Austin J. W. Hendy

Sharks and Rays (Chondrichthyes, Elasmobranchii) from the Late Miocene Gatun Formation of Panama

Abstract The late Miocene Gatun Formation of northern Panama contains a highly diverse and well sampled fossil marine assemblage that occupied a shallow-water embayment close to a purported connection between the Pacific and Atlantic (Caribbean) oceans. However, the diverse chondrichthyan fauna has been poorly documented. Based on recent field discoveries and further analysis of existing collections, the chondrichthyan fauna from this unit comprises at least 26 taxa, of which four species are extinct today. The remaining portion of the total chondrichthyan biodiversity has affinities with modern taxa and is therefore comprised of long-lived species. Based on known records of the modern geographic distribution range of the Gatun chondrichthyans, the fauna has mixed biogeographic affinities suggesting that around 10 million yr ago, a connection likely occurred between the Pacific Ocean and the Caribbean Sea. Given the known habitat preferences for modern chondrichthyans, the Gatun fauna was primarily adapted to shallow waters within the neritic zone. Finally, comparisons of Gatun dental measurements with other faunas suggest that many of the taxa have an abundance of small individuals, in agreement with previous studies that proposed this area as a paleonursery habitat for the species Carcharocles megalodon.

SPATIAL AND STRATIGRAPHIC VARIATION OF MARINE PALEOENVIRONMENTS IN THE MIDDLE-UPPER MIOCENE GATUN FORMATION, ISTHMUS OF PANAMA

ABSTRACT The middle–upper Miocene (Serravallian-Tortonian) Gatun Formation of Panama is one of the most diverse marine fossil assemblages in the Caribbean, and has been widely used as a baseline in studies investigating the effects of the late Neogene closure of the Central American Seaway. Despite being the focus of exhaustive paleoecological sampling studies, previous studies have not revealed the fine-scale spatial and temporal variation in the composition of the Gatun fauna. High-resoluton faunal inventories were conducted from over 600 stratigraphic horizons in the Gatun Formation, capturing more than 200 species, which represent mostly widespread or common, and typically macroscopic taxa. Cluster and detrended correspondence analyses (DCA) reveal a stratigraphic pattern of variation in the faunal composition of individual horizons as well as differences between sampling sites. Stratigraphic curves of DCA axis scores indicate relative shifts in water depth and sedimentation through the stratigraphy and among localities. Overall the Gatun reveals both coarse- and fine-scale temporal variations in paleobathymetry, reflecting long-term shifts in basin subsidence and accommodation space that is potentially overprinted by fifth- or sixth-order glacio-eustatic cycles. The formation accumulated during an overall phase of increasing accommodation space, with major intervals of transgression (lower Gatun), regression (middle Gatun), and further transgression to mid-shelf depths (upper Gatun). Shallowing through the middle part of the Gatun is largely the result of an increase in supply of pyroclastic and volcaniclastic sediments from the adjacent volcanic arc. These findings have implications for understanding the tectonic evolution of the Canal Basin.

Neogene molluscs, shallow marine paleoenvironments, and chronostratigraphy of the Guajira Peninsula, Colombia

The Neogene sedimentary fill of the Cocinetas Basin in northern Colombia preserves a rich record of marine invertebrates and can be analyzed in the context of a high-resolution stratigraphy and excellent chronostratigraphy. Molluscan fossils are highly diverse and often well preserved, offering a window into the rapidly changing paleoenvironments and biogeography of northern South America during parts of the Early to Middle Miocene and latest Pliocene to Pleistocene. Before the evolutionary and biogeographic implications of these fossils can be understood, however, their associated depositional environments and geologic ages must be determined. Here, we present preliminary results from paleoenvironmental, biostratigraphic, and strontium isotope chronostratigraphic analyses of sediments and fossils from the Uitpa, Jimol, Castilletes, and Ware formations found in Cocinetas Basin. The basal unit in the Neogene succession, the Uitpa Formation, comprises mudstones redeposited sandstones and molluscs typical of bathyal to outer shelf environments at its base. It is a shallowing-up sequence and is conformable with the overlying Jimol Formation, which comprises coarse-grained lithic calcarenite, coquina, and mudstone that represent a regressive–transgressive–regressive sequence. This sequence includes foreshore and transition zone through lower inner shelf environments, but generally poorly preserved invertebrate assemblages. The conformably overlying Castilletes Formation contains a varied suite of depositional environments with better-developed shell beds and thicker successions of intervening siltstone. A significant unconformity exists between the Castilletes Formation and the overlying Ware Formation, which represents a deltaic to coastal shoreface deposition environment, rich in shallow marine molluscs from a variety of ecotopes. Biostratigraphic assessment and strontium isotopic results from the Jimol and Castilletes formations indicate that these units contain fossils of latest Early Miocene through Middle Miocene age, while those of the Ware are approximately Late Pliocene in age. These results help to place the shallow marine assemblages of Cocinetas Basin into a wider geologic context that aids our understanding of how these faunas relate to the broader evolutionary and biogeographic history of the southern Caribbean during the Neogene. Additionally, the isotope dating and paleoecology of this fauna help to place co-occurring terrestrial and aquatic vertebrate assemblages into a local paleoenvironmental and chronostratigraphic framework.

