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On tigers and lions and defining species etc.

First of all, George's comment about hybridism between lions and 
tigers does not count for much. Apparently disparate genera within 
clades can sometimes hybridise. This depends on which group of 
animals you are looking at: some seem to be particular good at it. 
Example: _Tursiops_ (bottlenosed dolphin) has hybridised with 
_Pseudorca_, _Lagenorhynchus_ and _Grampus_. _Pseudorca_ and 
_Grampus_ are often put in a different 'subfamily' (the 
Globicephalinae or one of its many synonyms) from _Tursiops_.

Norm King wrote...

> I SUSPECT that what G.O pointed out is probably true, although I   
> am obviously not an expert.  I, too, am concerned about what            
> "generally more robust" means, as G.O pointed out in a subsequent  
> posting, and that sounds to me like a euphemism for "they really run 
> together," as far as skeletal features are concerned.  

George and Norm are both right to point out the problem here: yes it 
means that measurements overlap but that, generally, tigers of a given 
size have bones which are broader for their length than do lions. 
However, careful measurements can distinguish the two. This is 
actually true for a lot of related extant species which are clearly 
distinct but have similar postcrania - e.g., sheep and goats, yellow-
necked mice and wood mice (these four species in particular are 
problematical in British archaeological samples). Relevant to 
dinosaurs and other fossil taxa is that, if we didn't have (1) the live 
animals and (2) the skulls, we would rarely be able to distinguish the 
postcrania of these species. One wonders, in fact, whether we would 
have realised that these *are* separate species. 

Norm wrote...

> Then I think about Triceratops, and all its putative, one-time species
> that also ran together, meaning there was just one, or at least a very
> few, based on skeletal features of the skull.  What would you think if
> I looked at all those data, and then said I really don't think they
> are closely related, because some may have been striped and others
> spotted?

I would say I don't understand.

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