the biogeography of extant and recent groups is any guide the ratites seem to have their origin in or near New Zealand, which was separate from China long before they evolved. Now that I mention it, are > ratites really all that much closer (except in some obvious cases, in size) > to dino ancestors, than say a duck? Ratites are thought to be secondarily flightless, primarily on the basis of their pattern of dispersal (i.e. the fact that they must have dispersed to Australia, Madagascar, South America and most recently Africa after the Gondwanan split), which suggests they must have flown to most or all of those locations. Also, most ratites are large while dromaeosaurs are mostly small, and it seems that the earliest birds may have been small arboreal dromaeosaurs rather than large flightless theropods, with little obviously in common with ratites. As a side note, ducks are among the older bird lineages and a recent fossil anatid from Antarctica dates to the Cretaceous, so the first ducks seem to have been more closely-related to their theropod ancestors than the early ratites, which were more derived. Philip Bowles >>>>What is the sort of consensus on the origin of a Ratire birds and how >>>>they spread. [quoted text clipped - 15 lines] > near New Zealand, which was separate from China long before they > evolved. I suppose you mean the moa mitochondrial sequences showing them to be far separated from kiwis. I don't think the biogeographic conclusion is very robust, but I'll give you a high probability of Gondwanan origin. > Now that I mention it, are > [quoted text clipped - 6 lines] > Africa after the Gondwanan split), which suggests they must have flown > to most or all of those locations. Not so. The primary bases are two: first, paleognaths are, in every analysis of early bird phylogeny, deeply nested within birds, and are preceded by several nodes with flying birds on both sides; second, they have many clear adaptations to flight, retained from their flying ancestors, of which the most obvious is a pygostyle. > Also, most ratites are large while > dromaeosaurs are mostly small, Not true. Most dromaeosaurs are larger than most ratites. And even if this were true, so what? Size is one of the most labile characters in evolution. > and it seems that the earliest birds > may have been small arboreal dromaeosaurs rather than large flightless > theropods, with little obviously in common with ratites. If we took this seriously, wouldn't it argue against the monophyly of birds, and in favor of ratites being descended from something other than dromaeosaurs? > As a side note, ducks are among the older bird lineages and a recent > fossil anatid from Antarctica dates to the Cretaceous, so the first > ducks seem to have been more closely-related to their theropod > ancestors than the early ratites, which were more derived. That's not true. All living birds are related to their theropod ancestors by exactly the same amount. And the same would apply to all Cretaceous Neornithes. Ducks have one of the better fossil records among bird groups, better than that of paleognaths, but that doesn't mean they're an older group. In fact, based on the well established phylogeny, paleognaths as a group must be older than anseriforms as a group. Whether ratites, specifically, are older than anseriforms is not answerable from current data. On 19-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> wrote in message <J899e.3217$J12.426@newssvr14.news.prodigy.com>: [...] > > Ratites are thought to be secondarily flightless, primarily on the > > basis of their pattern of dispersal (i.e. the fact that they must have [quoted text clipped - 7 lines] > have many clear adaptations to flight, retained from their flying > ancestors, of which the most obvious is a pygostyle. Is it really the case that ratites are thought to have evolved less than 80 Ma, after Gondwanaland split up, and dispersed to their current locations by flight? Interesting then that every surviving lineage developed flightlessness independently...  SignatureJim Heckman > On 19-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> > wrote in message <J899e.3217$J12.426@newssvr14.news.prodigy.com>: [quoted text clipped - 17 lines] > their current locations by flight? Interesting then that every > surviving lineage developed flightlessness independently... We don't really know. Molecular clocks are not very well calibrated. I personally think that ratites lost flight at least 3 times, maybe more. But that's not based on any continental breakup scenario, and I have no idea how old the paleognath crown group is. The oldest fossils are, to my knowledge, Paleocene. But so what? Flying doesn't make birds totally mobile, able to ignore big oceans. Nor does merely having continuous land between two points mean that birds, flying or flightless, can spread between those points. Some tropical, flying birds will not cross a road cut, much less a river. And island arcs can form a set of stepping stones for dispersal across oceans. It's not a simple question. And while I'm at it, I'm fixing the thread title. > > On 19-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> > > wrote in message <J899e.3217$J12.426@newssvr14.news.prodigy.com>: [quoted text clipped - 16 lines] > > less than 80 Ma, after Gondwanaland split up, and dispersed to > > their current locations by flight? I'm going from lecture notes here, but supposedly analysis of the group indicates that they can't have diverged from their common ancestor more than 88 Ma at the earliest. Interesting then that every > > surviving lineage developed flightlessness independently... That simply suggests that the group had a predisposition to