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Re: Dromaeosaur questions (long, I think)



As someone who has published on theropod teeth (e.g., Pectinodon, etc.), I will 
confess that for the past 5 years I have been getting more uncomfortable about 
the taxonomic utility of theropod teeth. Although others have said this in the 
past, I have been slower in accepting it (and some of my colleagues still 
don't). Frankly, there is no reason why convergence can't occur , especially 
given the tens of millions of years of theropod evolution. You can only design 
a slicing-cutting tooth in a limited number of variants before you start 
repeating: long, recurved, large chiseled denticles; long, recurved, small 
chiseled denticles; long, straight, large chiseled denticles, long, straight 
small chiseled denticles, etc. I think you could work out the total number of 
possibilities on  paper in less than a half-hour (Someone interested in a 
Master's thesis?). 

It could be set up as a table, with the same features along the top and side, 
and an X in the cell for the X-Y combo. Then, using this predictive tool, to 
look at the fossil record for examples. It would be interesting to see if any 
combination pattern is more common/frequent than another. This type of analysis 
has NEVER been done. Thus, there is no independent test for the utility of 
teeth in theropod taxonomy, only an unsubstaniated assumption (criticising 
myself here).

Ken 

>>> "Mickey Mortimer" <Mickey_Mortimer111@msn.com> 12/30/03 23:50 PM >>>
Now that I'm back in my dorm with references, time to answer a few posts...

Matías Soto wrote-

> I can confirm now that here in Uruguay we have teeth from a Late
> Jurassic-Early Cretaceous dromaeosaur (and a big one, height = 28 mm.).
The
> teeth, besides bieng laterally compresed and apically recurved, shares a
lot
> of character with those from _Dromaeosaurus albertensis_ including low
> DSDI, torsionated anterior carina, chisel-shaped denticles...
> It cannot be a convergence. I know that there are some teeth worlwide that
> have this features too, which can be included (I suppose) in the
> Dromaeosaurinae.

Perhaps.  Low DSDI's are found in almost all theropods (except some
dromaeosaurs, Richardoestesia, Dryptosaurus, Eotyrannus and Gojirasaurus)
though, as are chisel-shaped denticles (as opposed to pointed denticles).

> 1) How distinctive is the twisted anterior carina?  Although Currie (1990,
> 1994, 1995) says it is diagnostic for _D. albertensis_, it appears other
> non-avian theropods shares this feature too: some _Saurnornitholestes_
> teeth, tyrannosaurids (Sankey et al., 2002), _Acrocanthosaurus_ and
> allosaurids (Currie & Carpenter, 2000) and even all carnosaurs (Feduccia,
> 2002, thanks Mickey!). It seems to me it doesn't have any diagnostic value
> by itself. What do you think?

I'd trust nothing Feduccia says about non-avian dinosaurs (and very little
he says about any Mesozoic dinosaur), but note Paronychodon and
Archaeopteryx are also supposed to have this character (Rauhut, 2002).

> 3) Do you know any other dromaeosaurid from South America (or even
Gondwana)
> from Late Jurassic-Early Cretaceous times? I think there aren't (of course
> there are possible dromaeosaurs from Late Cretaceous of Sudan, Brazil,
> Argentina, Madagascar), so, due to biogeographical and chronological
> reasons, besides the great relative size of the teeth, do you think it is
> convenient to create a new taxon?

undescribed dromaeosaur (Goodwin, Clemens, Hutchison, Wood, Zavada, Kemp,
Duffin and Schaff 1999)
Tithonian, Late Jurassic
Mugher Mudstone, Ethiopia
Material- (JN-96-2B/UCMP 170803) tooth
Reference- Goodwin, M. B., Clemens, W. A., Hutchinson, J. H., Wood, C. B.,
Zavada, M. S., Kemp, A., Duffin, C. J., and Schaff, C. R., 1999, Mesozoic
continental vertebrates with associated palynostratigraphic dtes from the
northwestern Ethiopian Plateau: Journal of Vertebrate Paleontology, v. 19,
n. 4, p. 728-741.

undescribed possible dromaeosaur (Currie, Rich and Rich 1996)
Early Aptian, Early Cretaceous
Wontohoggi Formation of the Strzelecki Group, Victoria, Australia
Material- (NMV P186343) tooth (Currie, Rich and Rich 1996)
Description- serrations only present on posterior edge.
Comments- This character is also known in troodontids and some basal
coelurosaurs.
Reference- Currie, P.J., Vickers-Rich, P., and Rich, T.H. (1996). "Possible
oviraptorosaur (Theropoda, Dinosauria) specimens from the Early Cretaceous
Otway Group of Dinosaur Cove, Australia." Alcheringa 20(1-2): 73-79.

undescribed 'velociraptorine' (Long 1998)
Early Albian, Early Cretaceous
Eumerella Formation of Otway Group, Victoria, Australia
Material- teeth
Description- teeth moderatly recurved with coarse posterior serrations and
no anterior serrations.
Comments- These characters are also found in troodontids and Microraptor.
Currie, Rich and Rich are studying these teeth.
Reference- Long, 1998. Dinosaurs of Australia and New Zealand and other
animals of the Mesozoic Era.

Only create a new taxon if you can distinguish your tooth from all other
named teeth.  I don't think size doesn't count as a distinguishing feature.
Besides, there are other large dromaeosaurs with 'dromaeosaurine' teeth,
like Achillobator.  It might be a good subject for a publication anyway, due
to its potential biostratigraphic importance.

> 4) Is it possible to estimate the total lenght of the animal?
> _D. bornholmensis_ lenght was estimated, for a 21 mm. high tooth, in more
> than 3 metres.

It's about twice the size of teeth in the Dromaeosaurus holotype, so may
have been 3-4 meters long.

Mickey Mortimer