P.-O. 2019.-Restes inédits de rongeurs caviomorphes du Paléogène de la région de Juanjui (Amazonie péruvienne) : systématique, implications macro-évolutives et biostratigraphiques.

Sharks occupy all living environments of the marine realm as well as some freshwater systems. They display varied and flexible feeding behaviours, but understanding their diet remains challenging due to their elusive ecology and the invasiveness of stomach content analyses in regard of their threatened status. As a potential alternative, we discuss the variability in δ 44/42 Ca values recorded in the tooth enamel of size-graded individuals belonging to three species of large sharks with distinct diets (Isurus oxyrinchus, Hexanchus griseus and Carcharodon carcharias). The preliminary results highlight shifts in diet linked to ontogeny (I. oxyrinchus and H. griseus) and spatial distribution (C. carcharias) characterizing feeding behaviour in these species at individual and population level. These outcomes agree with the results of traditional stomach analyses supporting that nontraditional stable isotopes thus represent new perspectives for the study of modern and extinct shark ecology. In addition, for the first time, the Sr/Ca elemental ratios measured in H. griseus reflect sexual differences that could be interpreted in terms of spatial segregation or physiological heterogeneities.

The Hangenberg crisis represents a mass extinction marked by a biodiversity turnover at the Devonian-Carboniferous boundary. However, the last million years before this dramatic event have been poorly investigated. Here we report new data on the size and abundances of vertebrate remains as well as carbon isotope data from the latest Famennian in the Montagne Noire (France). A significant decrease in fish abundance and a general reduction in the size of vertebrate remains are observed during a period of stable environment before the onset of the Hangenberg crisis. No perturbations are recorded by the carbon isotopes, supporting the stability of the environment. This significant change in the structuration of vertebrate communities prior to the Hangenberg crisis is not linked to any turnover in other faunal groups. That could be interpreted as changes in faunal repartition that predate mass extinctions.