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RE: Feathers are not magical things...



Hopefully this will not produce a mass "invisible Bcc:" posting from a
certain persona non grata: I apologize for having said something or other
that set him off which resulted in many of you receiving an email from the
individual in question.

(For those who did not receive it, count your blessings).

Okay, then...

> From: philidor11 [mailto:philidor11@snet.net]
>
> <That is to say, assuming a) feathers evolved a single time in the history
> of vertebrates (the simplest explanation) and b) the known presence of
> feathers in birds and only in those theropods which independant
> phylogenetic
> analyses
> [me:  also based on logical argument, including assumptions]

But of course.  Absolute knowledge, free of assumptions, is not permitted to
mere mortals.  That is why we need models and constructs like scientific
methodology to understand the Universe.

> place closer to
> birds than to other dinosaurian taxa and c) the lack of evidence to the
> contrary (i.e., therizinosaur body impressions with scales)
> means that as scientists we take the simplest explanation possible.  That
> explanation is that feathers evolved in the common ancestor of all
> maniraptorans and was passed on to all descendants.  Until such
> time that we
> find direct positive evidence to the contrary, we must assume that
> _Velociraptor_ and company were feathered.>
>
> As you also point out, the results of similar logical arguments have been
> refuted:
>
> <There might well have been featherless maniraptorans.  To use the example
> of maxillary fenestration from above, we do know that some members of the
> clade which ancestrally possessed these structures subsequently lost them:
> the therizinosauroid _Erlikosaurus_ and the
> caenagnathid oviraptorosaur _Chirostenotes_, for example.  Had
> the skulls of
> these guys never been found, we would have assumed that that had these
> structures.  However, given new information we accept the evidence given.>
>
> I think the last sentence a bit unclear, and hope you will clarify.
> Given the new information, would you say that there are exceptions to the
> inheritance of the ancestral character or that the analysis
> identifying the
> character as ancestral might be flawed and have to be redone?

The latter, although "flawed" might not be the best word choice.  Say we
plotted an X-Y scatter of limb measurements, and found a regression line
with all its appropriate stats: you know, the slope, the Y-intercept, the
r^2 value, etc.  Then we uncover new specimens relevent to the study, add
these new data, and find a new slope, Y-intercept, r^2 value, etc.

Was the original study "flawed"?  Perhaps in a very strict sense of the
term.  However, we as mere mortals cannot operate in a sphere of absolute
knowledge: all we can do is sample from the whole universe of data.  Our
models (regression lines, cladograms, etc.) are only as good as the data
that is put into them.  As new data is added, the conclusions might change.
They might change just a tiny little bit, and so the essential original
conclusions remain.  They may change a LOT, and so refute (for the moment)
the original conclusions.

This goes on all the time in all sciences: it is not simply a matter of
paleontology (or just dinosaur cladistics, or whatever).

>  Both seem
> possible outcomes.
> Also, note that the paragraph first quoted twice refers to using the
> 'simplest explanation'.  From past discussions, it seems you
> wouldn't argue
> that evolution invariably follows the simplest (with a specific
> definition)
> path.  Given that less simple explanations are possible
> consistent with the
> available data, would you assert that someone who argued a different
> hypothesis would be unscientific?

Yes.  See past discussions, or intro to scientific methodology texts, on
"parsimony" or "Occam's Razor".

In the sciences we choose the simplest explanation possible, since that
criterion requires the fewest additional assumptions.  This can be in
phylogenetics (if all known member of a particular clade are the only
organisms known to demonstrate a particular character state, and all known
representatives of that clade DO demonstrate that character where it can be
evaluated, then it is simpler to assume that derived feature evolved once
than it did multiple times) or physics (if the distribution of data points
from some relationships are equally well explained by a quadratic equation
or a forty-five order polynomial, go with the quadratic) or what have you.

> That someone who drew Velociraptor
> without feathers was outright wrong?  (In the same sense that someone who
> drew an animal whose fossils have been observed to have feather-like
> integument would be wrong to leave out the feather-like integument.)
> I'm asking here about the difference between inference and
> observation as it
> applies to 'scientific'.

Let me change your statement from the (for some bizarre reason emotionally
charged issue of) feathers to different comparable derived character states:

Say I find that _Nanotyrannus_ is indeed a valid taxon.  If I draw it with a
four-fingered hand, am I outright wrong?

If I draw a naked-skinned (i.e., hairless) _Hyracotherium_, am I outright
wrong?

If I draw an _Opisthocoelicaudia_ (for which the neck isn't known) with a
short neck, am I outright wrong?

