Disparification and extinction trade-offs shaped the evolution of Permian to Jurassic Odonata.

Owing to their prevalence in nowadays terrestrial ecosystems, insects are a relevant group to assess the impact of mass extinctions on emerged land. However, limitations of the insect fossil record make it difficult to assess the impact of such events based on taxonomic diversity alone. Therefore, we documented trends in morphological diversity, i.e., disparity, using wings of Permian to Jurassic Odonata as model. Our results show a decreasing trend in disparity while species richness increased. Both the Permian-Triassic and Triassic-Jurassic transitions are revealed as important events, associated with strong morphospace restructuring due to selective extinction. In each case, a recovery was assured by the diversification of new forms compensating the loss of others. Early representatives of Odonata continuously evolved new shapes, a pattern contrasting with the classical assertion of a morphospace fulfilled early and followed by selective extinctions and specialization within it.

Exceptional soft-tissue preservation of Jurassic Vampyronassa rhodanica provides new insights on the evolution and palaeoecology of vampyroteuthids.

Although soft tissues of coleoid cephalopods record key evolutionary adaptations, they are rarely preserved in the fossil record. This prevents meaningful comparative analyses between extant and fossil forms, as well as the development of a relative timescale for morphological innovations. However, unique 3-D soft tissue preservation of Vampyronassa rhodanica (Vampyromorpha) from the Jurassic Lagerstätte of La Voulte-sur-Rhône (Ardèche, France) provides unparalleled opportunities for the observation of these tissues in the oldest likely relative of extant Vampyroteuthis infernalis. Synchrotron X-ray microtomography and reconstruction of V. rhodanica allowed, for the first time, a high-resolution re-examination of external and internal morphology, and comparison with other fossil and extant species, including V. infernalis. The new data obtained demonstrate that some key V. infernalis characters, such as its unique type of sucker attachment, were already present in Jurassic taxa. Nonetheless, compared with the extant form, which is considered to be an opportunistic detritivore and zooplanktivore, many characters in V. rhodanica indicate a pelagic predatory lifestyle. The contrast in trophic niches between the two taxa is consistent with the hypothesis that these forms diversified in continental shelf environments prior to the appearance of adaptations in the Oligocene leading to their modern deep-sea mode of life.

Post-metamorphic ontogeny of Zoroaster fulgens Thomson, 1873 (Asteroidea, Forcipulatacea).

The complete ontogenetic development of an asteroid skeleton has never been described formally for any species. Here, we describe in detail the post-metamorphic ontogeny of Zoroaster fulgens Thomson, 1873. The major novelty of our work is the description of patterns of plate addition, the ontogeny of the internal ossicles, as well as the variability of ossicles according to their position along series. Seven specimens collected in the Rockall Basin (North Atlantic) were dissected with bleach and their anatomy was documented using a scanning electron microscope. The external anatomy was additionally observed on more than 30 specimens. We found that the overall structure of the skeleton does not change much between juveniles and adults, but the shape of individual ossicle changes during growth. Allometric scaling was particularly visible on the orals, ambulacrals and adambulacrals. The shape of an ossicle is more dependent of its position along the arm series than of its individual size. Many morphological features differentiate progressively during ontogeny, while others are expressed consistently among specimens. The study of this ontogenetic series allows discussing the homology between the structures present on the ossicles of Z. fulgens in particular and other forcipulatacean sea stars in general (i.e. muscles insertions and articulation areas). The new data obtained in this study provide a comprehensive framework of the anatomy and ontogeny of Z. fulgens that will help resolve taxonomic and phylogenetic controversies in the future.

Phanerozoic trends in the global diversity of marine invertebrates.

It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing 3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic.

Morphological disparity of ammonoids and the mark of Permian mass extinctions.

The taxonomic diversity of ammonoids, in terms of the number of taxa preserved, provides an incomplete picture of the extinction pattern during the Permian because of a strongly biased fossil record. The analysis of morphological disparity (the variety of shell shapes) is a powerful complementary tool for testing hypotheses about the selectivity of extinction and permits the recognition of three distinct patterns. First, a trend of decreasing disparity, ranging for about 30 million years, led to a minimum disparity immediately before the Permian-Triassic boundary. Second, the strongly selective Capitanian crisis fits a model of background extinction driven by standard environmental changes. Third, the end-Permian mass extinction operated as a random, nonselective sorting of morphologies, which is consistent with a catastrophic cause.