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Re: Dinosaur subspecies names? - when is a species not a species?

Gorgosaur@hotmail.com (Oyvind Padron) said:

>>And, indeed, there is a long standing debate over whether _C. corone_ and
>>cornix_ may in fact be different *species*:
>if you dig up the good old taxonomy rules from high school, we learned that
>in order to be a different species, the different animals can't get a
>fertile offspring.
>C.c.cornix and C.c.corone can easily get a fertile offspring.

Shame that the 'good old taxonomy' books got it all wrong according to
current thinking.

How do you treat ring species, for example, Greenish warbler _Phylloscopus
trochiloides _. This old world warbler is theorised to have originated south
of the Tibetan plateau. As a result of climatic changes, it was able to
extend its range west and east, then north on both sides of the plateau.
Eventually western and eastern populations meet in a central contact point
north of the plateau. Genetic and morphological changes have occurred in the
population as its range extends, such that there are a number of
recognisable subspecies throughout its range, each of which can mate and
produce fertile hybrid offspring with its immediate contact neighbour.
However where the westward/northward population meets the
eastward/northward, the races/subspecies of the species have diverged to
such an extent that they are reproductively isolated and behave as separate
species. Ornithology is currently split as to whether to treat the
north-eastern subspecies as a full species (Two-barred Greenish warbler
_P.plumbeitarsus) and if so, what then to do with other subspecies. (Irwin D
E, Bensch S & Price T D 2001: Speciation in a ring. Nature 409:333-337).

Presumably similar events have occurred in the past, with the splitting and
joining of continents, mountain building etc but gaps in the fossil record
would make this difficult to prove.

What about species that are normally geographically isolated? Ruddy duck
_Oxyura jamaicensis_, from North America and White-headed Duck _Oxyura
leucocephala_ wouldn't normally meet, unless man hadn't introduced the
former into the UK in 1950s. Now the ruddy duck is allegedly threatening the
WHD through inbreeding. Does this make the WHD a 'bad' species?

Species nowadays are generally considered 'good' when, where a contact zone
exists between two types, only limited interbreeding occurs (how limited it
needs to be is open to interpretation)

All the best

Mike Wall
Hants, UK