24 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



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the centrale. None appears in the specimen directly beneath the centrale. Below 

 the radiale is an uncertain fragment which appears to be the proximal end of the 

 metacarpal with a first phalange attached to its lower end. On the inner side of 

 the proximal end of this fragment is a small nodule which is apparently carpale I. 

 The distal portion of the foot was very broad and strong, with heavy, short 

 phalanges. As neither of the fore feet is complete, it is impossible to give the 

 phalangeal formula, but it is very probable that it was the usual reptilian number, 

 2. 3. 4i Si 3- The metacarpals have very broad proximal and distal extremities, 

 which narrow rapidly to a shaft not over half so wide as the ends. Viewed from the 

 sides the extremities are wider than the shaft, but the difference is not nearly so 

 great as in the horizontal view. The articular surfaces are flat. The phalanges 

 are broad, short, and thin, with only a slight constriction of the sides to indicate a 



shaft. The articulations are better formed than 

 in the metacarpals, as there are well-modeled 

 concave and convex surfaces indicating a consid- 

 erable freedom of motion. The shape of the ar- 

 ticulations between the phalanges indicates the 

 possibility of closing the hand, but also a con- 

 siderable resistance to any bending back of the 

 digits. The terminal phalanges are broad and 

 oval; the proximal articulation with the adjacent 

 phalange was close. The edges of the bone are 

 thin, but there is a distinct thickening on the 

 under side near the distal end and a distinct con- 

 cavity of the lateral edges, indicating the attach- 

 ment of a strong flattened claw or nail-like claw. 

 The interpretation of this type of limbs and 

 feet, so characteristic of some of the contemporary 

 amphibians and most of the contemporary coty- 

 losaurs, with the exception of the Captorhinidae, 

 has been in dispute. Abel accepts them as fosso- 

 rial. Matthew, in a review of Abel's Paleobiologie 

 (Science, March i, 191 2), expresses the opinion 

 that the animals were aquatic in habit. From 

 this conclusion we must enter our dissent. There is not a character shown in the 

 Limnoscelidae, Diadectidae, or Seymouriidae that could lend support to this hypothesis 

 unless it be the imperfect ossification of the mesopodium. The structure of the 

 body throughout is heavy; the tail is short and without propelling power, as indi- 

 cated by the short spines and chevrons. The fingers are short and stumpy, with 

 well-articulated phalanges and with the terminal ones clean-cut and provided with 

 heavy nails or blunt claws, all of which would be out of place if their main func- 

 tion was the support of a swimming web. In most, if not all, aquatic reptiles and 

 amphibians the foot is elongate with shapeless phalanges, not well articulated. 

 Furthermore, it is quite certain from the natural articulations that the elbow was 

 normally bent at an angle and it is very doubtful whether the fore-arm would 

 have been extended fully in line with the humerus. Nor can we now believe, in 

 opposition to views previously expressed by Case, that these animals were essen- 

 tially fossorial in habit, since the short, though powerful, legs (in some forms at 

 least) were not long enough to extend the hands in front of the head. It seems 

 more probable that these animals; as well as the Eryopidae, were marsh-dwelling 

 creatures, doubtless living among the rank vegetation in the vicinity of water. 



Fig. 12. — Diasparactus zenos Case. Res- 

 toration of right front foot. X yi. 



