The Chañares Formation: a window to a Middle Triassic tetrapod community

The Chañares Formation is known worldwide for its diverse and well‐preserved Ladinian non‐marine tetrapod assemblage, including a wide variety of archosauriform reptiles (proterochampsids, early offshoots of the crocodilian line and dinosaurian precursors) and synapsids represented by dicynodonts and cynodonts. This tetrapod record offers an opportunity to evaluate, within a taphonomic context, the palaeoecology of this Middle Triassic fauna. The taphonomic analysis of the Chañares assemblage, under precise stratigraphical control, indicates that it is a good representation of the original faunal composition allowing us to address the palaeoecological interactions between its components. Mass estimations and morphology‐based palaeobiological inferences of Chañares tetrapods are used to reconstruct the trophic structure of the community. Chañares tetrapod fauna was numerically dominated by middle‐sized herbivorous and small faunivorous cynodonts, whereas middle‐sized faunivorous cynodonts and large dicynodonts were less common. In contrast to the therapsids, which show a low species‐richness and high abundance, the archosauriforms are less abundant, but are the most taxonomically diverse group. The large paracrocodylomorphs (estimated body masses between 350 and 500 kg) are identified as the top predators of the community, and the traversodontid cynodonts and dicynodonts (estimated body masses reaching approximately 43 and 360 kg, respectively) are indentified as the base herbivores of the trophic pyramid. We conclude that the worldwide faunal composition in the Ladinian reveals two continental assemblages: an eastern Laurasian assemblage dominated by temnospondyl amphibians; and a western Gondwanan assemblage dominated by therapsids but including a wide diversity of archosauriforms.     

An overview of the geographic and chronologic distribution of west European cercopithecoids

Four genera of fossil cercopithecoid monkeys have been recorded from Miocene and Plio-Pleistocene deposits of West Europe: the subfamilyColobinae is represented byMesopithecus andDolichopithecus while the subfamilyCercopithecinae is represented byMacaca andParadolichopithecus. Mesopithecus, Dolichopithecus andParadolichopithecus have not been recorded in “Cromerian” and younger faunas, indicating that they belonged to a more archaic biocoenosis. In contrast, the genusMacaca was apparently able to adapt to the new environment of the middle and late Pleistocene of Europe, being the only primate, along with man, to live in this region, perhaps until very recent times.     

Were all trilobites fully marine? Trilobite expansion into brackish water during the early Palaeozoic

Trilobites, key components of early Palaeozoic communities, are considered to have been invariably fully marine. Through the integration of ichnological, palaeobiological, and sedimentological datasets within a sequence-stratigraphical framework, we challenge this assumption. Here, we report uncontroversial trace and body fossil evidence of their presence in brackish-water settings. Our approach allows tracking of some trilobite groups foraying into tide-dominated estuaries. These trilobites were tolerant to salinity stress and able to make use of the ecological advantages offered by marginal-marine environments migrating up-estuary, following salt wedges either reflecting amphidromy or as euryhaline marine wanderers. Our data indicate two attempts of landward exploration via brackish water: phase 1 in which the outer portion of estuaries were colonized by olenids (Furongian–early late Tremadocian) and phase 2 involving exploration of the inner to middle estuarine zones by asaphids (Dapingian–Darriwilian). This study indicates that tolerance to salinity stress arose independently among different trilobite groups.