54 



UNITED STATES NATIONAL MUSEUM BULLETIN 215 



1952). The formation is divided, into the following 

 zones (all established in the subsurface section of 

 Trinidad Leaseholds well Guayaguayare 163, coordi- 

 nates N:157646 hnks, E:572808 links): 



Ahathomphalus mayaroensis zone 

 Globotruncana gansseri zone 

 Globoiruncana lapparenti tricarinata zone 



The lowest zone of the Guayaguayare formation stUI 

 lacks Globotruncana gansseri Bolli and Ahathomphalus 

 mayaroensis (Bolli), but abounds in several subspecies of 

 Globotruncana lapparenti Brotzen, predominant among 

 which is the zonal marker Globotruncana lapparenti 

 tricarinata (Quereau). A few specimens of Globo- 

 truncana andori de Klasz were found in this zone. 

 The following species do not range into the younger 

 zones: Globotruncana lapparenti lapparenti Bolli, G. 

 lapparenti bulloides Vogler, G. lapparenti tricarinata 

 (Quereau), G. globigerinoides Brotzen, G. fomicata 

 Phimmer, and G. repanda, new species. 



The marker for the Globotruncana gansseri zone has 

 also been recorded from Turkey (under the synonym 

 of Globotruncana lugeoni TUev) and from mid-Pacific 

 sea moimts (Hamilton, 1953). The author has seen 

 it in material from Cuba and in the Navarro formation. 

 Globotruncana calcijormis (de Lapparent), G. contusa 

 (Cushman), G. gagnebini TUev and Abathomphalus 

 intermedia (Bolli) are other species occurring for the 

 first time in the Globotruncana gansseri zone; they con- 

 tinue into the Abathomphalus mayaroensis zone. 



The zonal marker of the Abathomphalus mayaroensis 

 zone is a typical and apparently short-hved species 

 which so far has not been recorded in publications from 

 outside Trinidad. However, the author has seen speci- 

 mens in material from the type locahty of the Mendez 

 shale (300 meters east of Mendez Station, kilometer 

 629.3 on the San Luis Potosi-Tampico railway, 

 Mexico) and from Bavaria. An outcrop containing a 

 fauna transitional between the Globotruncana gansseri 

 and Abathomphalus mayaroensis zones is known from 

 the Gautier River section (see p. 52). 



The maximiun recorded thickness of the Guaya- 

 guayare formation is about 500 feet. 



Evolutionary Trends 



In recent years much has been written on the evolu- 

 tionary trends of the genera under discussion. Hagn 

 and Zeil (1954, pp. 51-56) gave a condensed review of 

 the various interpretations. Although there might be 

 a relatively simple general pattern in the phylogeny 

 of Praeglobotruncana, Rotalipora, Globotruncana, and 

 Abathomphalus, the details are complex and little 

 studied. 



The evolutionary trend in Rotalipora, from a single 

 inflated early form to several compressed later species, 

 seems to be fairly well established. Of special interest 

 is the pattern of coUing during the evolution of Rotali- 

 pora. As may be expected, the early species, Rotalipora 

 roberti (Gandolfi) and R. ticinensis (Gandolfi), coil at 

 random, later becoming predominantly dextral in the 



Rotalipora appenninica (Renz) — R. reicheli Momod 

 group. Before the extinction of the genus, its latest 

 representatives, Rotalipora turonica Brotzen and R. 

 cushmani (Morrow), unexpectedly revert to random 

 coiling. This might represent a gerontic stage. 

 Whereas abrupt changes in coUing from one preferred 

 direction to the opposite one are known to take place 

 in later evolutionary stages of certain Globorotalia 

 species (BoUi, 1950), such a return to random coiling 

 had not, to the author's knowledge, been observed 

 before. 



Transitional stages exist between certain Rugoglo- 

 bigerina and Globotruncana species. This suggests a 

 close generic relationship of at least a nimiber of 

 GlobotruTwana species with Rugoglobigerinu species. It 

 may be assumed that species of Globotruncana branched 

 off independently from rugoglobigerinid forms on more 

 than one occasion between Turonian and Maestrichtian 

 time. One of the first attempts by Rugoglobigerina to 

 produce forms with one or more peripheral keels and 

 compressed chambers took place in the Turonian and 

 led to the short lived Globotruncana helvetica BoUi 

 which has no apparent direct descendants. The 

 single-keeled Globotruncana schneegansi Sigal developed 

 independently at approximately the same time from 

 similar forms, possibly via Globotruncana inomata, new 

 species. This seems to have been a more successful 

 mutation, as it appears that the single-keeled Globo- 

 truncana schneegansi gave rise to the double-keeled 

 Globotruncana renzi Gandolfi — G. angusticarinata Gan- 

 dolfi — G. concavata (Brotzen) — G. ventricosa White suite. 

 However, the possibflity that the single keeled Globo- 

 truncana schneegansi might have developed from late 

 representatives of Praeglobotruncana stephani (Gan- 

 dolfi) should not be overlooked. A tendency is 

 observed in late representatives of Praeglobotruncana 

 stephani for the aperture to move from an interio- 

 marginal, extramnbilical-umbUical position to an mn- 

 bihcal one. 



Globotruncana vnlsoni, new species, appears to have 

 developed independently from Rugoglobigerina ances- 

 tors in early Senonian titne. This species may have 

 given rise subsequently to the Globotruncana fomicata 

 Plmnmer — G. contusa (Cushman) suite. 



Globotruncana globigerinoides Brotzen whose relation 

 to rugoglobigerine forms is obvious, is a comparative 

 latecomer, appearing in Trinidad only after many other 

 typical Globotruncana species have already become 

 extinct. It initiates another attempt by the Rugoglo- 

 bigerinas to change their shape. Globotruncana lappa- 

 renti bulloides Vogler and G. lapparenti tricarinata 

 (Quereau) are connected by transition to G. globigeri- 

 noides; they are to a large degree contemporaneous. 



The Campanian Globotruncana repanda, new species, 

 is short lived and hkely to have sprung directly from a 

 Rugoglobigerina ancestor. 



Globotruncana gansseri BoUi, which is morphologically 

 simUar to the Tiuronian Globotruncana helvetica Bolli, 

 appears in the Maestrichtian, again with transitional 



