Re: Aquatic ceratopsians and such

["Jaime A. Headden" <qilongia@yahoo.com>]

Christopher Taylor (gerarus@westnet.com.au) wrote:

<Tereschenko, V. S. 2008. Adaptive features of protoceratopoids (Ornithischia:
Neoceratopsia). _Paleontological Journal_ 42 (3): 273-286.
 
"The analysis of some morphological characteristics of protoceratopoid
skeletons, the extent of mobility of the vertebral column, and the probable
adaptive significance of these features suggest that *Bagaceratops* had a
mostly aquatic mode of life, *Protoceratops* was semiaquatic, *Udanoceratops*
was facultatively aquatic, and *Leptoceratops* was predominantly terrestrial.
Protoceratopoids were quadrupeds, with the prevalence of hind limbs, probably
using slow or rapid trotlike gait. An asymmetrical locomotion was most likely
impossible. On dry land, *Bagaceratops* and *Protoceratops* moved slowly.
*Udanoceratops* and *Leptoceratops* approximately equally used rapid and slow
locomotor modes, although the second could run for a longer time than the
first.">

  Unfortunately with this paper is a glaring issue: The author refers to
transverse processes for each of the four studied "protoceratopoids" (by which
is apparently meant, as used in an earlier paper, as the stem of Neoceratopsia
and for the combination of Protoceratopsidae and Bagaceratopsidae, incorrectly
spelled by Tereschenko and attributed thusly -- it is referred to Gregory and
Brown, who coined Protoceratopsidae, and thus it should be
"Protoceratopsoidea"), but argues they are minimal to weakly developed to
virtually absent in the middle of the tail. These permit the tail a very high
aspect ratio (h:w), which, when combined with the author's observed
intervertebral articulations, allow the tail a high bilateral flexibility.
Unfortunately, this is tied to an alligator and an amphibian, and is linked to
a sculling function, thus providing the animals with a semi-aquatic behavior.

  Pedal phalanges are also figured, with a scale between claw-like in
*Protoceratops* and *Bagaceratops* to more hoof-like in *Leptoceratops* and
*Udanoceratops* (so that the latter two are less aquatic than the former two).
This marks the first time the vertebrae and the pes of *Udanoceratops* have
been figured to my knowledge in a press publication, although Tereschenko's
disseration on the vertebrae of "proceratopsoids" must be a gold mine, as well
as that of *Bagaceratops* (which has fantastically tall neural spines!).

  Now, the linkage here that seems troubling to me is that the neural spine
architechture and the incipient flexibility of the tail (greatest proximally
due to heterocoelous caudal centra, graduating to more rigid platycoelous in
the more distal caudals) are given as aquatic adaptations. The absence of
developed transverse (or costal) processes appears of little note, despite
being well-developed in the caudal organs of most (if not actually all)
sculling animals, and this would have serious implications, as it anchors the
otherwise important sculling muscles of caudofemoral suite to the base of the
tail, as in most other dinosaurs, few of whom have been proven to be any sort
of aquatic organisms of note, except for some members of modern birds and a few
of their ancestors like hesperornithiforms (in which, of course, such processes
are present in nearly all free caudals).

  The paper goes into some detail on the vertebral posture, giving some animals
a gradual dorsal arch and a relatively flexible neck and others with an
inflexible neck and highly arched dorsum (e.g., *Bagaceratops*); the flattest
dorsal arch is found in *Leptoceratops*, and *Udanoceratops* had one of the
more flexible necks of studied animals. Problematically, an arched dorsum is
present in animals in which the forward half of the trunk is inflexible, where
the forelimbs and shoulder girdle are required for the purpose of locomotion
focused in the fore-aft plane. This is at odds with the argument of a sculling
function in the tail, and in fact merely underscores the true absence of an
aquatic habitus in any of these detailed "protoceratopsoids".

  So in all, the paper argues without providing what I think of as prodigious
evidence of an aquatic lifestyle for some of the Mongolian ceratopsians,
arguing instead that the animals, however somewhat flexible in the tail they
may be, were not that very aquatic, but may have had some ability to swing.
This can be argued of a good deal of other dinosaurs, as well.

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

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