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Re: why isn't Tethyshadros insularis just a juvenile?



I should state that I am not suggesting anyone is stupid, or falsely stating 
data. If this is how things appeared then I apologise. 

Perhaps I should have started the email differently, as my points are an aside 
from what is obviously a fantastic and important set of specimens. 

I thought that I would make a few comments that (for once) were not about name 
priority or spelling, and raise the issue that ontogeny may have severe impact 
on phylogenetic analysis, something which is discussed often here. This is 
something of a new field in dinosaur paleontology, but it is only going to get 
bigger.



> >Given the lack of named hadrosaurs from contemporaneous deposits of Europe, 
> >it is likely that Tethyshadros is a valid taxon.
>Furthermore, Telmatosaurus could (I repeat, could) be
contemporaneous, in the geological sense of the term, as it is from the
lower Maastrichtian of Romania.

True, but it is only one taxon. Hadrosaur diversity for any given point
in time in other continents is around 4-6 species (sometimes even
more). In the North American late Cretaceous at least, hadrosaur
species tend to last no longer than about one million years, and
typically much less, down to about 300,000. Even if Tethyshadros is
contemporaneous with Telmatosaurus, the probability both being valid is
pretty high.


>> I'm saying that without histological analysis of limb bones a non-mature 
>> status for the holotype cannot be falsified.
>So you should cut a lot of limb bones all around the world. I am rather sure 
>that the mature status of most of hadrosauroids was never tested by 
>histological analysis.

Good point. This is in the process of being done for at least some taxa. Some 
furore was raised from Jack Horner's recent suggestion that as many as a third 
of all dinosaur taxa may be invalid as ontogenetic morphs.  I suspect the 
figure will eventually become even higher than this, including recently named 
taxa as well as historical ones.


>>
Given the larger body size of some referred specimens, isn't it
possible that some or many of 
 are there not because of a truly basal
phylogenetic position, but because of a non-mature status for the
holotype specimen? Even a half to 75% grown non-mature specimen might
still exhibit basal characters forcing it into a more basal
phylogenetic position.
>Are you saying that the subadults of
Maiasaura, Brachylophosaurus or Corythosaurus show such a mosaic of
basal and derived characters?

Without wanting to go into too many details of other people's current research; 
yes they do.


>The larger specimens of
Tethyshadros could just be older individuals or just larger individuals
because of intraspecific adult-size variability. Can you disprove this?
Can you exclude sexual dimorphism in this taxon? Can you do this in
absence of indisputable evidence of osteological immaturity and
juvenile features?

Sectioning of limb bones can show that specimens are of different ontogenetic 
status. Morphologic variability through ontogeny has been shown for all taxa 
subject to such analysis (as far as I know; if someone does know of an 
isometric ontogenetic series for dinosaurs, then I am wrong). Ontogeny 
(especially combined with stratigraphy) can explain morphological variation 
between specimens better than sexual dimorphism which has never been 
demonstrated conclusively in dinosaurs, and is near-impossible to test. 
intraspecific adult size variability would be faslifiable if one specimen 
turned out to have an EFS and another did not.


>> I'm not saying the specimen is not an
adult, it just would have been nice to have had a limb bone
histologically sectioned to confirm a mature status is all.
>Crazy man. Nice? Do you think you can cut the "Gioconda" at Louvre just to 
>confirm that the colors are not synthetic?
>FIRST
- No museum in the world would allow something like this. However, the
specimen is not "in the world", it is in Italy where the fossils are
State property. Therefore, things are even worse for the poor
paleontologist. No chance to obtain the permission to do >such a thing
from the Ministry in Rome. It easier fo
he USA President in Washinghton D.C. I
hope it is clear what I mean.
>THIRD
- You do not know if the bone has the kind of preservation that allows
the identification of the histological features. Maybe I am not so
stupid as you seem to think. Maybe I decided not to cut that precious
bone because it is obvious that it could not give us much information.
>FOURTH
- It is not necessary to cut the bone to take an histological sample. A
microsample taken drilling the bone could be enough in a well-preserved
bone. However, I do not have the instruments to do it here. Searching
for a permission from the State do do the drill and searching for the
instrument would take several months and economic resources that I did
not have. I will try this in the future, if I will be authorized, but I
am pessimistic about the possibility to obtain clear indications about
the ontogenic status of the holotype.

I appreciate that circumstances surrounding the specimen may not be ideal for 
histologic analysis; often this is the case. Museums are more often starting to 
allow sectioning of specimens, especially with the less invasive recent 
techniques commented upon by Dr. Holtz.


>SECOND - >In order to detect the
ontogenic status of a single individual, you need an ontogenic series
(i.e., a lot of well-preserved limbs of different sizes to section).
Sorry, we do not have that ontogenic series for Tethyshadros.

Detection of an EFS would have shown any of the specimens was approaching 
somatic maturity. Full histologic section would have revealed the presence of 
LAGs, or bone textures indicative of ontogenetic stage. An ontogenetic series 
is nice to have in order to place specimens in context with each other, but a 
single sample can be enough to establish whether or not an individual is mature.