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About 70 percent of tropical western Atlantic mollusk species have become extinct since the Pliocene, which has led to perceptions of a corresponding decline in diversity. However, a compilation of gastropod species from Plio-Pleistocene faunas of the United States Atlantic coastal plain and from Recent western Atlantic faunas indicates that regional diversity has not changed since the Pliocene. Gastropod diversity in the Pliocene Pinecrest Beds in Florida approximates that seen today on either coast of Florida. Gastropod diversity is not demonstrably different in the Recent tropical western Atlantic than in the Recent tropical eastern Pacific. High extinction rates must have been balanced by high origination rates., The late Cenozoic history of mollusk diversity in the tropical and subtropical western Atlantic has traditionally been viewed as one of a decrease in species richness by a series of [...]

Concentrations of fully articulated crabs are rare in the fossil record, especially for terrestrial and semi-terrestrial taxa, which tend to be represented by scarce, fragmentary and poorly preserved fossils due to preservational biases. A newly discovered fossiliferous locality at Bahia Bique, west of Panama City, Panama, yielded a collection of supratidal, intertidal and shallow subtidal invertebrates and vertebrates of mid-Holocene age. Notable discoveries include the first fossils of the sally lightfoot crab Grapsus, the first for the land crab Cardisoma in the Eastern Pacific and, remarkably, the most complete and abundant collection of fossil fiddler crabs, Uca, yet discovered. The abundance and exceptional preservation of fossil male, female, juvenile and adult individuals of Uca aff. ornata in eroded burrow infills suggest that rapid entombment and early diagenesis were crucial for their preservation. The habitat preference of extant U. ornata for soft muds of open intertidal mudflats indicates that part of Bahía Bique must have been a large estuarine mudflat with close proximity to freshwater influx, in contrast to the present-day gravel field where the fossils are found as ex situ boulders, cobbles and gravel-sized clasts eroded from rocks of the poorly known Pacific Muck. We examine the systematic relationships of fossil fiddler crabs from Bahía Bique via synthetic and cladistic approaches, and conclude that they were from an extinct population of the extant Uca ornata. The fidelity of living-death assemblages between the Bique faunule and extant faunas of the tropical Eastern Pacific confirm the Quaternary age of the assemblage, and stimulate a detailed discussion of the preservation and palaeoecology of terrestrial and semi-terrestrial crabs in tropical assemblages. [ABSTRACT FROM AUTHOR]

Limestones of the Upper Oligocene Antigua Formation of Antigua contain unusual burrows filled with the densely packed debris of shelly benthos. Unlined burrows (Planolites?) in deep-water biofacies at Half Moon Bay, parish of Saint Philip, are packed with a monospecific assemblage of large benthic foraminiferans (Lepidocyclina canelliLemoine & Douvillé) and a single brachiopod valve,Tichosinasp. A similar burrow in shallower-water biofacies at Hughes Point, parish of Saint Philip, is packed with echinoderm debris and, particularly, test fragments of the spatangoid echinoidLovenian. sp. Fragments of the same echinoid fill a conical burrow,Bergaueriaisp. The latter is probably a physical accumulation, the common fragments of echinoid being washed into an empty burrow. In contrast, the infill ofPlanolites? isp. is more likely to be an accumulation mediated by the burrower. [ABSTRACT FROM PUBLISHER]

Exceptionally low water levels on the Apalachicola River in the fall of 2012 exposed a limestone bench containing numerous, large stromatolites at the classic Alum Bluff section. The stromatolites are within the Lower Miocene Chipola Formation, and are overlain by the well-known, molluscanrich, calcareous quartz sands of the upper Chipola Formation. The largest stromatolite exceeds 2.0 m in diameter, but most of the hermispherical domes are between 0.5 to 1.0 m in diameter, with as much vertical relief. All appear to have nucleated over mangrove root systems or perhaps palm or other tree stumps. The interiors are firmly cemented and calcified, preserving sand-filled, eroded/ bioeroded wood structures surrounded by calcareous sandstone which is penetrated by a random tangle of calcareous tubules (interpreted as wood rhizomes). Finely-laminated boundstone surrounds some root structures at their base. Surrounding these hard interiors are one or more thick (2-9 cm) layers of weakly-cemented, medium-coarse calcareous quartz sand, also penetrated by a random tangle of calcareous tubules (thicker layers show rude bedding). Firm basal attachment, pronounced vertical relief, globose form, layered construction, burial within unconsolidated fossiliferious sands, and lack of evidence of karst or paleosol/caliche development, all support a microbial origin for these structures rather than diagenetic (concretionary) alteration of tap-roots or root balls. The stromatolites developed within the mouth of the Gulf Trough during the waning stages and infilling of this Eocene to Miocene marine channel that cut across northern Florida and southern Georgia. Large marine stromatolites of Cenozoic age are extremely rare, so their discovery in the Early Miocene of northern Florida was surprising. But given the widespread occurrence of coastal facies in the Cenozoic record of Florida and the Gulf Coastal Plain, similar occurrences might be expected. [ABSTRACT FROM AUTHOR]

Studies in systematic palaeontology are greatly aided when numerous, well-preserved specimens are available so that quantitative methods can be used to substantiate qualitative observations. This is often not the case for fossil decapod crustaceans due to their relatively low preservation potential. Here, we examined primarily two large collections of the well-preserved ghost shrimpGlypturusfrom the Holo-Pleistocene of Panama and the late Miocene of Florida. Using descriptive, bivariate, multivariate and geometric morphometric methods, two new species are described based on appendage material:Glypturus panamacanalensissp. nov. andG. sikesisp. nov. New characters are identified, and size-related and intraspecific variation are assessed for these taxa and modernG. acanthochirus. Taxonomic placement of single specimens from other localities was confirmed by multivariate methods. Furthermore,Glypturusis revised, especially with regard to Western Atlantic species that inhabited both carbonate and siliciclastic environments.Callianassa anguillensis,C. latidigata, andNeocallichirus? quisquellanusare referred to asGlypturussp. until more material is available to determine the validity of these species. Diversity withinGlypturusmay thus be underestimated, thereby also impacting the assessment of phylogenetic relationships. Minor propodi appear under-represented relative to major propodi, suggesting a taphonomic bias. Single specimens of interest include a specimen ofG. panamacanalensissp. nov. exhibiting a peculiar swelling in the fixed finger and another showing damage on the propodal upper margin, suggesting failed predation or antagonistic behaviour.Glypturusis first found in the Oligocene in the Western Atlantic and may have expanded its palaeobiogeographical range since the Miocene. The genus was still present on the Pacific side of the Isthmus of Panama in the Holo-Pleistocene, but is only known from the Western Atlantic today, suggesting a relatively recent extinction on the Pacific side. http://zoobank.org/urn:lsid:zoobank.org:pub:C7F0C071-F2AD-4684-B277-037B6F91BF0E [ABSTRACT FROM AUTHOR]