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Re: [Re: Non-serpentine lacertids (was RE:WHAT'S GOING ON?)]



chris brochu <cbrochu@fmnh.org> wrote:
> 
> >
> >Regardless, the point I'm making is that snakes evolved from >
>lacertilian(saurian) stock, but rather than calling them modified > >saurians
or what not, we have given them a separate name which makes > >distinguishing
between them a lot easier.
> 
> 
> I think I see one of the misunderstandings you may be having about
> phylogenetic taxonomy.  When we say "birds are dinosaurs" or "snakes are
> squamates," we are not saying "birds are no longer birds" or "snakes are >no
longer snakes."  Birds are still in their own group (Aves) - that this
> group is a member of Dinosauria does not change the distinctiveness of
> Aves, any less than making Aves a member of Vertebrata.

+++++++++++++++++++++++++++++++++++++++++++++++++++++

Well that's not exactly what my quibble is. I have no (more) issues with
calling birds dinosaur descendants. It's just that when someone like Norell or
Bakker, goes around saying that dinosaurs are still alive, just look at the
birds in your backyard, it seems a little rediculous. I mean by that logic I
should be able to say that therapsids are still alive, just look at your pet
dog/cat or yourself. Just because we descended from therapsid stock doesn't
mean we should go around calling ourselves living cynodonts.

Same with non-avian theropods. No one is going to confuse _Tyrannosaurus rex_
with a bird (yes there is homology and yes there is synapomorphy, but it's
still a long way off from calling _T.rex_ a bird). It's the ignoring of the
names that bothers me I guess. I don't really see a point to calling a bird a
dinosaur regardless of the fact that those are the creatures they descended
from.

-----------------------------------------------------------
 
> I do not regard myself as less of a human because I am also a primate and a
mammal.  Hominids still form a distinctive group, whether it is a subset of
Primates or not.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Yes, but no one is going around saying that humans are living therapsids or
that other apes make up the non-hominoid primata. A human is a hominid. That
doesn't mean that they didn't evolve from other primates, it just means that
hominids diverged enough to warrant their own name. Same with birds. They
diverged enough from dinosaurs to warrant their own name. But birds are a bit
different from humans. Birds are different enough to warrant a class under
traditional Linnean terms. Humans only get a familial "ranking." So a human
can rightly be called a primate and a mammal, but birds have become so diverse
that to say that a robin is both an avialan and a dinosaur seems a bit much.
Kinda like say a robin is an avialan and a reptilian. While true, the
differences are so vast that it seems like extra baggage to tag reptilian on
UNLESS when doing phylogenetic work. 

-----------------------------------------------
> 
> 
> >
> >Now admittedly these names came about in a more species static era, but >
>even in today's evolving world, it still is helpful to have names that >
>distinguish different groups of creatures.
> 
> Correct - which is why monophyletic groups can be named, whether they
> belong to a larger monophyletic group or not.  The difference is between
> restricting our taxonomy to natural (monophyletic) groups and adding a
> non-biological component to our taxonomy, formally recognizing >paraphyletic
assemblages as taxa.  And we can still refer to members of >these paraphyletic
assemblages with colloquial descriptors, such as >"fish."

++++++++++++++++++++++++++++++++++++++++++++++++++++++++

I hate to say it, but I'm afraid that you lost me a bit there. When were we
talking about paraphyletic taxa (the snake/lizard thing)?
 
-------------------------------------------------------- 
> 
> 
> >
> >And yes it is pidgeon holing, but this part only comes in when trying > >to
keep up our arbitrary boundaries while explaining an evolutionary > >history,
which of course makes no sense to do.
> 
> 
> The names are always arbitrary - this is true for all nomenclatural >systems
ever devised.  But in the phylogenetic system, the groups are not >arbitrary -
they exist (or at least are hypothesized) and are united by >common ancestry,
whether we choose to name them or not.  Most nodes on >most cladograms go
unnamed.  In previous systems, not all groups were >natural.
> Had we chosen to keep birds and nonavian dinosaurs separate, we would be
> erecting a nonnatural group by arbitrarily removing those things with
> unambiguous feathers from Dinosauria.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Again it seems that everyone thinks that I want to kick Aves out of
dinosauria. That is not the case. At this point in time, I have not the funds
nor the time to take on such a laborious task. Furthermore, with each new
fossil find (especially from that suspicously fossiliferous region in China)
it seems like a waste of energy to even bother trying to remove one from the
other.

All I'm saying is that as far as names go, I do think there should be a
boundary (albight a fuzzy one) that states what category the creature in
question falls under. Which ever category it is, that is the name it should be
called by. If it is one of those muddy transitionals then go ahead and give it
the non-avian prefix.

