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Re: Non-serpentine lacertids (was RE:WHAT'S GOING ON?)
>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
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.
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.
>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."
>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.
>> To summarize, a sauropod is a dinosaur, ankylosaurs are dinosaurs,
>> 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.
>> _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
>> A varanid is a lizard, an iguana is a lizard. Viperids are snakes and so
>"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
>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.
Let me know if you're interested in some references on phylogenetic taxonomy.
Christopher A. Brochu
Department of Geology
Field Museum of Natural History
1400 S. Lake Shore Drive
Chicago, IL 60605