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

Re: Holy BCF



In a message dated 96-10-15 15:42:58 EDT, mrowe@indiana.edu (Mickey P. Rowe)
writes:

<< Do the above two quotes seem rather inconsistent to everyone else or
 is it just me?  George, if you have an explanation as to why you're
 basing your main point on the occurence of something which you claim
 "seldom" occurs, I'm sure we'd all like to hear it.  In any case, it
 also appears to me that if what George is saying in the final
 paragraph is true, then it should show up in a cladistic analysis.
 So why doesn't it? >>

There is nothing unusually inconsistent about my arguments; I simply
neglected to emphasize the "scaling factor." Sorry about that.

Thus: if examining _extant species_ only, we would never know that most
archosaurs possessed extensive antorbital fenestrae. Neither living diapsids
nor crocodilians nor birds have such skull openings. Diapsids did not acquire
them, whereas crocs and birds secondarily modified them into sinus systems
and so forth. A straight-line interpolation between extant diapsids and
archosaurs will not reveal the antorbital fenestra; nor will a cladistic
analysis. You need the detail of the fossil record to show that most extinct
archosaurs had very large antorbital fenestrae. This is part of the basis
behind my statement that evolution seldom takes the "straight line" from
point A to point B. If points A and B are particularly distant in time or
morphospace, then a straight-line interpolation or a cladistic analysis is
not necessarily the tool to elucidate what happened in between A and B.

Once you have some of the details _in between_ A and B, however, such as
A --> A1 --> A2 --> ... --> Ax --> B, the finer resolution increases the
likelihood that a straight-line interpolation between A(i) --> A(i+1)
approximates reality between those two detail stages. The more details we
have, the more evolutionary stages we can envision, and the closer the
straight-line path through morphospace approximates reality.