Oh, we're going to be orthogenesists now?
I believe the preferred current term is 'Process Structuralist'
But if you read the paper you will see that it isn't really an argument along orthogenetic lines but rather a probabilistic one based on the comparative frequencies of bone loss to bone gain in the fossil record.
Sidor writes:
Evolutionary trends in morphological characters pose a problem similar to that of transition and/or transversion substitution probabilities in molecular systematics; not all character state changes are equally likely to occur [...]. The difference resides in the fact that whereas there are biophysical explanations for transition and/or transversion bias [...], the mechanisms underlying morphological biases are far less clear. In addition, not only can active evolutionary trends make some types of characters more probable to change than others (i.e., presence/absence characters), but they set up a systematic bias in the direction of character state change (i.e., changes from presence to absence). Perhaps because of the intractibility of assigning an objective differential weighting scheme to these types of characters, paleontologists have, on the whole, been content to consider all transitions to be equally likely [...]. Recognizing instances of biased morphological change is imperative for appropriately modeling character evolution in phylogeny reconstruction.
The fact that not all genotype changes are equiprobable should surely render wholly uncontroversial the suggestion that all phenotype changes are similarly not equiprobable. It follows naturally that the distribution of likelihood of possible phenotypic changes (and their associated genotypes) is going to affect the evolutionary trajectory of the population.
Dr. A writes:
Should we also paint ourselves with ochre and worship trees?
You totally should.
TTFN,
WK