THE NAUTILUS 103(4): 143-148, 1990 

Page 143 

A New Fossil Land Snail (Gastropoda: Pulmonata: Polygyridae) 
from the Middle Miocene of Northern Florida 

Kurt AufTenberg 
Roger W. Portell 

Florida Museum of Natural History- 
University of Florida 
Gainesville, FL 32611, USA 

ABSTRACT 

A new fossil land snail, Praficalella prisca n sp., is described 
from the C'harlton Member of the Coosavvhatchie Formation 
(middle Miocene) at Brooks Sink, Bradford (>ounty, Florida. 
This new species is assigned to Praticolella s.s. Martens, 1892 
based on sculpture, palatal lip expansion and a narrow con- 
striction behind the lip. This subgenus is presently confined to 
central and southern Texas and Mexico under environmental 
conditions known to have occurred in northern Florida during 
the Miocene. Praticolella prisca n. sp. appears to be the earliest 
know n member of the genus. 

Key words: Gastropoda; Polygyridae; Praticolella. Miocene; 
Florida. 

INTRODUCTION 

Collections of invertebrate fossils containing a new species 
of terrestrial gastropod, Praticolella prisca n. sp., were 
made by the authors in the mid 1980's from Brooks Sink, 
a large, nearly circular, vertical-walled sink hole located 
16.89 kilometers west of Starke, Bradford County, Flor- 
ida (figure 1 ). Brooks Sink provides one of the best natural 
exposures of Hawthorne Group sediments in Florida. 
Exposed in approximately 23.0 meters of section are, in 
ascending order, the Marks Head Formation, the undif- 
ferentiated Coosawhatchie Formation, and the Charlton 
Member of the Coosawhatchie Formation (figure 2). 

The age of the Charlton Member (formerly Charlton 
Formation) was considered to be Pliocene by Veatch and 
Stephenson (1911) and Cooke (1943, 1945). Based upon 
ostracods from this unit, identified by Harbans Puri as 
middle Miocene and/or upper Miocene, Pirkle (1956) 
reported the age to be older. More recently, Jones and 
Portell (1988) recognized the middle Miocene clypeas- 
teroid echinoid, Abertella aberti (Conrad, 1842) from 
this unit. Huddleston (1988) assigned an age of middle 
Miocene to the Charlton Member in Georgia based on 
molluscan faunas, stratigraphic relationships, and the oc- 
currence of several age-diagnostic planktonic foraminif- 
era. Jones and Portell (1988) reported over 30 fossil in- 
vertebrate taxa within the Charlton Member of the 

Coosawhatchie Formation at Brooks Sink including Pra- 
ticolella sp., the taxon described below. 

MATERIALS AND METHODS 

No fossilized shell material was recovered. The speci- 
mens representing this taxon are preserved only as in- 
ternal and external molds comprised of fine-grained do- 
lostone. We use the term external mold to indicate the 
impression in the matrix of the outer surface of the shell. 
The matrix containing the external mold UF 14397 was 
reduced and the specimen sonicated for observation of 
the shell ultrastructure under a scanning electron mi- 
croscope. Some of the specimens are incomplete in cer- 
tain aspects. Nevertheless, standard shell parameters were 
measured with vernier calipers whenever possible. All 
specimens are reposited in the Florida Museum of Nat- 
ural History, Invertebrate Paleontology Division, Uni- 
versity of Florida, Gainesville, Florida 32611. 

DESCRIPTION 

Family Polygyridae Pilsbry, 1930 
Subfamily Polygyrinae Pilsbry, 1895 
Genus Praticolella Martens, 1892 
Praticolella prisca new species 
(figures 3-10, table 1) 

Adult shell large (width 10.0-13.9 mm, height 6.7-10.0 
mm); helicoid, depressed-globose, 0.64-0.72 times as high 
as wide; spire moderately elevated, convex in outline 
(figures 3, 6, 7); base round and inflated; the 4.6-5.0 
convex whorls slowly increasing in size (figure 4); sutures 
impressed; body whorl large, slightly flattened at suture, 
round at periphery and below; deflection variable, slight- 
ly upward or downward in the final 0.25 whorl, but 
always descending very slightly before constricting and 
inflecting; narrowly constricted posterior to palatal lip, 
more deeply constricted along base (figures 4, 6); um- 
bilicus narrow, tubular, about 0.10 the diameter of shell 
and partially covered by reflected columellar lip (figures 
5, 8); the 1.7 protoconch whorls are smooth except for a 

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THE NAUTILUS, Vol. 103, No. 4 

Table I. Pratuulclla prisra new species. Linear shell mea- 
surements (mm I and whorl counts of holot\pe and 9 paratvpes. 
Most of the s[>ecimens are incomplete in some aspects, hence 
the different N for the measured parameters. 

