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Re: Rantings on Polled Ceratopsians



On Thu, 01 Feb 2001 17:23:03  
 Matthew Bonnan wrote:

Steve Brusatte said: 

  "Ceratopsians are often compared to cattle. <snip> However, has
  any serious thought been given to the possibility of _Monoclonius_
  being a primarily polled species? Polled, in terms of cattle, means
  possessing no horns. In many types of cattle, horns are not
  dimorphic or necessarily display features. Instead, they are
  caused by recessive genes (a series of two autosomal pp genes).
  On the other hand, being polled, is dominant (either Pp or PP). 

  "Could individuals attributed to the genus _Monoclonius_ actually
  have been polled members of a species, with polled in this sense
  meaning only a single horn, compared to three with _Triceratops_
  and other ceratopsian genera? Is there a possibility that
  elaborately horned ceratopsians, which are very common, were
  possessors of the recessive genes for several horns, such as those
  seen in cattle. Or, perhaps, in the ceratopsid lineage, the genes
  for horns were dominant (PP)?" 
   
  Hi, Steve and all.  I've been lurking for a while, doing
  paleontological things in the shadows. =)  However, I thought I
  might add my two cents to this question.  As I study sauropods, I
  would never claim to be a ceratopsian expert.  However, your
  suggestion is intriguing about the polling aspect of cattle and its
  implications for horns in Monoclonius and other ceratopsians.
   
  Before we look at cattle, it might be instructive to examine
  horned reptiles.  I am unaware (or at least forgetful) of any
  extant archosaurs with horns on the skull, so one might examine
  lepidosaurs (lizards, snakes, and the tuatara for those on the list
  who might not know) and see if polling or other such things
  happen in those lepidosaurs that do develop horns or such on
  their skulls.
   
Yes, I would be interested to know of any living archosaurs, or any reptiles, 
for that matter, that have genes for polling.  

  It is always tempting to look for modern analogs to dinosaurs in
  living mammals, but we must be very careful.  In the sauropods,
  the analogy to elephants has been overextended time and again
  for everything from locomotion to behavior in animals that were
  quite different from elephants.  The same may be happening with
  ceratopsians.  Yes, they have horns that remind us of present day
  cattle, but how far does the analogy go?  We must remember,
  too, that compared to mammals, so much anatomy and
  physiology in reptiles remains poorly known.  Most of us who
  have taken or teach comparative vert classes have the tendancy
  to emphasize mammalian anatomy and physiology as the "norm,"
  while short shifting the reptiles.  This has led sometimes, IMHO,
  to the expectation that the mammalian way of putting the limbs,
  verts, etc., together is the "best" or "ideal model" way, whereas
  other anatomical plans are sometimes viewed as being aberrant
  from those of mam! mals.  Walter Coombs (1975, Sauropod
  habits and habitats. Palaeogeography, Palaeoclimatology,
  Palaeoecology, 17: 1-33) describes the dangers of analogizing
  sauropods with elephants in his paper, and if memory isn't failing
  me this morning, so does Paul Upchurch (1994, Manus claw
  function in sauropod dinosaurs. GAIA, 10: 161-171).
   
Yes.  As I said in my first post, ceratopsians are often compared to cattle, 
but this doesn't mean a thing in a genetic or phylogenetic sense.  The only 
reason I was comparing them to cattle in this instance because cattle are the 
only animals in which I am positively sure possess a recessive gene for horns, 
and have polling.  Of course, I assume that other species also possess this 
gene.


  The polling idea is intriguing, and although not directly testable on
  dinosaurs, may have some testability elsewhere in extant reptiles
  and mammals.  I'd be interested to see what happens with horns
  in reptiles, and if there is something like polling.
   
I, too, am very interested in looking at reptile horns.  I am not in a position 
to do so, as a student with no access to a university library and a relatively 
weak knowledge of cladistics and genetics (although I am definitely making 
progress learning).  

However, I do think this would be a great project for somebody to take up, 
possibly myself at a later date.  No, this cannot be tested in dinosaurs 
unless, as I said, we can decipher an entire ceratopsian genome (for every 
genera/species!!), or we had an extremely large sample, all preserved at the 
same location at the same time and only of one species.  Even if this were the 
case, it would still be very hard to do any genetic work.

I am interested in more input on this idea.  Does anyone take seriously the 
idea that _Monoclonius_ may be a polled member of a species, and not a juvenile 
or individual species??

Steve

Steve Brusatte
Dino Land Paleontology
http://www.geocities.com/stegob


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