Hi Mick,
Anyway, l'm not so sure whether it's possible to decide whether a species is transitional or not based on fossil record or anything else. A good example is the platypus. It has characteristics that are kind of intermediate between reptiles and mammals (it's oviparous, it lactates but has no nipples, it is endothermic). Molecular phylogenies also put this species basally to the rest of mammalia. So it's transitional in the sense that it looks intermediate. But as far as I know nobody has ever suggested that eutherian and marsupial mammals evolved FROM the platypus, and there is no evidence of this. so it isn't transitional in what I understand to be the evolutionary sense.
You make a valid point.
When I suggest that
Archaeopteryx lithogaphica is a transitional, I am not specifically pointing to that individual, or even that species, but a morphologically simlilar taxon that is closely related. I would agree that
Archaeopteryx lithogaphica isn't necessarily the direct descendent of all birds, it may be a sister species or genus of one that was. As far as we know, one of the seven specimens may have been the last living example of
A.lithographica, & an as yet unknown sister clade went on to spawn the rest of the birds. It seems a more than reasonable inference to state that
A.lithographica was a taxon at least representative of an intermediate form, if it wasn't the intermediate itself.
The platypus example is a bit different, it isn't a fossil found at a relevant point in the geological record. It is an extant species, & a cladogram would simply show the divergence of it's clade relative to other mammalian clades, rather than infer that it is itself a transitional between modern & ancient taxa (which it can't be, obviously, since it is itself a modern taxon). The actual organism at the monotreme node was probably very different.
Mark
There are 10 kinds of people in this world; those that understand binary, & those that don't
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