64 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 

 Phalangial formulae of various Theropod dinosaurs. 



The more important progressive changes that have taken place in the 

 specialization of the fore limb and foot in the carnivorous dinosauria during 

 successive geological periods appears to be: (1) Eeduction in the number of digits, 

 (2) elongation of the penultimate phalanges, (3) lengthening of the scapula, 

 (4) shortening of the forearm, (5) relative reduction in size of the entire fore limb. 



With the exception of Ceratosaurus vrhich has both inner and outer fingers 

 reouced, 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 has entirely disappeared, and the fourth is only represented by a 

 vestigal metacarpal. Antrodemus appears to have gone still farther, iand apparently 

 the fourth has been lost and the third is somewhat reduced, and appro.ximately 

 the same condition obtains in the hand of CmnpsognatTius from the Upper Jurassic 

 of Bavaria. 



Our knowledge of the manus in the Cretaceous Theropodous dinosaurs is rather 

 meager at this time, but a specimen recently described by Lambe' (Gorgosaurus 

 libratus) from Upper Cretaceous (Belly Kiver) shows a still further reduction, there 

 being only two functional digits, the third being represented by the vestigal metacar- 

 pal onl}'. 



' Ottawa NaturalLst, toI. 28, 1914, pp. 13-17; Memoir 100, Geol. Surv. Canada, 1917, pp. 52-57, figs. 33-36. 