I suppose it could go something like this.

1) If it meets the basic criteria to be a dinosaur, it should be called a
dinosaur

2) If it meets the basic criteria to be a bird, it should be called a bird.

3) If it meets the basic criteria to become a dinosaur and meets a large part
of the criteria to be a bird then call it a non-avian ----

Now 2 of course will mesh with 1 for obvious reasons. But I think 2 should
take priority if it meets the younger taxa's criteria. Kinda like the reverse
of the ICZN double names rule. It allows for categorizations without the worry
of accidentally kicking something out.

As for what the basic criteria for each group is; well that is something that
needs looking into.

++++++++++++++++++++++++++++++++++++++++
 
> 
> 
> >
> >
> >> To summarize,  a sauropod is a dinosaur, ankylosaurs are dinosaurs,
> >
> >Certainly.
> >
> >> psittaciformes are birds and so are falconiformes.
> >
> >And they are also Dinosauria, using the phylogenetic definition.
> >
> >++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >
> >I'm not doubting their evolutionary roots, but I do have my > >reservations
about calling such obvious birds, dinosaurs (the same kind > >of reservations
that I would have when calling a python a saurian or > >mosasaur).
> >

> A point of clarification - snakes have been regarded as saurians since the
19th century.  So have archosaurs.  I think you mean "lacertilian" here.
> And since lacertilian is an ecological descriptor and not a taxon, I
> wouldn't call snakes lacertilians, either - though I would certainly call
them squamates, lepidosaurs, or saurians.  They belong to those groups for
precisely the same reason they belong to Vertebrata or Bilateralia.

++++++++++++++++++++++++++++++++++++++++++++++++++++

Just to make sure I have this right now. Lacertilians do not make up a formal
taxon.

Is this due to para/polyphyly?

AFAIK lacertilia comprised iguanians, gekkotians, scincomorphs, diploglossans
& platynotians. Varanidae falls under platynota and varanids are the closest
living relative to ophidians, so why wouldn't ophidia fit in? 

----------------------------------------------------------- 
> 
> 
> >
> >> _Caudipteryx_ and _Rahonavis_ are non-avian and/or avian theropods >
>>(or better yet, non-avian/avian maniraptorans).
> >
> >_Caudipteryx_ is probably related to Oviraptorosauria (non-avian) and
> >_Rahonavis_ is a basal avialan, possibly a basal avian, both within
> >Maniraptora.
> >
> >> A varanid is a lizard, an iguana is a lizard. Viperids are snakes and >
>>so are colubrids.
> >
> >"Lizard" and "snake" are wholly vernacular terms.
> >
> >
> >And "bird" isn't?
> 
> "bird" is certainly vernacular.  Aves, Avialae, and Neornithes are not.
 
> 
> 
> 
> >All pedantry aside, I hope you see my point. When there is no doubt as >
>to what category the animal belongs to, then use the name of said      >
>category. When the animal can't be easily pidgeon holed, then use the
>>non-whatever names for them.
> >
> >I mean does _Brachiosaurus_ really have to be called a non-avian
dinosaur?'
> 
> 
> If you're making a poing about dinosaurs that don't happen to be members >
of Avialae, and speak of Brachiosaurus, then yes.  If your point is
> independent of whether birds belong to Dinosauria or not, then no.  It
> might be more useful to call Brachiosaurus a sauropod, a saurischian, or
> even an amniote, depending on the context.
> 
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

I believe that I meant the former. Let me see if I can clarify my position
some.

At the AMNH there is a big emphasis on the dinosaurian ancestry of aves.
Stating that birds are dinosaur descendants and showing a theoretical
evolutionary path to aves from dinosauria is fine. Going around calling all
the fossil animals in both saurischia and ornithischia "non-avian" dinosaurs
is what I have a problem with. 

Birds evolved from a specific type of dinosaur in a specific limb of the
dinosaurian family tree. So there are only a select few dinosaurs that really
warrant being called non-avian, while the rest really don't need that moniker
attached to them.

----------------------------------------------------------------------


> Let me know if you're interested in some references on phylogenetic
>taxonomy.
> 
> chris
> 
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Sure, anything to help clarify this mess.

I know that cladistics is supposed to make life easier compared to traditional
Linnean and for the most part I can understand how, but when everyone starts
going around dropping perfectly valid categorizations because it turned out
that class A was related to family B, that is when things start to become a
headache.

Jura

Jurassosaurus's Reptipage: A page devoted to the study of the reptilia:

http://reptilis.webjump.com

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