D. M. S. Watson — llie Cheirotherium. , 397 



The few Cotylosaurian reptiles known from the European Trias 

 are all very small lizard-like animals, and as all known members of 

 this group have a very wide track they could not have been the 

 makers of the Cheirotherium footprints. The limbs of the remarkable 

 primitive Phvtosaurian from the Buiiter of Bernberg described by 

 Jaekel as PaltBorhimis are quite unknown, but there is every reason 

 for believing that they resembled those of the later form Ulystriosaurus, 

 which is shown by MacGregor's description of an American form, 

 and generally resemble those of modern crocodiles in proportions ; 

 these animals of course make a quite different type of track to 

 Cheirotherium. 



Other important Triassic groups are the Tortoises, which make an 

 extremely characteristic spoor, with the feet of opposite sides widely 

 separated, and each individual print very short from back to front, 

 with the impressions of cUiws standing clear of the sole. 



2. Hyperodapedon, the track of which must have been like that 

 of a heavily built lizard. 



3. The Lizards themselves, which make a sprawling track, are 

 of course quite out of the question. 



As Cheirotherium tracks are always found in terrestrial deposits, 

 and even in rocks which we have reason for believing were laid down 

 under arid conditions, it is unnecessary to discuss the marine groups 

 of the Ichthyosauria, Sauropterygia, and I'lacodontia. The only 

 remaining groups are the lightly built Thecodonts, of which Aetosaurun 

 and Oriiithosxichus are the best-known members, and the Dinosaurs. 

 These groups differ only slightly in structure, and it is almost certain 

 that the latter is derived from the former. The differences lie almost 

 entirely in the limbs. The fact that the proximal tarsals of the 

 Thecodonts are not rigidly articulated to the tibia and fibula suggests 

 that the whole foot was placed on tlie ground as in a lizard. The 

 whole structure of the liiud-leg suggests that it was carried in 

 a somewhat lizard-like manner with the femur at a considerable 

 angle with the body and the various sections of the leg considerably 

 flexed. This opinion is supported by the fact that the acetabulum 

 is imperforate, and also by the actual position of the legs in the type- 

 specimens of Aetosmirtcs, in which the animals still, to a large extent, 

 retain the form they had during life. 



There remain only the Dinosaurs, which in the known Triassic 

 forms seem to have been generally bipedal, ami resemble Cheirotherium 

 in having long heavy tails, so that the animal is balanced about the 

 pelvis, in the small size of their fore-legs, in the narrowness of the 

 pelvis, in the length of the leg, and in the narrowness of their track. 

 There can, in fact, be no doubt that Cheirotherium was a Dinosaur or 

 direct Dinosaur ancestor. 



It remains to compare the actual footprints with known 

 Dinosaurian feet. The excellent work of Lull on the American 

 tridactylous footprints from the Trias of Connecticut, which he has 

 successfully correlated with the lightly built carnivorous forms, such 

 as Anchisaurus, shows that we must look elsewhere for Cheirothertum. 

 The typical lightly impressed print of a Cheirotheroid pes has five 

 digits, of which the third is the longest and the fifth is turned 



