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| How should "Aves" be defined? |
| As a crown group (e.g., sensu Gauthier 1986) |
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23% |
[ 3 ] |
| As a total group (e.g., sensu Ax) |
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0% |
[ 0 ] |
| As a non-crown node-based clade (e.g., sensu Chiappe 1997, Sereno 1997) |
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30% |
[ 4 ] |
| As a non-total branch-based clade (e.g., sensu Marjanovic [unpublished]) |
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30% |
[ 4 ] |
| As an apomorphy-based clade (please specify). |
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15% |
[ 2 ] |
| Other (please explain). |
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0% |
[ 0 ] |
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| Total Votes : 13 |
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tmkeesey
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 Posted: Thu 01 Feb, 2007 7:47 am Post subject: |
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It's been a while since anyone's posted here. I just wanted to state a defense of the crown group definition:
The taxon Aves was originally named with members of the crown group in mind. Scientists of that time, including Linnaeus, had no knowledge of any stem-avians. Perhaps they would have considered certain stem-avians as "avian", perhaps not--we will never know.
Objectively, in this type of case, there are two things that could be done once the stem group is discovered. The usage can be extended to the total group, or retained for only the crown group. Any other decision is subjective.
There seems to be an idea that there is a kind of radius or perimeter around the crown group, where what is inside is "birdy enough" to be avian and what is outside is "not birdy enough". We've had various proposals about where to place that boundary: at feathers, at flight, at Archaeopteryx, at traditional non-avians, etc. This idea of a perimeter is a subjective one. Therefore, it can never be resolved.
There is no natural boundary for such a radius. Some stem-avians are closer to the crown group and some are further, but there is no natural cutoff point. Archaeopteryx had manual claws and teeth and may not have even been able to fly--is it really fair to say that it was completely 100% avian? Isn't it more accurate to call it a stem-avian which was relatively close to the crown group?
Of the objective choices, the crown group is clearly preferable to the total group. First, it prevents people from making unjustified inferences about members of the stem group. Second, let's face it, calling sauropods, pterosaurs, and ceratopsians "avians" is never going to fly (pun intended).
The in-between boundaries are important (with the possible exception of the Archaeopteryx one), but there are other possible names for them: Avifilopluma, Avialae, "Ornithes", etc. Whatever the older name Aves is given to should have some special significance, and a crown group is far more significant than any arbitrary radius around it.
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Nescio
Joined: 30 Sep 2006
Posts: 53
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| Posted: Thu 01 Feb, 2007 8:12 am Post subject: |
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| That sounds like a general comment on how traditional labels should be phylocodified. FWIW, the other of Linnaeus' classes that's survived vaguely intact (Mammalia) is commonly treated as a crown group. |
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tmkeesey
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| Posted: Thu 01 Feb, 2007 4:22 pm Post subject: |
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| Nescio wrote: | | That sounds like a general comment on how traditional labels should be phylocodified. |
It is!
Obviously each name should be taken on a case-by-case basis, but I think this is a good general principle.
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tmkeesey
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| Posted: Thu 01 Feb, 2007 4:59 pm Post subject: |
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| Nescio wrote: | | FWIW, the other of Linnaeus' classes that's survived vaguely intact (Mammalia) is commonly treated as a crown group. |
Leave us not forget Insecta, either.
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Nescio
Joined: 30 Sep 2006
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| Posted: Thu 01 Feb, 2007 6:08 pm Post subject: |
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| tmkeesey wrote: | | Nescio wrote: | | FWIW, the other of Linnaeus' classes that's survived vaguely intact (Mammalia) is commonly treated as a crown group. |
Leave us not forget Insecta, either. |
Linnaeus' Insecta included more or less the whole of what we now call Arthropoda, if I recall. I judged the subsequent restriction rather more drastic than the changes to Aves and Mammalia, where little has changed as far as the crown group is concerned. |
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tmkeesey
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| Posted: Thu 01 Feb, 2007 10:11 pm Post subject: |
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| Nescio wrote: | | Linnaeus' Insecta included more or less the whole of what we now call Arthropoda, if I recall. I judged the subsequent restriction rather more drastic than the changes to Aves and Mammalia, where little has changed as far as the crown group is concerned. |
Whoops, you're quite right.
