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Northern Arizona University, Flagstaff, Arizona, USA, recently installed a MIni CArbon DAting System (MICADAS) with a gas interface system (GIS) for determining the 14C content of CO2 gas released by the acid dissolution of biogenic carbonates. We compare 48 paired graphite, GIS, and direct carbonate 14C determinations of individual mollusk shells and echinoid tests. GIS sample sizes ranged between 0.5 and 1.5 mg and span 0.1 to 45.1 ka BP (n = 42). A reduced major axis regression shows a strong relationship between GIS and graphite percent Modern Carbon (pMC) values (m = 1.011; 95% CI [0.997–1.023], R2 = 0.999) that is superior to the relationship between the direct carbonate and graphite values (m = 0.978; 95% CI [0.959-0.999], R2 = 0.997). Sixty percent of GIS pMC values are within ±0.5 pMC of their graphite counterparts, compared to 26% of direct carbonate pMC values. The precision of GIS analyses is approximately ±70 14C yrs to 6.5 ka BP and decreases to approximately ±130 14C yrs at 12.5 ka BP. This precision is on par with direct carbonate and is approximately five times larger than for graphite. Six Plio-Pleistocene mollusk and echinoid samples yield finite ages when analyzed as direct carbonate but yield non-finite ages when analyzed as graphite or as GIS. Our results show that GIS 14C dating of biogenic carbonates is preferable to direct carbonate 14C dating and is an efficient alternative to standard graphite 14C dating when the precision of graphite 14C dating is not required. [ABSTRACT FROM AUTHOR]

This study aimed to resolve the taxonomy of cassid gastropods from the upper Eocene Ocala Limestone based on specimens collected from Florida Museum of Natural History locality AL004. In 1890, Dall described a specimen from this formation, collected in a nearby county as Phalium globosum (subfamily Phaliinae). However, further collection of cassids from AL004 suggested the presence of more than one morphologically distinct taxon. Eocene cassids are particularly interesting because that is presumably the time when cassids experienced rapid diversification, which has implications for the evolutionary history of echinoid-cassid predator–prey interactions. Based on 75 specimens from AL004, it appears that the specimens interpreted as belonging to two or more morphologically distinct taxa are more likely members of a single species with extreme morphological variability, redescribed here as Semicassis globosum. Results of morphometric analyses using nine qualitatively defined cassid morphotaxa (subfamily Phaliinae) suggest that S. globosum is characterised by high intraspecific variability in shell morphology that may reflect high ecophenotypic variability or elevated intraspecific genetic variability. This study highlights the challenges associated with delineating species status using low numbers of specimens, as a dearth of diagnostic material may lead to taxonomic "over-splitting," thereby resulting in an inflated estimate of biodiversity. [ABSTRACT FROM AUTHOR]

Turritellid gastropods are among the most widespread, abundant, and diverse mollusks in Plio-Pleistocene deposits of the Atlantic coastal plain and Florida, with at least 46 species and subspecies described over almost two centuries. Yet the systematic status of these common fossil species and their phylogenetic relationships--to each other and to turritellids living today in the western Atlantic--have never been investigated in detail. We make use of recent molecular phylogenetic work on living turritellids and new analyses of shell characters to review the group from this time interval to the present in a comprehensive phylogenetic analysis and assessment of their evolutionary history in the region. We conclude that 20 fossil and two Recent species are valid. Four of these species are placed in the genus Torcula Gray, 1847; five in Caviturritella new genus, and eleven in "Turritella" sensu lato. We identify Torcula perattenuata as the likely direct ancestor of one of the two turritellid species living today off the southeastern U.S. coast, Torcula exoleta, and we elucidate the fossil record of the other extant species, "Turritella" perexilis (senior synonym of Turritella acropora). We show that Caviturritella was extirpated from the United States Gulf and Atlantic coastal plains in the Early Pleistocene but is still represented in the western Atlantic by the living species C. variegata in the southern Caribbean. We also present the first detailed treatment of Plio-Pleistocene turritellid fossils from Georgia. Our analysis shows that the Plio-Pleistocene Pinecrest beds of Florida contain 18 co-occurring turritellid species, which is the highest turritellid species diversity in one formation known in the fossil record. [ABSTRACT FROM AUTHOR]