Roger W. Portell

Diversity of Atlantic Coastal Plain Mollusks Since the Pliocene

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.

Animal-plant relationships and paleobiogeography of an Eocene seagrass community from Florida

An excellent example of a preserved seagrass community occurs in the late Middle Eocene Avon Park Formation of west-central, peninsular Florida. This fossil assemblage provides some of the first detailed information about the evolutionary development of animal/seagrass interactions, and in addition, documents the pre-Miocene existence of seagrasses in Florida. The most common seagrasses present are species of Thalassodendron and Cymodocea. A strong Tethyan paleobiogeographic connection, previously noted among the Eocene molluscs of Florida, is also supported by the seagrasses and dugongs. We hypothesize that this assemblage of seagrasses was much more widespread in the Neotropics during the Paleogene and into the Neogene. Their absence now can be explained by the changing circulation patterns and cooling initiated by the closing of the Panamanian Isthmus and/or the onset of Plio-Pleistocene glaciation

Changes in invertebrate taxa at two pre-Columbian sites in southwestern Jamaica, AD 800–1500

Abstract Excavations at two pre-Columbian sites at Paradise Park, Parish of Westmoreland, Jamaica, revealed significant changes in mollusk use through time. The sites are located on a low dune ridge in a tropical forest between a mangrove swamp and sawgrass morass on Bluefields Bay. One site (Wes-15a) dates to the 9th century AD and contains only Ostionan (redware) pottery. It is located 240 m to the east of a Meillacan (White Marl/Montego Bay style) site dated to the 15th century AD (Wes-15b). The molluscan fauna in the Ostionan site is dominated by species that prefer freely circulating, high salinity seagrass habitats (i.e., Strombidae, Cardiidae, and Veneridae). In marked contrast, Lucinidae and Melongenidae dominate the Meillacan deposits, taxa that favor habitats of low circulation, lower salinity, and muddier substrates that are often associated with mangroves in Jamaica. Cultural and environmental factors that may have contributed to the observed shift in resource use are discussed.

The Miocene palaeobathymetry and palaeoenvironments of Carriacou, the Grenadines, Lesser Antilles

Carriacou, a small island in the Grenadines, Lesser Antilles, has a Cenozoic rock record that has been important in interpreting the geologic history of the Southern Lesser Antilles Arc Platform. The Lower-Middle Miocene sedimentary succession of the southeast and east coasts, consisting of the Belmont, Kendeace, Carriacou and Grand Bay formations, has been interpreted as a shallowing-upward sequence from turbidite basin to nearshore?/beach? palaeoenvironments. An earlier interpretation of the Belmont Formation as having been deposited in shallow water is at variance with the turbiditic nature of the succession; the included fossils are considered allochthonous. However, an interpretation of the Grand Bay Formation as deep water is supported by multiple lines of evidence, including sedimentology (turbidites), ichnology (autochthonous association of burrows typical of deep-water environments) and palaeontology (terrestrial, planktic, and shallow and deep water benthic species mixed together). The minimum depth of deposition of the Grand Bay Formation was 150–200 m. This suggests that the (unseen) contact between the Carriacou and Grand Bay formations is either an unconformity, formed following rapid deepening of the basin, or a fault, the Grand Bay Formation being deposited in a separate basin from the shallowing-upwards Belmont-Kendeace-Carriacou formations, against which it is now juxtaposed

AN OVERVIEW OF PREDATION EVIDENCE FOUND ON FOSSIL DECAPOD CRUSTACEANS WITH NEW EXAMPLES OF DRILL HOLES ATTRIBUTED TO GASTROPODS AND OCTOPODS

