loS THE rERMO-CARBONIFEROUS RED BEDS OF 



hooked claws, which in Dimetrodon became talon-hkc in size and form. The 

 elongate dorsal spines are now known to be exaggerated strvictures, and have 

 no great significance as adaptations. The animals were evidently highly pre- 

 daceous, able to rise from their normally prone position and develop con- 

 siderable speed for a short time, as they dashed upon their prey or attempted 

 to escape from some aggressive individual of their own kind. Dimetrodon 

 was evidently a ptirely terrestrial type, but the poorer articulations of the 

 limb bones of Clepsydrops, with its longer tail, have led to the contention that 

 it was more aquatic. However, these are not determinate characters. 



Arcocdis is characterized by the extreme length and slenderness of the 

 limb bones, the length of the feet, and the slender cervical vertebrae. These 

 are features which are always associated with the power of swift motion and 

 agility in leaping and climbing. Areoscelis undoubtedly equaled in speed and 

 agility almost any living form of similar kind. It was an arboreal, active 

 creature of great lightness and speed. 



The group Cotylosauriu is characterized as a whole Vjy the extreme short- 

 ness of the neck, the generally heavy and short body, the firm union of the 

 dorsal vertebrae, the powerful shoulder girdle, and the short and heavy limbs 

 and feet. In life the animals were heavy-bodied, large-headed, short-tailed 

 creatures, moving their bulky limbs in a slow, turtle-like manner, and 

 depending for protection upon an incipient armor or their tough skin. The 

 group contains many diverse forms, ranging from the molluscivorous Dia- 

 dcctes to the predaceous Limnoscelis. 



Diadectes. — The broad and powerful humeri of this form, with strong 

 processes for muscular attachment, suggest a fossorial animal. This idea is 

 supported by the shortness and strength of the lower limb bones and the 

 shape of the broad, powerful feet, with short phalanges and nail-like claws. 

 The broad, depressed body, the heavy shoulder girdle, the large orbits, and 

 the enormous pineal foramen are all characters which would go well with 

 fossorial habits. Williston has drawn attention to the fact, however, that 

 the fore-limbs in Diadectes, Diasparactas, etc., were too short to reach in 

 front of the nose to an efficient extent, and pertinently queries how such an 

 animal could dig a hole, as does a badger or a mole. It is not impossible, 

 however, to conceive that these animals excavated shallow burrows, and it 

 is altogether probable that the powerful limbs and feet were used in upturning 

 the earth, tearing apart vegetation, or displacing rocks in search of their food. 

 Abel has drawn attention to the similarity in the form of the humerus in 

 many swimming and fossorial forms, but there seems little likelihood that 

 Diadectes was aquatic in habit. 



The large eyes, and the apparently fully functional pineal eye, may be 

 indications of a crepuscular habit. The incipient armor of plates over the 

 anterior thoracic ribs, and the considerable probability that there was a 

 median row of dermal ossicles, show that the animal was subject to attack 

 from some predaceous creatures, probably the large Diinetrodons. 



