[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

Hey, glad to see that my post get a nifty discussion going. There has been 
so much stuff I can't address it all, but here's a shot. 

Jason I think suggested I might place all the archaeopterygians and sickle 
claws in a single family sort of like in PDW, but I tend to currently go for 
Deinonychosauria including Archaeopterygidae (Archaeopteryx, Anchiornis, 
Xiaotingia), Dromaeosauridae, Troodontidae. Of those the first and last are 
internally currently not very diverse, but dromaeosaurs are all over the place 
with little winged and probably arboreal microraptors, some very large 
runners, and long snouted unenlaginines. 

It is possible that loses of flight were relatively rare, with a single 
loss leading to all dromaeosaurs and troodonts, another loss to all 
therizinosaurs, and another to all oviraptorosaurs. That's the most 
scenario within the grand neoflightless hypothesis. But evolution is not 
particularly parsimonious. In fact it tends towards the intricate and bushy 
there is not intelligent goal behind it. The loss of flight in early fliers 
may have been as easy as pie, and multiple losses lead to assorted 
dromaeosaurs and troodonts. For example perhaps dromaeosaurines, 
velociraptorines and 
unenlagines each descended independently from fliers. It is notable that 
unenlagines include the flier Rahonavis. Perhaps different velociraptorines 
descended from fliers. The presence of very long tailed and shorter tailed 
therizinosaurs may indicate separate descents from different stages of tail 
abbreviation in fliers. It's possible that flight evolved, was lost again, 
reevolved, was lost again. The data is far too poor to test the alterantives 
is likely to never be sufficient to have more than a poor approximation of 
what went down. 

The rather poor success of Cenozoic continental flightless birds is not 
applicable to the  Mesozoic neoflightless protobird hypothesis because derived 
birds may have trouble being competitive without useful arms. And there all 
all the very large brained mammals ground birds have to contend with. Useful 
arms and hands should have given neoflightless protobirds a big advantage 
when competing against never volant dinosaurs with similar or lesser mental 

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. Jeholornids make poor ancestors 
for therizinosaurs in part because they lacked tooth rows (which are 
unlikey to have reevolved although it cannot be ruled out). 

Nor could the omnivoropterygids we know and love be actual ancestors for 
oviraptorosaurs because the latter were already extant. 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. 

Someone said something about it not being possible to tell if a flightless 
tetrapod with flight related features is neoflightless or not. We know that 
all current flightless birds are neoflightless. 

Someone was saying that early boids could not elevate their arms above 
horizontal so they could only glide. As I showed oh so long ago in PDW and 
in DA even a number of flightless theropods could easily elevate the 
humerus well above horizontal because they had laterally facing scapcoracoid 
glenoids. I had no trouble manipulating casts of Coelophysis rhodesensis to 
effect (drawing in my books). All winged protobirds and basal birds could do 
the same. What they could not do was elevate the wings all the way to 
vertical as most derived birds can do (as per wing clapping pigeons) due to 
dorsally facing shoulder glenoids. This is likely to have limited the flight 
abilities of proto/basal birds especially in the climb, but would not have 
barred basic powered flight. As I have shown in detail in my publications 
all large winged proto/basal birds had far more arm musculature than was 
needed for mere gliding, which requires no more muscle power than nonaerial 

And will not rediscuss my extensive discussion in the literature of why 
reversed halluxes are not critical for arboreality, why Archaeopteryx did have 
enough of reversable hallux for climbing (with pictures and everything), why 
forms in the process of becoming arboreal should not be expected to have a 
full suite of arboreal characters, yadda, yadda. 

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 
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 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 

Here's the thing. Are those who oppose my opposition to over reliance of 
cladistics really telling me I should be a cladist? Because if I had been so I 
would not have been able to propose the neoflightless hypothesis when Nancy 
was our 1st Lady, and only when winged microraptors were found in this 
centry would the hypothesis have been invented. Instead I got priority and the 
community was ready for the possiblity when winged dromaeosaurs turned up. 
Seriously, do you really think I should have toed the cladistic line all those 
years? And avoided the logical thinking that led to the hypothesis. Really? 
How would that work, please let me know.  

As for the noncladisitic testability of the neoflightless hypothesis I used 
to think alvarezsaurs were neoflightless. But as more fossils have come on 
line that theory is weak at best. In contrast the most basal flightless 
dromaeosaurs, troodonts, therizinosaurs and oviraptorosaurs have lots of flight 
type features that favor their being secondarily flightless.   

All that is needed to falsify the grand neoflightless hypothesis is to find 
always terrestrial ancestoral types for therizinosaurs and oviraptorosaurs 
while comparably suitable flying relatives or ancestors remain absent. I of 
course don't think that will happen but you never can tell. 

My therizinosaur paper in JVP in 84 actually was a shot at something at 
cladistic analysis -- and look at where that got me. The reason therizinosaurs 
were such a phylogenetic problem was the absence of sufficient fossils. As 
more data became available they proved to be derived theropods after all. Had 
I known the basal forms had folding arms I never would have considered them