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RE: Do we have dromaeosaurid evolution backward? Eshanosaurus Edition



On the subject of *Eshanosaurus deguichiianus* (Xu, Zhao & Clark, 2001):

Barrett (2009) select among the characters Zhao and Xu (1998) and xu et al. 
(2001) listed in comparison among sauropodomorphans and therizinosaurs ten 
characters, weighing them as either favorable toward therizinosauroids, 
sauropodomorphans, or neither (ambiguous). Of these, Barrett selected three 
characters that were exclusive to *Eshanosaurus* and *Therizinosauroidea* 
relative to *Sauropodomorpha*:

1. Denition reduced in size caudally over a broad range of tooth positions;
2. More dentition relative to the tooth row.
3. Labial "ridge" of the dentary with a sharp emargination, and indicating a 
distinct buccal recess.

  It should be noted that the mandibular fragment of IVPP V11579 (holotype of 
*Eshanosaurus deguchiianus* Xu et al., 2001) is a partial left dentary missing 
its mesial, distal and gular margins, meaning that other potential features 
must be either inferred or are unknowable at present. Dentition is known only 
in the rostral half of the mandible, but alveoli are preserved extending nearly 
to the posterior end of the dentigenous margin and it is this which is used to 
help infer the size of distal teeth.

  First, staggeringly distinct rostral to posterior tooth height (basoapical 
height) is characteristic of therizinosauroids in general, although it is 
absent in *Falcarius utahensis* as inferred from relative tooth diameters along 
the preserved margins (e.g., UMNH VP 14529; Zanno, 2010). If we were going by 
basalmost taxa as indicators of progressive evolution, then, we'd note that 
this feature would be convergent between *Eshanosaurus* and therizinosaurids, 
i.e., excluding *Falcarius* and *Beipiaosaurus*.

  Second, *Eshanosaurus deguchiianus* has ~37 tooth positions, inferring a 
dentate symphyseal region. While this is more than in sauropodomorphans 
generally, it is relatively equivalent among therizinosauroides, where it comes 
in in the middle or towards the upper end of the cline: *Falcarius utahensis* 
preserves 28 positions (Zanno, 2010), *Beipiaosaurus inexpectatus* 37 (Xu et 
al., 1999); *Alxasaurus elesitaiensis* ~40 (Zanno, 2010) and so forth. 
Progressive reduction of dentition, as argued by Zanno, appears to regard the 
number as generally diminishing as therizinosauroids evolve; should we then 
consider that a taxon that exists outside this cline relative to age should not 
be inferred to be part of it? Not exactly, but it raises doubt as to the 
effectiveness or value of this character. As noted by Barrett, many clades of 
maniraptoriform produce supernumerary dentition, among them *Pelecanimimus 
polyodon* and troodontids in general. There, concentration of dentition per 
centimeter (Zanno, 2010) presents an extreme to which the Lufeng jaw can be 
raised, and in this case, it compares well with some maniraptoriforms, and not 
so much with others; that these taxa are concentrated in *Therizinosauroidea* 
should have little bearing on the issue save to raise doubt, and is ambiguous.

  Third, while I would prefer to discuss the form of the lateral emargination 
elsewhere, it seems notable that the form of the lateral ridge extends towards 
the rostral end of the dentary in *Eshanosaurus*, but does not in 
*Erlikosaurus*. The ridge is located dorsally in therizinosauroids AND 
sauropodomorphans, but lower in ornithischians relative to the height of the 
bone, but in *Eshanosaurus* it is very low. A ridge is absent in *Falcarius 
utahensis*. I am not sure what Barrett (2009) means when he says that the ridge 
in *Eshanosaurus* is "almost identical to that of the therizinosauroids 
*Alxasaurus,* *Beipiaosaurus* and *Erlikosaurus*" because the morphology of the 
ridge differs in relative position and the formation of a sharp lamina 
caudally, which is absent in *Eshanosaurus*. They merely seem to share aspect 
of the degree of "buccal offset" lingually (thus, the "width" of the buccal 
shelf, if it can be called that), and extending into the rostral half of the 
jaw.

  This is not a comprehensive list, for which I had prepared a 
manuscript to discuss. However, because I do intend to get this 
published one of these days, I will not go into detail on my arguments 
per feature. These are merely the three features that Barrett argues set 
*Eshanosaurus deguchiianus* from sauropodomorphans by being relatively 
exclusive to therizinosauroids. In the case of dental count and form, I 
consider any tooth-based feature to be largely problematic, as it ignores 
diet-based convergence (the argument behind dismissal of other tooth-based 
features). The one non-dental feature used ignored several aspects of the ridge 
to qualify it as therizinosauroid-like. As stated here 
(http://theropoddatabase.blogspot.com/2011/01/oshanosaurus-zhaos-nomina-nuda-part-5.html),
 Mickey argues that the material is convergent on both therizinosauroids AND 
sauropodomorphans. It is untenable, although I can understand the temptation to 
place it with more care, to argue that the material is decent enough in 
preservation and quality to answer the question of what sort of animal it is.

