352 C. E. Beecher — Origin and Significance of Spines. 



only two simple types continued on into the Mesozoic, while 

 but one declining representative is living at the present time. 



Among the Ammonites, the chief spiny forms are those 

 occurring just before the final extinction of the group and 

 representing the beginning of the decline of the order (Crio- 

 ceras, Toxoceras, Ancyloceras, Ilamites, etc.). In the Dino- 

 saurian Reptiles, the great horned forms, Triceratops, Toro- 

 saurus™ etc., mark the extinction of the entire order. The 

 great horned mammals of the Eocene, the Dinocerata, have 

 left no descendants, and the giant Brontotheridae, after under- 

 going various horn modifications through the Miocene, con- 

 tinued no further. 



It is not desirable, however, to convey the impression that 

 the spines or horns are alone responsible for this wholesale 

 extinction. It has been shown that they are undoubtedly 

 often an expression of extreme specialization, and generally 

 they represent the limits to which superficial structures may 

 be differentiated. Although there may be other expressions 

 for similar conditions, yet the presence of spines is one, if not 

 the most evident, marker of the attainment of these limits. 

 The presence of a spine on an organ or part indicates the 

 limit of progression or regression of that part or organ. If 

 the spinose condition is general, or if it dominates important 

 functions, it then indicates the limit of progression and regres- 

 sion of the organism. 



Spinosity the Par acme of Vitality. 



The physiological interpretation of spinosity is a correlative 

 of the morphological aspect of the same condition, and, as it 

 was found that spinosity was a limit to morphological progress 

 or regress, it will now be shown that it also indicates the par- 

 acme or decline of physiological progress. Both inferences 

 are drawn from the individual or ontogenetic standpoint, as 

 well as from the racial or phylogenetic. 



In the spinose individual, the decline of vitality has been 

 studied by Geddes 20 in thorny plants. He concludes that they 

 show a "gradual death from point backwards (i. e. ebbing 

 vitality)" The requisite evidence is afforded in the experience 

 of gardeners who generally consider spiny plants as " always 

 given to die back," or as otherwise expressed, they " often 

 prune themselves." It is difficult to adduce the same kind 

 of evidence among animals, though there may be some degree 

 of semblance between this self-pruning of spiniferous plants 

 and the growth, death, and shedding of the antlers of the 

 modern Deer. Stronger evidence of the relations of spinosity 

 to the organism is afforded in the consideration of spines as 