Figure I . Location of Brooks Sink in Bradford Countv, Florida 
(SW/,, SW'/i, sec. 12, T7S, R20E, Brooker 7,5 Minute Quad- 
rangle). 

few a.\ial striations on the last 0.20 turn (figure 10); sub- 
-serjiient whorls are smooth except for a few a.xial stria- 
tions on the last 0.20 turn (figure 10); subsequent whorls 
and base with fine, irregular, oblique axial striations, 
strongest at the suture (figure 9); spiral sculpture absent; 
aperture lunate and relatively large, 0.85 times as high 
as wide; parietal and palatal barriers absent; palatal lip 
broadly expanded, thickened within (figure 7); in lateral 
view lip moderately reflected along periphery and base, 
expanded forward above, unreflected (figure 6). 

Etymology: The species name prisca is derived from 
the Latin priscus, meaning ancient. 

Type locality: Brooks Sink, 16.89 kilometers west of 
Starke, Bradford County, Florida (SW'/4, SWA, sec. 12, 
T7S, R20E, Brooker 7.5 Minute Quadrangle), Coosa- 
whatchie Formation, Charlton Member, approximately 
8.0 meters below surface. 

Holotype: UF 14446, 12.5 mm width, 8.9 mm height, 
internal mold, protoconch missing. 

Paratypes: Width 10.0-13.9 mm, height 6.7-10.0 mm; 
UF 14395, 5 adults, internal molds; UF 14397, 1 adult, 
external moid and rubber peel; UF 14406, 1 adult, ex- 
ternal mold; UF 14407, 1 adult, external mold and rubber 
peel; UF 14408, 1 adult, internal mold; UF 14450, 1 
partial adult body whorl, internal mold. 

Other material examined: UF 28983, 9 fragments, in- 
ternal molds; UF 14405, 1 .subadult, external moid and 
rubber peel; UF 14433, 1 adult, external mold and rubber 
peel; UF 14443, 1 adult, internal mold; UF 22347, 4 
adults and 3 fragments, internal molds; UF 22348, 6 
juveniles, internal molds, obtusely anguiate at periphery 
and have indications of growth stoppage at 3.5-4.0 whorls. 

COMPARATIVE REMARKS 

The external mold UF 14405 (figures 7, 8) is tentatively 
a.ssigned to this new species. It is slightly smaller and 
more depressed (10.5 mm wide, 6.7 mm height) than 
most of the other specimens. The palatal lip is simple. 

except basally where it is barely reflected. The body 
whorl is slightly constricted on the basal portion. How- 
ever, this specimen is identical to the larger, more globose 
specimens in other character-states such as sculpture, 
spire whorlation and umbilicus. It is our opinion that this 
is a small subadult of Praticolella prisca n. sp. and does 
not represent a second undescribed taxon. 

The classification of pulmonate land snails is based 
primarily on features of the soft anatomy making as- 
signment of fossil forms difficult. Within the Stylom- 
matophora several families have evolved strikingly sim- 
ilar shell forms. Convergences in helicoid families such 
as the Camaenidae, Polygyridae and Helminthoglypti- 
dae are frustratingly commonplace. However, careful 
analysis of various morphological shell character-states 
can elucidate differences and general trends within and 
between families. The combination of sculpture, palatal 
lip expansion and the narrow constriction of the body 
whorl suggest that this species is best assigned to the 
polygyrid genus Praticolella Martens, 1892. 

Praticolella Martens, 1892 is characterized in shell 
form by its relatively small size, depressed-globose shape, 
rounded periphery, narrow umbilicus and rounded base. 
The aperture is lunate and the lip is slightly expanded 
or reflected and thickened within. The sculpture is of 
fine, irregularly spaced axial striations (Pilsbry, 1940). 
Praticolella is divided into three subgenera based on 
genitalic anatomy and sculpture of the protoconch (Pils- 
bry, 1940). The subgenus Filapex Pilsbry, 1940 has dis- 
tinct spiral sculpture on the protoconch. Farragutia Va- 
natta, 1915 and Praticolella s.s. Martens, 1892 have 
smooth protoconchs. Farragutia is relatively smaller than 
Praticolella s.s., is slightly more depressed and has a less 
rounded base. Praticolella prisca n. sp. is clearly referred 
to Praticolella s.s. A close relationship to any extant species 
cannot be made. 

The polygyrid genera Mesodon s.s. Rafinesque, 1821, 
Neohelix s.s. Ihering, 1892 and Praticolella Martens, 1892 
are quite similar in general shell shape. Mesodon s.s. and 
Neohelix s.s. generalK have distinct, regular axial striae 
and engraved spiral lines, while Praticolella has a 
smoothish shell sculptured only by weak, irregular axial 

K. Auffenberg and R. W. Portell, 1990 

Page 145 

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Figure 2. Geologic section at Brooks Sink modified from Scott (1982). Asterisk indicates zone where Praticolella prisca new species 

growth striae. The maximum shell size of Praticolella 
and the minimum size of Mesodon s.s. overlap, while 
Neohelix s.s. is much larger. The relative palatal lip width 
and degree of reflection of Praticolella rarely attains that 
of Mesodon s.s. The possibilit\ that this new species is a 
small unsculptured Mesodon s.s. cannot be dismissed. 

