142 THE PERMO-CARBONIFEROUS RED BEDS OF 



The strong limbs, with longer foreleg than upper leg, and the strong feet, 

 with powerful claws, are ample evidence of an ability to run with some speed 

 and perhaps even leap or pounce upon prey. Abel, in his Paleobiologie, 

 points out that running and leaping animals have the foreleg longer than the 

 upper leg, and creeping animals have the proportions reversed. It is not 

 probable that Dimetrodon was ever capable of leaping any distance, but it 

 certainly was able to move swiftly for a short space. Probably it lay hidden 

 in the vegetation, and made short, scuttling rushes upon its prey, ending, 

 possibly, with a short pounce, which permitted its weight to add something 

 to the vigor of the attack by tooth and claw. 



Several efforts have been made to restore Dimetrodon , but it has always 

 been difficult to make an illustration of the dorsal crest which appears at all 

 probable. That it was a thin, high fin, with the elongate spinous processes 

 united by a thin membrane of skin, I have little doubt. Abel and Jaekel are 

 disposed to think that the spines were covered by a skin, but not connected. 

 To the author this seems highly improbable. Aside from the possible evi- 

 dence furnished by the condition of Chamcleo crista tiis,'' there is little possi- 

 bility that such weak structures could long survive serious breakages without 

 the support of mutual connection. 



The elongate spines were useless, so far as I can imagine, and I have been 

 puzzling over them for several years. The probable cause of their great 

 development is discussed upon a preceding page. It is impossible to conceive 

 of them as useful either for defense or concealment, or in any other way than 

 as a great burden to the creatures that bore them. They must have been a 

 nuisance in getting through the vegetation, and a great drain upon the crea- 

 ture's vitality, both to develop them and to keep them in repair. The genus 

 succeeded despite of them, or perished because of them. 



The presence of several species and large numbers of individuals indicates 

 that the genus was for a time at least successful, but this success probably 

 resulted from a dominance attained before the dorsal fins reached their full 

 size; from then on the spines became a burden and a possible cause of decline, 

 as suggested above. 



The most common species, D. iiicisivus, reached about 2 meters in length. 

 No specimen has as yet been found with a complete tail, but the rapid decrease 

 in size of the caudal vertebra suggests only a moderate length. D. gigas, 

 the largest known form, must have reached a length of at least 3 meters, 

 and, probably, single individuals were even longer. 



Edaphosauria. 



Edaphosaurus (fig. 29). — No single animal of the Permo-Carboniferous 

 fauna has been so much discussed or so greatly misinterpreted as this one. 

 Because of the possession of elevated dorsal spines the skeleton was very 

 naturally placed close to Dimetrodon, and it was restored with limbs, skull, 



* Case, Science, vol. xxix, p. 979, 1909. 



