278 



HISTORICAL GEOLOGY 

 TABULAR SUMMARY OF MESOZOIC LIFE 





Plants 



Protozoans 



Porifers and 

 Caelenterates 



Echinoderms 



Cretaceous 



Cryptogams and 

 Gymnosperms: 

 Much like earlier 

 Mesozoic. 



Angiosperms : Mono- 

 cotyledons and Di- 

 cotyledons attain 

 supremacy among 

 plants. 



Foraminifers 

 and Radiolari- 

 ans: Profuse. 



Sponges and Corals: 

 Abundant and 

 much like those of 

 the Jurassic. 



Crinoids : Greatly 

 reduced. 



Asterozoans : Pres- 

 ent. 



Echinoids: Both 

 regular and irregu- 

 lar forms common. 



Jurassic 



Cryptogams: Much 

 like Triassic. 



Gymnosperms : Cy- 

 cads culminate; 

 Conifers more mod- 

 ern in aspect. 



Angiosperms : 

 Monocotyledons? 



Foraminifers 

 and 



Radiolarians: 

 Very abundant 

 and highly di- 

 versified. 



Sponges: Very 

 abundant. 



Corals: Abundant 

 and all are Hexa- 

 coralla of modern 

 appearance. 



Crinoids: Very pro- 

 fuse and notabty 

 large. 



Asterozoans: Pres- 

 ent and of modern 

 appearance. 



Echinoids: Abun- 

 dant, with first ir- 

 regular, more mod- 

 ern forms. 



Triassic 



Thallophytes. 



Bryophytes. 



Pteridophytes: Ly- 

 copods almost ex- 

 tinct; Ferns and 

 Equisetse common. 



Gymnosperms : Cor- 

 daites become ex- 

 tinct; Cycads and 

 Conifers prominent. 



Foraminifers 



and 

 Radiolarians: 

 Present. 



Sponges: Present. 



Corals: Very abun- 

 dant, especially the 

 more modern Hexa- 

 coralla ; ancient 

 Tetracoralla be- 

 come extinct. 



Crinoids: Common. 



Asterozoans: 

 Present. 



Echinoids: Common 

 and all are regular 

 forms of ancient as- 

 pect. 



In early Mesozoic time arid climate conditions must have pre- 

 vailed over the western interior of the United States, as shown by 

 the Red Beds with some salt and gypsum. 



There is no good evidence of glaciation in the Mesozoic. 



Organic History 



"The life of the Mesozoic constitutes a very distinctly marked 

 assemblage of types, differing both from their predecessors of the 

 Paleozoic and their successors of the Cenozoic. In the course of 

 the era the plants and marine invertebrates remain throughout the 

 era very different from later ones. Even in the Vertebrates, how- 

 ever, the beginning of the newer order of things ma} r be traced." 1 

 1 W. B. Scott: Introduction to Geology, 2nd ed., p. 655. 



