NO. 2120. THE FORE LIMB OF ALLOSAURUS FRAGILIS—OILMORE. 513 



The more important progressive changes that have taken place in 

 the speciahzation of the fore Hmb and foot in the carnivorous dino- 

 sauria during successive geological periods now appear to be, (1) a 

 reduction in the number of digits ; (2) the elongation of the penulti- 

 mate phalanges; (3) a lengthening of the scapula; (4) the shortening 

 of the fore arm; (5) a relative reduction in size of the entire fore limb. 



With the exception of Ceratosaurus, which has both inner and outer 

 fingers reduced, all of the other known carnivores show that the 

 reduction in the number of digits takes place on the outside of the 

 foot. Beginning with the oldest known Theropods from the Triassic, 

 all are found to possess the full complement of five digits, though the 

 fifth is often rudimentary. In the Jurassic we find in Ornitholestes 

 that the fifth digit lias entirely disappeared, and the fourth is only 

 represented by a vestigal metacarpal. Allosaurus appears to have 

 gone still further and apparently the fourth has been lost and the 

 third is somewhat reduced, and approximately the same condition 

 obtains in the hand of Comsognaihus from the Upper Jurassic of 

 Bavaria. 



Our knowledge of the manus in the Cretaceous Theropodous dino- 

 saurs is rather meager at this time, but a specimen recently described 

 by Lambe ^ {Gorgosaurus libratus) from the Upper Cretaceous (Belly 

 River) shows a still further reduction, there being only two functional 

 digits, the third (fourth of Lambe) being represented by the vestigal 

 metacarpal only. 



1 Ottawa Naturalist, vol. 28, 1914, pp. 13-17. 

 81022°— Proc.N.M.vol.49— 15 33 