lose the power of flight, perhaps because gigantism made them poor fliers better-adapted to a terrestrial life (moas are the most primitive ratite lineage), or simply because the particular genetic makeup of the ratite ancestor gave the group a greater likelihood of adapting successfully to a terrestrial lifestyle than some other bird groups. As far as the fossil record (or lack of it) is any guide (which it often isn't), the ratites are a very recent introduction to Africa - there are no African fossil ratites outside Madagascar. This suggests that their migration to that continent at least occurred after Gondwana had started to break up. Philip Bowles >>>On 19-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> >>>wrote in message <J899e.3217$J12.426@newssvr14.news.prodigy.com>: [quoted text clipped - 20 lines] > group indicates that they can't have diverged from their common > ancestor more than 88 Ma at the earliest. This is relying on two things: some kind of DNA distances (presumably) and some kind of calibration point. The error bars on both of these are very large and seldom considered adequately. I'm guessing that the number you quote comes from Haddrath and Baker. Take it with a good-sized box of salt. > Interesting then that every > [quoted text clipped - 4 lines] > better-adapted to a terrestrial life (moas are the most primitive > ratite lineage), Presumably by "most primitive" you mean "are one of the two initial branches within ratites". But that has no implication of primitiveness in any morphological sense. > or simply because the particular genetic makeup of > the ratite ancestor gave the group a greater likelihood of adapting [quoted text clipped - 5 lines] > that their migration to that continent at least occurred after > Gondwana had started to break up. [...] > > Is it really the case that ratites are thought to have evolved > > less than 80 Ma, after Gondwanaland split up, and dispersed to [quoted text clipped - 6 lines] > idea how old the paleognath crown group is. The oldest fossils are, to > my knowledge, Paleocene. But so what? Could you say more about the 3 times you think ratites lost flight, and why you think so? Also, in a later post to this thread you say you don't think ratites are monophyletic, but paleognaths are. Could you say more about this, such as what is the phylogeny of living paleognaths? (As you can no doubt tell, I'm a complete layman.) [...] SignatureJim Heckman > [...] > [quoted text clipped - 15 lines] > the phylogeny of living paleognaths? (As you can no doubt tell, > I'm a complete layman.) All this is based on unpublished data, I'm afraid. There is a tiny little hint of it here, if you can get access to a copy: Cracraft, J.et al. 2004. Phylogenetic relationships among modern birds (Neornithes): Toward an avian tree of life. Pages 468-489 in Assembling the tree of life (J. Cracraft and M. J. Donoghue, eds.). Oxford University Press, New York. (Look at the c-myc tree.) But the evidence is pretty simple. There are two "groups" of living paleognath birds, the flightless ratites and the flying tinamous. A great deal of unpublished molecular evidence shows that tinamous are nested within the ratites. If that's true, either flight was lost multiple times in ratites (easy to do) or it was lost once and regained in tinamous (seemingly hard to do). On 27-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> wrote in message <y6Pbe.1377$Gd7.548@newssvr21.news.prodigy.com>: [...] > But the evidence is pretty simple. There are two "groups" of living > paleognath birds, the flightless ratites and the flying tinamous. A > great deal of unpublished molecular evidence shows that tinamous are > nested within the ratites. If that's true, either flight was lost > multiple times in ratites (easy to do) or it was lost once and regained > in tinamous (seemingly hard to do). Thanks. So which modern ratites are tinamous most closely related to? BTW, I'd like to take this opportunity to thank you for your many, many informative posts over in talk.origins (even if you don't snip nearly enough extraneous quoted material in them :-). I've learned a great deal from you by lurking there. SignatureJim Heckman > On 27-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> > wrote in message <y6Pbe.1377$Gd7.548@newssvr21.news.prodigy.com>: [quoted text clipped - 10 lines] > Thanks. So which modern ratites are tinamous most closely > related to? This is a difficult problem, but the current answer is quite satisfying: rheas. Since they're all from South America, that's way cool. > BTW, I'd like to take this opportunity to thank you for your > many, many informative posts over in talk.origins (even if you > don't snip nearly enough extraneous quoted material in them :-). > I've learned a great deal from you by lurking there. Thanks. It's a question of balance. I think some people snip too much. I need the context or I can't remember what we're talking about. On 28-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> wrote in message <1b5ce.8882$J12.5723@newssvr14.news.prodigy.com>: > > On 27-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> > > wrote in message <y6Pbe.1377$Gd7.548@newssvr21.news.prodigy.com>: [quoted text clipped - 13 lines] > This is a difficult problem, but the current answer is quite satisfying: > rheas. Since they're all from South America, that's way cool. Yes, it is. :-) It occurs to me now though to wonder why you think flight was lost at least 3 times in 'ratites'. I can see twice if tinamous do indeed form a clade with rheas, but where's the 3rd? Maybe there's a line of fossil paleognaths that we have good reason to believe could fly and to be nested within some modern