OBSERVATIONS ON TURBINELLA SCOLYMOIDES DALL, WITH DESCRIPTION OF A NEW SPECIES OF TURBINELLA EMILY H. VOKES TULANE UNIVERSITY
CONTENTS I. ABSTRACT ______------·------·- 63 11. DISCUSSION ______63 Ill. SYSTEMATIC DESCRIPTIONS. 68 IV. LOCALITY DATA 70 V. LITERATURE CITED .... ·------71 PLATE L __ ------· ------·------·-·------· ·------· ____ 65 PLATE 2------______------67 PLATE 3------69
I. ABSTRACT ing off Yucatan. In the summer of 1964, Turbinella scolymoides D all (Mollusca, the writer and her husband, Dr. Harold E. Gastropoda), described from the Pliocene of Vokes of the Geology Department of Tulane Florida, has been discovered in the Recent University, spent some time in Yucatan col fauna of Yucatan. It is suggested that the leering Recent mollusks in the company of common Recent species T. angtdata (So Dr. E. Wyllys Andrews, Tulane·s archaeolo lander in Lightfoot) developed independ g ist in residence in Merida and an accom ently in the Miocene of the southern Carib plished amateur malacologisr. By means of bean and subsequently invaded the indige a small fishing boar much of the northwest nous northern T. scolymoides population, ern coast of the peninsula was covered and, virtually replacing it except in the asylum for other localities nor visited, Dr. Andrews of the Yucatan area. The lower age limit of generously shared his personal collection in T. scolymoides is tentatively fixed at the order ro provide the Tulane Geology Depart Miocene-Pliocene boundary, possibly due ro ment with a suite of Yucarecan Mollusca. a warming trend in water temperatures at Among the specimens in the possession of the end of rhe Miocene. Dr. Andrews were three unusual representa tives of the genus Turbi11ella from Isla Hoi 1!. DISCUSSION box on the northeastern rip of Quintana Roo. The molluscan fauna of Yucatan, Mexico, The shells are full grown, smooth in outline, is of considerable interest, for some elements and bear almost no trace of the shoulder are more akin to the Plio~Pleisrocene fauna nodes of the typical T. angttlata (Solander ;, of southern Florida than those of any other Lightfoot), so common in the Yucad.n re western Atlantic area. Many of the Caloosa gion. These specimens appeared to verify harchee and posr-Caloosahatchee fossils are the statement made in an earlier smdy of the most closely related ro forms presently liv- genus Tttrbi11ella ( Vokes, 1964, p. 62) ro
EDITORIAL COMMITTEE FOR THIS PAPER: AXEL A. OLSSON, Coral Gables, Florida NORMAN E. WEISBORD, Florida Stare University, Tallahassee, Florida DRUID WILSON, United Stares Geological Survey, Washington, D. C.
63 64 Tulane StudieJ in Geology Vol. 4
the effect that it is possible the Florida Plio series of both species in which it can be seen cene species T. JcolymoideJ is still living tO that the large shells are readily distinguish day off Yucatan. Here indeed were three able but with decreasing size the differences specimens of the Florida fossil. Dr. Andrews dwindle. Apparently T. a?Zgulata and T . was prevailed upon to part with his "oddi JcolymoideJ are the end members of rwo ties" and they were brought back to Tulane lines which diverged somerime during the for further study. Miocene. But the entire Tttrbi?Zella group The discovery of these Recem specimens is so very conservative that little change has of T. JcolymoideJ Jed ro a derailed study of taken place in either line since the orig inal the relationship between T. JcolymoideJ and separation. For th is reason the two spec ies T. angulata. This study was enhanced by the still bear a marked resemblance to each addition of numerous specimens of Recent other, a resemblance which is in acrualiry a T. atzgulata from various Yucarecan Joca li· resemblance ro their common ancestor what ties which proved tO be invaluable for com ever ir may have been. There is a species of parative purposes. The primary result of the Tttrbi11ella in the Chipola Formation of study was ro demonstrate that T. JcO!) moideJ northwestern Florida, T. dalli Vokes, which is much closer ro T. angulata than was pre is the earliest known North American rep viously believed. Dall, in his original de resentative of the T . JcolymoideJ type. The scription of T. JcolymoideJ (1890, p. 98), namre of the ornamentation on the early stared that although the rwo were similar, whorls of this lower (or possibly middle) T. JcolymoideJ was distinguished by "hav Miocene species is identical with rhar o f ing a more elongated and acute spire and T. JcolymoideJ, although the adults differ canal, with two more whorls ro the same considerably. diameter