[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Princeton Field Guide



"So lets consider the consequences if a clade of fossil canids was found that 
was way too anatomically different to be in the genus Canis, or to have 
interbred with Canis species. Also that the different genus has clearly evolved 
from derived Canis species in a way that rendered Canis paraphyletic. Would it 
then be required to split living Canis into multiple genera despite their 
ability to
interbreed?"

The same can happen with species, too, since the loss of the ability to 
interbreed isn't precisely correlated to divergence-time or morphological 
disparity. There could be (and probably is, somewhere) a widespread continental 
species, a small population of which gets isolated on an island, and diverges 
from the parent population via genetic drift and selection to the point of 
being reproductively isolated, but is nested phylogenetically within the 
continental population. So to maintain a monophyletic species, one would either 
have to include the divergent island population, or split up continental 
populations that are effectively identical.

And hybrid speciation can cause problems with monophyletic species & taxa too; 
a hybrid population that ended up breeding true over the long term (and thus 
become an actual population rather than just an one-off freak, whether one 
calls the population a 'species' or not) could belong simultaneously to two 
monophyletically-defined species (or higher taxa, if the population is 
considered to be divergent enough to be its own species). I suppose it isn't 
actually *wrong* to  have a population be a member of two species or a species 
be a member of two (say) subgenera, but it's at least messy.

Ultimately, I think there needs to be some flexibility in the 'rules' -- 
whether monophyly or something else -- since biological reality is always more 
complex than definitions allow for.

William Miller

----- Original Message -----
From: GSP1954@aol.com
To: dinosaur@usc.edu
Sent: Tuesday, October 19, 2010 5:01:57 PM GMT -06:00 US/Canada Central
Subject: Re: Princeton Field Guide

Some additional comments on the too often unrealistic discussion of the 
field guide. 

It is of course not possible to provide an extensive description for each 
dinosaur species. In field guides for extant organisms the descriptions are 
entirely superficial descriptions of visually filed spottable identification 
markings and shapes (detailed technical morphology is not discussed), and 
these are consistently available for each species so the descriptions are 
similar in length for every species. The amount of information for dinosaurs 
ranges from almost as good as for living animals in those few cases in which 
feathers and their color patterns have been preserved and documented, to 
virtually nothing for many poorly known species, so the amount of information 
that can accompany the species ranges from extensive to zero. There is of 
course no need to include with each theropod species that it was bipedal, that 
was noted in the description for the entire group. Same for most of them being 
tridatcyl. Each species description includes only those features limited to 
that species that can be used to distinguish it from other species. In some 
cases there is no special features available so they are either "standard 
for the group" or "insufficient information." For example, what nontechnical 
feature/s suitable for a popular field guide distingush/es Argentinosaurus  
it from other giant titanosaurs? Suggestions, anyone?    

One person challanged me to define genus as though that point has critical 
meaning. It is not possible to define species either, but species are real. 
It is not possible to define life, but it is real. There is no way to 
precisely define battleship versus battlecruiser (HMS HOOD for example) versus 
heavy cruiser (Alaska class for example). Many terms are approximations, it 
does not mean that they cannot be used to describe and distinguish basic, 
comparable types. 

Canis poses an interesting problem for the current use in dinosaurology of 
genus as just a few species that form a monophyletic grade. Canis is a large 
genus with many fossil and extant species that vary considerably in size, 
anatomy and lifestyles. The living species can all interbreed easily and 
produce reproductlively viable hybirds (as per the new eastern coyote, which 
has 
considerable wolf in it so it is bigger, more social and can take down 
deer), so it is unlikely that the genus will be split up. So lets consider the 
consequences if a clade of fossil canids was found that was way too 
anatomically different to be in the genus Canis, or to have interbred with 
Canis 
species. Also that the different genus has clearly evolved from derived Canis 
species in a way that rendered Canis paraphyletic. Would it then be required 
to split living Canis into multiple genera despite their ability to 
interbreed?   