ABSTRACT Predators of extant decapod crustaceans are fairly well known, but unlike many other invertebrate clades, not much is known regarding predation evidence found on fossil decapods. Herein, we provide an overview of such predation and expand upon this through an extensive study of fossil decapod specimens from multiple museum collections. Thus far most examples of predation come from drill holes and stomach contents; bite marks, incisions or irregular holes, and possible regurgitated material are also known. The currently recognized predators of decapods in the fossil record are fish, plesiosaurs, ammonites, octopods, and gastropods. We also provide new evidence of unambiguous drill-hole predation in decapods, based on 33,593 nonmoldic Cenozoic (middle Eocene–Holocene) decapod remains originating from Europe, Asia, and North America, indicating that drilling predation in decapods is more common than currently recognized. Drill holes attributed to octopods (ichnotaxon Oichnus ovalis) and gastropods (O. simplex and O. paraboloides) were found in carapaces and appendages from the Pliocene of the Netherlands, the Pleistocene and Pliocene of the United States (Florida), and the Pleistocene and early Miocene of Japan. Six drill holes attributed to octopods were found in epifaunal and semiburrowing crabs; three drill holes attributed to gastropods were discovered in semiburrowing and epifaunal crabs, and in a burrowing mud shrimp; and the producer of two other drill holes in epifaunal crabs is unknown. Other possible drill holes occur in decapods from the Holocene and early Miocene of Japan and the late Eocene of the United States. Drill-hole predation intensities in decapod faunas by stratigraphic formation are low (≤2.7%), at least in part due to multiple biases such as preservation and molting.

Diversity patterns and biostratigraphy of Cenozoic echinoderms from Florida

Abstract Fossil echinoderms are an important faunal component in Cenozoic rocks of Florida and the southeastern Coastal Plain of the USA, that provide useful information regarding diversity patterns and paleoecology for the formations in which they were deposited. The research presented in this paper significantly improves what is known about the stratigraphic distribution and diversity patterns of echinoids, comatulid crinoids, asteroids, and ophiuroids from the Middle Eocene through Pleistocene strata of Florida. Biostratigraphic distribution of echinoderms, specifically the echinoids, has not been synthesized on a large scale for many years, and the first compilation of these taxa from the state is provided in this study. Echinoderms now are known from 25 formations that are exposed throughout the state. The echinoids are better documented and described than the other classes of echinoderms, yet even the echinoids were poorly known from some epochs, most notably the Miocene. Previously published information showed echinoid diversity decreasing significantly from the Eocene into the Oligocene, and continuing to decline into the Miocene. Our research shows the echinoid diversity does not drop from the Oligocene into the Miocene, but instead increases by at least five species. This marked change in alpha diversity during the Miocene is a result of careful examination of smaller size fractions of sediments, which contained fragmented components of echinoids such as test plates and spines, and the diligent collecting of moldic samples, which produced additional taxonomic and stratigraphic records. The record of other echinoderms is still poor, but fine-fraction sediments also have produced disarticulated ossicles of crinoids, asteroids, and ophiuroids from several formations that had no previous record of such echinoderms. The diversity pattern of echinoderms from Florida is a reflection of both intrinsic and extrinsic factors that affect (in varying degrees) the echinoderm-bearing formations from the Paleogene through the Neogene. One of the most influential appears to be collector bias against recovering incomplete echinoderms. Many of the new species or new records of taxa from stratigraphic units in the state are based on fossils that are poorly preserved or incomplete. Other biases include over-splitting of taxonomic groups, stratigraphic unit revisions, taphonomy, and preservation potential variation in carbonate versus siliciclastic environments. Significant refinement of the echinoderm biostratigraphy and diversity patterns has occurred due to detailed examination of field samples, museum collections, and literature reviews, as well as accounting for biases inherent in the fossil record of Florida.

Miocene sharks in the Kendeace and Grand Bay formations of Carriacou, The Grenadines, Lesser Antilles

Abstract. The Miocene chondrichthyan fauna from the Kendeace and Grand Bay formations consists of five species which have been identified from the remains of teeth. These are Carcharias taurus (sand-tiger shark), Isurus oxyrinchus (shortfin mako shark), Carcharocles megalodon (mega-tooth shark), Carcharhinus obscurus (requiem shark) and Hemipristis serra (extinct snaggletooth shark). No further skeletal fish remains, Chondrichthyes or Actinopterygii, were discovered. Teeth of Carcharhinus obscurus predominated, by greater than three to one, the other shark species found in these deposits.

