Highly resolved taphonomic variations within the Early Ordovician Fezouata Biota.

The Fezouata Biota (Morocco) is a Burgess Shale-type (BST) assemblage that provides a wealth of information on Early Ordovician ecosystems. Much work has been done to compare the preservation of the Fezouata Biota to other BSTs. However, studies investigating preservation variations within the Fezouata Biota are rare. Here, we use probabilities to investigate the preservation of various ecological categories of Fezouata eumetazoans. Complex taphonomic processes and phylum-specific constraints have led to the better preservation of predators/scavengers in this biota. However, no differences in preservation are observed between vagile and sessile taxa. Importantly, Tremadocian taxa are better preserved than Floian ones. As such, this study highlights the gradual closure of the BST window of preservation in the Zagora region of Morocco and constitutes a benchmark for future palaeoecological and evolutionary studies on the Fezouata Biota.

The endocast of the insular and extinct Sylviornis neocaledoniae (Aves, Galliformes), reveals insights into its sensory specializations and its twilight ecology.

Sylviornis neocaledoniae (Galliformes, Sylviornithidae), a recently extinct bird of New-Caledonia (Galliformes, Sylviornithidae) is the largest galliform that ever lived and one of the most enigmatic birds in the world. Herein, for the first time, we analyze its neuroanatomy that sheds light on its lifestyle, its brain shape and patterns being correlated to neurological functions. Using morphometric methods, we quantified the endocranial morphology of S. neocaledoniae and compared it with extinct and extant birds in order to obtain ecological and behavioral information about fossil birds. Sylviornis neocaledoniae exhibited reduced optic lobes, a condition also observed in nocturnal taxa endemic to predator-depauperate islands, such as Elephant birds. Functional interpretations suggest that S. neocaledoniae possessed a well-developed somatosensorial system and a good sense of smell in addition to its specialized visual ability for low light conditions, presumably for locating its food. We interpret these results as evidence for a crepuscular lifestyle in S. neocaledoniae.

Temperature-driven heterochrony as a main evolutionary response to climate changes in conodonts.

Can we predict the evolutionary response of organisms to climate changes? The direction of greatest intraspecific phenotypic variance is thought to correspond to an 'evolutionary line of least resistance', i.e. a taxon's phenotype is expected to evolve along that general direction, if not constrained otherwise. In particular, heterochrony, whereby the timing or rate of developmental processes are modified, has often been invoked to describe evolutionary trajectories and it may be advantageous to organisms when rapid adaptation is critical. Yet, to date, little is known empirically as to which covariation patterns, whether static allometry, as measured in adult forms only, or ontogenetic allometry, the basis for heterochrony, may be prevalent in what circumstances. Here, we quantify the morphology of segminiplanate conodont elements during two distinct time intervals separated by more than 130 Myr: the Devonian-Carboniferous boundary and the Carnian-Norian boundary (Late Triassic). We evidence that the corresponding species share similar patterns of intraspecific static allometry. Yet, during both crises, conodont evolution was decoupled from this common evolutionary line of least resistance. Instead, it followed heterochrony-like trajectories that furthermore appear as driven by ocean temperature. This may have implications for our interpretation of conodonts' and past marine ecosystems' response to environmental perturbations.

Probability-based preservational variations within the early Cambrian Chengjiang biota (China).

The Chengjiang biota (Yunnan Province, China) is a treasure trove of soft-bodied animal fossils from the earliest stages of the Cambrian explosion. The mechanisms contributing to its unique preservation, known as the Burgess Shale-type preservation, are well understood. However, little is known about the preservation differences between various animal groups within this biota. This study compares tissue-occurrence data of 11 major animal groups in the Chengjiang biota using a probabilistic methodology. The fossil-based data from this study is compared to previous decay experiments. This shows that all groups are not equally preserved with some higher taxa more likely to preserve soft tissues than others. These differences in fossil preservation between taxa can be explained by the interaction of biological and environmental characteristics. A bias also results from differential taxonomic recognition, as some taxa are easily recognized from even poorly preserved fragments while other specimens are difficult to assign to higher taxa even with exquisite preservation.

Contrasting Early Ordovician assembly patterns highlight the complex initial stages of the Ordovician Radiation.

The Early Ordovician is a key interval for our understanding of the evolution of life on Earth as it lays at the transition between the Cambrian Explosion and the Ordovician Radiation and because the fossil record of the late Cambrian is scarce. In this study, assembly processes of Early Ordovician trilobite and echinoderm communities from the Central Anti-Atlas (Morocco), the Montagne Noire (France), and the Cordillera Oriental (Argentina) are explored. The results show that dispersal increased diachronically in trilobite communities during the Early Ordovician. Dispersal did not increase for echinoderms. Dispersal was most probably proximally triggered by the planktic revolution, the fall in seawater temperatures, changes in oceanic circulation, with an overall control by tectonic frameworks and phylogenetic constraints. The diachronous increase in dispersal within trilobite communities in the Early Ordovician highlights the complexity of ecosystem structuring during the early stages of the Ordovician Radiation. As Early Ordovician regional dispersal was followed by well-documented continental dispersal in the Middle/Late Ordovician, it is possible to consider that alongside a global increase in taxonomic richness, the Ordovician Radiation is also characterized by a gradual increase in dispersal.

Cranial evolution in the extinct Rodrigues Island owl Otus murivorus (Strigidae), associated with unexpected ecological adaptations.

Island birds that were victims of anthropic extinctions were often more specialist species, having evolved their most distinctive features in isolation, making the study of fossil insular birds most interesting. Here we studied a fossil cranium of the 'giant' extinct scops owl Otus murivorus from Rodrigues Island (Mascarene Islands, southwestern Indian Ocean), to determine any potential unique characters. The fossil and extant strigids were imaged through X-ray microtomography, providing 3D views of external and internal (endocast, inner ear) cranial structures. Geometric morphometrics and analyses of traditional measurements yielded new information about the Rodrigues owl's evolution and ecology. Otus murivorus exhibits a 2-tier "lag behind" phenomenon for cranium and brain evolution, both being proportionately small relative to increased body size. It also had a much more developed olfactory bulb than congeners, indicating an unexpectedly developed olfactory sense, suggesting a partial food scavenging habit. In addition, O. murivorus had the eyes placed more laterally than O. sunia, the species from which it was derived, probably a side effect of a small brain; rather terrestrial habits; probably relatively fearless behavior; and a less vertical posture (head less upright) than other owls (this in part an allometric effect of size increase). These evolutionary features, added to gigantism and wing reduction, make the extinct Rodrigues owl's evolution remarkable, and with multiple causes.