The chasmosaurine cladogram in the new PLos One Sampson et al paper 
illustrates the potential problem in a dinosaur group. The chart is 
suspiciously 
progressive, with a series of chasmosaur taxa eventually leading over time to 
Anchiceratops, Arrhinoceratops and then the ultimate Triceratops clade. 
Because the chasmosaurs from Chasmosaurus to Vegaceratops appear to be 
paraphyletic they have to be split into a bevy of genera despite varying only 
in 
cranial adornments. This may well be an artifact of the cladogram based on the 
characters that happen to be analyzed, it is quite likely that the 
Chasmosaurus to Vegaceratops chasmosaurs are their own clade with minor 
variations in 
display organs that constitute a typical, multispecies genus. Assume that in 
the future some but not all cladograms find that Chasmosaurus belli and 
russeli are paraphyletic relative to a more derived and very distinctive 
chasmosaurine, while other chasmosaurs are monophyletic? How would that be 
handled 
at the genus level? 

I am also unpleased that the fragmentary Mexican chasmosaurine was given a 
genus name, Coahuilaceratops would have been better left incertae sedis. 
When I was in Spain I came across a bunch of iguanodonts that are clearly new 
taxa but they are too incomplete to name. 

At the SVP meeting it was interesting that some of the new work is 
emphasizing the importance of stratigraphy in determining taxa, a conclusion I 
came 
to while doing the book. The stratigraphic factor threatens to sink a number 
of genera in oversplit dinosaur groups. Phylogeny alone is not sufficient.  

Some of Z Armstrong comments are particularly inept in a naive, armchair 
critic manner so they need rebuttal. He claims that Huabeisaurus is very 
incomplete when most of the skeleton, including the vital shoulder girdles are 
figured by Glut in his suppl 2. His spurious speculation that I used photos of 
a grossly incomplete mounted skeleton is based on ignorance, and is the 
sort of idle misinformation that uninformed persons with keyboards and internet 
access have no apparent qualm distributing despite their lack of knowledge 
and because of their laziness (he didn't ask me). Huabeisaurus is the best 
basal titanosaur yet published, too bad we don't know what kind of skull it 
had. Malawisaurus and Phuwiangosaurus are less well known and in some cases 
lacking major shoulder and pelvic elements so I did not find them worth the 
production time available (I was particularly reluctant to do new skeletons 
when the pelvis is not known). The information I have is that the super 
mamenchisaur skeleton is much more complete than the very incomplete 
Argentinosaurus. Hopefully the size of Futalognkosaurus will be pinned down 
soon, 
information I have seen indicates it is in the 50-60 tonne class (its relative 
proportions also helps show that none of the S Amer supertitanosaurs approached 
100 tonnes as was commonly thought). 

As anyone who actually does lots of skeletal restorations knows, it is not 
always possible to tell what bones are and are not preserved in a specimen 
or species, so it is not practical to do every skeleton or species composite 
showing only the elements preserved, and one ends up doing a complete 
skeleton. Ergo, it is not viable to do a book in which there is consistency in 
showing only bones that are preserved. In the case of the field guide I used a 
combination of new work, and restorations already done in the past to keep 
the work and time load in reasonable limits, some of the latter were complete 
restorations although some elements are missing.   

It should be understood that it is possible to put only so much time and 
labor into writing and illustrating a given book. The advance was far larger 
than for any other type of adult market dinosaur book in order to make the 
hundreds of drawings possible, but it placed limits on what was doable form a 
business perspective. Producing dinosaur skeletal restorations plus side 
views is much more time and labor intensive than generating semi-standardized, 
surface only illustrations of birds or sharks. As it was I put as much 
effort into the book as was feasible. There are also marketing constraints, and 
a 
longer book would have been more expensive. 

There are the annoying errors in the book, am particularly vexed that I 
sent on old version of the Apatosaurus rearing and feeding in a tree full 
scene. And missed a few new taxa that had been described before the cut off 
date, 
which is hard to avoid with so much stuff coming out. 

GSPaul

</HTML>