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RE: Oviraptorid questions

Speaking of _Incisivosaurus_...
Guy Leahy

> Date: Thu, 27 Aug 2009 11:20:34 -0400
> From: nick.gardner@gmail.com
> To: xrciseguy@q.com; dinosaur@usc.edu
> Subject: Re: Oviraptorid questions
> Balanoff et al (2009) cited Senter et al (2004) as suggesting that
> Protarchaeopteryx and Incisivosaurus may be synonymous.
>>From Senter et al (2004), p. 3:
> "Here, Incisivosaurus is considered a junior synonym of
> Protarchaeopteryx. Data for Protarchaeopteryx were collected from the
> holotype of P. robusta (NGMC 2125) and the published description of P.
> gauthieri (Xu, Cheng, et al., 2002). P. gauthieri was originally
> described as the type species of a new genus, Incisivosaurus (Xu,
> Cheng, et al., 2002). However, the two species should be treated as
> congeners, as their overlapping elements are identical except for
> tooth count. These two species uniquely share a very bizarre
> dentition, which has a number of unusual attributes: (1) a single pair
> of enlarged, anteroposteriorly compressed teeth at the front of the
> premaxilla, (2) diminutive, peglike teeth immediately posterior to the
> enlarged pair of teeth, (3) diminutive, lanceolate posterior teeth,
> and (4) absence of teeth at the tip of the dentary (NGMC 2125; Xu,
> Cheng, et al. 2002) (Fig. 1). Also, despite the crushing of the skull
> in NGMC 2125, which is so extensive that for most upper teeth one
> cannot tell whether they are left or right teeth, it is clear that
> NGMC 2125 shares with "Incisivosaurus" (1) a short, high skull, (2)
> tall premaxilla, and (3) dentary with anterior margin strongly beveled
> so that the dorsal margin terminates in a 50-60 point (NGMC 2125; Xu,
> Cheng et al., 2002) (Fig 1). We consider these similarities,
> especially the dental characters, sufficient to demonstrate generic
> identity. A significant difference in tooth count (Ji et al., 1998;
> Xu, Cheng, et al., 2002) justifies the maintenance of separation of
> the two taxa at the species level. However, this difference does not
> compromise the utility of the genus as an operational taxonomic unit
> in the present analysis.
> Published descriptions state that serrations are absent on the teeth
> of "Incisivosaurus" (Xu, Cheng, et al. 2002) but present on those of
> NGMC 2125 (Ji et al., 1998). However, examination of NGMC 2125 by
> P.S., using a zoom lens as a makeshift microscope, revealed that the
> apparent serrations on the one preserved enlarged premaxillary tooth
> crown are places where the edges of the teeth are chipped. No
> serrations could be seen by P.S. on the posterior teeth, nor are any
> evident in the published photos of these teeth (Ji et al., 1998, fig.
> 1)."
> Effectively, Senter is only arguing that Protarchaeopteryx robusta and
> Incisivosaurus gauthieri are sister taxa. You could maintain generic
> separation or not depending on how you want to calibrate your
> genericometer, it doesn't really matter in this case, IMHO.
> Balanoff, A. M., X. Xu, Y. Kobayashi, Y. Matsufune, and M. Norell.
> 2009. Cranial Osteology of the Theropod Dinosaur Incisivosaurus
> gauthieri (Theropoda: Oviraptorosauria). American Museum Novitates,
> 3651: 35 p.
> Free online: http://hdl.handle.net/2246/5970
> Senter, P., R. Barsbold, B.B. Britt, and D.A. Burnham. 2004.
> Systematics and evolution of Dromaeosauridae. Bulletin of Gunma
> Natural History Museum 8: 1–20.
> Cheers,
> Nick Gardner
> http://whyihatetheropods.blogspot.com