;^|lard — 105 — Length of Day in the Past 



The Cretaceous Flora : — Several hypotheses have been offered to 

 explain the origins of our modern flora based upon the serious thought 

 and patient investigations of various workers in many fields, including 

 Geology and Paleobotany, Anatomy, Comparative Morphology, Ontogeny, 

 Phylogeny and Phytogeography. 



A great wealth of published material has been contributed by many 

 students to the subject of the evolution of the Angiosperms, and the sup- 

 posed origin of the great herbaceous group. Some of the most readable 

 expositions among these discussions have been contributed by Sinnott and 

 Bailey (1914), Berry (1914 to 1924), Bews (1916 to 1927) and many 

 others, and the papers of these able workers in this field deserve special 

 mention for their lucid and logical presentations. 



The Cretaceous Period in the geological time scale is of the greatest 

 interest to the paleobotanist, since it has afforded some of the most con- 

 vincing evidence of the status of the ancient flora which preceded the great 

 Tertiary transformations in plant life over all the earth. While all fossil 

 evidence is fragmentary, nevertheless it must always hold an important place 

 in all our concepts of evolution, and is rightly regarded one of the most 

 direct sources of our evolutionary information. 



The first recognizable remains of the flowering plants or Angiosperms 

 have been found in the Cretaceous rocks. The appearance of these plants 

 represents a biological event of first importance, culminating millions of 

 years of struggle and evolution of this great phylum of life with all manner 

 of crustal oscillations and climatic shiftings on sea and land. Plant life 

 was abundant in other forms everywhere, and had maintained itself through 

 eons of geological time preceding the Cretaceous Period but the flowering 

 plants, it is conceded, were presumably very rare in the flora until the lower 

 Cretaceous Period set in. There was then, seemingly, a very rapid evolu- 

 tion into the Angiospermous types over much of the world. While it is 

 assumed that none of the modern species of plants had made their appear- 

 ance in the Cretaceous Period, many of the recognized familiar genera of 

 the present-day types had appeared, among these being Acer, Platanus, 

 Magnolia, Quercus, Juglans, Sassafras, Salix, and many others. While the 

 botanist sometimes speaks of these as simpler and more generalized types, 

 they were probably merely different species in an early phylum called into 

 expression and preserved by increased variations of the edaphic and climatic 

 habitat. 



All evidence that philosophical botanists have emphasized in forming 

 their concepts of the evolution of plant life tends to favor the assumption 

 that the early Angiospermous types were predominantly woody forms. The 

 evidence for this concept is based in part upon the fossil material which 

 is mainly of woody forms, and in part upon the observed present-day pre- 

 dominance of the woody life-forms in the tropical and subtropical regions 

 of the earth. Large reptiles and subtropical plants appeared to have thrived 

 in high latitudes in Cretaceous times, indicating mild or even subtropical 

 temperatures over all the earth during this period. Because woody forms 

 of plant life appear to have constituted the dominant life-form everywhere 

 over a warm earth, as they do today in tropical and subtropical areas, this 

 may be one of the reasons why the woody forms have been so extensively 

 fossilized in the Cretaceous deposits. 