As for his other original classes (from 1758), Vermes and Pisces were paraphyletic, as was Amphibia, which was more expansive than later versions.
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David Marjanović
Joined: 24 Aug 2006
Posts: 137
Location: currently Paris
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| Posted: Fri 02 Feb, 2007 10:46 pm Post subject: |
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| tmkeesey wrote: | It's been a while since anyone's posted here. I just wanted to state a defense of the crown group definition:
The taxon Aves was originally named with members of the crown group in mind. Scientists of that time, including Linnaeus, had no knowledge of any stem-avians. Perhaps they would have considered certain stem-avians as "avian", perhaps not--we will never know.
Objectively, in this type of case, there are two things that could be done once the stem group is discovered. The usage can be extended to the total group, or retained for only the crown group. Any other decision is subjective. |
I don't think it's a good idea to act as if nobody had used that name since Linnaeus. What Article 10.1 is about is recent usage.
| Quote: | | There seems to be an idea that there is a kind of radius or perimeter around the crown group, where what is inside is "birdy enough" to be avian and what is outside is "not birdy enough". We've had various proposals about where to place that boundary: at feathers, at flight, at Archaeopteryx, at traditional non-avians, etc. This idea of a perimeter is a subjective one. Therefore, it can never be resolved. |
I don't even try to resolve it. I try to preserve current and recent usage as well as possible.
| Quote: | | Of the objective choices, the crown group is clearly preferable to the total group. First, it prevents people from making unjustified inferences about members of the stem group. Second, let's face it, calling sauropods, pterosaurs, and ceratopsians "avians" is never going to fly (pun intended). |
I agree that far.
| Quote: | | Whatever the older name Aves is given to should have some special significance, and a crown group is far more significant than any arbitrary radius around it. |
Article 10.1 trumps such theoretical considerations.
As for Mammalia, the crown-group definition of that one is in widespread use, but it's nowhere near alone. The Volaticotherium paper, to mention the latest example, used the one by Luo, Cifelli & Kielan-Jaworowska (2002) -- a node-based one anchored on Sinoconodon. Additionally, I think there are two important reasons why the crown-group definition is often used that don't apply for Aves: the crown and the alternative are very similar (there are few nodes between them), and there is no other name for the crown (while there is Neornithes). |
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dinoguy2
Joined: 22 Aug 2006
Posts: 41
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| Posted: Sat 03 Feb, 2007 9:00 pm Post subject: |
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Just out of curiosity, was Linnaeus aware of 'primitive' birds, like the kiwi or the tinamou, when he coined Aves? Also, if the crown is defined as Struthio + Passer, what if forms like those fall outside Aves? Will crown groups in PT be defined as nodes, or as "all members of Pan-Aves extant as of 200x"? If the later, what if we turn up a living sauropod? Does crown Aves change to include all of Saurischia? (Of course we won't, but I'm just using aves as an example here).
What if a crown group is defined based on extant members as of a set date, and then an extinct member of the stem lineage is cloned?  |
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David Marjanović
Joined: 24 Aug 2006
Posts: 137
Location: currently Paris
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| Posted: Sun 04 Feb, 2007 12:56 am Post subject: |
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| dinoguy2 wrote: | | Just out of curiosity, was Linnaeus aware of 'primitive' birds, like the kiwi or the tinamou, when he coined Aves? |
That is a good question. Checking Wikipedia articles, though, he was aware of the ostrich and one species of rhea. (Not the tinamous or kiwis, though.)
| Quote: | | Also, if the crown is defined as Struthio + Passer, what if forms like those fall outside Aves? |
It would no longer be the crown of Aves.
