THE MESEOSERE. 



415 



The similarity of the two periods as to the serai and climax dominants for 

 the areas controlled by cycads and gymnosperms during the Comanchean 

 may be seen by comparing the following list of genera with that already given 

 for the Jm'assic. It should be noted, however, that the species are almost 

 wholly different (Knowlton, 1910^:41, 43), and that angiosperms have 

 appeared in the Comanchean: 

 Pteridophyta: Dicksonia, Thyraopteris, Cladophlebis, Matonidimn, Gleichenia, Sagenop- 



teris, Taeniopteris, Angiopteridium, Oleandra, Ctenopteris, Equisetum. 

 Cycadales: Dioonites, Nilsonia, Pterophyllum, Ctenophyllum, Zamites, Cycadeospermum. 

 Coniferales: Cephalotaxopsis, Nageiopsia, Abietites, Pinus, Sequoia, Sphenolepidium. 

 Angiospermae: SaliciphyUum, Proteaephyllvim, Menispermites, Sapindopais, Acaciaephyl- 



lum. 



Succession during the Comanchean is marked by an outstanding event, such 

 as has occurred during no other geological period. This was the evolution 

 of an angiospermous flora, followed by its migration and assumption of domi- 

 nance in all parts of the earth. In this respect, the Comanchean differs from 

 all other periods, though the evolution and migration of the Glossopteris flora 

 during the Permian are somewhat comparable. The general serai development 

 during the Comanchean must have resembled that of the Jurassic, and this 

 must have been equally true of the cosere and clisere, though the latter was 

 perhaps less marked. But the origin of a new group of dominants along the 

 Atlantic coast, and their rapid spread to the westward by which they reached 

 the Pacific by the close of the period seems to introduce a new factor in the 

 development of vegetation. This may be more apparent than real, since it is 

 not improbable that the development of angiosperms began at least as early 

 as the Jurassic. As already suggested, the assumption of dominance by gym- 

 nosperms during the Mesophj^tic era may have been due to a period of inter- 

 mediate conditions, in which the appearance of angiosperms was as natural 

 a consequence as the disappearance of the pteroid dominants. 



The cvurent opinion as to the origin and spread of angiosperms is embodied 

 in the following extract from Chamberlin and Salisbiuy (1906: 3: 133) : 



"The view that seems best justified at the present stage of evidence is that 

 the angiosperms developed in the old lands of the eastern part of North 

 America, and that until the close of the Lower Cretaceous [Comanchean] they 

 had only spread westward as far as Kansas and the Black Hills, northward 

 as far as Greenland and eastward to the coast of Portugal, but not to Europe 

 generally, nor to the western part of North America, for they do not appear in 

 the Kootenay or Shastan series. As the northeastern part of North America 

 had long been land, and has left no record of plant life, there is nothing to 

 indicate how much earUer angiosperms may have begun their evolution there. 

 The Jurassic beds of the western part of the continent and of Europe give 

 negative evidence as to a dispersion earlier than the Cretaceous period. 



"In the most typical region on the Atlantic coast nearly half the known 800 

 species of Comanchean age are angiosperms. They began in marked minority 

 in the lowest Potomac and increased to an overwhelming majority in the upper- 

 most beds. The earliest forms are ancestral, but not really primitive, and 

 throw httle Ught on the derivation of the angiosperms. WMle some are 

 undifferentiated, the majority show definite resemblances to modern genera, 

 and some (as Sassafras, Ficus, Myrica, and Aralia) , are referred to living genera, 

 while others are given generic names implying the similarity of the fossil leaves 

 to those of Uving plants (as Saliciphyllum, \^ow-like leaves, Qiiercophyllum, 



