68 



UNITED STATES NATIONAL MUSEUM BULLETIN 215 



(d'Orbigny) , G. truncatulinoides (d'Orbigny) (Bolli, 

 1950 ; Ericson, G. Wollin and J. Wollin, 1954) . Changes 

 in the environment probably cause such sudden changes. 



The coiling of a few Lizard Springs Globorotalia 

 species has already been discussed in an earlier paper 

 (BoJli, 1950). Coiling ratios for several Globigerina and 

 Globorotalia species and groups of related species have 

 again been followed through the now better known 

 sections of the Lizard Springs formation. The basic 

 pictiu-e has changed little. The coiling ratios for a 

 hypothetical lowermost Lizard Springs given in the 

 earlier paper have now been observed. The probable 

 relation between Globorotalia aequa Cushman and Renz 

 and G. aragonensis NuttaU (via G. rex Martin) was not 

 realized at the time and G. wilcoxensis var. acuta 

 Toulmin is now regarded as a synonym of G. velascoensis 

 (Cushman). 



Some of the more significant results are briefly 

 discussed in the following paragraphs and shown on 

 text-figure 13. 



A genetic relationship between Globorotalia trinida- 

 densis BoUi, new species, G. pseudobulloides (Plummer), 

 G. uneinata Bolli, new species, G. angulata (White), 

 G. aequa Cushman and Renz, G. rex Martin, G. ara- 

 gonensis Nuttall, G. formosa gracilis Bolli, new species, 

 new subspecies and, G. formosa formosa BoUi, new 

 species, new subspecies, has been discussed in the 

 previous section. When following the coiling ratios of 

 these species we find that the stratigraphically older 

 forms {G. trinidadensis to G. angulata) coil at random, 

 thus representing the early evolutionary stage. With 

 the transition of G. angulata to G. aegua, a very rapid 

 change to an almost exclusively dextral coiling takes 

 place. This preference is maintained to the point of 

 extinction of the species at the top of the Globorotalia 

 rex zone. G. rex and G. formosa gracilis which apparently 

 branch off from the G. aegua gi'oup at the base of 

 Globorotalia rex zone maintain the same trend. G. 

 aragonensis and G. formosa formosa which are assumed 

 to develop from G. rex and G. formosa gracilis, respec- 

 tively, higher in the same zone, rapidly switch to 

 sinistral coUing. The change is more rapid in G. 

 aragonensis which becomes about 90 percent sinistral 

 in the Globorotalia aragonensis zone. The same trend is 

 maintained by this species until its extinction in the 

 Navet formation. Of G. formosa formosa, 64 percent 

 were found to coU sinistraUy before the extinction of 

 the species towards the top of the Globorotalia ara- 

 gonensis zone. A sample from the probable upper 

 part of the Globorotalia formosa formosa zone showed 

 10 percent of G. formosa formosa and 44 percent of 

 G. aragonensis coiling sinistraUy. Counts of another 

 sample presumably from lower in the G. formosa 

 formosa zone showed an almost exclusive dextral coiling 

 for both G. formosa formosa and G. aragonensis. 



Globorotalia compressa (Plummer), G. ehrenbergi 

 Bolli, new species, G. pseudomenardii BoUi, new species, 

 and G. elongata Glaessner represent another evolution- 

 ary sequence. AU investigated samples showed the 

 species coiling at random, with the exception of the 

 topmost sample in the Globorotalia pseudomenardii zone. 



There, apparently shortly before its extinction, 80 to 

 85 percent of the specimens of the zonal marker were 

 found to coU sinistraUy. G. elongata maintains random 

 coUing throughout its range. 



Globorotalia velascoensis (Cushman) has a strong 

 preference for sinistral coiling throughout most of its 

 range. Only in its very early stages does the species 

 coil at random. The very rapid change from random 

 to sinistral coUing in G. velascoensis occurs concurrently 

 with that of the G. angulata-G. aegua group to dextral 

 coUing. These changes take place within a short 

 interval in the section studied, probably within less 

 than 100 feet. From this it may be assumed that 

 either the change to a strongly preferred direction of 

 coUing took place within a short time interval or the 

 abrupt change might indicate a hiatus. 



Throughout the upper Lizard Springs Globorotalia 

 broedermanni Cushman and Bermudez is found to coil 

 almost exclusively sinistraUy. No random-coUing an- 

 cestral forms indicating an earlier evolutionary stage 

 of this species were seen in the lower Lizard Springs. 

 This suggests the presence of a hiatus between lower 

 and upper Lizard Springs. The ancestral forms of 

 6. broedermanni and G. wilcoxensis-G. guetra would be 

 expected to occm- in the missing beds. 



Globorotalia wilcoxensis Cushman and Ponton and 

 G. quetra BoUi, new species, which probably developed 

 from G. whitei Weiss were found to have a strong 

 preference for dextral coUing throughout their distri- 

 bution in the upper Lizard Springs. 



The above results on coUing ratios are based on 

 approximately 25 samples, the majority of them 

 coming from one section (Trinidad Leaseholds, Ltd., 

 Guayaguayare weU 159). For this tj^e of investi- 

 gation it would be desirable to have a greater number 

 of samples avaUable from well established stratigraphic 

 sequences. The results obtained from the rather 

 limited sources are however regarded as conclusive to 

 warrant the presentation of the tentative picture that 

 is discussed above and shown on text-figure 13. 



Acknowledgments 



The writer is indebted to The Trinidad OU Company 

 for permission to publish this paper and to use the 

 Company's laboratory and drafting facUities at Pointe- 

 a-Pierre. Trinidad Petroleum Development, Ltd., 

 kindly gave permission to make use of some of their 

 well sections. 



The writer wishes to thank Dr. H. G. Kugler, Con- 

 siUting Geologist to Central Mining Investment Cor- 

 poration and Mr. J. B. Saunders, Paleontologist of The 

 Trinidad OU Company, for reading and discussing the 

 manuscript. Thanks are due to Dr. A. R. Loeblich, Jr., 

 of the U. S. National Museum and to Mrs. Helen 

 Tappan LoebUch, Research Associate, Smithsonian 

 Institution, for their help extended in the completion 

 of the paper. 



lUustrations are camera lucida drawings prepared by 

 Patricia and Lawrence Isham of the U. S. National 

 Museum. 