Or, to go back to feathers:
If I drew a _Hesperornis_ without feathers, am I outright wrong?

The short answer: no, I would not be "outright wrong"; however, I would be
unscientific.  (These are different types of things).  It is, ultimately, a
burden of proof issue.

> <Something that seems to come out in "Jura"'s posts, and as well in
> discussions with Ruben and others, is a sort of Platonic typology or
> idealism: that is, that there is a dinosaur "kind" and an avian "kind" and
> that never the twain shall meet.  Thus, since we have lots of
> dinosaurs with
> scales, there for it is an aspect of the dinosaur "type" to have scales.>
>
> If there are 1,000 'species' of dinosaurs and 990 are known to have scales
> and not feathers (numbers and knowledge of integumentary structures
> invented), then I would be correct to say, "Almost all dinosaurs
> have scales
> and not feathers."  In this situation, if I were asked to
> describe a typical
> dinosaur, I would not include feathers because feathers are not typical.

Analogy time again:
The vast majority of mammals have hindlimbs.  Indeed, it is correct to say
"almost all mammals have hindlimbs".  If I were asked to draw a typical
mammal, I would draw hindlimbs.

If I were asked to draw a baleen whale, however...

And therein lies the point of phylogeny (NOT cladistics, but phylogeny: that
is, the history of the interrelatedness and evolution of life).

> (Hope nobody ever asks me!  And that I'd have sense enough not to answer.)
> This is not a reference to Platonic idealism, it's simple use of
> prevalence.
> I frequently have to write about the typical person who gambles
> or who plays
> a particular lottery game.  I don't have the sense that I'm dealing with
> archetypes.

But see the point above about whales (or bats, in the earlier example).  If
you were drawing a "typical" dinosaur (whatever that means), go with scales.

_Velociraptor_, however, is NOT a typical dinosaur in this sense!!  It is
deeply nested within a clade for which every known integumentary record
shows feather structures.

And this is where the difference between Platonic and Darwinian models come
into play.  Platonic models of life says "the type is real; variations from
the type represent oddities".  The Darwinian model says "the type is a human
construct; variations (both within species and down along lineages, bringing
with them their historical baggage) are the reality".

> <Evolution happens, and one type changes into
> another, until the boundaries (from a morphological standpoint)
> are blurred
> into non-existence.>
>
> >From this, would you conclude that if you wanted to name easily
> distinguishable groups, then you should base the groups on animals which
> have been substantially distinguished from their distant ancestors by
> evolution, and not on those distant ancestors?  That would avoid
> fuzziness.

Actually, I would say that "easily distinguishable groups" are ones for
which their early historical record is poorly known.  When no dinosaurs were
known between _Compsognathus_ and _Archaeopteryx_, then the morphological
gap between typical dinosaurs and birds was great.  With the additional
discoveries of non-avian maniraptorans and of additional basal birds, there
are no distinct morphological jumps between "bird" and "non-bird".  Thus,
assignment of the names "bird" or "Avialae" or "Aves" are arbitrary.  (That
isn't to say they aren't important: after all, we need names and labels in
order to talk about things!!).

Similar cases exist where we have good fossil sampling near the origin of
groups: when does a non-tetrapod become a tetrapod?  A non-mammal become a
mammal?

Cases which are currently "cut-and-dry" are so because we LACK good sampling
for the transitional taxa: There is little disagreement between what is a
turtle and what isn't a turtle, for example; or betwen what is a bat and
what isn't.  In both cases, we have (or do not currently recognize) the
forms of the closest sister taxa of these groups (whatever they may be) and
the oldest known representatives of these clades.

In other words, fuzziness (or non-arbitrariness, if you like) can only be
avoided when we don't have good information!  The addition of good
information in the origins of groups shows that the "distinctive" features
of taxa do not appear all at once, but are spread over considerable time and
a fair amount of morphological diversity.

> <The reason reconstructing the historical pattern of
> evolution is importance is because that background is necessary for a
> testable and reciprocal study of the transformations and adaptations in
> Life.>
>
> I'm not sure I understand.  If phylogenetic analysis is in the background,
> what's in the foreground?

All sorts of stuff!!:
        *Models of adaptation and functional morphology
        *Patterns of biogeography
        *Evolutionary tempos and modes (e.g., Punctuated Equilibrium vs. 
Phyletic
Gradualism; Red Queen matters, etc.)
        *And just about anything else that gets published in journals like
Paleobiology and Journal of Experimental Zoology and the like.

> Thanks for taking the time to explain and clarify.
>
                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796