Praticolella prisca n. sp. superficially resembles the 
Miocene camaenids Pleurodonte crusta (Dall, 1890) and 
Pleurodontites diespiter (Dall, 1890). These species. 

however, have papillose sculpture, shells which are larger 
and more depressed than Praticolella prisca n. sp. and 
body whorls which descend greatly over the last V4 turn. 

DISCUSSION 

The method of preservation of fossil mollusks has an 
important bearing on the interpretation of certain mor- 
phological characters. Internal molds are particularly dif- 

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THE NAUTILUS, Vol. 103, No. 4 

Figures 3-6. Praticolella prisca new species. Holotype, UF 14446, apertural, dorsal, basal, and lateral views, x6.4. 

ficiilt to interpret. For example, if a shell with an inter- 
nally thickened palatal lip is filled with and encased in 
sediment and the shell dissolves, the thickened portion 
of the lip may appear as a constriction on the outside of 
the body whorl. A true constriction may be greatly en- 
hanced by this process. Praticolella prisca may in fact 
be only slightly constricted behind the lip or not con- 
stricted at all, only thickened internally. With more ad- 
equate material the true nature of this character-state 
will be better known. 

To our knowledge Praticolella prisca n. sp. represents 
the oldest known member of this genus. Fossil forms of 
Praticolella s.s. Martens, 1892 from probably the late 
Pleistocene epoch of Texas are attributed to extant species 

(Hubricht, 1983, 1985). This subgenus is presently con- 
fined in its native distribution to savannah and xeric 
habitats in southern and central Texas and Mexico. A 
similar savannah-like environment is known to have oc- 
curred in northern and central Florida during the Mio- 
cene (Webb, in press). This ecological association is com- 
patible with the taxonomic assignment of Praticolella 
prisca n. sp. 

Thirteen genera (23 species, 1 subspecies) of land snails 
have been recorded from the Miocene sediments of Flor- 
ida (Dall, 1890, 1915; Mansfield, 1937). Eleven of these 
genera are extant. If current taxonomic assignments are 
correct, eight genera (61%) have Caribbean affinities, 
four genera (31%) probably emigrated from areas west 

K. Auffenberg and R. W. Portell, 1990 

Page 147 

Figures 7-10. Praticolella prisca new species. 7, 8. UF 14405, apertural and basal views of rubber peel of external mold of 
probable subadult (see Comparative Remarks), x6.6. 9, 10. Paratype, UF 14397, scanning electron micrograph of protoconch of 
external mold. 9. x28. 10. x47. 

of Florida, and one genus (8%) came from tfie north. 
The buiimuiid genus Hyperaulax Pilsbry, 1897, which 
has an enigmatic distribution of several species from the 
Miocene of Florida and a single extant species on Fer- 
nando de Noronha Island off Brazil, is considered here 
to be part of the Caribbean component of the Miocene 
fauna. Many of the Miocene terrestrial vertebrates of 
Florida are believed to have been associated with both 
mesic and xeric tropical habitats (Auffenberg, 1963; Webb 
1978, in press) and some appear to be closely related to 
groups now found in dry regions of Central America and 
Mexico. It is possible that some of these Florida Miocene 
land snails attributed to genera presently found only in 
the Caribbean region may be more appropriately as- 

signed to genera occurring in mesic or xeric areas of 
Central America and Mexico and thus entered Florida 
via a dry tropical corridor along the Gulf of Mexico. 

The fifty genera of native land snails presently found 
in Florida reveal a different zoogeographic pattern than 
is suggested by the fossil record. Of this current land 
snail fauna, sixteen genera (32%) are well-represented in 
the Caribbean region, six genera (12%) probably entered 
Florida from the West, while twenty-eight (56%) came 
from the North. This present zoogeographic pattern re- 
flects the strong post-Miocene trend toward cooler, wetter 
climates, allowing immigration of the northern taxa into 
Florida. However, the timing of this immigration can 
not be determined from the fossil record. 

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THE NAUTILUS, \ol. 103, No. 4 

ACKNOWLEDGMENTS 

We are grateful to Glen Harris and Joe Gissy of the 
Container Corporation of America for access to Brooks 
Sink. We also thank Fred G. Thompson and Douglas S. 
Jones of the Florida Museum of Natural Histor\ for re- 
vicwiiig the manuscript. Kenneth C. Emberton of the 
Philadelphia Academy of Natural Sciences also reviewed 
the manuscript and shared his knowledge of the Poly- 
gyridae. We also acknowledge Walter Auffenberg. S. 
David Webb, and Gary S, Morgan of the Florida Museum 
of Natural History for their insight into the vertebrate 
paleontology of Florida. Micrographs were taken on a 
Hitachi 5-415A scanning electron microscope, Depart- 
ment of Zoology, University of Florida. This paper rep- 
resents University of Florida Contribution to Paleobiol- 
ogy 348. 

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Cooke, C. W 194.5 Geology of Florida. Florida Geological 
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Dall, W. H. 1890. Contributions to the Tertiary fauna of 
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Dall, VV H 191.5 Monograph of the molluscan fauna of the 
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Hubricht, L. 1985. The distributions of the native land mol- 
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