Evolutionary Patterns among Living and Fossil Kogiid Sperm Whales: Evidence from the Neogene of Central America.

Kogiids are known by two living species, the pygmy and dwarf sperm whale (Kogia breviceps and K. sima). Both are relatively rare, and as their names suggest, they are closely related to the sperm whale, all being characterized by the presence of a spermaceti organ. However, this organ is much reduced in kogiids and may have become functionally different. Here we describe a fossil kogiid from the late Miocene of Panama and we explore the evolutionary history of the group with special attention to this evolutionary reduction. The fossil consists of cranial material from the late Tortonian (~7.5 Ma) Piña facies of the Chagres Formation in Panama. Detailed comparison with other fossil and extant kogiids and the results of a phylogenetic analysis place the Panamanian kogiid, herein named Nanokogia isthmia gen. et sp. nov., as a taxon most closely related to Praekogia cedrosensis from the Messinian (~6 Ma) of Baja California and to Kogia spp. Furthermore our results show that reduction of the spermaceti organ has occurred iteratively in kogiids, once in Thalassocetus antwerpiensis in the early-middle Miocene, and more recently in Kogia spp. Additionally, we estimate the divergence between extant species of Kogia at around the late Pliocene, later than previously predicted by molecular estimates. Finally, comparison of Nanokogia with the coeval Scaphokogia cochlearis from Peru shows that these two species display a greater morphological disparity between them than that observed between the extant members of the group. We hypothesize that this reflects differences in feeding ecologies of the two species, with Nanokogia being more similar to extant Kogia. Nanokogia shows that kogiids have been part of the Neotropical marine mammal communities at least since the late Miocene, and gives us insight into the evolutionary history and origins of one of the rarest groups of living whales.

Preface: La Guajira, Colombia: a new window into the Cenozoic neotropical biodiversity and the Great American Biotic Interchange

Over the past four years, we have conducted extensive fieldwork in the Cocinetas Basin of La Guajira Peninsula, including geological mapping, stratigraphic descriptions, and exhaustive paleontological collection of plants, microfossils, and marine and terrestrial invertebrates and vertebrates. Moreno et al. (Swiss J Paleontol 134: 1–39, 2015) provide an overview of these efforts, including a revised Neogene stratigraphy for Cocinetas Basin and redefined (Jimol and Castilletes formations) and newly named (Ware Formation) lithostratigraphic units. Hendy et al. (Swiss J Paleontol 134, 2015) utilize the extensive invertebrate fossil record of the basin to develop paleoenvironmental interpretations and a chronostratigraphic framework buttressed by 87Sr/86Sr isotopic analyses and biostratigraphy. This geological exploration highlights the tremendously diverse and important fossil assemblages throughout the Jimol, Castilletes and Ware formations. These new fossil data will be of great value for future paleobiogeographic, paleogeographic, paleooceanographic and paleoenvironmental interpretations. Already, the faunal and floral fossil record of Cocinetas Basin indicates that once the humid ecosystem of the Neogene underwent drastic climatic changes over the last two million years.

Paleoenvironmental and Paleobiogeographical Implications of a Middle Pleistocene Mollusc Assemblage from the Marine Terraces of Baía Das Pipas, Southwest Angola

