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Re: Triceratops ontogeny paper

Here's another article on the same subject:


Guy Leahy

--- Tim Williams <twilliams_alpha@hotmail.com> wrote:

> John R. Horner and Mark B. Goodwin (2006).  Major
> cranial changes during 
> _Triceratops_ ontogeny.  Proceedings of the Royal
> Society B: Biological 
> Sciences.  273: 2757-2761.
> Abstract: "This is the first cranial ontogenetic
> assessment of 
> _Triceratops_, the well-known Late Cretaceous
> dinosaur distinguished by 
> three horns and a massive parietal?squamosal frill.
> Our analysis is based on 
> a growth series of 10 skulls, ranging from a 38cm
> long baby skull to about 
> 2m long adult skulls. Four growth stages correspond
> to a suite of 
> ontogenetic characters expressed in the postorbital
> horns, frill, nasal, 
> epinasal horn and epoccipitals. Postorbital horns
> are straight stubs in 
> early ontogeny, curve posteriorly in juveniles,
> straighten in subadults and 
> recurve anteriorly in adults. The posterior margin
> of the baby frill is 
> deeply scalloped. In early juveniles, the frill
> margin becomes ornamented by 
> 17?19 delta-shaped epoccipitals. Epoccipitals are
> dorsoventrally compressed 
> in subadults, strongly compressed and elongated in
> adults and ultimately 
> merge onto the posterior frill margin in older
> adults. Ontogenetic trends 
> within and between growth stages include: posterior
> frill margin transitions 
> from scalloped to wavy and smooth; progressive
> exclusion of the 
> supraoccipital from the foramen magnum; internal
> hollowing at the base of 
> the postorbital horns; closure of the midline nasal
> suture; fusion of the 
> epinasal onto the nasals; and epinasal expansion
> into a morphologically 
> variable nasal horn. We hypothesize that the changes
> in horn orientation and 
> epoccipital shape function to allow visual identity
> of juveniles, and signal 
> their attainment of sexual maturity."