OCCURRENCE OF THE ATLANTIC GHOST CRAB OCYPODE QUADRATA FROM THE UPPER PLEISTOCENE TO HOLOCENE ANASTASIA FORMATION OF FLORIDA

Abstract More than 500 nearly complete specimens of the Atlantic ghost crab Ocypode quadrata (Fabricius) were collected from the upper Pleistocene to Holocene Anastasia Formation along beaches in Brevard County, Florida. Such whole-body decapod crustaceans are rare in Quaternary deposits of the southeastern United States. The low degree of disarticulation and the posture of the crabs indicate that they died while in their burrows, probably by winterkill. Fossil O. quadrata were found in two conditions: those with a clearly crab-like form, bearing a loose, friable matrix of shell hash with little cementation, no visible abrasion, no calcite infilling, and no attached fossil or Recent epibionts; and those that were barely recognizable as crabs, with a thick layer of heavily cemented matrix, a highly sand-abraded (polished) surface, some voids filled with calcite-cemented grains or calcite crystals, and some with Recent epibionts in exposed cavities. The nonabraded crabs with friable matrix have been recently exhumed from a poorly consolidated part of the Anastasia Formation or from the sand dunes or upper beach escarpment by storm waves, whereas the abraded crabs have been cast upon the beach from the nearshore subtidal zone by storm waves. Deposition of the Anastasia Formation is thought to have occurred approximately 110,000 YBP. The barrier-island–sand-dune system along the central East Coast of Florida is believed to have formed within the last 7000 yr. The abraded fossil crabs could have accumulated over the past 110,000 yr, but the nonabraded specimens, if derived from the existing beach, are considerably younger.

Island slopes and jumbled shell beds

Shell beds pose questions of provenance, but determining the degree of pre-depositional transport of bioclasts can be speculative. Bioclastic beds deposited on a broad, shallow continental shelf may consist of a minimally transported accumulation. In contrast, islands may have steep shelves and accumulate disharmonious bioclastic assemblages in deeper water. The latter are a signature of the stratigraphic record on many islands. Herein, we contrast differing examples of jumbled shell beds preserved around islands. The Lower Permian Mengkarang Formation of Sumatra preserves deep-water facies at the base of a volcanic section. Nektonic cephalopods overlie a fine-grained ash containing a diverse association of terrestrial pollen. The Lower Miocene Montpelier Formation of Jamaica yields allochthonous packstones and slide blocks of reef limestone embedded in chalk; the ichthyofauna indicates deposition in ≥200 m water depth. Abundant evidence that deposition occurred in a deep-water turbidite basin flanking a volcanic island is found in the Middle Miocene Grand Bay Formation of Carriacou, the Grenadines. Diverse, deeper water taxa are preserved in association with land snails, hermatypic scleractinians, algal balls and planktic pteropods. The famous Upper Pliocene Bowden shell beds, Jamaica, preserve terrestrial, shallow-water, deep-water and planktic taxa.

FIRST REPORT OF COSTACOPLUMA COLLINS AND MORRIS, 1975 (DECAPODA: BRACHYURA: RETROPLUMIDAE) FROM THE EOCENE OF ALABAMA, U.S.A.

Abstract Nine specimens of retroplumid crabs collected from the late early or early middle Eocene Tallahatta Formation in southern Alabama form the basis for description of a new species, Costacopluma grayi. The discovery confirms the extension of the range of the genus into the Eocene and represents the first occurrence of Costacopluma in the United States. As a result of the geologic range extension, the genus is now known to be contemporary with two other retroplumid genera, Retrocypoda, and Retropluma.