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What ever happened to Planicoxa?

It became ignored. Just like every other ornithischian on this list. :-)

But anyway, I'm back to studying ornithischians after staring at allosaurs for 
my research paper in IB English class.  Such joy! Realizing I had yet again 
forgotten this Cedar Mountain ornithopod in all of my attempts to look at the 
relationships between various ornithopods, I quickly cracked open my copy of 
"Mesozoic Vertebrate Life" (ed. Tanke and Carpenter, 2001) to the paper 
describing it. It was placed as at least an iguanodontian, and possibly an 
iguanodontid.  My curiousity overwhelmed me and I decided to add it to David 
Norman's cladistic analysis from his paper on Probactrosaurus (Norman, 2002).  
Fukuisaurus, Jinzhousaurus, and Nanyangosaurus were added as well. I deleted 
Eolambia on the basis of a conversation I had with Jason Head last weekend at 
the "Dinosaurs in the New Millenium" symposium. Apparently, there's some 
taxonomic trouble with this species and we'll probably see some revision in the 
near future.  Ah, well, onto the analysis...

Heuristic Search
50% Majority rule consensus of 9 MPTs, 129 steps
CI 0.67, HI 0.33, and RI 0.85-

     `--+--+--Iguanodon atherfieldensis
        |  `--+--I. bernissartensis
        |     `--Ouranosaurus
                                      |  `--Parasaurolophus

Planicoxa is the sistergroup to Euhadrosauria (lambeosaurines and 
hadrosaurines) based on- anterior process of ilium strongly downturned (54.1), 
dorsal margin of ilium prominently everted with a pendant flange (56.1), and 
posterior blade of ilium rectangular (57.1).  It is placed in the Hadrosauridae 
based on- femoral anterior intercondylar groove fully enclosed forming a canal 
(64.2).  Both species of Iguanodon and Ouranosaurus form an Iguanodontidae 
based on- ventral edge of jugal strongly angular (16.1).  Iguanodon 
bernissartensis and Ouranosaurus are united based on- dentary ramus deepens 
rostrally (24.1), and coronoid process elevated, but obliquely shaped (25.0).

So, Planicoxa is actually derived within Iguanodontia, being the sistergroup to 
the Euhadrosauria, a result which actually surprised me, since I had first 
thought it was much more basal, maybe some sort of hadrosauroid in that whole 


DiCroce, T. and K. Carpenter.  New Ornithopod from the Cedar Mountain Formation 
(Lower Cretaceous) of Eastern Utah. pgs. 183-196 of D. Tanke and K. Carpenter 
(eds.), Mesozoic Vertebrate Life, Indiana University Press: Bloomington (2001).
Kobayashi, Y. and Y. Azuma.  A New Iguanodontian (Dinosauria: Ornithopoda) from 
the Lower Cretaceous Kitadani Formation of Fukui Prefecture, Japan. Journal of 
Vertebrate Paleontology 23(1): 166-175, (2003).
Norman, D. On Asian Ornithopods (Dinosauria: Ornithischia). 4. Probactrosaurus 
Rozhdestvensky, 1966. Zoological Journal of the Linnean Society 136: 113-144, 
Wang, X. and X. Xu.  A new iguanodontid (Jinzhousaurus yangi gen. et sp. nov.) 
from the Yixian Formation of western Liaoning, China. Chinese Science Bulletin 
46(19): 1669-1672, (2001).

Nick Gardner
aim s/n Eoraptor22

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