Cursoriality in bipedal archosaurs

Modern birds have markedly foreshortened tails and their body mass is centred anteriorly, near the wings. To provide stability during powered flight, the avian centre of mass is far from the pelvis, which poses potential balance problems for cursorial birds. To compensate, avians adapted to running maintain the femur subhorizontally, with its distal end situated anteriorly, close to the animal's centre of mass; stride generation stems largely from parasagittal rotation of the lower leg about the knee joint. In contrast, bipedal dinosaurs had a centre of mass near the hip joint and rotated the entire hindlimb during stride generation. Here we show that these contrasting styles of cursoriality are tightly linked to longer relative total hindlimb length in cursorial birds than in bipedal dinosaurs. Surprisingly, Caudipteryx, described as a theropod dinosaur, possessed an anterior centre of mass and hindlimb proportions resembling those of cursorial birds. Accordingly, Caudipteryx probably used a running mechanism more similar to that of modern cursorial birds than to that of all other bipedal dinosaurs. These observations provide valuable clues about cursoriality in Caudipteryx, but may also have implications for interpreting the locomotory status of its ancestors.     

Linkage of the Indiana kindred of Gerstmann-Str?ussler-Scheinker disease to the prion protein gene.

The Indiana kindred variant of Gerstmann-Str?ussler-Scheinker disease has amyloid plaques that contain prion protein (PrP), but is atypical because neurofibrillary tangles like those of Alzheimer disease are present. To map the position of the disease causing gene, we used three markers for linkage analyses. A missense mutation at codon 198 of the PrP gene (PRNP) is found in all definitely affected individuals and yields a maximum lod score of 6.37 (theta = 0). The disease also is concordant with the two other PRNP-region markers. These results demonstrate tight linkage of the disease-causing gene to PRNP and support the hypothesis that the codon 198 mutation is the cause of IK-GSS. Our studies also suggest that methionine/valine heterozygotes at PRNP codon 129 have a later age of onset of the disease than codon 129 valine/valine homozygotes.     

Mutant prion proteins in Gerstmann-Str?ussler-Scheinker disease with neurofibrillary tangles.

Two families with Gerstmann-Str?ussler-Scheinker disease (GSS) are atypical in possessing neocortical neurofibrillary tangles (NFTs), which are few or absent in other kindreds with GSS, in addition to amyloid plaques that react with prion protein (PrP) antibodies and protease-resistant PrP accumulation in the brain. A leucine substitution at PrP codon 102 has been genetically linked to GSS in some families. We examined the PrP gene in these families. A serine for phenylalanine substitution was found at codon 198 in the Indiana patients; arginine for glutamine substitution at codon 217 in the Swedish patients. These mutations in PrP are the first to be associated with the appearance of both PrP amyloid plaques and neocortical NFTs in GSS patients.