[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Ah ha! That's where therizinosaurs came from
Greg Paul writes:
<The potential link between jeholornids and therizinosaurs is much weaker than
that between omnivoropterygids and oviraptorosaurs. The reason that jeholornids
are interesting is because they show that long tailed herbivorous fliers were
out and about, and were potential ancestors for neoflightless long tailed
herbivores like basal therizinosaurs.>
See, it's that matter-of-fact statement there about therizinosaurs being
neoflightless that makes me think Paul isn't just throwing this one out to
provoke debate. This is despite me refuting the argument about tailedness, Paul
continues to use it! So a second time (and I think this is actually the third,
since the issue was raised about a year or so ago):
Caudal vertebrae in the four specimens currently described (Ji et al., 2002;
Zhou and Zhang, 2002; Zhou and Zhang, 2003) vary between 25 and 27, with the
complete complete sequence (IVPP V13353) counting up to 27. That's at what
appears to be adult size, coming close to the sizes of two additional specimens
with one very small IVPP V13350 juvenile, and with a sacrum having six
vertebrae. Despite this, the caudal vertebrae form a tail sequence that itself
is 7.4x the length of the ilium, compares to *Archaeopteryx lithographica*'s
6.3x (but that's using the Solnhofen, which has an incomplete and likely
truncated caudal series, regardless of whether the length is diagnostic as
Elzanowski has argued on the matter), and which has fewer (~24) vertebrae.
*Shenzhouraptor* (which Paul ignores as the effectively correct name) has a
relatively long tail based solely on vertebral elongation, while the issue is
ambiguous and likely very different in therizinosaurs.
Therizinosaurs suffer from lack-of-tail-itis, which is congenital.
*Alxasaurus elesitaiensis* preserves upwards of 14 caudal vertebrae, with
hypotheses (Zanno, 2010) implying a low end of 30 and likely more.
*Beipiaosaurus inexpectatus* has a minimum of 31 caudals (Xu et al., 2003, with
an additional caudal from the original slab added in), comprised of two
articulated sequences of 14 and 11, and five floating vertebrae near the ilium;
the two gaps bear a sizeable gap between them corresponding (based on the size
of the vertebrae alone) to a measurably large sequence of about 10 or so
vertebrae, of which five are present scattered on the slab. I would thus infer
a low end of 36 [Zanno, 2010 infers 35, but states the count as 30], despite
their length, with a possible vertebra adding to the sequence at the tip (which
may be incomplete); the methodology of Grillo & Azevedo (2011) may actually
produce an accurate number.
There is a high level of ambiguity in the sequence of caudal vertebrae
present in the Crystal Geyser Quarry (n=67) that produced the holotype of
*Falcarius utahensis*, and the actual count is not inferred, largely due [I'm
sure] to age variation in the quarry. Taking into account the aspect of distal
caudals in the Quarry, which become elongated, it should be apparent that this
is true in *Gallimimus bullatus*, *Tyrannosaurus rex*, *Allosaurus fragilis*
and any number of other tetanurans for which this morphology is diagnostic. It
is, in short, plesiomorphic. What Paul is trying to argue is that tail _length_
matters on its face, rather than take into account the quanta of caudal count
or even morphology.
<Jeholornids make poor ancestors for therizinosaurs in part because they lacked
tooth rows (which are unlikey to have reevolved although it cannot be ruled
*Shenzhouraptor sinensis* lacks tooth rows? When was _this_ published? The
mandible does actually preserve teeth in IVPP V13274, and their absence is
arguable in the other specimens (especially the holotype: Ji et al., 2002, who
concede the poor preservation up front). And yes, they make extremely poor
ancestors, which is why we're all scratching our heads when Paul pronounces
therizinosauroids are neoflightless.
<Nor could the omnivoropterygids we know and love be actual ancestors for
oviraptorosaurs because the latter were already extant.>
I've heard this argument before. "How could birds come from dinosaurs if
there are still dinosaurs?" Or "How could humans evolve from apes when there
are still apes?" Certainly not both arguments from YOU, sir, but they are
essentially the same, and essentially equally poorly conceived and illogical
when considering the data involved (with which Greg Paul is aware of, having
cited it in _DotA_). The response is always the same, as you should be well
aware of, and the subject is in the TalkOrigins archive
(http://www.talkorigins.org/faqs/archaeopteryx/challenge.html), but there's a
handy-dandy reference at
I know you're not joking on a basic premise of the problem of the
superposition of the geological colum in regards to recovery of _known_
fossils, because you continue in all seriousness:
<At best there was a common ancestor whose morphology would be more
transitional than the fossils we got. If those creatures existed hopefully they
will show up in the earlier sediments present in NE China or elsewhere. One can
hope -- and it basically worked for deinonychosaurs so its not a long shot.>
Tongue-in-cheek this is not. You transition through several phylogenetic
inferences in this section, and I baffles me how this argument, made way back
in _PDW_ could continue to be made?
