dinosaur taxon vs. dinosaur lineage

[Ken Kinman]

Dear All,
     It seems like "truncated clades" as distasteful to strict cladists as
the phrase "paraphyletic group".  So maybe I should make them sound even
more innocuous (and they are indeed *not* harmful if they are presented
explicitly).
     Most biologists probably now agree that birds evolved from dinosaurs---
that there is a real dinosaur-bird lineage, and it clearly not extinct as a
lineage.  Strict cladists only recognize lineages as formal taxa, and they
zealously object to a non-nested division of this lineage into dinosaurs and
birds.
     That is where exgroup markers help us have our cake and eat it too.
They would allow us to formally divide a dinosaur taxon from a bird taxon
(Aves), and yet the {{Aves}} marker explicit shows that the dinosaur-bird
lineage as a whole has not gone extinct.  Banging people over the head with
statements like "birds ARE dinosaurs"  just comes across as Ivory Tower
cladistic pedantry.
      You can get the same information across by saying birds are dinosaur
descendants, and I have presented a very simple classificatory convention
that can be used to explicit show this in formal classifications.
      I have also used such markers for reticulate evolution, specifically
the chimaeric nature of eukaryote cells.  My bacterial classification has
outgroup markers for organelles:  mitochondria (from within Class
Proteobacteracea), peroxisomes (from within Class Posibacteracea), and
chloroplasts (from within Class Coccogonea).  If Margulis is right about
undulipodia evolving from spirochaetes, we could also put a marker for that
organelle in Class Spirochaetea.  And organlles are just the start of how
one could store "reticulation" information on "hybrids" in classifications.
     Anyway, back to the dinosaur-bird situation.  The problem there is that
Archaeopteryx turns out to be a lousy place to divide dinosaurs and birds
(just as anchoring mammals on monotremes is a bad idea, rather than on
osteological synapomorphies).  This is exactly what I am attempting to do
with an expanded Class AVES.
     Forms like Deinonychus and Oviraptor should have never been classified
as dinosaurs in the first place.  They had feathers, and they have been
found fossilized brooding their nests of eggs (with ornithoid shell
microstructure).  If you saw some these outside you window, you would
probably think they were oversized geese with an Archaeopteryx-like tail.
     All we have to do now is find where the biggest and most useful gap is,
and redraw the line.  It will be osteologically, but vaned feathers will be
at node closeby (just as hair arose around the time of our osteologically
defined Mammalia).
     As for Reptilia (reptiles).  They are all the amniotes that lack the
Mammalia and Aves synapomorphies.  If the strict cladists want to call them
non-mammalian, non-avian amniotes----be my guest.  I'm going to call them
reptiles, just as scientists in the pre-cladistic era did (and many still
do).
          ------ Cheers,  Ken Kinman



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