"Archaeopteryx; bird or reptile, or both?"

Cladistics treats all known species as terminal nodes on a phylogeny. If by transitional you mean an internal node on the phylogeny (i.e. a node that branches into daughter species), then the answer is no. This is because phylogenetics only infers the existence of internal nodes based on the fact that we don't know what they are. If we knew what species were represented by these internal nodes, then we would treat them as terminal nodes of a tree with different topology.This is a bit of nitpicking for the cladists. If you want my real opinion, I would guess that Archaeopteryx is about as "transitional" as any other species.just my two cents.mick

Hi Mark,This is a reply to you and PaulK.I know I made a rather petty point, but i think it's worth making simply because the question "why are so many transitional forms missing" is such a common criticism on the part of creationists of the fossil record. This question misunderstands the fact that, according to the evolutionary theory, all species and all individuals are transitional.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.does the archaeopteryx represent a transitional form en route from being a reptile to beign a bird? I think the only reasonable answer is "maybe", due to lack of data. I don't think that apparently intermediate morphology tells us anything about the evolutionary process leading from one group to another.cheers,mick