Abstract Quaternary raised marine terraces containing the remains of diverse, shallow water marine invertebrate faunas are widespread across the coast of Angola. These deposits and faunas have not been studied in the same detail as contemporaneous features in northwest and southernmost Africa. We analyzed the fossil assemblages and sedimentology of two closely spaced middle Pleistocene marine terrace deposits in Baía das Pipas, southwest Angola. This revealed 46 gastropod and 29 bivalve species, along with scleractinian corals, encrusting bryozoans, polychaete tubes, barnacles, and echinoids. The fauna is characteristic of intertidal and nearshore rocky substrates and sandy soft-bottom habitats. Sedimentological analysis is consistent with faunal data and indicates an upper shoreface paleoenvironment along a gravel coast. This diverse fauna stands out as a rare example of a marine Pleistocene assemblage from over 6,000 km of the West African coast. The assemblage is dominated by extant tropical West African molluscs, including species from the “Senegalese fauna” that colonized northern Africa and beyond during Pleistocene interstadials. Additionally, as along the modern coast of the Namibe Desert, the influence of the cool-water Benguela Current is apparent in the paleofauna by the occurrence of a few temperate species. The distribution and thermal tolerances of extant species identified in the Pipas fauna indicate that this region experienced similar climatic and oceanographic conditions as that of the present during this interstadial. Seasonal temperature varied between ∼20 and 28°C and resulted from upwelling in this tropical setting.

Quaternary intertidal and supratidal crabs (Decapoda, Brachyura) from tropical America and the systematic affinities of fossil fiddler crabs

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.

New records of Humiriaceae fossil fruits from the Oligocene and Early Miocene of the western Azuero Peninsula, Panamá

espanolPara entender el origen de la diversidad de los bosques de America Central, se necesita integrar estudios de plantas actuales y fosiles. En este trabajo, describimos fosiles de Humiriaceae, excavados de dos nuevas secuencias sedimentarias en la Peninsula de Azuero, Panama. Los fosiles fueron encontrados en depositos marinos-marginales del Oligoceno (una localidad) y del Mioceno temprano (dos localidades). Describimos nuevos especimenes y aumentamos la descripcion morfologica de Lacunofructus cuatrecasana Herrera, Manchester et Jaramillo para las localidades del Oligoceno y Mioceno temprano y presentamos un nuevo registro de Sacoglottis sp., para el Mioceno temprano. Estos nuevos registros expanden los rangos de distribucion geografica y temporal para ambos taxones, y ademas demuestran que la familia Humiriaceae fue un importante constituyente de los primeros bosques en America Central. La evidencia presentada tambien sugiere que hubo dispersiones de especies de Humiriaceae entre Centro y Sur America mucho antes del cierre del Istmo de Panama. Se necesitan mas estudios para establecer con claridad si el origen de Humiriaceae se dio en America Central o Sur America. EnglishUnderstanding the origin of the diversity in Central American forests requires the integration of both extant and fossil taxa. Here, we provide a description of Humiriaceae fossils from two new sedimentary sequences in the Azuero Peninsula, Panama. Fossils were recovered from Oligocene (one locality) and Early Miocene (two localities) marginal marine deposits. We describe new specimens and augment the generic description of Lacunofructus cuatrecasana Herrera, Manchester et Jaramillo, and present a new record of Sacoglottis sp. Our results expand the temporal and geographical distribution of both taxa and show that Humiriaceae was an important constituent of early Central American forests, and that this family was dispersed in between Central and South America before the final closure of the Central American Seaway. Further studies are necessary to establish whether the origin of this family was in Central or South America.

Neogene Caribbean elasmobranchs: Diversity, paleoecology and paleoenvironmental significance of the Cocinetas Basin assemblage (Guajira Peninsula, Colombia)

The Cocinetas Basin is located on the eastern flank of La Guajira Peninsula, northern Colombia (South Caribbean). During the late Oligocene through Pliocene, much of the basin was submerged. The extensive deposits in this area suggest a transition from a shallow marine to a fluvio–deltaic system, with a rich record of invertebrate and vertebrate fauna. The elasmobranch assemblages of the early Miocene to late Pliocene succession in the Cocinetas Basin (Jimol, Castilletes and Ware formations, and Patsúa Valley) are described for the first time. The assemblages include at least 30 taxa of sharks 5 (Squaliformes, Pristiophoriformes, Orectolobiformes, Lamniformes and Carcharhiniformes) and batoids (Rhinopristiformes and Myliobatiformes), of which 24 taxa are reported from the Colombian Neogene for the first time. Paleoecological interpretations are based on the feeding ecology, and on estimates of the paleohydrology (relative salinity, temperature) using stable isotope compositions of oxygen in the bioapatite of shark teeth. The isotopic composition of the studied specimens corroborates paleoenvironmental settings for the studied units that were previously estimated based on the sedimentology and biology of the 10 taxa. These Neogene elasmobranch assemblages from the Cocinetas Basin, provide new insights of the shark and ray diversity inhabiting the coastal and estuarine environments of the northwestern margin of South America, both during the existence of the gateway between the Atlantic and Pacific Oceans, and following its closure.