But on this specific further point:
Except we are only now finding sister taxa to the nodes where troodontids and
dromaeosaurs split, and it turns out it's a lot more complex than you even
thought of, and still plastic (you know, prone to constant shifting). For
instance, the uncertainty results in us treating *Microraptoria* (NOT
*Microraptor zoui* alone) as a clade of basal dromaeosaurs, but so too
*Unenlagiidae/Unenlagiinae* [I'd prefer a rank-neutral variant name]. By
constrast, troodontids show less defined variation, but it was there, too.
These groups are more complex, and they keep moving around, sometimes shifting
taxa to the other side and sometimes forcing them apar with respect to
*Avialae* and sometimes taxa move into the *Avialae*. To say that it "worked
for deinonychosaurs" is to assume we actually HAVE the correct picture, or a
semblance of it. How long did we think segnosaurs weren't theropods before
cladistic analysis, or the descriptive analysis of the skull of *Erlikosaurus
andrewsi* (Perle et al.)?
<Someone said something about it not being possible to tell if a flightless
tetrapod with flight related features is neoflightless or not.>
That was me! Yay! Maybe now if what I'm about to say on this subject, like my
repeating about therizinosaur tails, were to be spoken by someone that Paul
likes, he'll not denegrate that individual and name him/her as he named Jason
earlier in his email.
<We know that all current flightless birds are neoflightless.>
Bullhockey. We have basal taxa to the entirety of avian-ness (*Neornithes*)
which show flight retained based on our assumptions on the anatomy involved.
*Ichthyornis dispar*? Once inferred to be basal to terns, flighted due to
environment and the high disparity of leg/wing length, and extreme development
of the forelimb and pectoral girdle. *Hesperornis regalis*? Trickier, once
inferred to be a loon, or grebe, or with both; but also because it is
phylogenetics that infers flight at the base (phylogenetic bracketing_; basal
taxa do not appear to be flighted, but we assume it so because of sister-taxa.
And so on. When, however, we arrive at the base of *Avialae,* we find taxa
lacking pygostyles in general and with long caudal counts, small sacral counts
and very, very short ilia, small pectoral girdles, no keels or no ossification,
no alulae, unreversed halluces with few adaptatations for perching or with
often terrestrial indicators in phalangeal/ungual morphology/proportions,
retained third manual digits and fingers often with large claws,
feather-strength indicators (although that's been questioned), broad and now
narrow furcula, two completely different forms of arrangement for a triosseal
canal indicating it is convergent, and a questionable gradient on expansion and
orientation of the scapular glenoid.
What is the problem here? Paul infers that the process for losing flight
shows the _same_ features as for gaining flight, based on the phylogenies
produced by others, which he then uses his "method" to contradict by arguing
that the entire system is convergent across multiple lineages. Thus, when he
maps the above features to his anti-phylogeny, he can arrive at loss-of-flight
characteristics. This becomes the primary hypothesis. But how to test it ... I
know, look at birds! Wait, isn't that circular reasoning? That's why we ask
that such an argument find a test to the loss of flight. You have to find a way
to discriminate a developing flight condition from a developing loss of flight
condition, and when Paul writes:
<The loss of flight in early fliers may have been as easy as pie,>
He makes an argument that _requires_ some method to assess, and offers none.
What we have is the inference of a single gain in flight, without any actual
data to show otherwise. Things seem to get busy, but animals get less-leggy,
less-feathery, larger and ever so larger from a basal small seeming scansorial
gradient. Even *Ornithomimosauria* seems to arise from this, along with
*Tyrannosauroidea*, as they all stem from a lineage that looked an aweful lot
like *Sinosauropteryx prima*.
<Someone said I am inconsistent in rejecting cladograms that contradict the
neoflightless hypothesis while accepting those that do. But this is illogical.
Say the cladograms for years contradict the neoflightless hypothesis and I pay
them little mind because it is my conclusion that they are defecitve due to
lack of sufficient fossil data and because the nonneoflightless hypothesis>
This was also me, but I think Tim Williams also said it.
