Vertebrates of the El Pelillal locality (Campanian, Cerro del Pueblo Formation), southeastern Coahuila, Mexico

A new locality named El Pelillal (Cerro del Pueblo Formation, Late Cretaceous, Campanian) in the southeastern area of the State of Coahuila, Mexico yields an assemblage of vertebrates that is important for correlation due to its frequent occurrence in other localities along the Cerro del Pueblo Formation outcrops. It is located in the Municipio de Ramos Arizpe, Coahuila. Among the vertebrates found are: fishes (Lepisosteida

Paleobiological implications of Campanian coprolites

Vertebrate coprolites (153 samples) in association with vertebrate and plant remains in the Upper Cretaceous (Campanian) sediments of the Cerro del Pueblo Formation, in southeastern Coahuila, Mexico, represent at least ten morphotypes, ranging from ca. 1 cm to 3 cm. At least one suggests a carnivore origin due to the presence of abundant bone fragments, but most of the coprolite morphotypes were produced by either omnivores or herbivores. Analysis of inclusions of the coprolites revealed plant remains, such as stems and isolated vascular elements, and papillate and non-papillate cuticles. Two seed types have been recognized within two coprolite morphotypes. The first one has lythraceous affinity, being comparable to members of a morphological complex within Nesaeeae. The second seed type, which shows adaptations for water dispersal, belongs to Ranunculaceae, and is described as Eocaltha zoophila gen. et sp. nov. Although Eocaltha evolved a mechanism for abiotic dispersal, the seeds were apparently occasionally ingested by a vertebrate. The presence of seeds of E. zoophila in a coprolite suggests that the organism that produced it was looking for a high-quality diet perhaps represented by the seeds, and served indirectly as a biotic seed dispersal agent. The combination of abiotic and biotic dispersal syndromes, plus the fact that the seeds appear to be scarified suggest a case of diffuse coevolution. Interactions, as herbivory, during the Cretaceous prompted biotic dispersal of angiosperm diaspores as revealed by the presence of seeds of E, zooyhila. (C) 1998 Elsevier Science B.V. All rights reserved

Climatic reconstruction of two Pliocene floras from Mexico

The role that climate plays in influencing the physiognomy of modern and fossil plant communities is widely acknowledged and forms the basis for several palaeoclimate proxies. In this work, both univariate Leaf Margin Analysis and multivariate Climate/Leaf Analysis Multivariate Program (CLAMP) were used for the climatic reconstruction of two fossil localities of the Atotonilco El Grande Formation. Using the predominantly North American and Asian calibration data set PHYSG3BRC, supplemented with new African material, results from two sites, Los Baños (present position 20°18′18″N, 98°42′44.4″W) and Sanctorum (20°18′18.5″N and 98°46′52.2″W), indicate that during the Pliocene a mesothermal climate existed with mean annual temperatures between 12 and 22°C, with the most likely being approximately 15°C, and a mean annual temperature range of 21°C. A distinct seasonal variation in rainfall is evident with a mean annual relative humidity of 60–70%. Differences between the sites can be explained by differences in depositional regime and spatial heterogeneity in the predominantly Quercus-dominated woodland. The continuous subsequent uplift of the Sierra Madre Oriental, the resulting development of a rain shadow, and the eventual disappearance of a palaeolake appear to have caused a transition to the modern xerophytic shrub vegetation

Behavioural responses of freshwater zooplankton vary according to the different alarm signals of their invertebrate predators

Single behavioural interactions between two freshwater planktonic crustaceans and invertebrate predators from different zones of the common environment were studied. The planktonic prey organisms were the cladoceran Ceriodaphnia dubia and the copepod Notodiaptomus conifer. The three invertebrate predators were the shrimp Macrobrachium borellii, the crab Trichodactylus borellianus and the larva of the dipteran midge Chaoborus. Feeding experiments were first performed to document the effects of exposure time and prey density on predation. All the selected predators fed on C. dubia and N. conifer, and predation rates were dependent on prey density and exposure time. The ability of microcrustaceans to modify their swimming and avoidance behaviour when faced with cues from each predator was then analysed. The cladoceran was more vulnerable to decapod predation, whereas the prey microcrustaceans were taken equally by the dipteran larvae. The analysis showed that the microcrustaceans detected the presence of at least one invertebrate predator through the predator alarm signals. The cladoceran responded to chemical signals from the three predators but copepods modified their behaviour only in the presence of infochemicals of M. borellii. The different outcomes suggest that macrocrustaceans have different vulnerabilities when faced with the same predator and so have evolved specific and different strategies to reduce invertebrate predation.Fil: Gutierrez, Marìa Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Rojas Molina, Florencia Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: de Azevedo Carvalho, Debora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentin