KEPTILE RECONSTRUCTION- — GILMORE. 279 



be gleaned from the fact that 18 months of steady labor of one man 

 was devoted to this specimen from the time it was received at the 

 museum until ready for exhibition to the public. The pose adopted 

 is one suggested by a careful study of living lizards, and is an atti- 

 tude often assumed by those land forms of the present day when 

 slightly irritated — that is, with the front of the body raised from 

 the ground, the rear portion lowered with hind legs spread out, 

 head raised, with jaws open, showing the rows of strong, slightly re- 

 curved teeth, as if angrily defying some one who had suddenly 

 blocked his path. 



Aside from the large head and strong short limbs, the most 

 striking feature of Bimetrodon is the high dorsal fin along the back, 

 formed by the lengthening of the neural spines of the vertebrae. 

 These range in length from 6 inches on the neck to over 3^ feet above 

 the center of the back, where they reach their maximum develop- 

 ment, becoming successively shorter as the tail is approached. That 

 in life these tall spinous processes were united by a thin membrane 

 of scaled skin there is little doubt. The foreign savants, Professors 

 Abel and Jaekel, are disposed to think the spines were covered by 

 skin, but not connected, but this seems highly improbable. 



The one living lizard which appears to throw some light on the so- 

 lution of this problem, and which is very remotely related to Dime- 

 trodon is Basiliscus plumifrons from tropical America. The crest on 

 the back shown in the inset in plate 6, though not so high or extensive 

 as in Dimetrodon, is nevertheless supported by the elongated spinous 

 processes of the vertebrae and these bear a striking resemblance to the 

 crest of the extinct form. In general appearance all of the basilisks, 

 of which there are several species, suggest the idea of lizards upon 

 whose backs has been grafted a fish's fin, and it seems that in this 

 animal we have the best suggestion of the probable appearance in life 

 of the Bimetrodon fin or crest along the back. 



In trying to account for some practical use for this unusual ap- 

 pendage it has been suggested that it may have resembled some of the 

 ancient vegetation and thus served to conceal the animal as it lay in 

 wait for its prey or for better concealment from its enemies. Pro- 

 fessor Case, the acknowledged authority on the Permian reptiles, says 

 of these : 



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

 puzzling over them for several years. 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 creature's vitality, 

 both to develop them and to keep them in repair. The genus succeeded despite 

 of them, or perished because of them. 



