Auffenberg et al. (2015) just released a new paper on fossils from the Miocene in Florida. The land shells fossils have hitherto been considered as Odontostomidae, which as extant species occur in the southern part of South America. Consequently, some ‘mental flexibility’ was needed to explain the biogeography of these fossils.
“Orthalicoid terrestrial snails recorded from the lower Miocene portion of the upper Oligocene to lower Miocene Tampa Member of the Arcadia Formation (Hawthorn Group) of southern Florida and the lower Miocene St. Marks Formation of northern Florida are reviewed. These taxa, previously allocated to the genus Hyperaulax Pilsbry, 1897 (Odontostomidae), are reassigned to Tocobaga new genus (Bulimulidae) on the basis of a distinctive suite of morphological characters, particularly those of the peristome and the embryonic whorl sculpture. Examination of all type material of the fossil taxa historically assigned to Hyperaulax reveals that only three species are separable (Partula americana Heilprin, 1886; Bulimulus americanus wakullae Mansfield, 1937; and Bulimus floridanus Conrad, 1846). The varietal names Bulimulus americanus var. partulinus and B. americanus var. laxus, both Dall, 1890, are indistinguishable from the nominate form in any important morphological character. Bulimulus heilprinianus, Bulimulus stearnsii, both Dall, 1890, and Bulimulus ballistae, Bulimulus remolina, Bulimulus tampae, and Bulimulus tortilla, all Dall, 1915, are synonyms of B. floridanus Conrad, 1846. The status of B. a. wakullae from northern Florida is problematic. Although clearly not conspecific with P. americana, it is tentatively assigned to Tocobaga new genus and is herein elevated to species level. The biogeography of Tocobaga new genus is tentatively discussed. Fossiliferous deposits in North America and South America have not yielded taxa with the combination of shell characters found in the new genus and relationships with other bulimulid genera are unknown. However, it is probable that the new genus, like other non-marine mollusks from the Tampa Member of the Arcadia Formation, dispersed to Florida after contact between the Caribbean Plate and the Bahama Platform (circa 38 Ma)”.
Auffenberg, K., Slapcinsky, J. & Portell, R.W., 2015. A revision of the fossil taxa assigned to Hyperaulax (Gastropoda: Odontostomidae), with the description of a new genus (Gastropoda: Bulimulidae). – The Nautilus 129: 54–62.