flightless forms? [...] SignatureJim Heckman > On 28-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> > wrote in message <1b5ce.8882$J12.5723@newssvr14.news.prodigy.com>: [quoted text clipped - 18 lines] > > Yes, it is. :-) It occurs to me now though to wonder why you think flight > was lost at least 3 times in 'ratites'. I can see twice if tinamous do > indeed form a clade with rheas, but where's the 3rd? Maybe there's a line > of fossil paleognaths that we have good reason to believe could fly and to > be nested within some modern flightless forms? No, it's 3 because of where the tinamous go in the tree, i.e. there are three ratite branches to pass by before you get to them. There are flying paleognath fossils (sometimes termed "lithornithiforms"), but no analyses I know of put them within ratites. On 28-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> wrote in message <gndce.2488$zu.1094@newssvr13.news.prodigy.com>: >> Yes, it is. :-) It occurs to me now though to wonder why you think >> flight was lost at least 3 times in 'ratites'. I can see twice if [quoted text clipped - 7 lines] > flying paleognath fossils (sometimes termed "lithornithiforms"), but no > analyses I know of put them within ratites. Oh, of course. I'd just assumed that the earliest node was the split between rheas+tinanous and everything else. But of course nothing you've said should have led me to conclude that. So what *are* the nodes within paleognaths, as far as we know? SignatureJim Heckman > On 28-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> > wrote in message <gndce.2488$zu.1094@newssvr13.news.prodigy.com>: [quoted text clipped - 15 lines] > you've said should have led me to conclude that. So what *are* the > nodes within paleognaths, as far as we know? "As far as we know" might be pushing it a bit. I'll stick with "as far as I know". As far as I know, ostriches are the sister group of all other living paleognaths. The Australasian paleognaths go together, as do the South American paleognaths. The ostrich thing is more strongly supported than the rest. I will note that the person outside my group who is most seriously involved with paleognath phylogeny would strongly disagree with all of this. On 29-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> wrote in message <GIrce.2642$zu.1573@newssvr13.news.prodigy.com>: [...] > > Oh, of course. I'd just assumed that the earliest node was the split > > between rheas+tinanous and everything else. But of course nothing [quoted text clipped - 8 lines] > who is most seriously involved with paleognath phylogeny would strongly > disagree with all of this. OK, thanks. Out of curiosity, how would this outside person disagree? SignatureJim Heckman > On 29-Apr-2005, John Harshman <jharshman.diespamdie@pacbell.net> > wrote in message <GIrce.2642$zu.1573@newssvr13.news.prodigy.com>: [quoted text clipped - 15 lines] > > OK, thanks. Out of curiosity, how would this outside person disagree? He wouldn't like a single one of the nodes I have mentioned. For details, see Lee, K., J. Feinstein, and J. Cracraft. 1997. The phylogeny of ratite birds: Resolving conflicts between molecular and morphological data sets. Pages 173-211 in Avian molecular evolution and systematics (D. P. Mindell, ed.). Academic Press, San Diego. > >>>>What is the sort of consensus on the origin of a Ratire birds and how > >>>>they spread. [quoted text clipped - 18 lines] > I suppose you mean the moa mitochondrial sequences showing them to be > far separated from kiwis. The data I'm thinking of doesn't suggest that moas are 'far' separated from kiwis, at least on the information I've got - it does suggest that the NZ ratites are the most primitive and more closely-related to one another than to those elsewhere, and that ostriches (which have no fossil record) are the most derived group, supporting the idea of a recent migration to Africa. > Not so. The primary bases are two: first, paleognaths are, in every > analysis of early bird phylogeny, deeply nested within birds, This in itself isn't revealing. While it's usually assumed that the first birds could fly, until the discovery of Microraptor the compelling reason for believing this was that the known flightless groups are all thought to be secondarily flightless - which, besides being circular, doesn't logically follow. After all, at some stage a flightless ancestor evolved flight and some of its descendants lost it again - that doesn't rule out the possibility that the flightless ancestor was a bird that had yet to evolve flight rather than a dinosaur. and are > preceded by several nodes with flying birds on both sides; I'll give you that one. second, they > have many clear adaptations to flight, retained from their flying > ancestors, of which the most obvious is a pygostyle. [quoted text clipped - 13 lines] > birds, and in favor of ratites being descended from something other than > dromaeosaurs? Okay, let me lay out my train of thought here - Bob Keeter wondered whether there was any evidence ratites are particularly close relatives of the dinosaurs, I assume based on superficial similarities between flightless ratites and theropods. What I'm pointing out here is merely that the bird-ancestors among the theropods didn't bear many similarities to the ratites - Microraptor, which may be the closest we've found morphologically to the ancestral bird, was a lot smaller than most ratites, it wasn't terrestrial and it may have been able to fly. Therefore what I was getting at was that, even though ratites resemble 'traditional' theropods, they don't resemble the ancestral birds and so their morphology isn't a reason for implying a close relationship. > > As a side note, ducks