Rantings on Polled Ceratopsians

["Steve Brusatte" <dinoland@lycos.com>]

Hey,
Ceratopsians are often compared to cattle.  Of course, this means absolutely 
nothing in a genetic or phylogenetic sense, as ceratopsians are no more closely 
related to cattle than humans are to crocodiles (in a general sense...).

Many researchers, including Sampson and Dodson, have suggested that horns and 
frills may be sexually dimorphic or display features in many species of 
ceratopsians, and did not develop until the individual reached sexual maturity. 
 Sampson, and other researchers, have gone as far to suggest that many 
different species of named ceratopsians may not be unique species (or genera) 
at all, but rather the male/female form of a different species.  

In this sense, horns and frills may have been used stricly as display, with 
species such as _Monoclonius_ not possessing quite an elaborate display of 
horns (only one).  Of course, many have suggested that _Monoclonius_ may be a 
subadult species of another centrosaurine dinosaur.

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)?

This is just a ranting on my part, based on a lot of reading and speculation.  
Of course, there is no way to really plop this into any type of phylogenetic 
analysis, and no way to be sure without some sort of dinosaurian genome or a 
really, really large sample.  

However, I would be interested in the opinions of others.  Most of the above is 
likely nonsense, but by an analogue to modern cattle, may make some sense.  

I do agree, though, that the horns and crests of ceratopsians were likely used 
for display purposes, as Sampson and his colleagues have written.

Steve

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Steve Brusatte-DINO LAND PALEONTOLOGY
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