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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
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: firstname.lastname@example.org Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Faculty Director, Earth, Life & Time Program, College Park Scholars
Faculty Director, Science & Global Change Program, College Park Scholars
Mailing Address: Thomas R. Holtz, Jr.
Department of Geology
Building 237, Room 1117
University of Maryland
College Park, MD 20742 USA