| Quote: | | Will crown groups in PT be defined as nodes, or as "all members of Pan-Aves extant as of 200x"? |
There's no general rule; both possibilities exist.
| Quote: | | If the later, what if we turn up a living sauropod? Does crown Aves change to include all of Saurischia? |
Yes. (Well, Eusaurischia.)
| Quote: | | What if a crown group is defined based on extant members as of a set date, and then an extinct member of the stem lineage is cloned? |
Hm. If it wasn't extant at the set date... |
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tmkeesey
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| Posted: Mon 05 Feb, 2007 6:20 am Post subject: |
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| dinoguy2 wrote: | | Also, if the crown is defined as Struthio + Passer, what if forms like those fall outside Aves? |
Then they would not be avian. But Aves would still be a crown group.
Incidentally, Gauthier and de Queiroz [2001] use Struthio camelus, Tetrao major (=Tinamus major), and Vultur gryphus as specifiers, although, as has been noted, Tinamus major was named after Linnaeus' time, so maybe it should be left out. (It is pretty unlikely to change the content, in any event.)
| dinoguy2 wrote: | | Will crown groups in PT be defined as nodes, or as "all members of Pan-Aves extant as of 200x"? |
The PhyloCode allows for any type of definition as long as it has proper specifiers. The construction of your second option is explicitly mentioned as "branch-modified node-based". (Well, actually, it would be more like, "The last common ancestor of all extant members of [insert branch-based clade here], and all descendants thereof.")
| Quote: | | If the later, what if we turn up a living sauropod? |
For precisely this reason, I think it's probably best in general to define crown groups using simple node-based definitions. (There may be exceptions, of course.)
| Quote: | | What if a crown group is defined based on extant members as of a set date, and then an extinct member of the stem lineage is cloned? ;) |
Ha! Never thought of that. Well, sir, what you want is the thread here: http://www.phylonames.org/forum/viewtopic.php?t=14
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ottscay
Joined: 23 Aug 2006
Posts: 27
Location: Wyoming
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| Posted: Mon 12 Feb, 2007 5:44 pm Post subject: |
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| tmkeesey wrote: |
There seems to be an idea that there is a kind of radius or perimeter around the crown group, where what is inside is "birdy enough" to be avian and what is outside is "not birdy enough". We've had various proposals about where to place that boundary: at feathers, at flight, at Archaeopteryx, at traditional non-avians, etc. This idea of a perimeter is a subjective one. Therefore, it can never be resolved. |
Well, yes and no; I personally like crwon groups (now), and have no objection with restricting Aves to the crown group. Otoh, all names are subjective (e.g. claiming that extant organisms are important because they are frequently studied and a convenient line to draw is still subjective, if easier inapplication) and that doesn't mean they aren't useful.
And usefulness really is the crux of any phylogeny. David is right that there has clearly been significant usage of the term "Aves" in the last 2 centuries that included extinct taxa, and the down side of this is there will surely be a lot of angst if we try to get people to stop appyling the term bird to extinct forms.
Of course that may also be good for people to practice, I'm just saying it isn't open and shut with the crown group either. |
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dinoguy2
Joined: 22 Aug 2006
Posts: 41
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| Posted: Fri 13 Apr, 2007 9:14 am Post subject: |
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| ottscay wrote: |
And usefulness really is the crux of any phylogeny. David is right that there has clearly been significant usage of the term "Aves" in the last 2 centuries that included extinct taxa, and the down side of this is there will surely be a lot of angst if we try to get people to stop appyling the term bird to extinct forms. |
As I may have mentioned before, this kind of thinking is extrememly important if anybody here seriously wants to get PhyloCode off the ground. Define Aves as something unorthodox enough, be it Struthio+Passer or Corvus+Passer, and you just lost ornithology, who will simply pretend PC doesn't exist.
