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Re: BCF in perspective (long)



Here's a longer reply to John R. Hutchinson's post of 95-12-03
16:45:48 EST. His comments are in <<double angle brackets>>:

<<Just wondering...I haven't been paying as much attention to
this whole BCF-BADD issue as I'd like to have been (hey, crunch
time is on with exams and such), but how is the fossil record and
predominately accepted (i.e. BADD) phylogeny reconciled with the
BCF concept that birds arose in the Triassic, and then gave rise
to either all dinosaurs (which would then be birds, not
dinosaurs) or all theropods or all coelurosaurians or whatever?>>

<<In other words, the ultimate question is, what is the phylogeny
proposed by BCF (really briefly)? Did basal theropods arise from
birds and then diversify into coelurosaurs, ceratosaurs, et al?
If that, then birds would be dinosaurs still, unless BCF proposes
a paraphyletic "dinosauria" (saurischia + ornithischia + aves??).
Are (according to BCF) birds basal dinosauria; are they also the
ancestors of ornithischia and sauropoda? Does BCF propose a
renaming of Dinosauria?>>

Let me answer your later questions first. The way it works is
that the various theropod lineages, as well as the pre-theropod
lineages of Basitheropoda (for _Longisquama_), Lagosuchia, and
Herrerasauria, and the post-theropod lineage of Enantiornithes,
arose as side branches of the "central lineage" (which I noted in
my earlier response) that runs from the common ancestor of
Dinosauria to the robin. This lineage, of course, can be traced
back to the first archosaur (and for that matter, back to some
little Precambrian ball of snot, as Dan Chure once said).
Dinosauria is defined cladistically (in BCF) as the clade
descended from the last common ancestor of _Megalosaurus_ and
_Iguanodon_, which by coincidence were the first two dinosaurs to
be scientifically described. In BCF, these two genera represent
the two great branches of the dinosaur dichotomy, which I call
Phytodinosauria (Bakker's name) and Aves (Linnaeus's name).

Now, here's a little more phyletic detail of those two branches.
I'm still working on this (some of this appeared in a previous
posting, and I've updated and corrected it a bit):

Phytodinosauria
     Sauropoda (presently including a stunning array of families)
     Prosauropoda (presently including about 5 families)
     Segnosauria
     Lesothosauria
     Ankylosauria (at least 3 families)
     Stegosauria (4 families)
     Heterodontosauria
          Euheterodontosauria (including only
               Heterodontosauridae)
          Pachycephalosauria (2 families)
          Ceratopia (3 families)
     Ornithopoda (circa 8 families)
Aves
     Basitheropoda (presently including only _Longisquama_)
     Lagosuchia
     Herrerasauria
     Ceratosauria (presently including Podokesauridae,
          Halticosauridae, and Ceratosauridae)
          Spinosauria (presently including Archaeornithoididae,
               Baryonychidae, Spinosauridae)
          Neoceratosauria (presently including Abelisauridae,
               Noasauridae, and Velocisauridae)
     Protoaviformes (presently including only _Protoavis_)
     Megalosauria (presently including Eustreptospondylidae and
          Megalosauridae)
     Carnosauria (presently including Sinraptoridae and
          Allosauridae)
     Coeluria (presently including Coeluridae, Dryptosauridae,
          and Troodontidae)
          Ornithomimosauria (presently including Harpymimidae and
               Ornithomimidae)
          Tyrannosauria (presently including Compsognathidae,
               Itemiridae, and Tyrannosauridae)
     Archaeopterygiformes (presently including Archaeopterygidae
          and Dromaeosauridae)
     Carinatae (including Alvarezsauridae and Enantiornithes)
          Oviraptorosauria (presently including Elmisauridae,
               Caenagnathidae, and Oviraptoridae)
          Avimimiformes
     Ornithurae (including Hesperornithidae, Ichthyornithidae,
          and all modern birds)

As you read down the chart, you converge on modern birds. Doubly
indented groups within Aves are major side branches from the main
archo-to-bird lineage.

I'm nowhere near certain about the detailed placement of some of
these groups (input would be welcomed), but I _have_ to publish
MM #2 soon. Also, lots of individual nodes aren't well resolved
because of the scarcity of specimens.

Note that I include Ornithurae _within_ Carinatae (not an error),
because the keeled sternum developed well before the pygostyle
tail. Certainly _Mononykus_ shows this!

MM #2 third printing will not list any bird taxa above
Archaeopterygiformes, but I'm planning to include Mesozoic birds
in future printings, after I accumulate and digest the necessary
references.

