16 



TITANOTHEEES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



of his "Systema naturae" (1735-1768), did not 

 dream of the succession of species of mammals in 

 time; he did not know of a single phylum, much less 

 of polyphyla. Darwin's theory of descent and 

 divergence implied the existence of phyla, but when 

 he published "The origin of species" (1859.2) he also 

 did not ls;now of a single phylum or a single direct line 

 of descent. Waagen (1869.1) was the first to dis- 



tively rapid gain or loss of certain characters. This 

 definition relates to the hard parts, which are pre- 

 served in fossUization; the principle applies equally 

 to characters of all kinds. 



In contemporaneous Linnaean genera and species 

 we observe differences of many kinds, such as differ- 

 ences in color and proportion, and, more rarely, we 

 may note the presence or absence of simple characters 



A Contemporojieous LiruzcbeoJi Syste/n Zoology 



X 



c 



' Su2).\Fam..l 





JFAM I LY 



_A ^^ 



Sub. Fam,. 2 



)T 



"^ 





. Spec. 



Spec./ 



\ I -^^f^^^ /'^Si^.Fa.nv.4^ 



.' , I ' Gerv. Gerv) 



;■"■•• J \ ^ ^ ^ 



Spec./ \ y V -^ 



\ 



RECENT EXISTING PERIOD ^ --^ ' 



B Geologic /. Phylogenetlc SystejTh Ihleontolo^y 



/ ^^ ^ /T? 



/ — ~~-^'^^, \ \\ 



/ 



LOWER/ 

 0LI60CENE ,^ / 





/A 



\ 



/! \ 



1 ^ 



\ 



UPPER^ , 

 EOCENE \ 



\ >^j 

 \ 



MIDDLE EOCEP _ 



\ 



\ 



\ 



^ jA V-.^\\ V:. V" ^ \\ \\ i i ,, I \\ I y'l 



EARLY EOCENE 



\ 



/ 



Figure 14. — Contrast between the Linnaean and phylogenetic systems of classification of sub- 

 families, genera, and species 



cover a continuous phylum (namely, of ammonites) — 

 that is, successive hereditary stages, which he named 

 "mutations." Many direct phyla of invertebrate 

 animals have since been made known. 



In this monograph we first learn the full meaning of 

 a mammalian phylum — namely, a phylum is a con- 

 tinuous geologic line of descent diverging from other 

 phyla (1) in the gradual transformation of every 

 character in size and proportion and (2) in the rela- 



of teeth, vertebrae, or claws. The "species" of Lin- 

 naeus are now known to be actually superspecies and 

 to include one or more modern species, subspecies, and 

 geographic races and varieties, distinguished by differ- 

 ences in coloring, habit, proportion, or otherwise. 

 These differences are due in part to environment and 

 in part to habit. They represent the different bodily 

 effects produced on animals of similar ancestral stock 

 under different environments, in which somatic changes 



