Re: Thescelosaurus & Tenontosaurus

["Jaime Headden" <jaemei@hotmail.com>]

Okay, to reiterate:

I posted a message contained a possible connection between 
*Thescelosaurus* and *Tenontosaurus*. I said that the long-tailed 
Tenonto was derived from *Thescelosaurus*, but I made a mistake in my 
research. I appologize.

*Thescelosaurus* is actually the younger genus, so the roles _would_ be 
switched, if I stayed on this line, but I'm not. Instead, I'm refining 
it.

One:  *Thescelosaurus'* pelvis is more reminiscent of the Tenonto than 
it is of its other relatives, *Hypsilophodon* and -- to a degree -- 
*Dryosaurus*. The postacetabular process is abbreviated and dorsally 
"lifted", with a stubby pubis (in the Tenonto, this is just shorter) but 
the ischium is narrow, slender, while the Tenonto's is broad 
rostrocaudally. There is precedence for the similarities: 
*Hypsilophodon*, thick ischium -- *Dryosaurus*, thin and curved -- 
*Camptosaurus*, thick and booted with slight curved -- *Iguanodon*, long 
and curved, robust but still slender. The morphism is varied, so the 
ischium isn't really diagnostic to separate the two.

Two: the femora are almost identical; the Tenonto's is broader distally, 
like a ball, while *Thescelosaurus'* is not, but both are strait, the 
notch at the capitulum for the ilio-femoralis muscle (I don't know the 
notch's scientific name).

Three: the humeri are also nearly identical, save for the Tenonto's 
larger deltopectoral crest, which is unique for almost all the 
iguanodontoid ornithopods. (I don't see the scapula as diagnostic, for 
it, like the Tenonto's humerus, is the only occasion for the proximal 
widening to this degree.)

Four: the jugal bone does not over the proximal maxilla as much as it 
does in all other ornithopods -- except for *Tenontosaurus* and 
*Ouranosaurus*. This causes a short orbit ventrally. (The skeletal 
restoration of *Thescelosaurus* -- in _The Complete Dinosaur_ by Farlow 
and Brett-Surman, an excellent book in my estimation -- shows this very 
low skull rather well. I restored *Thescelosaurus'* skull indepentenly 
of Greg Paul's bones-in-a-silhouette restoration, based on the dorsal 
cranial bones as in the original specimen, before the new find, and came 
up with a more dryosaur--tenontosaur-ish skull. I even got the mandible 
nearly the same as in GSP's. But I disagree with the low head on it's 
sheer, very similar in fact to *Ouranosaurus*.)

Five: the manus and pes of the two are more similar than in any other 
iguanodont to either; the ulnae and radii are both arranged similarly 
and stiffened so; the pes in *Tenontosaurus* is more robust than in 
*Thescelosaurus*, but the Tenonto was a whole lot bigger, besides, and 
required the extra support.

Six: the vertebrae count in the following dinosaurs:
*Hypsilophodon*: cerv. - 9, dors. - 15, sac. - 5, caud. - 40+
                             total - 69+

*Dryosaurus*: cerv. - 10, dors. - 13, dorsac. - 1, sac. - 6, caud. - 47
                             total - 77

*Camptosaurus*: cerv. - 11, dors. - 13, sac. - 5, caud. - 50
                             total - 79

*Tenontosaurus*: cerv. - 12, dors. - 16, sac. - 5, caud. - 59
                             total - 92

*Thescelosaurus*: cerv. - 9, dors. - 14, dorsac. - 1, sac. - 6, caud. - 
48
                             total - 78

-- all figures are based on GSP's reconstructions; *Hypsilophodon's 
tail-tip is hidden, so I can't count the rest, and *Thescelosaurus* may 
have a second dorsosacral, making the sacrals number only 5.

*Thescelosaurus* resembles *Dryosaurus* most in this systematic, while 
there seems to be a hypsi--dryo--campto--tenonto trend going on, with 
*Thescelosaurus* building off of *Dryosaurus*, which is my own theory 
(previously, I had supposed a hypsi--thescelo--dryo connection, but this 
was based on impromptu publishing, eager to present, rather than 
research thouroughly, as I try to do here).

a plausible clade:

Hypsilophodon
|
Dryosaurus---------
|                         \-------------------------
Camptosaurus   Tenontosaurus   |
|                                                   Thescelosaurus
Iguanodon

\ = where clade requires intermediate genus or species to clarify: a 
ghost taxa.

I am an optimistic amateur, but I feel I am making a good, scientific 
query here. Please, feel free to critique.

Jaemei

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