"Theropods" would be all the avian dinosaurs from Ceratosauria
through Archaeopterygiformes. "Maniraptorans" would be all the
avian dinosaurs from Coeluria to Ornithurae. "Tetanurans" would
be all the avian dinosaurs from Megalosauria to Ornithurae. "Non-
avian dinosaurs" would be the same as Phytodinosauria.

<<Further questions follow: how is the fossil record reconciled
with this new phylogeny (which has been well documented with
cladistic analyses rather than eyeballed for gross similarities,
right?)?>>

BCF accounts for the fossil record _much_ better than BADD. For
example, BADD has a tough time reconciling the fact that the most
birdlike theropods are all Cretaceous forms, appearing well after
the Late Jurassic _Archaeopteryx_. In BCF, the larger birdlike
theropods (dromaeosaurids, oviraptorids, etc.) are the flightless
descendant forms of _Archaeopteryx_-like dino-birds. It is
natural that they would be found in the fossil record after their
ancestral forms. The big problem with BADD is that it wants the
ancestors of birds to look like dromaeosaurids and oviraptorids,
etc. This is unwarranted, because there is no reason for a common
ancestral form to look more like one descendant than another.

<<Taking a Longisquama-like ancestor for Aves leaves a lot to be
explained; where are the transitional forms between those two?>>

Where are the transitional forms between Aves (more specifically,
_Archaeopteryx_) and ANYTHING in BADD?? _Longisquama_ had a
furcula and what look like pre-feathers or feather-like
structures. That's more birdlike than any phytodinosaur. Too bad
we only have the front end! I would bet $50 that when the
complete animal is at last discovered, it will have a pelvis and
hindlimb very reminiscent of those of lagosuchians: much more
erect and dinosaur-like than Sharov admitted in his original
description in 1970 (and which everyone has taken as gospel ever
since).

<<How are the trends within non-avian (or post-avian) theropod
evolution accounted for (in short, did birds begat dromaeosaurs,
which begat non-avian maniraptorans, which begat coelurosaurs,
which begat carnosaurs, which begat ceratosaurs; or what?)?
Does BCF propose that theropod phylogeny is actually the mirror
image of BADD phylogeny, or is there massive polytomy at the
bird-nonavian theropod transition in which all theropod groups
arise in the Triassic/Jurassic? Or what?>>

The above tabulated phylogeny should be of some assistance here.

<<The big picture conjured by BCF just doesn't make sense to me,
even without any speculative stories to explain the origin of
flight, which (sans fossil evidence) are just stories, and
inconsequential to the phylogeny (which must come first). Don't
get me wrong - I applaud G.O.'s effort and obvious hard thought
involved in the BCF idea (*if nothing else, it's been a great
mental exercise for all of us*), but a complete phylogeny is the
foundation of the whole hypothesis. Invoking origin of flight
scenarios (which inevitably must depend on the phylogeny
proposed) to explain BCF seems like a circular argument to me. In
summation, nice job G.O., but how about showing us a simple,
inclusive version of your phylogeny? If you're going to convince
anyone, that's the #1 thing you'll need; a phylogeny backed up
with solid fossil evidence - not origin stories. BADD has a
reasonably decent phylogeny, reasonably decent fossils, and
(depending on the storyteller of course) a story that's as
entertaining as any other; how about BCF?>>

See my earlier response to this posting, and the phylogeny above.
If you haven't read _Mesozoic Meanderings_ #2, or at least my
article in the June 1994 _Omni_, then you have _not_ seen the BCF
Big Picture, which does indeed exist. I have the 5500-word _Omni_
article on my hard drive (sans Luis Rey's neat illustration and
the little phylogenetic chart that _Omni_ worked up, of course).
I've been publishing very detailed phylogenies of the individual
groups in my series for Gakken's _Dino-Frontline_ magazine, and
so far I've finished all but the tail end of Ornithischia as far
as Phytodinosauria is concerned. With issue #15 I start on Aves,
that is, the theropods. I am working on a series of booklets
called _Historical Dinosaurology_ in which I present updated and
enlarged English-language versions of my Gakken articles. The
first issue, on Stegosauria, is almost finished. Given enough
free time, I'll have it out early next year (yeah, yeah). I
figure it will run 15-20 issues altogether (the rest of my life).

<<All of this is IMHO of course; I probably made some mistakes
(I'm not yet a mega-cladist, give me time), but I just wanted to
get a clearer view of the issue. Sorry for the War and Peace
discursiveness; too much coffee. :-)>>

Whew.