There is no "nonneoflightless hypothesis," it is the null. This is what all
other arguments apart from _DotA_ are: "Ground up," "Trees down," "WAIR" and
"the Hopp-Orsen hypothesis" are hypotheses for developing flight; your argument
is to pretend flight came first, and this simply differs from the initial
hypothesis that flight evolved in birds once. Your argument differs from
Huxley, Marsh, Ostrom, Gauthier, and even Feduccia and the other BANDits, etc.,
in which progressive birdiness developed on a lineage resulting in
more-bird-like taxa, rather than several less-bird-like taxa. You reverse the
clinal trope from what is assumed to be the null, no one does the opposite.
<does not appear as logical. Say that as new fossils come online some
cladograms start supporting the neoflightless hypothesis. Am I supposed to
automatically say that since cladistics is offering support for the
neoflightless hypothesis I must now reject the latter? I do not think
cladistics is useless. My concern is that cladistics has become overly dominant
to the point it prevents thinking outside the box of the cladistic results at
any given time.>
Cladistic output improves with more data. It is a separate inference that
newer fossils will improve the analysis, as they may result in branches that
have nothing to do with major lineages and thus seldom shake the tree. A new
oviraptorid described tomorrow will not see us with a novel oviraptorosaurian
position or array of the basal forms; but finding new basal taxa does cause the
tree to adjust, and may (as in *Xiaotingia zhengi*) pull otherwise "stable"
taxa with it. Despite this, such trees are looked on with caution, while the
stable trees which hold despite other inclusions of such data are given higher
levels of confidence due to integrity of data measures and mean output of
similar trees with different data sets. This is akin to five different groups
using different sets of data to arrive at the same conclusion; when a sixth
group uses another set of data and arrives at a divergent conclusion, we trust
that analysis a lot less.
<Here's the thing. Are those who oppose my opposition to over reliance of
cladistics really telling me I should be a cladist?>
There is no opposition to reliance on the cladistic methodology here. Paul
rejects the methodology, and does not make a case for occassional use of the
processes involved. He eschews it, and the results, in favor of his own
methods, inferring that his are more useful or competitive, despite not showing
a way to distinguish the processes. When cladistic methodology recovers a
topology that conforms with some of his previous-published arguments, it is
declared he is right (again) and Paul crows eventual victory. These methods are
not competitive; Paul lacks a methodology entire, merely a phyletic lumping
process which is subjective to the extreme, while the cladistic methodology
uses parsimony as its discriminating mechanism. Regardless of whether we
_should_ be using parsimony and mathematic processes to recover phylogenetic
topologies and affirm or deny hypotheses of descent, cladistic methodology can
be tested using known processes and math, while Paul's cannot. Further,
confirmation biases in data selection can be fixed in various points of the
data matrix used, including taxon selection, specific coding of sequences, and
amount of sequence to code. Are such biases apparent when Paul's "scientific"
argument avers "therizinosaurs are neoflightless"? I say yes.
This makes the cladistic methodology _scientific_, and Paul's "method"
decidedly not so.
No one is asking Paul to become a cladist; we are saying he should have some
faculative understanding of the system he disregards before calling it or its
results into question. It is a tool, like any else.
Clark, J. M., Perle A., & Norell, M. A. 1994. The skull of *Erlicosaurus [sic]
andrewsi*, a Late Cretaceous "segnosaur" (Theropoda: Therizinosauridae) from
Mongolia. _American Museum Novitates_ 3115:1-39.
Grillo, O. N. & Azevedo, S. A. K. 2011. Recovering missing data: Estimating
position and size of caudal vertebrae in *Staurikosaurus pricei* Colbert, 1970.
_Anais da Academia Brasileira de Ciências_ 83(1):61-71.
Ji Q., Ji S.-a., You H.-l., Zhang J.-p., Yuan C.-q., Ji X.-x., Li J.-l. & Li
Y.-x. 2002. [Discovery of an avialae bird - Shenzhouraptor sinensis gen. et sp.
nov - from China.]. _Geological Bulletin of China_ 21(7):363-369 [in Chinese]
Xu X., Cheng T.-n., Wang X.-l. & Chang C.-s. 2003. Pygostyle-like structure
from *Beipiaosaurus* (Theropoda, Therizinosauroidea) from the Lower Cretaceous
Yixian Formation of Liaoning, China. _Acta Geologica Sinica_ 77(3):294-298.
Zhou Z.-h. & Zhang F.-h. 2002. A long-tailed, seed-eating bird from the Early
Cretaceous of China. _Nature_ 418:405–409.
Jaime A. Headden
The Bite Stuff (site v2)
"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