Imagine if PC was spearheaded by entomologists attempting to define every major chordate group as the stem, i.e. Aves = Ornithodira, Mammalia = Synapsida, etc. Would you be willing to jump onboard that system? I think there is, by necessity, going to be a LOT of politics around this before the year 20xx, or else it will simply fail, which would be bad news, since almost all of paleontology (among others) has already adopted this currently anarchic system of classification. |
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tmkeesey
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| Posted: Fri 13 Apr, 2007 8:09 pm Post subject: |
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| dinoguy2 wrote: | | As I may have mentioned before, this kind of thinking is extrememly important if anybody here seriously wants to get PhyloCode off the ground. Define Aves as something unorthodox enough, be it Struthio+Passer or Corvus+Passer, and you just lost ornithology, who will simply pretend PC doesn't exist. |
I suspect that the vast majority of ornithologists, who focus on extant organisms, will not care at all. You may lose some paleornithologists, though, true.
(BTW, Corvus + Passer??? Is that a typo? Nobody has ever proposed anything remotely that silly.)
| Quote: | | Imagine if PC was spearheaded by entomologists attempting to define every major chordate group as the stem, i.e. Aves = Ornithodira, Mammalia = Synapsida, etc. Would you be willing to jump onboard that system? |
To be fair, those are much more radical differences than between Aves sensu Chiappe or Marjanovic and Aves sensu Gauthier.
(Pedantic Note: Ornithodira is node-based, not a total group, although the content is similar. The total group has variously been called Ornithosuchia, Avemetatarsalia, Panaves, or pan-Aves, and perhaps a few other names as well.)
| Quote: | | I think there is, by necessity, going to be a LOT of politics around this before the year 20xx, or else it will simply fail, which would be bad news, since almost all of paleontology (among others) has already adopted this currently anarchic system of classification. |
Yes, it's a shame in many ways that this system hasn't been in place much longer, so that a lot of variable usage could have been avoided. But, you have to work with what you're given....
I do think most of the controversy has to do with converted names. New clade names are rarely controversial. (And when they are, it's generally due to etymological issues, etc.--think Euarchontoglires or Whippomorpha.)
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dinoguy2
Joined: 22 Aug 2006
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| Posted: Sat 14 Apr, 2007 3:33 am Post subject: |
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| tmkeesey wrote: |
(BTW, Corvus + Passer??? Is that a typo? Nobody has ever proposed anything remotely that silly.) |
Yeah, just a little hyperbole
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I do think most of the controversy has to do with converted names. New clade names are rarely controversial. (And when they are, it's generally due to etymological issues, etc.--think Euarchontoglires or Whippomorpha.) |
One reason I dislike using converted names. I'd much rather adapt them than convert them (i.e., give them possibly non-cladistic definitions as close to pre-PT usage as possible, and come up with new names for their equivelent clades). Define Dinosauria as "Perforate acetabulum as in the common ancestor of Iguanodon, Megalosaurus, and all its descendants, except Avipluma" (self destructing apo-group! Granted, the last bit wouldn't go over too well and I grimaced typing it, but I said pre-PT usage...), and "Dinosauriclae" or what have you as Triceratops + Passer. |
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tmkeesey
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| Posted: Sat 14 Apr, 2007 6:11 am Post subject: |
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But the problem (and one of the major points of creating the PhyloCode in the first place) is that there often is no such thing as one standard "pre-PT usage" for a name. "Dinosauria" is better than most, but it still had some are-they-in-or-are-they-out taxa ("lagosuchians", pterosauromorphs, archaeopterygids). And that's still ignoring any taxonomic scheme from the 1800s! (Herrerasaurids, Eoraptor, and Silesaurus are also are-they-in-or-are-they-out taxa, but those arguments are phylogenetic, not taxonomic.)
(Where are you getting the "-iclae" suffix from, BTW?)
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Last edited by tmkeesey on Sat 14 Apr, 2007 6:29 am; edited 1 time in total |
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