>>After all, Lewis & Clarke got across the US without motor vehicles.
Yes, but that is nothing compared to what the polynesians did when they reached the remote islands in the Pacific Ocean without the benefit of motorized power. Even Homo erectus may have built boats or at least simple rafts.
>However, by and large, most people find that transport over longer distances works considerably better if you do happen to have a car, train or plane handy. Before internal combustion engine technology became available, we lived with the limitations imposed by the technology available then, now we exploit the opportunities afforded by newer technology.
Agreed. Nevertheless, DNA deteoriates rapidly once the organism died. Therefore paleontologists have been unable to use DNA to ascertain relationships except in some rare cases where DNA has been preserved in fossils. It is now known from mtDNA evidence that Neanderthals last shared a common ancestor with modern humans some 500,000 years ago, whereas all living humans shared a common ancestor around 100,000 to 150,000 years ago.
>>The same applies to taxonomy: before DNA sequence information became available, people worked with what they had: morphology.
That is not all taxonomists used though. Many relied on developmental biology. It is amazing how similar the early embryos of various vertebrate groups are. These similarities provide important clues to their common ancestry. Unfortunately, many practicing cladists simply ignore embryological evidence.
>Now DNA information is easily available, and systematists are using it. It is not necessarily the magic bullet many people assume it to be, but it certainly does provide a huge amount of additional informationa nd a totally different perspective on the evolution of groups of organisms.
Indeed. DNA evidence can be very informative. mtDNA evidence has also provided additional information about past migrations. Morphology alone would not have been as informative. Since the past cannot be directly observed, all sorts of evidence that provide clues about what actually happened in the past are welcome.
>>As far as pythons, specifically, are concerned, I might add that there has not so far been a comprehensive, published DNA-based study of the different genera. The most recent revision, on which the currently most widely accepted genera are based, was by Kluge (1993), and was based entirely on morphology.
And of course, we all know that the so-called "monophyletic" groups that are delineated using morphology often turn out to be paraphyletic or even polyphyletic when DNA evidence becomes available. Kluge's morphological analyses are no exception.
>>Finally, as far as your charcaters are concerned, the various pythong genera have been defined based on a wide suite of often skeletal characters. The type of characters that you say are inconsistent are the ort of *identifying* charcaters that you will find in herpetoculture books or field guides - they are not necessarily the main characters used in reconstructing phylogenies, which led to the definition of the genera in the firstplace.
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>>Cheers,
>>
>>WW
>>-----
>> WW Home
Unfortunately, the morphological characters used to reconstruct phylogenies are often convergent similarities instead of Hennigian synapomorphies. This is especially true of cladistic analyses using morphological characters. The cladists favor using as large a set of characters as possible, while spending little or no time anlyzing the goodness of the characters they use. Some even claim that their ignorance of character goodness somehow made their analyses "objective." Ignorance is definitely not objectivity.
Below is a critique of current cladistic methodology from Feduccia et al. (2005):
It should give one pause that while paleontologists employing cladistic methodology use a list of a hundred or more characters that link birds and theropods, most are simple binary designations, one step removed from the organisms. The vast majority are plesiomorphic, not qualifying as Hennigian synapomorphies, and in this view there is no accounting for acceptance of large groupings of the characters that are co-correlated. Thus, 15 or more characters may simply represent one character complex, diluting their phylogenetic resolving power. These facts have rendered modern cladistic methodology a form of ¡§Sokalian¡¨ phenetics, which can be termed ¡§cladophenetics.¡¨ Homology is usually ascertained in an a posteriori fashion to conform to the established cladogram, and embryonic connectivity and position are largely ignored. It should also be a matter of concern that bipedal reptiles first appeared in prearchosaurian lineages as the Permian Eudibamus (Berman et al., 2000). Of further concern should be the fact that among basal archosaurs, most ornithosuchids (without the ankle) would easily reach the ceratosaur level in any cladogram. The inability of cladistic methodology to deal with convergence has been pointed out time and again (Carroll and Dong, 1991; Feduccia, 1999a). This methodology always groups as clades convergent avian pairs such as loons and grebes, which form the bones of their swimming feet by disparate means embryologically, and most recently the pelecaniform wing-propelled divers, the plotopterids, form a cladistic clade with penguins (Mayr, 2005), another convergent pair. Dodson (2000, p. 504) correctly notes that: Cladistics systematically excludes data from stratigraphy, embryology, ecology, and biogeography that could otherwise be employed to bring maximum evolutionary coherence to biological data. Darwin would have convinced no one if he had been so restrictive in his theory of evolution. What was once ¡§Hennigian cladistics¡¨ has now turned into a distinctive methodology, nicely summarized by Fisher and Owens (2004, p. 39): ¡§The phylogenetic approach is a statistical method for analyzing correlations between traits across species.¡¨ And, like the earlier statistical approaches of the 1970s, this approach frequently groups ecological morphologies instead of clades: the methodology is incapable of discerning massive convergence.
Literature cited
Feduccia, Alan, Theagarten Lingham-Soliar, and J. Richard Hinchliffe 2005. Do Feathered Dinosaurs Exist? Testing the Hypothesis on Neontological and Paleontological Evidence. JOURNAL OF MORPHOLOGY 266:125¡V166
