[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: pterosaur stuff



> [...] couldn't possibly be an ornithocheirid. Too many characters don't
fit the pattern, starting with not a short 'mandible', but a ridiculously
short 'mandible.'

Now, I don't know an ornithocheirid when I see one. But... a short, stout
mandible is expected in a juvenile.

> Sometime in the next few weeks, somewhere in Denver, someone will show you
a slide of a tiny pterosaur and tell you that it is a juvenile or a recent
hatchling. It will have a short snout and big eyes. It will have short wings
and not much of a tail.

Sounds like a list of juvenile characters.

> At this point I draw your attention to:
>
> www.pterosaurinfo.com/scapho_clade.html
>
> Here you'll find a scaled graphic depiction of what PAUP found in one
clade of pterosaurs derived from a sister taxon to Scaphognathus
crassirostris.

PAUP*, or cladistics in general for that matter, is completely _incapable_
from telling you if a character is ontogenetic variation. If you have adults
and juveniles of the same species in a matrix, there's not even a guarantee
that they'll turn out as sistergroups (chimp babies would probably cluster
with adult humans instead of with adult chimps).
        To put it in impolite terms, Feduccia is completely right in that
_if_ you put garbage in, you get garbage out of cladistics.

> You'll note two lineages, both taking the first step with reduced
variations of Scaphognathus, the so-called 'juvenile' specimens. Following
those you'll find even smaller pterosaurs, some of the smallest pterosaurs
known, including that Denver juvenile with the short snout and big eyes.
Hopefully you'll see that the larger ancestral taxa to their left also have
a short snout and big eyes.

Mmm... instead I see that their "descendants" to the right have extra-long
snouts, and are smaller than the "ancestors" and therefore have smaller
eyes.

> This looks like a phylogenetic sequence to me.

Sorry, but that's unscientific -- it means precisely nothing.

> In the other lineage, a more familiar phylogenetic growth pattern through
a stepped series of ever slightly larger pterodactylids can be seen. The
interesting thing is from No. 9 -- which everyone but me thinks is a
hatchling -- to No. 12 and AMNH 1942, the pterosaur gets taller, but the
torso remains the same size. Sounds more like evolution, which works on one
or two parts at a time, rather than ontogeny, which packs on the ounces and
pounds in a more widespread fashion, give or take during the awkward
adolescence period.

Then I suggest you have a better look at your very own ontogeny. Your head
hasn't grown much since your birth. Your extremities have grown first, and
then your torso has grown.
        This is even a source of individual variation. In most adult people,
the arms hang just so far down that the wrist is just above the hip joint or
so. I have kept more juvenile proportions; my hands cover the middle third
of my thighs when I stand upright. (I think my forearms are longer than
usual.) My brother, on the other hand, is peramorphic, so to say; he has an
extra-long torso.

> The point is: size squeezes do occur and they happen alot in pterosaurs.
Those tiny pterosaurs are adults, so it's no big surprise that they are
found far from land, alone, fully ossified and fully fledged (provided with
adequate wings in this case).

If they're juveniles, the surprise is no greater. Even among birds,
megapodiid chicks can fly within hours of hatching. Looks like this was the
norm for pterosaurs, along with a slow growth strategy like that of basal
birds.
        This sounds like a great strategy to avoid intraspecific
competition -- different ontogenetic stages occupy different ecological
niches. Like in crocodiles, sort of.

> Point two: Take a closer look at the phalangeal patterns, the pelves, the
palates, the tooth arcades of these tiny pterosaurs and you'll see that they
don't look like miniature versions of anything we know from the fossil
record. They are unique.

_As expected._ In humans, tooth count and even tooth shape (of the canines
and premolars) changes with age. Take into account that pterosaurs didn't
change teeth just once...

> Sure they share characters with other pterosaurs both up and down the
line, but as a total package you'll never find a match, even taking into
account allometric growth possibilities.

I think you aren't taking all of them into account.