From: salem@pangea.Stanford.EDU (Bruce Salem)
Newsgroups: talk.origins
Subject: Re: I need transitional knowledge
Date: 10 Jan 1993 23:19:27 GMT
Organization: Stanford Univ. Earth Sciences
NNTP-Posting-Host: pangea.stanford.edu

In article <1993Jan9.045359.13856@panix.com> arandia@panix.com (Joel Arandia) writes:
>I'm not a biologist, heck, I'm not even a scientist.  I'm not a creationist.
>I'm just confused.  Could someone(maybe with a phd) explain to me how a fossil
>becomes transitional?  

	Would someone with a MS in Geology do? I'm not sure that PhDs
with real work to do would bother with this group. They might tell you
to enroll in a course somewhere. Now I have had the paleontology and
biology courses having also carried a minor in the latter area, maybe
I can give you a sufficient explqination of what it means for a fossil
to be transitional.

>I mean who decides that a fossil is transitional and 
>what marks it thus?

	A sequence of fossils must be described and dated so that the
relative ages are known. Then the morphology must compare in a general
way so that specfic characters can be compared, and one of the fossils
in the middle of the sequence must possess some character intermediate
in form between younger and older fossils of the series. Since the
comparisons are often for traits that distinguish taxa such as class
or order or family, it is not required that we know that the fossils
represent the species on the main lineage, but may be side branches
that are representative of the gross change. An example of this sort
of thing is that the bones that make up the jaw of reptiles are different
from those of mammals, bones of eather type can be found in most mammals
and reptiles, but they have different function, but their developmental
anatomy can be traced back into common structures. If the ancestral stock
of all mammals was a reptile than some vestage of this change in the
jaw anatomy of reptile begomming mammal-like to becomming indistinguishable
from modern mammals might be found in the fossil record, and indeed it is
found in a sequence of Permean aged mammal-like reptiles. You should
see Jim Merritt's FAQs for a reference. In hominid fossils of the past
5 million years transitional features of brain case volume, bipedalism,
and details of the boney anatomy are transitional between traits in the
great apes and humans.

>  Some creationist guy is buggin me and telling me that
>Archeopteryx is a MOSAIC form.  I guess he means that just because something
>has attributes or both bird and reptile doesn't mean that it's related to 
>either.  Yeah, it does sound stupid, but I can't figure out a good rebutt.
>And what are the other 'birds' that he tells me are in the same strata?
>
>ruprecht

	The afinities of Archeopteryx are not as clear as one might
think, especially as there are contenders for rights to be close to
the ancester of birds. Proaves, if it is really what it seems to be is
in many more bird-like than Archeopterys and is Triassic rather than
Jurassic in age. The latter looks like a thecodont with feathers and lacks
some important avain characters. No one doubts that birds and reptiles have
some important common characters, and that the similarities between
certain dinosaurs and birds is even greater. The true history of birds
and their relationship with other reptiles may have to await more
fossil finds.

Bruce Salem