Gerardo González-Barba

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.

Condrictios fósiles del Plioceno Superior de la Formación Horcón,Región de Valparaíso, Chile central

Se describen doce taxa de condrictios fosiles provenientes de rocas asignadas al Plioceno Superior de la Formacion Horcon, region de Valparaiso, Chile central; se discuten sus registros previos, implicancias paleobiogeografi cas y paleoambientales. La fauna comprende Callorhinchus sp., Heterodontus sp., Carcharodon carcharias, Isurus oxyrinchus, Galeorhinus galeus, Carcharhinus brachyurus, Hexanchus griseus, Squatina sp., Pristiophorus sp., Rajidae, Dasyatidae y Myliobatidae. Esta es una de las asociaciones de condrictios mas diversas del Neogeno Tardio de Chile y del resto de America del Sur.

DECAPODA (THALASSINIDEA AND PAGUROIDEA) FROM THE EOCENE BATEQUE AND TEPETATE FORMATIONS, BAJA CALIFORNIA SUR, MÉXICO: SYSTEMATICS, CUTICLE MICROSTRUCTURE, AND PALEOECOLOGY

ABSTRACT Seven species of shrimps referable to the Thalassinoidea and four species referable to the Paguroidea have been recovered from the Eocene Bateque and Tepetate formations of Baja California Sur, México. The large number of callianassid and paguroid taxa found in these essentially equivalent, very similar formations, is unusual in the decapod fossil record. Only a few other occurrences of such large numbers of fossil paguroid and thalassinoid taxa within a single unit are known; these occurrences range in age from Eocene to Miocene. Cuticular studies indicate that callianassid chelae were bioeroded, possibly by algae. An unusual occurrence of a hash of callianassid chelae may have sequence-stratigraphic value.

Late Miocene chondrichthyans from Lago Bayano, Panama: Functional diversity, environment and biogeography

Abstract. This newly described chondrichthyan fauna from the late Miocene Chucunaque Formation of Lago Bayano reveals a prolific and highly diverse assemblage from Panama, and one of the richest shark faunas from the Neotropics. Strontium geochronology indicates an age of 10–9.5 Ma for the chonrichthyan-bearing strata. Field efforts resulted in 1429 identifiable specimens comprising at least 31 taxa, of which at least eight are new to the documented fossil record of Panama. With this information an analysis of functional diversity was conducted, indicating ecosystems dominated by generalist species feeding upon a wide range of organisms, from plankton to marine mammals. A probabilistic approach of paleobathymetric estimation suggests a neritic environment. Previous studies based on foraminifera have suggested that the Chucunaque Formation had a greater Pacific Ocean affinity, making this the first Miocene chondrichthyan fauna described from the Pacific shelf of Panama. However, our geographic comparisons show that this fauna has mixed Caribbean and Pacific biogeographic affinities, which likely supports the previously purported connection between chondrichthyan faunas during the late Miocene.

DECAPOD CRUSTACEANS (BRACHYURA) FROM THE EOCENE TEPETATE FORMATION, BAJA CALIFORNIA SUR, MEXICO

ABSTRACT A large collection of brachyuran specimens from the middle Eocene Tepetate Formation, Baja California Sur, Mexico, has yielded sufficiently well-preserved specimens to provide revised descriptions and diagnoses for genera and species previously known from the area. Revised, more complete descriptions are given for Eriosachila bajaensis Schweitzer et al., 2002, and Lobonotus mexicanus Rathbun, 1930. A gone-placid specimen is questionably referred to Carcinoplax, which has a well-established Pacific record during the Miocene. All of the specimens of Amydrocarcinus dantei Schweitzer et al., 2002, thus far collected for which gender can be determined are males, suggesting that there may have been environmental or behavioral segregation of males and females of this species. Analysis of benthic and planktonic foraminiferans suggests that the Tepetate Formation was deposited in subtropical conditions, probably within the photic zone but below the seasonal thermocline, perhaps below 100–120 m. The age of the Tepetate Formation, according to larger foraminiferans, is middle Eocene, and according to planktonic foraminiferans is further constrained as upper middle Eocene (Bartonian). This age corresponds to the P14 foraminiferal zone based upon the Berggren et al. (1995) scheme and the E13 zone based upon the work of Berggren and Pearson (2005).