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Jean-Michel (email@example.com) wrote:
<In a post on the titanosaurs thread, HP Jaime says that *Achillobator* is
a puzzle (which I understod) and *Bagaraatan* is a "friggin' nightmare".
This is really my question to explain, as it involved my perspective on
the animal. Essentially, *Achillobator* has features that seem to come
from two grades of theropod, and both close to each other, but yet each
are disparate of the other. Questions of wether it was chimaeric have been
raised before, and may be in part true; having them all as a single
animal, including a single pelvis rather than two different animals found
next to one another and leaving non-matching elements that nonetheless fit
one another, seems to show that there was something tricky going on. I
doubt cladistics will solve anything in this matter, but inclusive
analyses such as Hwang et al., 2002, on *Microraptor* have supported a
basal dromaeosaur model alongside creatures with different anatomy and
almost no synapomorphies like *Microraptor* itself. Personally, I see the
two suites of features (basal maniraptor versus dromaeosaurid) and the few
autapomorphies given either scenario, as being mutually negating ... yet
cannot get over the completely unique dromaeosaurid anatomy that places
the taxon there.
Hence, *Achillobator* is a puzzle.
You get a different story with *Bagaraatan*. Here you have an animal
with several very distinct and frankly bird-like postcranial bones,
pelvis, and limbs ... but then looking at the jaw, you get features from
across the tetanuran board, and it plays tricks on your mind. The
postcrania by itself makes sense, but a carnosaurian antarticular,
tyrannosaurine surangular with large foramina, ceratosaurine/dromaeosaurid
narrow and long dental alveoli, deep mandibular symphysis but still quite
narrow as in dromaeosaurs. Its something I have trouble thinking easily
about, leading me on paths both wonderous and tortuous. This is why I
describe the nemegtian *Bagaraatan* as a "friggin' nightmare", barring a
more explicit epithet.
Hope this helps,
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
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