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RE: Monoclonius recurvicornis..a new generic name




> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu] On Behalf Of
> Jaime A. Headden
> Sent: Tuesday, October 19, 2004 5:36 PM
> To: dinosaur@usc.edu
> Cc: heby@libero.it
> Subject: Re: Monoclonius recurvicornis..a new generic name
>   *Monoclonius procurvicornis* has been considered a junior synonym of
> *Centrosaurus apertus* for some time, as specimens and further skulls of
> *C. apertus* have shown a variety of orientations and shapes of the nasal
> and orbital horncores. Orbital horncores in several ceratopsids, including
> *Centrosaurus,* *Einiosaurus,* and several new centrosaurs in press, show
> that they form from separate ossification centers than chasmosaur horns,
> usually in the middle of a pit that developes a triangular horn core.

Actually, the postorbital horns of centrosaurines form exactly as they do in
chasmosaurines--that is, as outgrowths of the postorbital bone. With
advanced age, the horns are often resorbed and left as pits. I think it was
Brown or someone, way back in the day, who suggested that these pits were
sites for an "extra" unossified horncore. No evidence supports this.

Andy