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

re: Half-a-dactylus

On February 11th David Peters wrote:

<I've matched 60 pterosaur taxa against 170 characters and PAUP came up
with a single tree.>

To which David Unwin wrote:

<An analysis of this size, based on a character data set with (I
substantial missing data, and it produces a single tree? Is that an
alarm bell
I can hear?>

Had I relied on the literature and the drawings therein, there would
have been substantial missing data, indeed. I don't know why more care
was not put into original works, but much has been overlooked, ignored
and mistaken. For instance, why have the palatal elements of P. antiquus
and P. kochi been ignored for so long?

As for PAUP, it is extremely helpful in weeding out mistakes. For
instance, sometimes it would appear that a wing has phalanges of certain
proportions, but PAUP analysis shows that sister taxa have different
ratios. In such a case one can go back to the fossil and discover that a
bone end  did not really stop, but rather disappared beneath other bones
or the matrix.

<And in this single tree two taxa that do no share any overlapping
elements, and
thus no directly observable/scorable synapomorphies, are paired
together. Hmmm,
the alarm bell is ringing so loudly its about to fly right off the wall.

Imagine finding a sauropod skull all by itself. Then imagine finding a
sauropod sans skull all by itself. From what we know about sauropods,
often we can decide from cladistical analysis whether or not that skull
belongs with that body. The same is happening here. With or without a
body, Cearadactylus belongs in the Ornithocheiridae. With our without a
head Arthurdactylus belongs in the same family. How close they are to
each other is the only sticking point. Other taxa with heads resembling
Cearadactylus and bodies resembling Arthurdactylus provide the clues as
to how close or how far  apart the two are, IMHO. The "tree-biter"
Anhanguerid is also not too far away cladistically, but then again,
they're all close.

I'm just trying to be a good detective and I don't mind stumbling a bit
in my search for the best answer. If you have any specific questions,
rather than "alarm bells" send them to me. I'd be happy to answer them
for you, if I can.

For instance, I can give you  [D.U.] a complete accounting of why
Cearadactylus is not a ctenochasmatid -oid or what have you. Best done
in private correspondence.

David Peters
St. Louis