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Gobiceratops, a Quick Note

  Alifanov, V. R. 2008. [The tiny horned dinosaur *Gobiceratops minutus*
   gen. et sp. nov. (Bagaceratopidae, Neoceratopsia) from the Upper
   Cretaceous of Mongolia.] _Paleontologicheskii Zhurnal_ 2008(6):49-60.
   (Reprinted in _Paleontological Journal_ 42(6):621-633.)

  One look at the skull and your first impression is "That's a juvenile!". 
Alifanov addresses this topic in his discussion of the taxon, which ordinarily 
you'd think would be referred to *Bagaceratops* as a juvenile of the type 
species (as it is even from the same formation):

  "The mature age stage of the holotype of *Gobiceratops minutus* gen. et
   sp. nov. is supported by the solid connection of bones of the braincase
   and skull roof; incidentally, this provided insignificant deformation of
   the specimen in the burial. In addition, the premaxillae are fused
   ventrally (this is not observed in some larger specimens of
   bagaceratopids), the nasal and prefrontal are fused on the right side,
   the prefrontal and lachrymal are fused on the left side, and fusion is
   also observed in the vomers, pterygoids, palatines, and ventral bones
   of the braincase. Partial fusion is also observed between the
   pterygoids and between the quadrates and quadratojugals.

  "The young age of the holotype of *Gobiceratops minutus* gen. et sp.
   nov. is supported by the predentary bone, which is broken in the lower
   part at the suture because of incomplete fusion with the dentaries.
  "The data considered suggest that the holotype is a young individual."

  I can only say that one cannot be "young" and osteologically "mature" in this 
sense, or if they can, it's gotta be weird. Skeletal maturity usually follows 
sexual maturity in mammals, reptiles, but not birds, such that one should 
expect suturing and fusion of elements in an adult, but its clear that the 
differential fusion is odd for this animal, especially with loose regions of 
the mandible skull roof, etc., that simultaneously concluding the animal to be 
mature and young (a subadult?) is inconsistent. The skull is clearly juvenile 
in its aspect, but does the bone support this conclusion? Does it preserve 
finished bone or is the surface still highly textured?

  Most interesting is that Alifanov has not looked at the possibility that 
ceratopsians fuse many cranial bones relatively early in their ontogeny, a 
respect that occurs to the frontals and parietals in virtually all 
ceratopsians, and the nasals in the basal ones. This should make it certainly 
harder to compare *Gobiceratops* positively against taxa and make a 
differential diagnosis that does not conclude closely that the specimen belongs 
potentially to another taxon.

  Indeed, the diagnosis reads like a description fo a juvenile skull:

  "Tiny horned dinosaur, with large orbits and large lower temporal fenestrae. 
Preorbital region of skull short and low, and occipital region high and wide. 
Rostral bone absent. Antorbital fossae located under orbits; subnarial 
fenestrae located in line with their anterior margin, wider and slightly higher 
than nares. Supraoccipital large and wide. Dorsally, prefrontals lacking 
contact with frontals because of long posterior processes of nasals, which 
reaching orbital border. Nasal horn in shape of slightly projecting tubercle 
with wide base. Frontals with medially concave orbital borders and massive 
posterolateral processes. Nasofrontal suture V- or U-shaped. Postorbitals and 
parietal adjoining each other, excluding frontals from formation of border of 
upper temporal fenestrae. Parietal wide, with short medial crest in occipital 
part of bone. Fenestrae in parietal absent. Occipital process of maxillae long, 
reaching line of posterior orbital border.
 Quadratojugal process of jugals having well-pronounced crest with wide base. 
Quadratojugals large, open laterally. Dentaries lacking angular process. 
Surangulars and angulars approximately equal in area of lateral surface. 
Splenials reaching occipitally line of middle of adductor fossae. Each jaw with 
six functioning teeth."

  Lack of fusion of some elements, including the rostral (leading to its 
absence), size of the orbits, orbits overslinging the antorbital 
fossa/fenestra, low tooth count, relatively triangualr skull with broad 
parietal region and extremely short antorbital region, extent and size of the 
maxilla, are all juvenile aspects. Some of these (no parietal fenestra, nasals 
fussed) are plesiomorphies.

  Alifanov continues to justify the taxonomy by supporting the variability and 
uniqueness of other named taxa, such as *Lamaceratops* and *Platyceratops*, 
*Breviceratops*, by arguing that the specimens are different, and thus unique, 
arguing that dissenters such as Makovicky are underassessing taxonomic 
variability. I can only say that this specimen is a juvenile, is quite young, 
and does not look as though supportive information on its taxonomic identity 
can substantively separate it from *Bagaceratops*. The occipital region, which 
Alifanov uses to primarily distinguish it from *B. rozhdestvenksii*, is 
disarticulated (unfused and juvenile), and clearly not useful in distinguishing 
the taxa.


Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)