in the young shell." This state Jn the posr-Caloosahatchee beds, presum ment is nor borne our by a suite of speci ably PleistOcene is age, of southern Florida mens. Fifty shells, perfect to the apex, were there is a third species which seems to be an measured at an arbitrary diameter of 20 mm. offshoot of the T. angttlata stack. T his new The specimens which were identifiable as species, T. hoerlei, is described at the end of T. JcolymoideJ had exactly the same number this paper. K nown from a few localities in of whorls as did the T. angulata group. The western Palm Beach County, it may be only entire lor was remarkably consistent in hav a variant of T. angulata. ing five whorls at the diameter of 20 mm. The close relationship of T. JcolymoideJ, The maximum variation was from 4 Y2 ro T. a?Zgt~!ata, and T . hoerlei, n. sp., might seem 5 Y2 whorls with 80% of the specimens hav ro cast some doubt on the ancestry of the ing five. In fact, at a roral height of less Recent T. angttlflta. It was suggested in the rhan 80 mm the rwo forms are indistin earlier T1trbinella study that T. angt~fala ,vas guishable. As the size of the shell increases apparently more closely related tO certain the degree of divergence is more noticeable. South and Central American species than ro At heights of more than I20 mm there is no the Floridian T. JcolyrnoideJ. In a paper question of separation. This presents a seri which preceded the writer's 1964 study, al ous problem tO the field geologist, for most though only seen subsequently, another new specimens found are of a small size and are species of Tm·binel!a was described from the not truly distinctive. Plate I shows a growth Miocene Pirabas Li mesrone of Pan\, Brazil. ------PLAT E 1 TOP ROW: Turbi?Zella mzgrtlata (Selander in Lightfoot ), left to right: ( I ) Recent,R-68 (4) Pleistocene,TU727 (7) Pleisrocene,TU 201 (2) Recent, R -68 (5) Pleistocene, TU 731 ( 8) Recent, R-52 (3) Recent,R-75 (6) Recent, R -75 BOTTOM ROW: Tu·rbinella JcolymoideJ Dall, left ro right: ( I ) Pliocene, TU 79 ( 4) Pliocene, TU 539B ( 7) Pliocene, TU 79 ( 2) Recent, R-92 ( 5) Recent, R-92 (8) Pliocene, TU 539B (3) Recent, R-92 (6) Pliocene, TU 536 No. 2 Observatiom on T urbinella scolymoides 65
PLATE l 66 Tulane StudieJ in Geology Vol. 4
This new species, T. tuberculata (Ferreira) as is the addition of a fourth columellar (see description below) , is almost identical plication. This latrer criterion is always un with the Recent T. angulata. In the same reliable for mosr large specimens develop Pirabas beds there is another Turbinella, an additional fold whatever the locality. T. braJiliatla (Maury), which was based on Thus we have T. angulata existing in the a juvenile specimen. By analogy with the Miocene of northern Colombia with near young of T. angulata, which T. braJiliana relatives in Costa Rica and Brazil. At the strongly resembles, it is not improbable that same rime in the more northern reaches of the new species is simply the adult of the Caribbean, we find T. textiliJ (Guppy) Maury's juvenile. An absolute decision must in the Bowden Formation of Jamaica and a await better material. • The discovery of this new species, if indeed it be such, together closely related form in the middle Miocene with the two middle Miocene species, T. of Santo Domingo. The latter was figured magdaletwmiJ (Weisbord) from Colombia by Pilsbry ( I922, pl. 25, fig. 3) forT. valida and T. Jcopula (Olsson) from Costa Rica, Sowerby, but is nor that species as was tends to confirm the original suggestion that demonstrated in the Turbinella study (p. the Recent T. angulata has had a separate 48). T. JcolynzoideJ would almost certainly history in the southern Caribbean, for it is seem to be a descendant of the more north impossible not to consider these forms as ern form both on geographic and morpho directly ancestral to the Recent species. T. logic grounds. It is concluded that T. Jcoly magdalenemiJ, especially, is so close to T. rnoideJ represents a side branch on the fami mzgulata that it is probably conspecific. It ly tree developing independently from the was originally separated because it had fewer southern T. angulata line. The northern nodes (five) and an additional columellar population was invaded by the more vigor fold. Examination of comparably sized ous southern form at some post·Miocene specimens from the Caribbean off northern time. A few remnants of the T. Jcolynzoides South America and Panama show that five line seem to have found asylum off the Yu nodes are to be expected in large specimens catan Peninsula.t