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Re: smallest pterosaurs



> > Have you already read the following SVP meeting abstract for this year?
It
> > agrees that all those small pterosaurs are well ossified and were most
> > likely able to fly and independent from their parents -- it just says
they
> > weren't adult or anywhere near:
>
> Question I pose is -- how do Unwin and Deeming know they are indeed
juvenile, and not some sort of small adult? They could be juveniles. I just
need a way of knowing for sure.

I don't know if they've looked at the bone texture. But keep the bone
histology in mind -- the *Pterodactylus* and *Rhamphorhynchus* cut up by
Padian, Horner & de Ricqlès were all not adult, lacking an external
fundamental system. This means at least that pretty large but still growing
individuals of both existed.

> Is the holotype of P. kochi (No. 23 of Wellnhofer) a juvenile? Or an
adult?

There is evidence -- the proxies I've mentioned, and the plots by Jouve -- 
that it's a juvenile. What evidence is there that says it's adult?

> It 'looks' like a smaller version of the larger germanodactylids, but
cladistic analysis indicates that it is phylogenetically derived from even
smaller taxa, such as No. 12 and before that, No. 9. The narrow-snouted,
gracile-necked pterosaurs universally referred to ?P. kochi, such as No. 21,
are not ?P. kochi, but not far removed either.

I can only repeat: Cladistics is _fundamentally incapable_ of telling you if
a specimen is adult or not. If you put a definite baby into your matrix, do
you think PAUP* would spit it out??? Instead it would show up in all trees,
and there is no guarantee that it would cluster with adults of its own
species, because, to varying but not easily predictable extents, ontogeny
recapitulates phylogeny.

If you scored adult and baby chimps, and humans, for snout length, relative
head size, relative orbit size, tooth count and a few more characters, and
added this to a primate matrix, the baby chimps would cluster with us
instead of with their parents.

> > In these individuals all skeletal elements
> > of the flight apparatus including the pteroid are ossified and, in
addition
> > to containing structural fibres, the flight membranes were approximately
> > the same shape and proportions as those of the adults.
>
> Are U & D describing adult characters above?

They are describing flight-related characters. If the pteroid is not a
dermal bone (but either an endochondral one -- like a centrale -- or a
tendon ossification), it should ossify _relatively_ late; one should think
that it wouldn't ossify long before the young became flighted, because
before they'd be rather useless.

> > Moreover, critical components of the fore and hind
> > limbs show isometric growth patterns
>
> Are these isometric growth patternsphylogenetic or ontogenetic in nature?

If they are right, then the character "stuff grows (0) allometrically, (1)
isometrically in ontogeny" is phylogenetically useful -- but probably
correlated to all others that have to do with hyperprecocial flight ability,
so I'd try to make sure I used only one of those characters in a matrix.

> In support of the latter U & D will have to connect each juvenile, or at
least some juveniles, to conspecific,  or at least congeneric, adults using
cladistic analysis or reconstructions, using matching body parts that are
not subject to isometric growth patterns.

Correct. Except that cladistic analysis has the above limitations.

> This is further supported by the discovery of these fossils
> preserved in locations far from any likely nesting site.
>
> >>>> Are U & D leaving the door open to the possibility that they're
looking at adults?

I don't think so. They just mention that the locations are _consistent_ with
the specimens being hyperprecocial juveniles -- they didn't have to be
either adult or clinging to a parent to get there, they just had to be able
to fly. Of course this one sentence doesn't rule out the other two
possibilities.

> >>>>> While the literature labels every tiny pterosaur a juvenile, I
wonder if U & D has tested previous assertions? And if so, what is their
"litmus test"? [see below for questions regarding the currently accepted
"litmus tests" for immaturity]

What is your litmus test for adulthood? The presence of an external
fundamental system?

> >>> Okay, Dr. Unwin has set a minimum adult wingspan of 40 cm. Which
pterosaur is this? Does it have a pelvis large enough to pass an egg of the
correct size?

I don't think size is so critical if the egg has a soft shell -- as seems to
be the case.

> And yes, I'm aware of the various size-independent characters used
previously, but the questions to those tests are:
>
> 1. why in cladistic analylsis do entire clades of pterosaurs (basal
ornithocheirids + cycnorhamphids) appear to be immature using these tests?

Nobody says they really _are_ clades. They could be artefacts of the
inclusion of size- and/or ontogeny-related characters. PAUP* gives you the
shortest trees for your matrix, not necessarily the one for the real animals
some of whose properties are encoded in the matrix. Don't interpret too much
into a cladogram.

> 2. why do some tiny pterosaurs (Mesadactylus and Nyctosaurus gracilis, for
instance) appear to be mature according to these tests?

Which tests? Bone histology?

> 3. why in cladistic analysis, do the tiny pterosaurs appear at the bases
of major clades and complete the spectrum of pterosaur diversity to create a
single most parsimonious tree?

Because ontogeny recapitulates phylogeny, juveniles often show
plesiomorphies that the adults lack. There are tons of examples. -- As to
why there's a single MPT, this is either a pure coincidence of your matrix,
or you've won in the German lotto (6 out of 49).

> 4. considering the alternative theory for a moment: why should a
'hypothetical' tiny adult pterosaur, hypothetically stunted by a premature
hormone surge (or a phylogenetic series of same over thousands of years),
ever develop 'mature' bone characters when nothing else about them, except
perhaps their hypothetical ability to reproduce, appears to be 'mature'?

If by "bone characters" you mean histological characters, then the answer is
simple: because it (almost or completely) stops growing.