Barrett, P. M. 2009. The affinities of the enigmatic dinosaur *Eshanosaurus 
deguchiianus* from the Early Jurassic of Yunnan Province, People's Republic of 
China. _Palaeontology_ 52(4):681-688.
Xu X., Tang Z.-l. & Wang X.-l. 1999. A therizinosauroid dinosaur with 
integumentary structures from China. _Nature_ 399:350-354.
Xu X., Zhao X.-j. & Clark, J. M. 2001. A new therizinosaur from the Lower 
Jurassic Lower Lufeng Formation of Yunnan, China. _Journal of Vertebrate 
Paleontology_ 21:477-483.
Zanno, L. E. 2010. Osteology of *Falcarius utahensis* (Dinosauria: Theropoda): 
Characterizing the anatomy of basal therizinosaurs. _Zoological Journal of the 
Linnaean Society_ 158:196-230.
Zhao X.-j. & Xu X. 1998. The oldest coelurosaurian. _Nature_ 394:234-235.

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

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


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)


----------------------------------------
> Date: Wed, 24 Aug 2011 18:02:34 +1000
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: Do we have dromaeosaurid evolution backward?
>
> I can see the intuitive attraction of your idea of a predatory
> coelurid-ornitholestid-eudromaeosaur central axis from which other
> (non-predatory) groups emanated - including small aerial paravians.
> Call it Killers-Came-First or KCF. :-)
>
>
> As I see it, one major problem with this idea is that if large,
> pennaceous feathers originally evolved for aerodynamic purposes, these
> feathers are unlikely to have arisen in "large" (2-4m long) theropods
> that used their forelimbs for catching prey. Further, if the
> flight-related features of avialans and microraptorines evolved
> separately, it implies that large, pennaceous feathers evolved at
> least twice independently.
>
>
> Anyhoo, back to _Ornitholestes_. Yes, the alleged non-carnivorous
> characters of _Ornitholestes_ do have a spotty distribution among
> theropods (carnivorous, herbivorous, and somewhere in between). I was
> using Zanno and Makovicky's study more as a starting point rather than
> the sine qua non.
>
>
> I'm not actually arguing that _Ornitholestes_ was herbivorous. Even
> having relatively few teeth in a short tooth row (~40% basal skull
> length) are features that _Ornitholestes_ shares with some
> eudromaeosaurs, especially _Dromaeosaurus_ (relatively few large
> teeth, tooth row < 50% basal skull length).
>
>
> However, certain features in _Ornitholestes_ do give me pause. The
> skull is relatively small compared to the postcranium. The front
> teeth are rather conical (as mentioned previously) and the dentary is
> decurved (also as mentioned previously). These features, combined
> with the short metatarsus (relative to the femur), make this critter
> stand out from the pack. It looks to me like _Ornitholestes_ was
> shifting away from a hypercarnivorous diet - which fits with those
> phylogenies that have Therizinosauria as the next clade up from
> _Ornitholestes_ within Maniraptora.
>
>
> Sure, dromaeosaurids do tend to have (very) short metatarsi. But in
> _Velociraptor_ and _Deinonychus_ the short metatarsus may be connected
> with the highly specialized pedal anatomy, such as associated with
> resisting torsional forces - especially if eudromaeosaurs used their
> hypertrophied sickle-claws to grip large prey. Yes, I know I'm
> talking out of my ass here - I have no biomechanical support for this
> explanation for short metatarsi in eudromaeosaurs. But even allowing
> for an incipient sickle-claw in _Ornitholestes_, the pes is not much
> like that of eudromeosaurs at all. In its overall proportions, the
> pes of _Ornitholestes_ is strikingly similar to that of _Falcarius_.
>
>
> Finally, _Eshanosaurus_. Obviously you disagree with Barrett (2009)'s
> argument that _Eshanosaurus_ has features that exclude it from the
> Sauropodomorpha. In any case, it's not too difficult to believe that
> a small, herbivorous tetanuran theropod (although perhaps not a
> therizinosaur) was present in the Early Jurassic. _Eshanosaurus_
> could be an early "therizinosaur-mimic" among non-maniraptoran
> theropods.
>
>
>
>
> Cheers
>
> Tim
>
>
>
>
>
> On Tue, Aug 23, 2011 at 8:49 PM, Mickey Mortimer
> <mickey_mortimer111@msn.com> wrote:
> >
> > Tim Williams wrote-
> >
