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More on the genus problem

The idea that the genus problem can be solved by defining genera in a 
simple phylogenetic manner as the last node before two sister species is 
defective. Assume that ungulates were extinct and known only from two complete 
skeletons, a giraffe and a bison. On the cladogram they form their own two 
species clade, and should then be the same genus. Obviously this is absurd even 
we accept multispecies genera, but why? Because of a piece of reality that 
sends cladistics screaming in terror....

Morphological GRADE!!!!!!

The prior is an extreme example to make a point. More practically take 
Diplodocus and Barosaurus, and assume they are each known from one diagnostic 
specimen and are sister taxa forming their own two species clade. They should 
be one genus. Except that Barosaurus has a much longer neck, significantly 
shorter tail, longer arms, and a number of vertebral detail differences that 
exceed the variation even seen in Varanus, and are also much more variable 
than are some dinosaur groups split into many genera (hypacrosaurs, 
centrosaurs, chasmosaurs). Likewise Brachiosaurus and the perfectly named 
Giraffatitan are too gradistically divergent to place in one genus. If genera 
are going 
to remain multiple species taxa as I suspect they will - find it hard to 
see Homo being shrunk down to just sapiens with the neanderthals a new genus 
for instance, then grade will be part of the formula.