Limb proportions and avian terrestrial locomotion

• Published in: Journal für Ornithologie 2002-07, Vol.143 (3), p.356-371
• Main Authors: Christiansen, Per, Bonde, Niels
• Format: Article
• Language: English
• Subjects: Body size; Diaphysis; Feathers; Femur; Kinematics; Limbs; Locomotion; Phylogenetics; Phylogeny; Posture
• ISSN: 0021-8375; 2193-7192; 1439-0361; 2193-7206
• DOI: 10.1007/BF02465486

SummaryPhylogenetic systematics unanimously concludes that birds (Archaeopteryx + crownclade Aves) are a subgroup of the theropod dinosaurs. The discovery of non-avian theropods from China with large pennaceous feathers offers additional support to this relationship and implies further that feathers cannot be used to define birds, as is traditionally advocated. A recent paper proposed that the feathered oviraptorosaurCaudipteryx was in fact a secondarily flightless bird. This was indicated by the anteriorly placed centre of gravity and the subsequent horizontal femoral posture and associated elongation of the lower leg compared to the trunk. A horizontal femoral posture was not present in non-avian theropods and is associated with profound proportional changes, particularly a thicker diameter to resist the increases in bending and torsional moments about the diaphysis. However, double graphic integration analysis of a more accurate model shows that the centre of gravity inCaudipteryx is situated no further anteriorly than in other non-avian theropods. The long limbs ofCaudipteryx are not surprising as limb length is related to phylogeny and body size. Primitive non-avian theropods have proportionally shorter limbs at any given size than more advanced forms, and small species have proportionally longer limbs than large species, as in extant mammals. Other theropods are known with proportionally very long limbs. The femoral morphology ofCaudipteryx is identical to those of other nonavian theropods, strongly arguing against avian limb kinematics. It is methodologically flawed to substitute functionally inferred characters for phylogenetic analyses.