Dwarf quadruped dinosaurs

["Sebastian Apesteguia" <ninjasarg@hotmail.com>]

Small size and quadrupedal posture will be in perfect concordance if 
morphological constraints does not support other thing, beyond size.

There are a lot of structural constraints that would make a full grown 
Apatosaurus probably as quadrupedal as a juvenile of its own. Furthermore, 
those sauropod intra-generic structural constraints would make a dwarf 
Magyarosaurus as quadrupedal as a bulky Epachthosaurus.

However, some lineages, such as dwarf horse-sized saltasaurine titanosaurs 
(e.g. Neuquensaurus, Saltasaurus) have some poorly discussed specializations 
on the ilium, sacrum and limb proportions that would have make these guys 
facultative bipeds (see ?The Titanosaur metacarpus? in the forthcoming 
?Sauropodomorpha: The Thunder lizards?). But their partially biped 
possibilities have probably nothing to do with size (as demonstrated by 
quadruped dwarf ankylosaurians), but to morphological features proper of its 
lineage.

Dwarf saltasaurines were related to a Northern Patagonia Latest K island 
environment (Apesteguia, S. 2002. Greater Gondwana and the Kawas sea coastal 
tetrapod fauna, Campanian-Maastrichtian. Boletim do 6º Simpósio sobre o 
Cretáceo do Brasil / 2º Simposio sobre el Cretácico de América del Sur. Sao 
Pedro, Brasil: 143-147. AND Apesteguia, S. 2002. Successional structure in 
continental tetrapod faunas from Argentina along the Cretaceous. Boletim do 
6º Simpósio sobre o Cretáceo do Brasil / 2º Simposio sobre el Cretácico de 
América del Sur. Sao Pedro, Brasil: 135-141), a fact reinforced by the 
?Carnotaurus? genic drift (see VARGAS, A. 2002. La extrema reducción del 
radio y ulna en la evolución de ?Carnotaurus sastrei?: Posible pérdida de 
función de los genes Hoxa11 y Hoxd11. Ameghiniana 39: 17R).

The same kind of environment is probably related to the subsistence in 
Southern Gondwana  (Northern Patagonia and Antarctic Peninsula) of dwarf 
ankylosaurs and (if it is not an iguanodontian lower jaw!) small 
ceratopsians such as ?Notoceratops? and even dwarf carcharodontosaurids (see 
2004 Argentinian Meeting of Vertebrate Paleontology abstracts, or I?ll post 
the abstract after the meeting at my web site). Of course, dwarfs carchs are 
still bipeds!

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