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Re: Rantings on Polled Ceratopsians





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.
 
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).
 
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.
 
Good question,
 
Matthew Bonnan
Dept. Biological Sciences
Northern Illinois University
DeKalb, IL 60115
mbonnan@niu.edu
mbonnan@hotmail.com
 


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