> >> > Not to contradict you here ;) , but Zanno and Makovicky actually left 
> >> > Ornitholestes unassigned, as they said its diet was inconclusive.
> >>
> >> To me, the fact that _Ornitholestes_ didn't fall in with the
> >> predominantly predatory theropods is itself interesting.
> >
> > Eh, lots of carnivorous taxa have at least one character Zanno and 
> > Makovicky identify as herbivory-related.
> > Decurved dentary- Masiakasaurus.
> > Dentary symphysis U-shaped- abelisaurids, carcharodontosaurids.
> > Conical anterior teeth- coelophysoids, megalosauroids, compsognathids.
> > Elongate anterior teeth- Daemonosaurus, Masiakasaurus, Ornitholestes.
> > Unserrated premaxillary teeth- coelophysids, spinosaurines, juvenile 
> > tyrannosaurines, most basal coelurosaurs, microraptorians.
> > Teeth lack recurvature- spinosaurines.
> > Heterodont dentition- More or less developed in most theropods, but notable 
> > in e.g. tyrannosaurids.
> > Pubic shaft anteriorly concave- some tyrannosaurids.
> > Pubis retroverted- Herrerasaurus, dromaeosaurids.
> > And that's not even mentioning carnivorous birds.
> >
> >> I guess I interpreted Zanno and Makovicky's statement a little
> >> differently: "Intermediate numbers of CHTs in these taxa may indicate
> >> omnivory or dietary specializations not manifest widely in other
> >> coelurosaurians (e.g., insectivory)." Clearly _Ornitholestes_ could
> >> not be assigned to the same trophic category as compsognathids,
> >> tyrannosaurids and dromaeosaurids.
> >
> > Again, the only coding difference from compsognathids is the decurved 
> > (right) dentary (since compsognathids are miscoded as lacking conical 
> > anterior teeth).
> >
> >> > The only "herbivorous" characters it is coded as having are-
> >> > 1. Decurved dentary.  Not obviously true in the left mandible, this is 
> >> > also found in Masiakasaurus, Coelurus and many (probably insectiviorous 
> >> > or piscivorous) Mesozoic birds.
> >>
> >> Also in _Eshanosaurus_, a likely herbivore. The diet of
> >> _Masiakasaurus_ has been the subject of much speculation: fruit, fish,
> >> insects? As for _Coelurus_, the dentary is the only cranial material
> >> known for this genus, and this element is extremely slender and
> >> gracile.
> >
> > And many other sauropodomorphs, where Eshanosaurus probably belongs.
> > Has anyone seriously suggested fruit for Masiakasaurus?  Surely it's too 
> > large to be an insectivore.  Fish sure, but that's hypercarnivory.
> >
> >> > Given the fairly large, recurved teeth and generally 
> >> > carnosaurian-tyrannosauroid nature of the taxon, I would doubt if 
> >> > Ornitholestes had more plants in its diet than modern coyotes and such.
> >>
> >> I also thought that the teeth of _Ornitholestes_ were rather conical,
> >> especially the premaxillary teeth. Am I mistaken here? This
> >> appraisal of _Ornitholestes_ dentition comes from Paul (1988). I
> >> disagree with GSP's "neoflightless" hypothesis, but surely I can trust
> >> him when it comes to determining the shape of a theropod's teeth.
> >
> > I dunno, my examination of the holotype suggests the anterior teeth have a 
> > flat lingual side.  But as noted above, this isn't much of an indicator of 
> > diet.  Besides the carnivorous taxa with conical anterior teeth, you also 
> > get herbivorous taxa with D-shaped teeth like Incisivosaurus (first pair), 
> > Pelecanimimus and Falcarius.
> >
> >> > The "rather weak cursorial abilities" are based on a tibia which 
> >> > seemingly doesn't exist.  I'd like to know what happened to whatever 
> >> > bone Osborn identified as a tibia.
> >>
> >> Actually, I wasn't thinking of the phantom tibia at all. The
> >> metatarsus of _Ornitholestes_ is only about half the length of the
> >> femur. Even compsognathids and archaeopterygids had longer metatarsi
> >> (~ three-quarters the length of the femur). The mt/femur ratio of
> >> _Ornitholestes_ is about the same as that of the basal therizinosaur
> >> _Falcarius_.
> >
> > The metatarsofemoral ratio is ~57% in Ornitholestes, but Velociraptor's is 
> > 42% (IGM 100/986).  Eudromaeosaurs' in general are low, which might be 
> > another ancestral character shared with
> > Ornitholestes (but not basal birds, oviraptorosaurs, troodontids, 
> > ornithomimosaurs, etc.).
> >
> > Mickey Mortimer
> >
> >