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Re: Horner's Pachy Lumpin' - Your Thoughts?




>> It is absolutely counterintuitive that an animal would first grow horns
>> and then shrink them to fairly blunt knobs. But, on a smaller scale, the
>> same thing happens to the "epoccipitals" of ceratopsids (which I frankly
>> expect to turn out one day to be homologous to pachycephalosaur spikes).
>> Perhaps more importantly, the horns of *Triceratops* (even when
>> *Torosaurus* is not included) _change curvature_ during ontogeny, from
>> backward-pointing to forward-pointing. The only way to change the
>> curvature of a bone is to deposit bone on one side and _remove it_ from
>> the other. Here we have the large-scale absorption the pachy-lumper
>> scenario requires.
>>
>Another ceratopsid case of metaplasia: the postorbital and nasal horns of
>young Pachyrhinosaurus are indeed horns, but as they aged the postorbital
>horns get resorbed and remodeled into pits and the nose horn into the
>distinctive mound.

Exactly. And if you delve deeper into various abstracts, or attend meetings 
you'll have seen that postorbital horn resorption occurs in chasmosaurines too.


-- 
Thomas R. Holtz, Jr.
Email: tholtz@umd.edu    Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
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http://www.geol.umd.edu/~tholtz/
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Mailing Address:    Thomas R. Holtz, Jr.
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