are among the older bird lineages and a recent > > fossil anatid from Antarctica dates to the Cretaceous, so the first [quoted text clipped - 3 lines] > That's not true. All living birds are related to their theropod > ancestors by exactly the same amount. All living birds - I'm talking about the ancestral birds in both lineages, one of which presumably diverged from the basal neornithid earlier than the other, and so would have been a closer (though still distant) relative of the theropods due to the greater closeness in time. Unless the anatids and the ratites diverged at exactly the same point in the Cretaceous, logically one group would have been more closely-related to their ancestors than the other. And the same would apply to all > Cretaceous Neornithes. The Cretaceous was a long period. You may as well say that living humans are as closely-related to the ancestral eutherian as, say, a pangolin from Messel, on the basis that both have lived within the last 60 million years, even though there are 50-odd million years between the Messel deposits and the present day. Philip Bowles >>>>>>What is the sort of consensus on the origin of a Ratire birds and how >>>>>>they spread. [quoted text clipped - 25 lines] > fossil record) are the most derived group, supporting the idea of a > recent migration to Africa. I have no idea what you mean by "primitive" and "derived" here, nor do I know what data you're thinking of. Lee and Cracraft? >>Not so. The primary bases are two: first, paleognaths are, in every >>analysis of early bird phylogeny, deeply nested within birds, [quoted text clipped - 4 lines] > groups are all thought to be secondarily flightless - which, besides > being circular, doesn't logically follow. It's also completely wrong. The reason it's assumed that the first birds could fly is that "bird" is defined by flight. If you mean that the first Aves could fly, then the reason is that both branches of the initial divergence that defines the clade have flying members, regardless of which definition you prefer. That is, flight is parsimoniously optimized to be present in the most recent common ancestor. Microraptor, being outside Aves by any definition, has nothing to do with it. > After all, at some stage a > flightless ancestor evolved flight and some of its descendants lost it > again - that doesn't rule out the possibility that the flightless > ancestor was a bird that had yet to evolve flight rather than a > dinosaur. All true, but irrelevant. It's not just flightlessness that is relevant here, but all the morphological characters uniting Neornithes and excluding all other birds and theropods, as well as the characters uniting various other clades of birds outside Neornithes. > and are > [quoted text clipped - 34 lines] > birds and so their morphology isn't a reason for implying a close > relationship. OK, that's sensible. But we should note that there's no reason to do this anyway. Partially, we may be arguing the same thing, that resemblances between ratites and various non-avian theropods like Struthiomimus are either primitive (and shared with flying birds too) or convergent. You are invoking the tree to show this in an informal and indirect way by mentioning "ancestors". I'm invoking the tree directly. >>>As a side note, ducks are among the older bird lineages and a recent >>>fossil anatid from Antarctica dates to the Cretaceous, so the first [quoted text clipped - 7 lines] > lineages, one of which presumably diverged from the basal neornithid > earlier than the other, No, they both diverged from the basal neornithid at exactly the same time, because the divergence between paleognaths and neognaths *is* the basal divergence in Neornithes. The fact that neognaths later diverged into Galloanserae and Neoaves, and Galloanserae into Galliformes and Anseriformes, is irrelevant. The language you are using suggests that there is some "main trunk" of bird evolution that throws off side branches from time to time, rather than a tree that splits and splits again. > and so would have been a closer (though still > distant) relative of the theropods due to the greater closeness in > time. Unless the anatids and the ratites diverged at exactly the same > point in the Cretaceous, logically one group would have been more > closely-related to their ancestors than the other. We usually don't use "closely related" in this sense, for good reason. What you are asking is whether some particular clade is older than another, and we have no good evidence for that. Further, the clades you are referring two are unclear. I don't think ratites are a clade, though paleognaths are. But even the age of paleognaths depends on how you define it, as a stem-based, node-based, or character-based group. Same with ducks; presumably you mean either Anseriformes or Anatoidea, and neither of these has a clear definition either, though they are clades. I would agree that a stem-defined Paleognathae is older than Anseriformes by any definition, but this doesn't translate into ratites being older than ducks, nor into any sort of special "relationship" to theropods. > And the same would apply to all > [quoted text clipped - 5 lines] > last 60 million years, even though there are 50-odd million years > between the Messel deposits and the present day. Like I said, I wouldn't use your implicit definition of "related". What does it get us? Cladistic relationships at least can be determined. I will concede that a Messel pangolin is older than I am, and thus closer in time to that common ancestor. It may even be more similar to that common ancestor by some measure or other. But more closely related? No. |
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