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RE: Dinosaur Planet, parts 3 & 4

the dangers of assumption (phyletic bracketing) is that it limits what dinosaur 
"could", "had", or "did" by the animals we have today. I tend to take phyletic 
bracketing with a grain of salt because I question whether a secondarily 
aquatic reptile is truly representative of the "primitive" archosaur. It has 
all sorts of derived features that tend to be ignored so that it can be a 
stand-in for the primitive condition, namely: major changes in the skulls 
(broader than deep, loss of antorbital fenestra, reduction of supratemporal 
fenestra, complete modification of the suspensorium, etc.), procoelus 
vertebrae, body that is wider than deep, greatly reduced pubis that is excluded 
from the acetabulum, greatly reduced limbs, secondarily semi-erect posture, 
extensive development of body armor, ad naseum. 

One must also becareful in the assumptions made about birds (i.e., picking the 
stand-in). Witmer argued by phyletic bracketing that birds and crocs lack 
muscular cheeks, therefore ornithischians lack them as well. But this totally 
ignores condors and other vultures that have a non-muscular cheek. While I 
agree that it is doubtful that ornithischians evolved a new set of cheek 
muscles, there is still evidence for a cheek of some type, even if fleshy. 
Afterall, cheek armor is known for ankylosaurs and those structures had to have 
skin in which to develop. Furthermore, although the inset tooth rows of 
ornithischians (which is what Galton used as evidence for the cheeks), is 
clearly distinct from the non-inset condition of theropods. Ankylosaurs have 
exaggerated this inset condition.

As for footprints, as I pointed out in Eggs, Nests and Baby Dinosaurs, the 
hatchling hadrosaur tracks from Utah do NOT occur with adult tracks. Yet, this 
is not what is expectedof the Horner hadrosaur-parental care model. The 
smallest prints that co-occur with adult tracks in any of the mines are 
half-size. That pattern repeats itself everywhere (including the Puluxy River 
track sites). I can only conclude from the evidence is that juveniles really 
were segregated from the adults until about half-size. I know that this flies 
in the face of what has become conventional wisdom (the new dogma), but I can't 
see it any other way. 

As for the tooth weather that Jack refers to in the hatchling Maiasaura, which 
he uses to prove that the babies were being fed by the adults in the nest, I 
pointed out to him long, long ago, that many embryos grind their teeth (the 
classic study was of rats). Now Chiappe and crew have demonstrated that in the 
Argentine sauropod embryos. 


>>> "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu> 
That's why I said "simplest assumption by phylogeny".  Additionally, as
mentioned, I pointed out that the phylogenetic inference would be only
during the first few weeks of life (as in crocodilians): after that, they
might well have been on their own.

> What
> evidence there is indicates that the smallest footprints in track
> sites are half- or more adult size. There are NO baby tracks with adults.

But this might also be taphonomic, as a baby sauropod wouldn't be expected
to make a footprint except in soft sediment.  So unless the same tracksites
also preserve the footprints of non-sauropods of the same expected body size
as baby sauropods as well as the half-grown and larger ones, the possibility
remains that the absence is preservational.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796